1
Specification for Bridge Design
Section 10 - Foundations
10.1. SCOPE
Provisions of this section shall apply for the design of spread footings, driven piles, and drilled shaft
foundations.
The probabilistic LRFD basis of this Specification, which produces an interrelated combination of
load, load factor, resistance, resistance factor, and statistical reliability, shall be considered when
selecting procedures for calculating resistance other than that specified herein. Other methods,
especially when locally recognized and considered suitable for regional conditions, may be used if the
statistical nature of the factors given above are considered through consistent use of reliability theory
and are approved by the Owner.
10.2. DEFINITIONS
Batter Pile - Pile driven at an angle inclined to the vertical to provide higher resistance to lateral
loads.
Bearing Pile - A pile whose purpose is to carry axial load through friction or point bearing.
Combination Point Bearing and Friction Pile - Pile that derives its capacity from contributions of
both point bearing developed at the pile tip and resistance mobilized along the embedded shaft.
Combined Footing - A footing that supports more than one column.
Competent Rock - A rock mass with discontinuities that are open not wider than 3.2 mm.
Deep Foundation - A foundation that derives its support by transferring loads to soil or rock at some
depth below the structure by end bearing, adhesion or friction, or both.
Drilled Shaft - A deep foundation unit, wholly or partly embedded in the ground, constructed by
placing fresh concrete in a drilled hole with or without steel reinforcement. Drilled shafts derive their
capacity from the surrounding soil and/or from the soil or rock strata below its tip. Drilled shafts are
also commonly referred to as caissons, drilled caissons, bored piles, or drilled piers.
Effective Stress - The net stress across points of contact of soil particles, generally considered as
equivalent to the total stress minus the pore water pressure.
Friction Pile - A pile whose support capacity is derived principally from soil resistance mobilized
along the side of the embedded pile.
Isolated Footing - Individual support for the various parts of a substructure unit; the foundation is
called a footing foundation.
2
Specification for Bridge Design
Length of Foundation - Maximum plan dimension of a foundation element.
Overconsolidation Ratio (OCR) - Defined as the ratio of the preconsolidation pressure to the current
vertical effective stress.
Pile - A relatively slender deep foundation unit, wholly or partly embedded in the ground, that is
installed by driving, drilling, auguring, jetting, or otherwise and that derives its capacity from the
surrounding soil and/or from the soil or rook strata below its tip.
Pile Bent - A type of bent using piles as the column members.
Pile Shoe - A metal piece fixed to the penetration end of a pile to protect it from damage during
driving and to facilitate penetration through very dense material.
Piping - Progressive erosion of soil by seeping water that produces an open pipe through the soil
through which water flows in an uncontrolled and dangerous manner.
Plunging - A mode of behavior observed in some pile load tests, wherein the settlement of the pile
continues to increase with no increase in load.
Point-Bearing Pile - A pile whose support capacity is derived principally from the resistance of the
foundation material on which the pile tip rests.
RQD - Rock Quality Designation.
Shallow Foundation - A foundation that derives its support by transferring load directly to the soil or
rock at shallow depth.
Slickensides - Polished and grooved surfaces in clayey soils or rocks resulting from shearing
displacements along planes.
Total Stress - Total pressure exerted in any direction by both soil and water.
Width of Foundation - Minimum plan dimension of a foundation element.
10.3. NOTATION
The units shown after the description of each term are suggested units. Other units that are consistent
with the expressions being evaluated may be used.
A
=
effective footing area for determination of elastic settlement of footing subjected to
eccentric loads (mm2) (10.6.2.2.3b)
Ap
=
area of pile point or base of drilled shaft (mm2) (10.7.3.2)
As
=
surface area of pile shaft (mm2) (10.7.3.2)
asi
=
pile perimeter at the point considered (mm) (10.7.3.4.3c)
Au
=
uplift area of a belled drilled shaft (mm2) (10.8.3.7.2)
B
=
footing width (mm); pile group width (mm) (10.6.3.1 .2c)
B’
=
effective footing width (mm) (10.6.3.1.5)
Cae
=
secondary settlement coefficient estimated from results of laboratory consolidation testing
of undisturbed soil samples (DIM) (10.6.2.2.3c)
Cc
=
compression index (DIM) (10.6.2.2.3c)
3
Specification for Bridge Design
Cce
=
compression ratio (DIM) (10.6.2.2.3c)
Ccr
=
recompression index (DIM) (10.6.2.2.3c)
Co
=
uniaxial compressive strength of rock (MPa) (10.6.2.3.2)
CPT
=
cone penetration test (10.5.6)
Cre
=
recompression ratio (DIM) (10.6.2.2.3c)
Cv
=
coefficient of consolidation (mm2/YR) (10.6.2.2.3c)
Cw1,Cw2 =
correction factors for groundwater effect (DIM) (10.6.3.1.2c)
c
=
cohesion of soil (MPa); undrained shear strength (MPa) (10.6.3.1.2b)
cq, c
=
soil compressibility factor (DIM) (10.6.3.1.2c)
c1
=
undrained shear strength of the top layer of soil as depicted in Figure 3 (MPa) (10.6.3.1.2b)
c2
=
shear strength of lower soil layer (MPa) (10.6.3.1.2b)
*
=
reduced effective stress soil cohesion for punching shear (MPa) (10.6.3.1.2a)
D
=
pile width or diameter (mm); diameter of drilled shaft (mm) (10.7.3.4.2a) (10.8.3.3.2)
D’
=
effective depth of pile group (mm) (10.7.2.3.3)
Db
=
depth of embedment of pile into a bearing stratum (mm) (10.7.2.1)
Df
=
foundation embedment depth taken from ground surface to bottom of foundation
(mm) (10.6.3.1.2b)
Di
=
pile width or diameter at the point considered (mm) (10.7.3.4.3c)
Dp
=
diameter of the tip of a drillaD shaft (mm); diameter of bell (mm) (10.8.3.3.2) 10.8.3.7.2)
dq
=
depth factor (DIM) (10.6.3.1.2c)
Ds
=
diameter of socket when pile or drilled shaft is socketed into rock (mm) (10.7.3.5)
Dw
=
depth to water surface taken from the ground surface (mm) (10.8.3.1.2c)
d
=
depth factor for estimating tip capacity of piles in rock (DIM) (10.7.3.5)
Em
=
estimated rock mass modulus (MPa); rock mass modulus (MPa) (C10.6.2.2.3c) (10.6.2.2.3d)
Eo
=
intact rock modulus (MPa) (10.6.2.2.3d)
Ep
=
modulus of elasticity of pile (MPa) (10.7.4.2)
Es
=
soil modulus (MPa) (10.7.4.2)
eB
=
eccentricity of load parallel to the width of the footing (mm) (10.6.3.1.5)
eL
=
eccentricity of load parallel to the length of the footing (mm) (10.6.3.1.5)
eo
=
void ratio at initial vertical effective stress (DIM) (10.6.2.2.3c)
Fr
=
reduction factor for point resistance of large diameter drilled shafts (DIM) (10.8.3.3.2)
f ’c
=
28-day compressive strength of concrete (MPa) (10.6.2.3.2)
fs
=
sleeve friction measured from a CPT (MPa) (10.7.3.4.3a)
fsi
=
unit local sleeve friction resistance from CPT at the point considered (MPa) (10.7.3.4.3c)
g
=
gravitational acceleration (m/s2)
H
=
horizontal component of inclined loads (N); distance from tips of piles to top of lowest
stratum (mm) (10.6.3.1.3b)
Hc
=
height of compressible soil layer (mm) (1 0.6.2.2.3c)
Hd
=
height of longest drainage path in compressible soil layer (mm) (10.6.2.2.3c)
Hs
=
height of sloping ground mass (mm); depth of embedment of pile or drilled shaft
socketed into rock (mm) (10.6.3.1.2b) (10.7.3.5)
c
4
Specification for Bridge Design
Hs2
hi
I
Ip
=
=
=
=
iq, i
K
Kc
Ks
Ksp
k
L
L/
Lf
=
=
=
=
=
=
=
=
=
distance from bottom of footing to top of the second soil layer (mm) (10.6.3.1.2b)
length interval at the point considered (mm) (10.7.3.4.3c)
influence factor for the effective embedment of a pile group (DIM) (10.7.2.3.3)
influence coefficient to account for rigidity and dimensions of footing (DIM);
moment of inertia of pile (mm4) (10.6.2.2.3d) (10.7.4.2)
load inclination factors (DIM) (10.6.3.1.2c)
load transferfactor (DIM) (10.8.3.4.2)
correction factor for sleeve friction in clay (DIM) (10.7.3.4.3c)
correction factor for sleeve friction in sand (DIM) (10.7.3.4.3c)
dimensionless bearing capacity coefficient (DIM) (10.7.3.6)
empirical bearing capacity coefficient from Figure 10.6.3.1.3d-1 (DIM) (10.6.3.1.3d)
length of foundation (mm) (10.6.3.1.5)
effective footing length (mm) (10.6.3.1.5)
depth to point considered when measuring sleeve friction (mm) (10.7.3.4.3c)
Li
=
depth to middle of length interval at the point considered (mm) (10.7.3.4.3c)
N
=
standard Penetration Test (SPT) blow count (Blows/300 mm) (10.7.2.3.3)
N
=
average (uncorrected) SPT blow count along pile shaft (Blows /300 mm) (10.7.3.4.2b)
Nc
=
bearing capacity factor (DIM) (10.6.3.1.2b)
Nq, N
=
bearing capacity factors (DIM) (10.6.3.1.2c)
Ncm, Nqm
=
modified bearing capacity factors (DIM) (10.6.3.1.2b)
Ncm, Nqm ,Nm
=
modified bearing capacity factors (DIM) (10.6.3.1.2b)
Ncorr
=
corrected SPT blow count (Blows/300 mm) (10.7.2.3.3)
N corr
=
average value of corrected SPT blow count (Blows/300 mm) (10.6.3.1.3b)
Nm
Nms
Nu
Nm
N1
=
=
=
=
=
N2
=
nh
*
PL
po
=
=
=
Qep
=
Qg
QL
QLg
Qn
Qp
QR
=
=
=
=
=
=
bearing capacity factor (DIM) (10.6.3.1.2b)
rock parameter (DIM (10.6.2.3.2)
uplift adhesion factor for bell (DIM) (10.8.3.7.2)
modified bearing capacity factor (DIM) (10.6.3.1.2c)
SPT resistance, corrected for depth (Blows /300 mm); number of intervals between the
ground surface and a point 8D below the ground surface (1 0.6.2.2.3b-1) (10.7.3.4.3c)
number of intervals between 8D below the ground surface and the tip of the pile
(l0.7.3.4.3c)
rate of increase of soil modulus with depth (MPa/mm) (10.7.4.2)
limiting pressure obtained from pressuremeter test result (MPa) (l0.6.3.1.3d)
total horizontal pressure at the depth where the pressuremeter test is performed
(MPa) (10.6.3.1.3d)
passive resistance of soil arAilable throughout the design life of the structure (N)
(10.6.3.3)
nominal resistance of pile group (N) (10.7.3.10.1)
nominal lateral resistance of single pile (N) (10.7.3.11)
nominal lateral resistance of pile group (N) (10.7.3.11)
nominal resistance (N) (10.6.3.3)
nominal load carried by pile point (N) (10.7.3.2)
factored resistance (N) (10.6.3.3)
5
Specification for Bridge Design
Qs
Qsbell
Qug
Qult
Qr
q
qc
=
=
=
=
=
=
=
qc1
=
qc2
=
q
qn
qo
qp
qR
qs
qsbell
qu
qult
q1
=
=
=
=
=
=
=
=
=
=
q2
=
Ri
r
ro
Sc
Se
SPT
Ss
Su
sc, sq, s
sd
T
t
td
t1, t2
V
Wg
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
nominal load carried by pile shaft (N) (10.7.3.2)
nominal uplift resistance of a belled drilled shaft (N) (10.8.3.7.2)
nominal uplift resistance of a pile group (N) (10.7.3.7.3)
total nominal bearing resistance (N) (10.7.3.2)
maximum shear resistance between the foundation and the soil (N) (10.5.5)
net foundation pressure applied at 2Db/3 (MPa) (10.7.2.3.3)
static cone resistance (MPa); average static cone resistance over a depth B below
the equivalent footing (MPa) (10.6.3.1.3c) (10.7.2.3.3)
minimum average static cone resistance over a depth yD below a pile tip (MPa)
(10.7.3.4.3b)
minimum average static cone resistance over a distance 8D above the pile tip
(MPa) (l0.7.3.4.3b)
limiting point resistance (MPa) (l0.7.3.4.2a)
nominal bearing resistance (MPa) (10.6.3.1.1)
vertical stress at base of loaded area (MPa) (10.6.2.2.Sb)
nominal unit point resistance (MPa) (10.7.3.2)
factored bearing resistance (MPa) (10.6.3.1.1)
unit shear resistance; nominal unit skin resistance (MPa) (10.6.3.3) (10.7.3.2)
nominal unit uplift resistance of a belied drilled shaft (MPa) (10.8.3.7.2)
average uniaxial compression strength of the rock core (MPa) (10.7.3.5)
nominal bearing resistance (MPa) (10.6.3.1.1)
ultimate bearing capacity of footing supported in the upper layer of a two-layer
system, assuming the upper layer is infinitely thick (MPa) (10.6.3.1.2a)
ultimate bearing capacity of a fictitious footing of the same size and shape as the
actual footing, but supported on surface of the second (lower) layer of a two-layer
system (MPa) (10.6.3.1.2a)
reduction factor accounting for the effect of load inclination (DIM) (l0.6.3.1.3b)
radius of circular footing or B/2 for square footing (mm) (l0.6.2.2.3d)
initial total vertical pressure at foundation level (MPa) (10.6.3.1.3d)
consolidation settlement (mm) (10.6.2.2.3a)
elastic settlement (mm) (10.6.2.2.3a)
standard penetration test (10.5.5)
secondary settlement (mm) (10.6.2.2.3a)
undrained shear strength (MPa) (10.6.3.1.2b)
average undrained shear strength along pile shaft (MPa) (10.7.3.7.3)
shape factors (DIM) (10.6.3.1.2b) (10.6.3.1.2c)
spacing of discontinuities (mm) (10.7.3.5)
time factor (DIM) (10.6.2.2.3c)
time for a given percentage of one-dimensional consolidation settlement (YR) (10.6.2.2.3c)
width of discontinuities (mm) (10.7.3.5)
arbitrary time intervals for determination of Ss (YR) (10.6.2.2.3c)
vertical component of inclined loads (N) (10.6.3.1.3b)
weight of block of soil, piles and pile cap (N) (10.7.3.7.3)
X
Y
Z
=
=
=
width of pile group (mm) (10.7.2.3.3)
length of pile group (mm) (10.7.3.7.3)
total embedded pile length (mm) (10.7.3.4.3c)
Su
6
Specification for Bridge Design
z



=
=
=
=
=
=
c
=

=
depth below ground surface (mm) (10.8.3.4.2)
adhesion factor applied to Su, (DIM) (10.7.3.3.2a)
reduction factor (DIM) (10.6.2.2.3d)
coefficient relating the vertical effective stress and the unit skin friction of a pile or drilled
shaft (DIM) (10.7.3.3.2b)
punching index (DIM) (10.6.3.1.2b)
factor to account for footing shape and rigidity (DIM) (1 0.6.2.2.3d)
density of soil (kg/m3) (10.6.3.1.2b)
angle of shearing resistance between soil and pile (DEG) (10.6.3.3)
efficiency factor for pile or drilled shaft group (DIM) (10.7.3.10.2)
empirical coefficient relating the passive lateral earth pressure and the unit skin friction of
a pile (DIM) (10.7.3.3.2c)
reduction factor for consolidation settlements to account for three-dimensional effects
(DIM) (1 0.6.2.2.3c)
settlement of pile group (mm) (10.7.2.3.3)
f
=
final vertical effective stress in soil at depth interval below footing (MPa) (10.6.2.2.3c)
o
=
initial vertical effective stress in soil at depth interval below footing (MPa) (10.6.2.2.3c)
p
=
maximum past vertical effective stress in soil at depth interval below footing (MPa)
(10.6.2.2.3c)
pc
=
current vertical effective stress in the soil, not including the additional stress due to the
footing loads (MPa) (10.6.2.2.3c)

=
resistance factor (10.5.5)

E

m
z

=
=
=
=
 ep =
resistance factor for passive pressure (10.6.3.3)
f
=
angle of internal friction of soil (DEG) (10.6.3.3)
g
=
resistance factor for the bearing capacity of a pile group failing as a unit consisting of the
piles and the block of soil contained within the piles; group resistance factor (10.7.3.10.1)
L
=
pile group resistance factor for lateral loads (DIM) (10.7.3.11)
q
=
rsistance factor for the total bearing capacity of a pile for those methods that do not
distinguish between total resistance and the individual contributions of tip resistance and
shaft resistance (10.7.3.2)
 qs =
resistance factor for the shaft capacity of a pile for those methods that separate the
resistance of a pile into contributions from tip resistance and shaft resistance (10.7.3.2)
 qp =
resistance factor for the tip capacity of a pile for those methods that separate the
resistance of a pile into contributions from tip resistance and shaft resistance (10.7.3.2)
 =
u =
 ug =
resistance factor for shear between soil and foundation (10.5.5)
1
=
effective stress angle of internal friction of the top layer of soil (DEG) (10.6.3.1.2c)

=
reduced effective stress soil friction angle for punching shear (DEG) (10.6.3.1.2a)
*
resistance factor for the uplift capacity of a single pile (10.7.3.7.2)
resistance factor for the uplift capacity of pile groups (10.7.3.7.3)
10.4. DETERMINATION OF SOIL PROPERTIES
7
Specification for Bridge Design
10.4.1. Subsurface Exploration
Subsurface explorations shall be performed for each substructure element to provide the necessary
information for the design and construction of foundations. The extent of exploration shall be based on
subsurface conditions, structure type, and project requirements. The exploration program shall be extensive
enough to reveal the nature and types of soil deposits and/or rock formations encountered, the engineering
properties of the soils and/or rocks, the potential for liquefaction, and the groundwater conditions.
Borings shall be taken at pier and abutment locations, sufficient in number and depth, to establish a
reliable longitudinal and transverse substrata profile. Samples of material encountered shall be taken
and preserved for future reference and/or testing. Boring logs shall be prepared in detail sufficient to
locate material strata, results of penetration tests, groundwater, any artesian action, and where samples
were taken.
Special attention shall be paid to the detection of narrow, soft seams that may be located at stratum
boundaries.
If so requested by the Owner, boring and penetration test holes shall be plugged to prevent water
contamination.
Subsurface explorations shall be made to competent material of suitable bearing capacity or to depth
where added stresses due to estimated footing load is less than 10 percent of the existing effective soil
overburden stress, whichever is the greater. If bedrock is encountered at shallow depths, the boring
shall advance a minimum of 3000 mm into the bedrock or to the proposed foundation depth,
whichever is greater.
Laboratory and/or in-situ tests shall be performed to determine the strength, deformation, and flow
characteristics of soils and/or rocks and their suitability for the foundation selected.
10.4.2.
Laboratory Tests
10.4.2.1. General
Laboratory tests shall be carried out in conformance with the relevant AASHTO or ASTM standards
or Owner-supplied standards and may include the following tests for soils and rocks.
10.4.2.2. Soil Testings
Laboratory soil tests may include:

Water Content - ASTM D 4643

Specific Gravity - AASHTO T 100 (ASTM D 854)

Grain Size Distribution - AASHTO T 88 (ASTM D 422)

Liquid Limit and Plastic Limit - AASHTO T 90 (ASTM D4318)

Direct Shear Test - AASHTO T 238 (ASTM D 3080)

Unconfined Compression Test - AASHTO T 208 (ASTM D 2166)

Unconsolidated-Undrained Triaxial Test - ASTM D 2850

Consolidated-Undrained Triaxial Test - AASHTO T 297 (ASTM D 4767)

Consolidation Test - AASHTO T 216 (ASTM D 2435 or D 4186)
8

Specification for Bridge Design
Permeability Test - AASHTO T 215 (ASTM D 2434)
10.4.2.3. Rock Tests
Laboratory rock tests may include:

Determination of Elastic Moduli - ASTM D 3148

Triaxial Compression Test - AASHTO T 286 (ASTM D 2664)

Unconfined Compression Test - ASTM D 2938

Splitting Tensile Strength Test - ASTM D 3967
10.4.3.
In-situ Tests
10.4.3.1. General
In-situ tests may be performed to obtain deformation and strength parameters of foundation soils or
rock for the purposes of design and/or analysis. The tests shall be performed in accordance with the
appropriate standards recommended by ASTM or AASHTO and may include the in-situ soil tests and
in-situ rock tests.
10.4.3.2. In-Situ Soil Tests
In-situ soil tests include:

Standard Penetration Test - AASHTO T 206 (ASTM D 1586)

Static Cone Test - ASTM D 3441

Field Vane Test - AASHTO T 223 (ASTM D 2573)

Pressuremeter Test - ASTM D 4719

Plate Bearing Test - AASHTO T 235 (ASTM D 1194)

Well Test (Permeability) - ASTM D 4750
10.4.3.3. In-Situ Rock Tests
In-situ tests may include:

Deformability and Strength of Weak Rock by an In-Situ Uniaxial Compressive Test - ASTM D 4555

Determination of Direct Shear Strength of Rock Discontinuities - ASTM D 4554

Modulus of Deformation of Rock Mass Using the Flexible Plate Loading Method - ASTM D 4395

Modulus of Deformation of Rock Mass Using a Radial Jacking Test - ASTM D 4506

Modulus of Deformation of Rock Mass Using the Rigid Plate Loading Method - ASTM D 4394
9
Specification for Bridge Design

Stress and Modulus of Deformation Determination Using the Flatjack Method - ASTM D 4729

Stress in Rock Using the Hydraulic Fracturing Method - ASTM D 4645
10.5. LIMIT STATES AND RESISTANCE FACTORS
10.5.1. General
The limit states shall be as specified in Article 1.3.2; foundation-specific clarifications are contained in
this section.
10.5.2.
Service Limit States
Foundation design at the service limit state shall include:

Settlements,

Lateral displacements, and

Bearing resistance estimated using the presumptive bearing pressure.
Consideration of settlement shall be based upon rideability and economy.
10.5.3.
Strength Limit State
Foundation design at the strength limit state shall include:

Bearing resistance, except presumptive bearing pressure;

Excessive loss of contact;

Sliding at the base of footing;

Loss of lateral support;

Loss of overall stability; and

Structural capacity.
Foundations shall be proportioned such that the factored resistance is not less than the effects of
factored loads specified in Section 3.
10.5.4.
Extreme Event Limit States
Foundations shall be designed for extreme events as applicable.
10.5.5.
ResIstance Factors
Resistance factors for different types of foundation systems at the strength limit state shall be taken as
specified in Tables 1 through 3, unless regionally specific values are available.
10
Specification for Bridge Design
Where pile foundations are specified, the contract documents shall specify the level of field pile
capacity verification required. The field verification specified shall be consistent with the value of  v
taken from Table 2.
Resistance factors for the service limit state shall be taken as 1.0.
A further reduction in Pn for piles should be considered when pile driving difficulty is expected.
Table 10.5.5-1 - Resistance Factors for Strength Limit State for
Shallow Foundations
11
Specification for Bridge Design
12
Specification for Bridge Design
Table 10.5.5-2 - Resistance Factors for Geotechnical Limit State
in Axially Loaded Piles
13
Specification for Bridge Design
Table 10.5.5-3 - Resistance Factors for Geotechnical Strength
Limit State in Axially Loaded Drilled Shafts
10.6. SPREAD FOOTINGS
10.6.1. General Considerations
10.6.1.1. General
Provisions of this Article shall apply to design of isolated footings and, where applicable, to combined
footings. Special attention shall be given to footings on fill.
Footings should be designed so that the pressure under the footing is as nearly uniform as practicable.
The distribution of soil pressure shall be consistent with properties of the soil or rock and the structure
and with established principles of soil and rock mechanics.
14
Specification for Bridge Design
10.6.1.2.Depth
The depth of footings shall be determined in consideration of the character of the foundation materials
and the possibility of undermining. Footings at stream crossings shall be founded at a depth at least
600 mm below the maximum anticipated depth of scour as specified in Article 2.6.4.4.1.
Consideration should be given to the use of either a geotextile or graded granular filter layer to reduce
susceptibility to piping in rip rap or abutment backfill.
10.6.1.3. Anchorage
Footings that are founded on inclined smooth solid rock surfaces and that are not restrained by an
overburden of resistant material shall be effectively anchored by means of rock anchors, rock bolts,
dowels, keys, or other suitable means. Shallow keying of large footing areas shall be avoided where
blasting is required for rock removal.
10.6.1.4. Groundwater
Footings shall be designed in consideration of the highest anticipated groundwater table.
The influences of groundwater table on the bearing capacity of soils or rocks and on the settlements of
the structure should be considered. In cases where seepage forces are present, they should also be
included in the analyses.
10.6.1.5. Uplift
Where foundations are subjected to uplift forces, they shall be investigated both for resistance to
pullout and for their structural strength.
15
Specification for Bridge Design
10.6.1.6. Nearby Structures
Where foundations are placed adjacent to existing structures, the influence of the existing structures on
the behavior of the foundation and the effect of the foundation on the existing structures shall be
investigated.
10.6.2. Movement and Bearing Pressure at the Service Limit State
10.6.2.1. General
Movement of foundations in both vertical settlement and horizontal lateral displacement directions
shall be investigated at the service limit state.
Lateral displacement of a structure shall be evaluated where:

Horizontal or inclined loads are present,

The foundation is placed on embankment slope,

The possibility of loss of foundation support through erosion or scour exists, or

Bearing strata are significantly inclined.
10.6.2.2. Movement criteria
10.6.2.2.1. General
Vertical and horizontal movement criteria shall be developed to be consistent with the function and
type of structure, anticipated service life, and consequences of unacceptable movements on structure
performance. The tolerable movement criteria shall be established by either empirical procedures or
structural analyses or by consideration of both.
10.6.2.2.2. Loads
Immediate settlement shall be determined using load combination Service, as specified in Table 3.4.11. Time-dependent settlements in cohesive soils may be determined by using the permanent loads
only.
Settlements caused by embankment loadings behind bridge abutments shall be investigated.
In seismically active areas, consideration shall be given to the potential settlements of footings on sand
resulting from vibration induced by earthquake.
10.6.2.2.3. Settlement Analyses
16
Specification for Bridge Design
10.6.2.2.3a. General
Foundation settlements should be estimated using deformation analyses based on the results of
laboratory testing or in-situ testing. The soil parameters used in the analyses should be chosen to
reflect the loading history of the ground, the construction sequence, and the effect of soil layering.
Both total and differential settlements, including time dependent effects, shall be considered.
The total settlement, including elastic, consolidation, and secondary components, may be taken as:
St = Se + Sc +Ss
(10.6.2.2.3a-1)
where:
Se
=
elastic settlement (mm)
Sc
=
consolidation settlement (mm)
Ss
=
secondary settlement (mm)
Other factors that can affect settlement, e.g., embankment loading and lateral and/or eccentric loading
and for footings on granular soils, vibration loading from dynamic live loads or earthquake loads,
should also be considered, where appropriate.
The distribution of vertical stress increase below circular (or square) and long rectangular footings,
i.e., where L > 5B, may be estimated using Figure 1.
Figure 10.6.2.2.3a-1 - Boussinesq Vertical Stress Contours for
Continuous and Square
Footings Modified After Sowers (1979)
17
Specification for Bridge Design
10. 6.2.2.3b. Settlement of Footings on Cohesionless Soils
Settlements of footings on cohesionless soils may be estimated using empirical procedures or elastic
theory.
The elastic settlement of footings on cohesionless soils may be estimated using the following:
Se =
q 1  v  A 
o
2
Es z
(10.6.2.2.3b-1)
where:
qo
=
load intensity (MPa)
A
=
area of footing (mm2)
Es
=
young’s modulus of soil taken as specified in Table 1 in lieu of the results of laboratory
tests (MPa)
z
=
shape factor taken as specified in Table 2 (DIM)
v
=
poisson’s Ratio taken as specified in Table 1 in lieu of the results of laboratory tests (DIM)
Unless Es varies significantly with depth, Es should be determined at a depth of about 1/2 to 2/3 of B
below the footing. If the soil modulus varies significantly with depth, a weighted average value of Es.
may be used.
The following nomenclature shall be used with Table 1:
N
=
Standard Penetration Test (SPT) resistance
N1
=
SPT corrected for depth
Su
=
undrained shear strength (MPa)
qc
=
cone penetration resistance (MPa).
18
Specification for Bridge Design
Table 10.6.2.2.3b-1 - Elastic Constants of Various Soils After U.S
Department of the Navy (1982) and Bowles (1988)
Table 10.6.2.2.3b-2 - Elastic Shape and Rigidity Factors, EPRI
(1983)
19
Specification for Bridge Design
10.6.2.2 3c. Settlement of Footings on Cohesive Soils
For foundations on stiff cohesive soils, the elastic settlement may be determined using Equation 10.6.2.2.3b-1.
For foundations on cohesive soils, both immediate and consolidation settlements shall be investigated. In highly
plastic and organic clay, secondary settlements may be significant and shall be included in the analysis.
Where laboratory test results are expressed in terms of void ratio (e), the consolidation settlement of
footings on saturated or nearly saturated cohesive soils may be taken as:

For initially overconsolidated soils (i.e.,  p/ >  o/ )
Ss =

(10.6.2.2.3c-1)
For initially normally consolidated soils (i.e.,  p/ =  o/ ):
Ss =

 p/
 f/ 
 H c  

  Ccr log /  Cc log / 
o
p 
 1  eo   

 f/ 
 H c  

  Cc log / 
p 
 1  eo   

(10.6.2.2.3c-2)
For initially underconsolidated soils (i.e., .,  p <  o/ )
/
Sc
=
  / 
 H c  
 f 
C
log

 c
  / 


1

e
o


 pc 
(10.6.2.2.3c-3)
Where laboratory test results are expressed in terms of vertical strain,  v , consolidation settlement
may be taken as:

For initially overconsolidated soils (i.e.,  p/ >  o/ ):
Sc

=
 / 
 /
p
 f

C
log
re
 / 
 /
 o 
 p






(10.6.2.2.3c-4)
For initially normally consolidated soils (i.e.,  p/ =  o/ ):
Sc =


Hc C re log
 / 
Hc Cce log  /f 
 p 
(10.6.2.2.3c-5)
Fkr initially underconsolidated soils (i.e.,  p/ <  o/ ):
 ' 
Sc  H c H ce log ' f 
 
 pc 
(10.6.2.2.3c-6)
where:
Hc
=
height of compressible soil layer (mm)
eo
=
void ratio at initial vertical effective stress (DIM)
Ccr
=
recompression index determined as specified in Figure 1 (DIM)
Cc
=
compression index determined as specified in Figure 1 (DIM)
Cce
=
compression ratio determined as specified in Figure 2 (DIM)
Cre
=
recompression ratio determined as specified in Figure 2 (DIM)
 'p
=
maximum past vertical effective stress in soil at depth interval below footing (MPa)
20
Specification for Bridge Design
 'o
=
initial vertical effective stress in soil at depth interval below footing (MPa)
 'f
=
final vertical effective stress in soil at depth interval below footing (MPa)
 'pc
=
current vertical effective stress in the soil, not including the additional stress due to the
Void ratio, e
footing loads (MPa)
Vertical stain, ev
Figure 10.6.2.2.3c-1 - Typical Consolidation Compression Curve for
Overconsolidation Soil – Void Ratio Versus Vertical Effective
Stress, EPRI (1983)
Figure 10.6.2.2.3c-2 - Typical Consolidation Compression Curve for
Overconsolidation Soil - Vertical Strain Versus Vertical Effective
Stress, EPRI (1983)
If the footing width is small relative to the thickness of the compressible soil, the effect of threedimensional loading shall be considered and may be taken as:
Sc(3-D) =  c Sc(1-D)
where:
c
=
reduction factor taken as specified in Figure 3 (DIM)
(10.6.2.2.3c-7)
21
Specification for Bridge Design
22
Specification for Bridge Design
Sc(1-D) =
single dimensional consolidation settlement (mm)
Figure 10.6.2.2.3c-3 - Reduction Factor to Account for Effects of
Three-Dimensional Consolidation Settlement, EPRI (1983)
The time (t) to achieve a given percentage of the total estimated one-dimensional consolidation
settlement may be taken as:
t =
TH 2d
cv
(10.6.2.2.3c-8)
where:
T
=
time factor taken as specified in Figure 4 (DIM)
Hd
=
height of longest drainage path in compressible soil layer (mm)
cv
=
a coefficient taken from the results of laboratory consolidation testing of undisturbed soil
samples or from in-situ measurements using devices such as a piezoprobe or piezocone
(mm2/YR)
Secondary settlement of footings on cohesive soil may be taken as:
Ss =
 t2 

 t1 
CaeHclog 
(10.8.2.2.3c-9)
where:
t1
=
time when secondary settlement begins, i.e., typically at a time equivalent to 90 percent
average degree of consolidation (YR)
t2
=
arbitrary time that could represent the service life of the structure (YR)
Cae
=
coefficient estimaded from the results of laboratory consolidation testing of undisturbed
soil samples (DIM)
23
Specification for Bridge Design
Figure 10.6.2.2.3c-4 - Percentage of Consolidation as a Function of
Time Factor, T, EPRI (1983)
10.6.2.2.3d. Settlements of Footings on Rock
For footings on competent rock, designed in accordance with Article 10.6.3.2.2, elastic settlements
may generally be assumed to be less than 15 mm. When elastic settlements of this magnitude are
unacceptable or when the rock is not competent, an analysis of settlement based on rock mass
characteristics shall be made. Where rock is broken or jointed and the criteria for competent rock are
not met, the influence of rock type, condition of discontinuities, and degree of weathering shall be
considered in the settlement analysis.
The elastic settlement of footings on broken or jointed rock may be taken as:

For circular (or square) footings;

  qo 1  v 2
in which:
Ip

 Erl
p
 
=
(10.6.2.2.3d-1)
m
z
(10.6.2.2.3d-2)
For rectangular footings;

  qo 1  v 2
BIE
p
(10.6.2.2.3d-3)
m
in which:
1/ 2
L
 
B
Ip   
z
(10.6.2.2.3d-4)
24
Specification for Bridge Design
where:
qo
=
vertical stress at base of loaded area (MPa)
v
=
Poisson’s Ratio (DIM)
r
=
radius of circular footing or B/2 for square footing (mm)
Ip
=
influence coefficient to account for rigidity and dimensions of footing (DIM)
Em
=
rock mass modulus (MPa)
z
=
factor to account for footing shape and rigidity (DIM)
Values of Ip may be computed using the  z values presented in Table 10.6.2.2.3b-2 for rigid footings.
Where the results of laboratory testing are not available, values of Poisson’s ratio, v, for typical rock
types may be taken as specified in Table 1. Determination of the rock mass modulus, E m , should be
based on the results of in-situ and laboratory tests. Alternatively, values of Em may be estimated by
multiplying the intact rock modulus, E0 , obtained from uniaxial compression tests by a reduction
factor,  E , which accounts for the frequency of discontinuities by the rock quality designation
(RQD), using the following relationship (Gardner 1987):
Em
=
 E Eo
(10.6.2.2.3d-5)
in which:
E =
0.0231 (RQD) - 1.32  0.15(10.6.2.2.3d-6)
For preliminary design or when site-specific test data cannot be obtained, guidelines for estimating
values of E0, such as those presented in Table 2, may be used. For preliminary analyses or for final
design when in-situ test results are not available, a value of  E = 0.15 should be used to estimate Em.
The magnitude of consolidation and secondary settlements in rock masses containing soft seams or
other material with time-dependent settlement characteristics may be estimated by applying
procedures specified in Article 10.6.2.2.3c.
25
Specification for Bridge Design
Table 10.6.2.2.3d-1- Summary of Poisson’ s Ratio for Intact Rock
Modified
After Kulhawy (1978)
Table 10.6.2.2.3d-2- Summary of Elastic Moduli for Intact Rock
Modified After Kulhawy (1978)
10.6.2.2.4. Loss of Overall Stability
26
Specification for Bridge Design
Overall stability shall be investigated at the service limit state using the provisions of Article 3.4.1.
10.6.2.3. Bearing Pressure At The Service Limit State
10.6.2.3.1. Presumptive Values for Bearing Pressure
The use of presumptive values shall be based on a knowledge of geological conditions at or near the
bridge site.
10.6.2.3.2. Semiempirical Procedures for Bearing Pressure
Bearing pressure of rock may be determined using empirical correlation with RQD or the
Geomechanic Rock Mass Rating System, RMR, or Norwegian Geotechnical Institute, NGI, Rock
Mass Classification System. Local experience shall be considered in the use of these semiempirical
procedures.
If the recommended value of allowable bearing pressure exceeds either the unconfined compressive
strength of the rock or the allowable stress on the concrete, the allowable bearing pressure shall be
taken as the lesser of the unconflned compressive strength of the rock or the allowable stress on the
concrete. The allowable bearing stress of concrete may be taken as 0.3 f/c.
10.6.3. Resistance at the Strength Limit State
10.6.3.1. Bearing Resistance Of Soils Under Footings
10.6.3.1.1. General
Bearing resistance shall be determined based on the highest anticipated position of groundwater level
at the footing location.
The factored resistance, qR, at strength limit state shall be taken as:
qR =
 qn =
 qult
(10.6.3.1.1-1)
where:
qn = qUlt
=
resistance factor specified in Article 10.5.5
=
nominal bearing resistance (MPa)
Where loads are eccentric, the effective footing dimensions L’ and B’, as specified in Article
10.6.3.1.5, shall be used instead of the overall dimensions L and B in all equations, tables, and figures
pertaining to bearing capacity.
10.6.3.1.2. Theoretical Estimation
10.6.3. 1.2a. General
The nominal bearing resistance should be estimated using accepted soil mechanics theories based on
measured soil parameters. The soil parameters used in the analysis shall be representative of the soil
shear strength under the considered loading and subsurface conditions.
27
Specification for Bridge Design
The nominal bearing resistance of footings on cohesionless soils shall be evaluated using effective
stress analyses and drained soil strength parameters.
The nominal bearing resistance of footings on cohesive soils shall be evaluated for total stress analyses
and undrained soil strength parameters. In cases where the cohesive soils may soften and lose strength
with time, the bearing resistance of these soils shall also be evaluated for permanent loading
conditions using effective stress analyses and drained soil strength parameters.
For footings on compacted soils, the nominal bearing resistance shall be evaluated using the more
critical of either total or effective stress analyses.
Where it is necessary to estimate nominal bearing resistance of cohesive soils, such as clays, and
compacted soils by effective stress analyses, Equation 10.6.3.1.2c-1 shall apply.
If local or punching shear failure is possible, the nominal bearing capacity may be estimated using
reduced shear strength parameters c* and in Equation 10.6.3.1.2b-1 and 10.6.3.1.2c-1. The reduced
shear parameters may be taken as:
c* =
* =
0.67c
tan
-1
(10.6.3.1.2a-1)
(0.67 tan )
(10.6.3.1.2a-2)
where:
c*
=
reduced effective stress soil cohesion for punching shear (MPa)
*
=
reduced effective stress soil friction angle for punching shear (DEG)
Where the soil profile contains a second layer of soil with different properties affecting shear strength
within a distance below the footing less than HCRIT, the bearing capacity soil system shall be
determined using the provisions for two-layered soil systems herein. The distance HCRIT may be taken as:
HCRIT
q 
3B ln  1 
 q2 
=
B

2 1  
L

(10.6.3.1.2a-3)
Where:
q1
=
ultimate bearing capacity of footing supported in the upper layer of a two-layer system,
assuming the upper layer is infinitely thick (MPa)
q2
=
ultimate bearing capacity of a fictitious footing of the same size and shape as the actual
footing but supported on surface of the second (lower) layer of a two-layer system (MPa)
B
=
footing width (mm)
L
=
footing length (mm)
28
Specification for Bridge Design
Footings with inclined bases should be avoided wherever possible. Where use of an inclined footing
base cannot be avoided, the nominal bearing capacity determined in accordance with the provisions
herein shall be further reduced using accepted corrections for inclined footing bases available in the
literature.
10.6.3.1.2b. Saturated Clays
The nominal bearing resistance of a layer of saturated clay, in MPa, determined from undrained shear
strength may be taken as:
qult = cNcm +gDf Nqm x 10-9
(10.6.3.1.2b-1)
where:
c = Su
=
undrained shear strength (MPa)
Ncm, Nqm
=
modified bearing capacity factors that are functions of footing shape, embedment
depth, soil compressibility, and load inclination (DIM)

=
total, i.e., moist, density of clay (kg/m3)
Df
=
embedment depth taken to the bottom of the footing (mm)
The bearing capacity factors Ncm and Nqm may be taken as:

For Df/B 2.5, B/L 1 and H/V 0.4
Ncm =

Nc [ 1+0.2 (Df/B)] [1 + 0.2 (B/L)] [1 - 1.3 (H/V)]
(10.6.3.1.2b-2)
For Df/B > 2.5 and H/V 0.4
Ncm = Nc[1 + 0.2(B/L)][1 - 1.3(H/V)]
Nc
Nqm
=
5.0 for use in Equation 2 on relatively level soil
=
7.5 for use in Equation 3 on relatively level soil
=
Ncq from Figure 1 for footing on or adjacent to sloping ground
=
1.0 for saturated clay and relatively level ground surface
=
0.0 for footing on sloping ground or adjacent to sloping ground
(10.6.3.1.2b-3)
In Figure 1, the stability number, Ns, shall be taken as:


For B < Hs
Ns = 0
(10.6.3.1.2b-4)
Ns = [gHs/c] x 10-9
(10.6.3.1.2b-5)
For B Hs
where:
B
=
footing width (mm)
L
=
footing length (mm)
29
Specification for Bridge Design
Where a footing supported on a two-layered cohesive soil system is subjected to an undrained loading,
the nominal bearing capacity may be determined using Equation 1 with the following interpretations:
c1
=
undrained shear strength of the top layer of soil as depicted in Figure 2 (MPa)
Ncm
=
Nm, a bearing capacity factor as specified below (DIM)
Nqm
=
1.0 (DIM)
Figure 10.6.3.1 .2b-1 - Modified Bearing Capacity Factors for
Footing in Cohesive Soils and On or Adjacent to Sloping Ground after
Meyerhof (1957)
Where the bearing stratum overlies a stiffer cohesive soil, Nm may be taken as specified in Figure 3
Where the bearing stratum overlies a softer cohesive soil, Nm may be taken as:
Nm
=
m 
in which:
 1


 ksc N c   sc N c
 m

(10.6.3.1.2b-6)
BL
2B  L H s2
k
=
c1/c2
c1
=
shear strength of upper soil layer (MPa)
c2
=
shear strength of lower soil layer (MPa)
Hs2
=
distance from bottom of footing to top of the second soil layer (mm)
sc
=
1.0 for continuous footings
=
1+
B  N qm 
for rectangular footings with L < 5B (10.6.3.1 .2b-8)
L  N c 
(10.6.3.1.2b-7)
30
Specification for Bridge Design
where:
Nc
=
bearing capacity factor determined herein (DIM)
Nqm
=
bearing capacity factor determined herein
Where a two-layered cohesive soil system is subjected to drained loading condition, the nominal
bearing capacity shall be determined using Equation 10.6.3.1.2c-4.
H
=
unfactored horizontal load (N)
Hs
=
height of sloping ground mass (mm)
V
=
unfactored vertical load (N)
Figure 10.6.3.1.2b-2- Two - Layer Soil Profiles
31
Specification for Bridge Design
Figure 10.6.3.1.2b-3 - Modified Bearing Capacity Factor for TwoLayer Cohesive Soil with Softer Soil Overlying Stiffer Soil, EPRI
(1983)
10.6.3.1.2c. Cohesionless Soils
The nominal bearing resistance of a layer of cohesionless soil, such as sands or gravels, in MPa, may
be taken as:
Qult = 0.5 g  BCw1 N m x 10-9 + g  Cw2 Df Nqm x 10-9
(10.6.3.1
.2c-1)
where:
Df
=
footing depth (mm)

=
total, i.e., moist, density of sand or gravel (kg/m3)
B
=
footing width (mm)
Cwl,Cw2 =
coefficients as specified in Table 1 as a function of Dw (DIM)
Dw`
=
depth to water surface taken from the ground surface (mm)
N m
=
modified bearing capacity factor (DIM)
Table 10.6.3.1.2c-1 - Coefficients Cw1 and Cw2 for Various Groundwater
Depths
Dw
Cw1
Cw2
0.0
0.5
0.5
Df
0.5
1.0
> 1.5B + Df
1.0
1.0
For intermediate positions of the groundwater table, values of Cw1 and Cw2 may be determined by
interpolation between the values specified in Table 1.
The bearing capacity factors N m , and Nqm may be taken as:
32
Specification for Bridge Design
N m = N  s c i 
Nqm =
(10.6.3.1.2c-2)
Nqsqcqiqdq
(10.6.3.1 .2c-3)
where:
N
Nq
=
bearing capacity factor as specified in Table 2 for footings on relatively level ground
(DIM)
=
Nyg as specified in Figure 1 for footing on or adjacent to sloping ground (DIM)
=
bearing capacity factor as specified in Table 2 for relatively level ground (DIM)
=
0.0 for footing on or adjacent to sloping ground (DIM)
sq , s  =
shape factors specified in Tables 3 and 4, respectively (DIM)
cq , c  =
soil compressibility factors specified in Tables 5 and 6 (DIM)
iq , i =
load inclination factors specified in Tables 7 and 8 (DIM)
dq
depth factor specified in Table 9 (DIM)
=
The following interpretation shall apply:

In Tables 5 and 6, q shall be taken as the initial vertical effective stress at the footing depth, i.e.,
vertical stress at the bottom of the footing prior to excavation, corrected for water pressure.

In Tables 7 and 8, H & V shall be taken as the unfactored horizontal and vertical loads,
respectively.

In Table 9, values of dq shall be taken as applicable if the soils above the footing bottom are as
competent as the soils below the footing. If the soils are weaker, use dq = 1.0.
Table 10.6.3.1.2c-2 - Bearing Capacity Factors N and Nq for Footings
on
Cohesionless Soil (Barker et al. 1991)
Friction Angle,
(  f ) (deg)
28
30
32
34
36
38
40
42
44
46
N
Nq
17
22
30
41
58
78
110
155
225
330
15
18
23
29
38
49
64
85
115
160
33
Specification for Bridge Design
Table 10.6.3.1.2c-3 - Shape Factor sq for Footings on Cohesionless
Soil (Barker et al. 1991)
Table 10.6.3.1.2c-4 - Shape Factor s for Footings on Cohesionless
Soil
(Barker et al. 1991)
B/L
1
2
5
10
s (dim)
0.60
0.80
0.92
0.96
Table 10.6.3.1.2c-5 - Soil Compressibility Factors C and cq for
square Footings on
Cohesionless Soil (Baker et al. 1991)
34
Specification for Bridge Design
Table 10.6.3.1.2c-6 - Soil Compressibility Factors C and cq for
Strip Footings on
Cohesionless Soil (Baker et al. 1991)
Table 10.6.3.1.2c-7 - Load Inclination Factors i and iq for Loads
Inclined in
Direction of Footing Width (Baker et
al. 1991)
35
Specification for Bridge Design
Table 10.6.3.1.2c-8 - Load Inclination Factors i and iq for Loads
Inclined in
Direction of Footing Width (Baker
et al. 1991)
Table 10.6.3.1.2c-9 - Depth Factor dq for Cohesionless Soils (Baker
et al. 1991)
Where a footing supported on a two-layered cohesive soil system is subjected to a drained loading, the
nominal bearing capacity may be taken as:

q ult
 B
 H 

 21  K tan1  B    1  '
1
 q 2   c1' cot 1'  e   L 
  c1 cot 1' (10.8.3.1.2c-4)
K
K


'
in which:
K
1  sin2  'f
1  sin2 1'
(10.6.3.1.2c-5)
36
Specification for Bridge Design
37
Specification for Bridge Design
where:
c1
=
undrained shear strength of the top layer of soil as depicted in Figure 3 (MPa)
q2
=
ultimate bearing capacity of a fictitious footing of the same size and shape as the actual
footing but supported on surface of the second (lower) layer of a two-layer system (MPa)
 1'
=
effective stress angle of internal friction of the top layer of soil (DEG)
Figure 10.6.3.1.2c-1 - Modified Bearing Capacity Factors for
Footings in Cohesionless Soils and On or Adjacent to Sloping Ground
after Meyerhof (1957)
10.6.3.1.3. Semiempirical Procedures
10.6.3.1.3a. General
The nominal bearing resistance of foundation soils may be estimated from the results of in-situ tests or
by observed resistance of similar soils. The use of a particular in-situ test and the interpretation of test
results should take local experience into consideration. The following in-situ tests may be used:
38
Specification for Bridge Design

Standard penetration test (SPT),

Cone penetration test (CPT), and

Pressuremeter test.
10.6.3.1.3b Using SPT
The nominal bearing resistance in sand, in MPa, based on SPT results may be taken as:

D 
qult = 3.2 x 10-5 N corr B  C w1  C w2 f R i (10.6.3.1.3b-1)
B 

where:
N corr
=
average value of corrected SPT blow count within the range of depth from footing
base to 1.5B below the footing (Blows/300 mm)
B
=
footing width (mm)
Cw1, Cw2
=
correction factors for groundwater effect, as specified in Table 10.6.3.1.2c-1 (DIM)
Df
=
footing embedment depth taken to the bottom of the footing (mm)
Ri
=
reduction factor accounting for the effect of load inclination, specified in Tables 1 and 2
(DIM
H
=
unfactored horizontal load for use in determining H/V ratio in Tables 1 and 2 (N) or
(N/mm)
V
=
unfactored vertical load for use in determining H/V ratio in Tables 1 and 2 (N) or (N/mm)
Table 10.6.3.1.3b-1 - Load Inclination Factor, Ri for Square
Footings
39
Specification for Bridge Design
Table 10.6.3.1.3b-2 - Load Inclination Factor, Ri for
Rectangular Footings
40
Specification for Bridge Design
10..6.3.1.3c. Using CPT
Based on CPT result, the nominal bending resistance, in MPa, for footings on sands or gravels may be
taken as:
qult
=

8.2 x 10-5 qcB  C w1  C w2

Df
B

R i

(10.6.3.1.3c-1)
where:
qc
=
average cone resistance within a depth B below the bottom of footing (MPa)
B
=
footing width (mm)
Df
=
footing embedment depth bottom of the footing (mm)
Ri
=
correction factor for load inclination, as specified in Tables 10.6.3.1.3b-1 and 10.6.3.l.3b-2 (DIM)
Cw1,Cw2 =
correction factors for groundwater effect, as specified in Table 10.6.3.l.2c-1 (DIM)
41
Specification for Bridge Design
10.6.3.1.3d. Use of Pressuremeter Test Results
The nominal bearing resistance of foundation soils, in MPa, determined from results of pressuremeter
test results, may be taken as:
qult =
[ro + k(pL - po)] Rt
(l0.6.3.1.3d-1)
where:
ro
=
initial total vertical pressure at foundation level (MPa)
k
=
empirical bearing capacity coefficient from Figure 1 (DIM)
pL
=
average value of limiting pressures obtained from pressurerneter tests within the depth of
1.5B above and below the foundation level (MPa)
po
=
total horizontal pressure at the depth where the pressuremeter test is performed (MPa)
Rt
=
correction factor for load inclination, as specified in Tables l0.6.3.I.3b-1 and 10.6.3.1.3b2 (DIM)
If the value of PL varies significantly within a depth of 1.5B above and below the foundation level, a
special averaging technique should be used
Empirical bcaring capacity
coefficient
Square
Foundation
B/L = 0
Strip
Foundation
B/L=0
Depth Coefficient, Df /B
42
Specification for Bridge Design
Soiltype
Clay
Consistency
very firm
(PL-Po) (MPa)
Class
Soft to very
firm
<
1.1
1
Loose
0.77- 3.8
2
Sand and
Loose
0.38 – 0.77
2
Gra vel
Veyy dense
2.9 – 5.8
4
< 0.67
1
Silt
Loose to
Meedium
Dense
1.1 – 2.9
2
Very Law
strength
0.96-2.9
2
Low strength
2.9 – 5.8
3
Medium to high
strength
5.7-9.6+
4
Rock
Figure 10.6.3.1.3d-1 - Values of Empirical Capacity Coefficient,
k (After Canadian Geotechnical Society 1985)
10.6.3.1.4. Plate Load Tests
The nominal bearing resistance may be determined by plate load tests, listed in Article 10.4.3.2,
provided that adequate subsurface explorations have been made to determine the soil profile below the
foundation.
The nominal bearing resistance determined from a load test may be extrapolated to adjacent footings
where the subsurface profile is similar.
10.6.3.1.5. Effect of Load Eccentricity
For loads eccentric to the centroid of the footing, a reduced effective area, B’ x L’, within the confines
of the physical footing shall be used in geotechnical design for settlement or bearing resistance. The
design bearing pressure on the effective area shall be assumed to be uniform. The reduced effective
area shall be concentric with the load.
The reduced dimensions for an eccentrically loaded rectangular footing may be taken as:
B/ = B - 2eB
(10.6.3.1.5-1)
L/ = L - 2eL
(10.6.3.1.5-2)
where:
eB
=
eccentricity parallel to dimension B (mm)
eL
=
eccentricity parallel to dimension L (mm)
Footings under eccentric loads shall be designed to ensure that:
43

Specification for Bridge Design
The factored bearing resistance is not less than the effects of factored loads, and
44

Specification for Bridge Design
For footings on soils, the eccentricity of the footing, evaluated based on factored loads, is less than
1/4 of the corresponding footing dimension, B or L.
For structural design of an eccentrically loaded foundation, a triangular or trapezoidal contact pressure
distribution based on factored loads shall be used.
For footings that are not rectangular, similar procedures should be used based upon the principles
specified above.
10.6.3.2. Bearing Resistance Of Rock
10.6.3.2.1. General
The methods used for design of footings on rock shall consider the presence, orientation, and
condition of discontinuities, weathering profiles, and other similar profiles as they apply at a
particular site.
For footings on competent rock, reliance on simple and direct analyses based on uniaxial compressive
rock strengths and RQD may be applicable. Competent rock shall be defined as a rock mass with
discontinuities that are open not wider than 3.2 mm. For footings on less competent rock, more
detailed investigations and analyses shall be performed to account for the effects of weathering and the
presence and condition of discontinuities.
10.6.3.2.2. Semiempirical Procedures
The nominal bearing resistance of rock may be determined using empirical correlation with the
Geomechanics Rock Mass Rating system, RMR, or Norwegian Geotechnical Institute, NGI, Rock
Mass Classification System. Local experience shall be considered in the use of these semiempirical
procedures.
The factored bearing pressure of the foundation shall not be taken to be greater than the factored
bearing strength of the footing concrete.
10.6.3.2.3. Analytic Method
The nominal bearing capacity of foundations on rock shall be determined using established rock
mechanics principles based on the rock mass strength parameters. The influence of discontinuities on
the failure mode shall also be considered.
10.6.3.2.4. Load Test
Where appropriate, load tests may be performed to determine the nominal bearing capacity of
foundations on rock.
10.6.3.2.5. Limits on Load Eccentricity
The eccentricity of loading, based on factored loads, shall not exceed three-eighths of the
corresponding footing dimensions B or L.
45
Specification for Bridge Design
10.6.3.3. Failure By Sliding
Failure by sliding shall be investigated for footings that support inclined load and/or are founded on
slopes.
For foundations on clay soils, the possible presence of a shrinkage gap between the soil and the
foundation shall be considered. If passive resistance is included as part of the shear resistance required
for resisting sliding, consideration shall also be given to possible future removal of the soil in front of
the foundation.
The factored resistance against failure by sliding, in N, may be taken as:
QR =  Qn =  TQT +  ep Qep
(10.6.3.3-1)
where:
T
=
resistance factor for shear resistance between soil and foundation specified in Table
10.5.5-1
QT
=
nominal shear resistance between soil and foundation (N)
 ep =
resistance factor for passive specified resistance in Table 10.5.5-1
Qep
nominal passive resistance of soil available throughout the design life of the structure (N)
=
If the soil beneath the footing is cohesionless, then:
QT = V tan 
(10.6.3.3-2)
for which:
tan 
=
tan  f for concrete cast against soil
=
0.8 tan  f for precast concrete footing
where:
f
=
internal friction angle of soil (DEG)
V
=
total vertical force(N)
For footings that rest on clay, the sliding resistance may be taken as the lesser of:

The cohesion of the clay, or

Where footings are supported on at least 150 mm of compacted granular material, one-half the
normal stress on the interface between the footing and soil, as shown in Figure 1 for retaining
walls. The following notation shall be taken to apply to Figure 1.
qs
=
unit shear resistance, equal to Su or 0.5  'v , whichever is less
QT
=
area under qs diagram (shaded area)
Su
=
undrained shear strength (MPa)

=
vertical effective stress (MPa)
'
v
46
Specification for Bridge Design
Figure 10.6.3.3-1 - Procedure for Estimating Sliding Resistance for
Walls on Clay
10.6.4. Structural Design
The structural design of footings shall comply with the requirements given in Article 5.13.3.
10.7. DRIVEN PILES
10.7.1. General
10.7.1.1. USE
Piling should be considered when footings cannot be founded on rock, stiff cohesive, or granular
foundation material at a reasonable expense. At locations where soil conditions would normally permit the
use of spread footings, but the potential for erosion exists, piles may be used as a protection against scour.
10.7.1.2. Pile Penetration
Required pile penetration should be determined based on the resistance to vertical and lateral loads
and the displacement of both the pile and the subsurface materials. In general, unless refusal is
encountered, the design penetration for any pile should be not less than 3000 mm into hard cohesive or
dense granular material and not less than 6000 mm into soft cohesive or loose granular material.
Unless refusal is encountered, piles for trestle or pile bents shall penetrate a distance equal to at least
one-third the unsupported length of the pile.
Piling used to penetrate a soft or loose upper stratum overlying a hard or firm stratum, shall penetrate the
firm stratum by a distance sufficient to limit movement of the piles and attain sufficient bearing capacities.
10.7.1.3. Resistance
47
Specification for Bridge Design
Piles shall be designed to have adequate bearing and structural resistances, tolerable settlements, and
tolerable lateral displacements.
The supporting resistance of piles should be determined by static analysis methods based on soil
structure interaction, load testing, the use of the pile driving analyzer, or other stress-wave
measurement technique, with CAPWAP. The resistance of piles should be determined through a
suitable combination of subsurface investigations, laboratory and/or in-situ tests, analytical methods,
pile load tests, and reference to the history of past performance. Consideration shall also be given to:

The difference between the resistance of a single pile and that of a group of piles;

The capacity of the underlying strata to support the load of the pile group;

The effects of driving the piles on adjacent structures;

The possibility of scour and its effect; and

The transmission of forces, such as negative skin friction or downdrag forces, from consolidating
soil.
Resistance factors for pile capacities obtained from field load tests or from the pile driving analyzer
shall be as specified in Table 10.5.5-2.
10.7.1.4. Effect Of Settling Ground And Down Drag Loads
Possible development of downdrag loads on piles shall be considered where:

Sites are underlain by compressible clays, silts, or peats;

Fill has recently been placed on the earlier surface; and

The groundwater is substantially lowered.
Downdrag loads shall be considered as a load when the bearing resistance and settlement of pile
foundations are investigated.
The downdrag loads may be determined as specified in Article 10.7.3.3, with the direction of the skin
friction forces reversed. The factored drag loads shall be added to the factored vertical dead load
applied to the deep foundation in the assessment of bearing capacity at the strength limit state.
The downdrag loads shall be added to the vertical dead load applied to the deep foundation in the
assessment of settlement at service limit state.
10.7.1.5. Pile Spacing, Clearances And Embedment
Center-to-center pile spacings shall not be less than the greater of 750 mm or of 2.5 pile diameters or
widths. The distance from the side of any pile to the nearest edge of the footing shall be greater than
225 mm.
48
Specification for Bridge Design
The tops of piles shall project at least 300 mm into footings after all damaged pile material has been
removed. If the pile is attached to the footing by embedded bars or strands, the pile should extend no
less than 150 mm into the footing. Where a reinforced concrete beam is cast-in-place and used as a
bent cap supported by piles, the concrete cover at the sides of the piles shall be greater than 150 mm,
plus an allowance for permissible pile misalignment, and the piles shall project at least 150 mm into
the cap. Where pile reinforcement is anchored in the cap satisfying the requirements of Article
5.13.4.1, the projection may be less than 150 mm.
10.7.1.6. Batter Piles
Batter piles should be avoided where downdrag loads are expected and in Seismic Zone 3 and 4.
Batter piles may be used in the foundation where the lateral resistance of vertical piles is inadequate to
counteract the horizontal forces transmitted to the foundation or when increased rigidity of the entire
structure is required.
10.7.1.7. Groundwater Table And Buoyancy
Bearing capacity shall be determined using the groundwater level consistent with that used to calculate
load effects. The effect of hydrostatic pressure shall be considered in the design.
10.7.1.8. Protection Against Deterioration
As a minimum, the following types of deterioration shall be considered:

Corrosion of steel pile foundations, particularly in fill soils, low pH soils, and marine
environments; and

Sulfate, chloride, and acid attack of concrete pile foundations.
The following conditions should be considered as indicative of a potential pile deterioration or
corrosion situation:

Resistivity less than 100 ohm/mm,

pH less than 5.5,

pH between 5.5 and 8.5 in soils with high organic content,

Sulfate concentrations greater than 1000 ppm,

Landfills and cinder fills,

Soils subject to mine or industrial drainage, and

Areas with a mixture of high resistivity soils and low resistivity high alkaline soils.
The following water conditions should be considered as indicative of a potential pile deterioration or
corrosion situation:

Chloride content greater than 500 ppm,

Sulfate concentration greater than 500 ppm,
49
Specification for Bridge Design

Mine or industrial runoff,

High organic content,

pH less than 5.5, and

Piles exposed to wet/dry cycles.
When chemical wastes are suspected, a full chemical analysis of soil and groundwater samples shall
be considered.
10.7.1.9.Uplift
Pile foundations designed to resist uplift forces should be checked for resistance to pullout and
structural ability to carry tensile stresses.
10.7.1.10. Estimated Lengths
Estimated pile lengths for each substructure shall be shown on the plans and shall be based upon
careful evaluation of available subsurface information, static and lateral capacity calculations, and/or
past experience.
10.7.1.11. Estimate And Minimum Tip Elevation
Estimated and minimum pile tip elevations for each substructure should be shown on the contract
plans. Estimated pile tip elevations shall reflect the elevation where the required ultimate pile capacity
can be obtained. Minimum pile tip elevations shall reflect the penetration required to support lateral
pile loads, including scour considerations where appropriate, and/or penetration of overlying
unsuitable soil strata.
10.7.1.12. Piles Through Embankment Fill
Piles to be driven through embankments shall penetrate a minimum of 3000 mm through original
ground unless refusal on bedrock or competent bearing strata occurs at a lesser penetration. Fill used
for embankment construction shall be a select material that shall not obstruct pile penetration to the
required depth. The maximum size of any particles in the fill shall not exceed 150 mm. Predrilling or
spudding pile locations should be specified where required, particularly for displacement piles.
10.7.1.13. Test Piles
Test piles shall be considered for each substructure to determine pile installation characteristics,
evaluate pile capacity with depth, and establish contractor pile order lengths. Piles may be tested by
static loading, dynamic testing, driveability studies, or a combination thereof, based upon the
knowledge of subsurface conditions. The number of test piles required may be increased in
nonuniform subsurface conditions. Test piles may not be required where previous experience exists
with the same pile type and ultimate pile capacity in similar subsurface conditions.
50
Specification for Bridge Design
10.7.1.14. Wave Equation Analysis
The constructibility of the pile foundation design should be evaluated using a wave equation computer
program. The wave equation should be used to confirm that the design pile section can be installed to
the desired depth and ultimate capacity as well as within the allowable driving load levels specified in
Article 10.7.1.16 using an appropriately sized driving system.
10.7.1.15. Dynamic Monitoring
Dynamic monitoring may be specified for piles installed in difficult subsurface conditions, such as
soils with obstructions and boulders or a steeply sloping bedrock surface, to evaluate compliance with
structural pile capacity. Dynamic monitoring may also be considered for geotechnical capacity
verification where the size of the project or other limitations deter static load testing.
10.7.1.16 . Maximum Allowable Driving Stresses
Driving loads may be estimated by wave equation analyses or dynamic monitoring of force and
acceleration at the pile head during pile driving.
The maximum driving loads for top driven piles shall not exceed the following factored resistances,
with nomenclature and resistance factors as given in Sections 5 or 6, as appropriate.



Steel Piles:
+ Compression:
0.90  Fy Ag
+ Tension:
0.90  Fy An
Concrete Piles:
+ Compression:
0.85  f/c Ac
+ Tension:
0.70  Fy As
Prestressed Concrete Piles:
+ Compression:
 (0.85 f/c - fpe) Ac
+ Tension - Normal Environments:
 (0.25 f c' + fpe) Ac,
+ Tension - Severe Corrosive Environments:
 fpe Aps
10.7.2. Movement and Bearing Resistance at the Service Limit State
10.7.2.1. General
For purposes of calculating the settlements of pile groups, loads shall be assumed to act on an
equivalent footing located at two-thirds of the depth of embedment of the piles into the layer that
provides support as shown in Figure 1.
For piles in cohesionless soils, foundation settlement shall be investigated using all applicable loads in the
Service Load Combination specified in Table 3.4.1-1. For piles in cohesive soil, the Service Load
Combination shall also be used with all applicable loads, except that the transient loads may be omitted.
All applicable service limit state load combinations in Table 3.4.1-1 shall be used for evaluating lateral
displacement of foundations.
51
Specification for Bridge Design
Figure 10.7.2.1-1 - Location of Equivalent Footing (After Duncan and
Buchignani 1976)
10.7.2.2. Criteria For Horizontal Movement
The provisions of Article 10.6.2.2 shall apply.
Design horizontal movements should not exceed 38 mm.
10.7.2.3. Settlement
10.7.2.3.1. General
52
Specification for Bridge Design
The settlement of a pile foundation shall not exceed the tolerable settlement, as selected according to
Article 10.6.2.2.
10.7.2.3.2. Cohesive Soil
Procedures used for shallow foundations shall be used to estimate the settlement of a pile group, using
the equivalent footing location specified in Figure 10.7.2.1-1.
10.7.2.3.3. Cohesionless Soil
The settlement of pile groups in cohesionless soils can be estimated using results of in-situ tests and
the equivalent footing location shown in Figure 10.7.2.1-1.
The settlement of pile groups in cohesionless soils may be taken as:
Using SPT:
=
Using CPT:
 =
360qI X
N corr
qXI
2q c
(10.7.2.3.3-1)
(10.7.2.3.3-2)
for which:
I = 1 - 0.125
Ncorr =
D/
 0.5
X

 1.92 
0.77log10  '  N
  v 

(10.7.2.3.3-3)
(10.7.2.3.3-4)
where:
q
=
net foundation pressure applied at 2Db/3, as shown in Figure 10.7.2.1-1; this pressure is
equal to the applied load at the top of the group divided by the area of the equivalent
footing and does not include the weight of the piles or the soil between the piles (MPa).
X
=
width or smallest dimension of pile group (mm)

=
settlement of pile group (mm)
I
=
influence factor of the effective group embedment (DIM)
D/
=
effective depth taken as 2Db/3 (mm)
Db
=
depth of embedment of piles in layer that provides support, as specified in
Figure 10.7.2.1-1 (mm)
Ncror =
representative average corrected for overburden SPT blow count over a depth X below
the quivalent footing (Blows/300 mm)
N
measured SPT blow count within the seat of settlement (Blows/300 mm)
=
53
Specification for Bridge Design
 'v
=
effective vertical stress (MPa)
qc
=
average static cone resistance over a depth X below the equivalent footing (MPa)
10.7.2.4. Horizontal Displacement
The horizontal displacement of a pile foundation shall not exceed the tolerable lateral displacement, as
selected according to Article 10.7.2.2.
The horizontal displacement of pile groups shall be estimated using procedures that consider soilstructure interaction.
10.7.2.5. Presumptive Values For End Bearing
The provisions of Article 10.6.2.3 shall apply.
10.7.3. Resistance at the Strength Limit State
10.7.3.1. General
The resistances that shall be considered include:

Bearing resistance of piles,

Uplift resistance of piles,

Punching of piles through strong soil into a weaker layer, and

Structural resistance of the piles.
10.7.3.2. Axial Loading Of Piles
Preference shall be given to design process based upon static analyses in combination with field
monitoring during driving or load tests. Load test results may be extrapolated to adjacent substructures
with similar subsurface conditions. The bearing resistance of piles may be estimated using analytical
methods or in-situ test methods.
The factored bearing resistance of piles, QR, may be taken as:
 Qn =  q Qult
(10.7.3.2-1)
QR =  Qn =  qp Qp +  qs Qs
(10.7.3.2-2)
Qp
(10.7.3.2-3)
QR =
or
For which:
=
Qs =
qp Ap
qs As
(10.7.3.2-4)
54
Specification for Bridge Design
where:
q
=
resistance factor for the bearing resistance of a single pile specified in Article 10.5.5 for
those methods that do not distinguis between total resistance and the individual
contributions of tip resistance and shaft resistance
Qult
=
bearing resistance of a single pile (N)
Qp
=
pile tip resistance (N)
Qs
=
pile shaft resistance (N)
qp
=
unit tip resistance of pile (MPa)
qs
=
unit shaft resistance of pile (MPa)
As
=
surface area of pile shaft (mm2)
Ap
=
area of pile tip (mm2)
 qp =
resistance factor for tip resistance specified in Table 10.5.5-2 for those methods that
separate the resistance of a pile in to contributions from tip resistance and shaft resistance
 qs
resistance factor for shaft resistance specified in Table 10.5.5-2 for those methods that
=
separate the resistance of a pile into contributions from tip resistance and shaft resistance
10.7.3.3. Semiempirical Estimates Of Pile Resistance
10.7.3.3.1. General
Both total stress and effective stress methods may be used, provided that the appropriate soil strength
parameters are available. The resistance factors for the skin friction and point resistance, estimated
using semiempirical methods, shall be as specified in Table 10.5.5-2.
10.7.3.3.2. Shaft Resistance
One or more of the three specified procedures identified below may be used, as appropriate.
10. 7.3.3.2a .  -Method
The  -method, based on total stress, may be used to relate the adhesion between the pile and a clay to
the undrained strength of the clay. The nominal unit skin friction, in MPa, may be taken by:
Qs =  Su
(10.7.3.3.2a-1)
where:
Su
=
mean undrained shear strength (MPa)

=
adhesion factor applied to Su (DIM)
The adhesion factor,  , may be assumed to vary with the value of the undrained strength, Su , as
shown in Figure 1.
55
Specification for Bridge Design
Figure 10.7.3.3.2a-1 - Design Curves for Adhesion Factors for Piles
Driven into
Clay Soils ( after Tomlinson
1987)
10. 7.3.3.2b.  -Method
The  -method, based on effective stress, may be used for predicting skin friction of prismatic piles.
The nominal unit skin friction, in MPa, may be related to the effective stresses in the ground as:
qs =
  v/
where:
 'v
=
vertical effective stress (MPa)

=
a factor taken from Figure 1
(10.7.3.3.2b-1)
56
Specification for Bridge Design
Figure 10.7.3.3.2b-1 -  Versus OCR for Displacement Piles (after
Esrig and Kirby 1979)
The Nordlund method may be used to extend the  method to nonprismatic piles in cohesive soils, in
which case the resistance factor may be taken as that for the  method as specified in Table 10.5.5-2.
10. 7.3.3.2c.  -Method
The  -method, based on effective stress, may be used to relate the unit skin friction, in MPa, to
passive earth pressure as:
qs =  (  'v + 2 Su)
where:
 'v + 2Su
=
passive lateral earth pressure (MPa)

=
an empirical coefficient taken from Figure 1 (DIM)
(10.7.3.3.2c-1)
57
Specification for Bridge Design
Figure 1 0.7.3.3.2c-1 -  Coefficient for Driven Pipe Piles (after
Vijayvergiya and Focht 1972)
10.7.3.3.3. Tip Resistance
The nominal unit tip resistance of piles in saturated clay, in MPa, may be taken as:
qp =
Su
=
9 Su
(10.7.3.3.3-1)
undrained shear strength of the clay near the pile base (MPa)
10.7.3.4. Pile Resistance Estimates Based On In-Situ Tests
10.7.3.4.1. General
The resistance factors for the skin friction and tip resistance, estimated using in-situ methods, shall be
as specified in Table 10.5.5-2.
10.7.3.4.2. Using SPT
This method shall be applied only to sands and nonplastic silts.
10. 7.3.4.2a. Pile Tip Resistance
58
Specification for Bridge Design
The nominal unit tip resistance, in (MPa), for piles driven to a depth Db into a cohesionless soil
stratum may be taken as:
qp
0.038N corrD b
 q
D
=
(10.7.3.4.2a-1)
for which:
Ncorr

 1.92 
 N
0.77 log10
  / 

 v 
=
(1 0.7.3.4.2a-2)
where:
Ncorr =
representative SPT blow count near the pile tip corrected for overburden pressure,  v/
(Blows/300 mm)
N
=
measured SPT blow count (Blows/300 mm)
D
=
pile width or diameter (mm)
Db
=
depth of penetration in bearing strata (mm)
q
=
limiting point resistance taken as 0.4Ncorr for sands and 0.3Ncorr, for nonplastic sift (MPa)
10.7.3.4. 2b. Skin Friction
The nominal skin friction of piles in cohesionless soils, in MPa, may be taken as:

For driven displacement piles:
qs

=
0.0019 N
(10.7.3.4.2b-1)
For nondisplacement piles (e.g., steel-H piles):
qs
= 0.00096 N
(10.7.3.4.2b-2)
where:
qs
=
unit skin friction for driven piles (MPa)
N
=
average (uncorrected) SPT-blow count along the pile shaft (Blows/300 mm)
10.7.3.4.3. Using CPT
10. 7.3.4.3a. General
CPT may be used to determine:

The cone penetration resistance, qc which can be used to determine the tip capacity of piles, and

Sleeve friction, fs which can be used to determine the skin friction capacity.
59
Specification for Bridge Design
10. 7.3.4.3b. Pile Tip Resistance
Tip resistance, qp, in MPa, may be determined as shown in Figure 1.
For which:
qp
where:
qc1
=
=
q c1  q c2
2
(10.7.3.4.3b-1)
average qc, over a distance of yD below the pile tip (path-a-b-c); sum qc values in both the
downward (path a-b) and upward (path b-c) directions; use actual qc values along path a-b
and the minimum path rule along path b-c; compute qc1 for y-values from 0.7 to 4.0 and
use the minimum qc value obtained (MPa)
qc2
=
average qc over a distance of 8D above the pile tip (path c-e); use the minimum path rule
as for path b-c in the qc1, computations; ignore any minor “x” peak depressions if in sand
but include in minimum path if in clay (MPa)
The minimum average cone resistance between 0.7 and 4 pile diameters below the elevation of the pile
tip shall be obtained by a trial and error process, with the use of the minimum-path rule. The
minimum-path rule shall also be used to find the value of cone resistance for the soil for a distance of
eight pile diameters above the tip.
60
Specification for Bridge Design
Figure 10.7.3.4.3b-1 - Pile End-Bearing Computation Procedure
(after Nottingham and Schmertmann 1975)
10. 7.3.4.3c. Skin Friction
The nominal skin friction resistance of piles, in N, may be taken as:
Qs
=
Ks,
c
 N1 L i
  
i 1 8D i
N2


f siasihi   f siasihi 
i 1


(10.7.3.4.3c-1)
where:
Ks,c
=
correction factors: Kc for clays and Ks for sands from Figure 1 (DIM)
Li
=
depth to middle of length interval at the point considered (mm)
Di
=
pile width or diameter at the point considered (mm)
61
Specification for Bridge Design
fsi
=
unit local sleeve friction resistance from CPT at the point considered (MPa)
asi
=
pile perimeter at the point considered (mm)
hi
=
length interval at the point considered (mm)
Ni
=
number of intervals between the ground surface and a point 8D below the ground surface
N2
=
number of intervals between 8D below the ground surface and the tip of the pile
Figure 10.7.3.4.3c-1 - Shaft Friction Correction Factors Ks and Kc
(after Nottingham and Schmertmann 1975)
10.7.3.5. Piles Bearing On Rock
The resistance factor for the tip resistance of piles bearing on rock shall be taken as specified in
Table 10.5.5-2.
Where pile width and rock discontinuity spacing each exceed 300 mm and where unfilled
discontinuity thickness is less than 6.4 mm or discontinuities filled with soil or rock debris are less
than 25 mm wide.
The nominal unit end bearing resistance, qp, of piles driven to rock, in MPa, may be taken as:
qp
=
3qu Ksp d
(10.7.3.5-1)
62
Specification for Bridge Design
for which:
Ksp
S
3 d
D
=
(10.7.3.5-2)
t
10 1  300 d
sd
d  1  0.4
HS
 3.4
DS
where:
qu
=
average uniaxial compression strength of the rock core (MPa)
d
=
depth factor (DIM)
Ksp
=
bearing resistance coefficient from Figure 1(DIM)
sd
=
spacing of discontinuities (mm)
td
=
width of discontinuities (mm)
D
=
pile width (mm)
Hs
=
depth of embedment of pile socketed into rock taken as 0.0 for piles resting on top of
bedrock (mm)
Ds
=
diameter of socket (mm)
This method shall not be applied to soft stratified rocks, such as weak shale or weak limestone.
Piles bearing on weak rocks shall be designed treating the soft rock as soil, specified in Article
10.7.3.3, for piles bearing on cohesive material and Article 10.7.3.4 for piles bearing on cohesionless
material.
63
Specification for Bridge Design
Figure 10.7.3.5-1 - Bearing Capacity Coefficient (after Canadian
Geotechnical Society 1985)
10.7.3.6. Pile Load Test And Field Monitoring
Compressive, tensile, and lateral load testing of piles shall conform to:

Test Method for Piles Under Static Axial Compressive Load - ASTM D 1143

Method of Testing Individual Piles Under Static Axial Tensile Load - ASTM D 3689

Method of Testing Piles Under Lateral Loads - ASTM D 3966
The resistance factor for the axial compressive resistance and axial uplift capacity obtained from pile
load tests shall be as given in Table 10.5.5-2.
Pile driving analyzer field tests shall conform to:
Test Method for High Strain Dynamic Testing of Piles - ASTM D 4945
The resistance factor for the axial resistance obtained from the pile driving analyzer shall be as given
in Table 10.5.5-2.
10.7.3.7. Uplift
10.7.3.7.1. General
Uplift shall be considered when the force effects, calculated based on the appropriate strength limit
state load combinations, are tensile.
64
Specification for Bridge Design
When piles are subjected to uplift, they should be investigated for both resistance to pullout and
structural ability to resist tension and transmit it to the footing.
65
Specification for Bridge Design
10.7.3.7.2. Single-Pile Uplift Resistance
The uplift resistance of a single pile shall be estimated in a manner similar to that for estimating the
skin friction resistance of piles in compression specified in Articles 10.7.3.3 and 10.7.3.4.
Factored uplift resistance in N may be taken as:
QR
=
 Qn =  u Qs
(10.7.3.7.2-1)
where:
Qs
=
nominal uplift capacity due to shaft resistance (N)
u
=
resistance factor for uplift capacity specified in Table 10.5.5-2
10.7.3.7.3. Pile Group Uplift Resistance
Pile group factored uplift resistance, in N, shall be taken as:
QR
=
 Qn =  ug Qug
(10.7.3.7.3-1)
where:
 ug =
resistance factor specified in Table 10.5.5-2
Qug
nominal uplift resistance of the group (N)
=
The uplift resistance, Qug , of a pile group shall be taken as the lesser of:
The sum of the individual pile uplift resistance, or
The uplift capacity of the pile group considered as a block.
For pile groups in cohesionless soil, the weight of the block that will be uplifted shall be determined
using a spread of load of 1 in 4 from the base of the pile group taken from Figure 1. Buoyant unit
weights shall be used for soil below the groundwater level.
In cohesive soils, the block used to resist uplift in undrained shear shall be taken from Figure 2. The
nominal group uplift resistance may be taken as:
Qn
=
Qug
=
(2XZ + 2YZ) Su + Wg
where:
X
=
width of the group, as shown in Figure 2 (mm)
Y
=
length of the group, as shown in Figure 2 (mm)
Z
=
depth of the block of soil below pile cap taken from Figure 2 (mm)
(10.7.3.7.3-2)
66
Specification for Bridge Design
Su
=
average undrained shear strength along pile shaft (MPa)
Wg
=
weight of the block of soil, piles, and pile cap (N)
The resistance factor for the nominal group uplift capacity, Qug, determined as the sum of the
individual pile resistance, shall be taken as the same as that for the uplift capacity of single piles as
specified in Table 10.5.5-2.
The resistance factor for the uplift capacity of the pile group considered as a block shall be taken as
specified in Table 10.5.5-2 for pile groups in clay and in sand.
Figure 10.7.3.7.3-1 - Uplift of Group of Closely Spaced Piles in
Cohesionless Soils
(after Tomlinson 1987)
Figure 10.7.3.7.3-2 - Uplift of Group of Piles in Cohesive Soils
(after Tomlinson 1987)
10.7.3.8. Lateral Load
For piles subjected to lateral loads, the pile heads shall be fixed into the pile cap. Any disturbed soil or
voids created during the driving of the piles shall be replaced with compacted granular material.
67
Specification for Bridge Design
The effects of soil-structure or rock-structure interaction between the piles and ground, including the
number and spacing of the piles in the group, shall be accounted for in the design of laterally loaded piles.
10.7.3.9. Bearing Resistance Of Batter Piles
The bearing resistance of a pile group containing batter piles may be determined by treating the batter
piles as vertical piles.
10.7.3.10. Group Axial Load Resistance
10.7.3.10.1. General
Pile group factored resistance, in N, shall be taken as:
QR
=
 Qn =  gQg
(10.7.3.10.1-1)
where:
g
Qg
= nominal resistance of the group (N)
=
group resistance factor specified herein
10.7.3.10.2. Cohesive Soil
If the cap is in firm contact with the ground, no reduction in efficiency shall be required.
If the cap is not in firm contact with the ground and if the soil is stiff, no reduction in efficiency shall
be required.
If the cap is not in firm contact with the ground and if the soil at the surface is soft, the individual
resistance of each pile shall be multiplied by an efficiency factor  , taken as:


= 0.65 for a center-to-center spacing of 2.5 diameters,


= 1.0 for a center-to-center spacing of 6.0 diameters.

For intermediate spacings, the value of  may be determined by linear interpolation.
The group resistance shall be the lesser of:

The sum of the modified individual resistance of each pile in the group, or

The resistance of an equivalent pier consisting of the piles and the block of soil within the area
bounded by the piles.
When determining the equivalent pier:

The full shear strength of soil shall be used to determine the skin friction resistance,

The total base area of the equivalent pier shall be used to determine the end bearing resistance, and

The additional resistance of the cap shall be ignored.
68
Specification for Bridge Design
The resistance factor for an equivalent pier or block failure shall be as given in Table 10.5.5-2 and
shall apply where the pile cap is or is not in contact with the ground. The resistance factors for the
group resistance calculated using the sum of the individual resistances are the same as those for the
single pile resistance, as given in Table 10.5.5-2.
10.7.3.10.3. Cohesionless Soil
The bearing capacity of pile groups in cohesionless soil shall be the sum of the resistance of all the
piles in the group. The efficiency factor,  , shall be 1.0 where the pile cap is or is not in contact with
the ground.
The resistance factor is the same as that for single piles, as specified in Table 10.5.5-2.
10.7.3.10.4. Pile Group in Strong Soil Overlying a Weak or Compressible Soil
If a pile group is embedded in a strong soil deposit overlying a weaker deposit, consideration shall be
given to the potential for a punching failure of the pile tips into the weaker soil stratum. If the
underlying soil stratum consists of a weaker compressible soil, consideration shall be given to the
potential for large settlements in that weaker layer.
In lieu of local guidance, the investigation of the capacity of underlying soft soils may be based on
computation of the superimposed load, assuming that the distribution of pressure spreads out below
the pile tips by projecting the area bounded by the pile tips on a slope of two vertical to one horizontal.
The resistance at any depth below the pile tips shall be determined based on the projected size of a
notional footing. Bearing capacity shall be based on criteria for spread footing specified herein.
10.7.3.11. Group Lateral Load Resistance
Pile group factored resistance for lateral loads, in N, shall be taken as:
QR =
 Qn   L QL
(10.7.3.11-1)
where:
QL
=
nominal lateral resistance of a single pile (N)
QLg =
nominal lateral resistance of the group (N)
L
=
pile group resistance factor specified in Table 10.5.4-2

=
group efficiency factor as defined herein
The individual resistance of each pile shall be multiplied by an efficiency factor,  , taken as:

 = 0.75 for cohesionless soil

 = 0.85 for cohesive soil
The lateral resistance of the group shall be taken as the sum of the modified individual resistance of
each pile in the group.
10.7.4. Structural Design
69
Specification for Bridge Design
10.7.4.1. General
The structural design of driven concrete and steel piles shall be in accordance with the provisions of
Sections 5 and 6, respectively.
10.7.4.2. Buckling Of Piles
Piles that extend through water or air shall be assumed to be fixed at some depth below the ground.
Stability shall be determined in accordance with provisions for compression members in Sections 5
and 6 using an equivalent length of the pile equal to the laterally unsupported length, plus an
embedded depth to fixity.
The depth to fixity below the ground may be taken as:
 For clays:
1.4

Ep I p
0.25
Es
(mm)
(10.7.4.2-1)
For sands:
1.8
Ep I p
nh
0.2
(mm)
(10.7.4.2-2)
where:
Ep
=
modulus of elasticity of pile (MPa)
Ip
=
moment of inertia of pile (mm4)
Es
=
soil modulus for clays = 67 Su (MPa)
Su
=
undrained shear strength of clays (MPa)
nh
=
rate of increase of soil modulus with depth for sands as specified in Table 1 (MPa/mm)
Table 10.7.4.2-1 - Rate of Increase of Soil Modulus with Depth nh
(MPa/mm) for Sand
10.8. DRILLED SHAFTS
10.8.1.
General
10.8.1.1. Scope
The provisions of this section shall apply to the design of drilled shafts other than drilled piles
installed with continuous flight augers that are concreted as the auger is being extracted.
70
Specification for Bridge Design
10.8.1.2. Embedment
Shaft embedment shall be sufficient to provide suitable vertical and lateral load capacities and
acceptable displacements.
10.8.1.3. Shaft diameter and enlarged bases
Where rock-socketed shafts require casing through the overburden soils, the contract documents shall
specify that the socket diameter be at least 150 mm less than the inside diameter of the casing. For
rock-socketed shafts not requiring casing through the overburden soils, the socket diameter may be
equal to the shaft diameter through the soil.
In stiff cohesive soils, an enlarged base, bell, or underream may be used at the shaft tip to increase the
tip bearing area to reduce the unit end bearing pressure or to provide additional resistance to uplift
loads.
Where the bottom of the drilled hole is cleaned and inspected prior to concrete placement, the entire
base area may be taken to be effective in transferring load.
10.8.1.4. Resistance
The provisions of Article 10.7.1.3 and Table 10.5.4-3 shall apply with the substitution of the term
“Drilled Shaft’ for “Pile,” as applicable.
The method of construction may affect the drilled shaft resistance and shall be considered as part of
the design process. Drilled shafts shall be constructed using the dry, casing, or wet method of
construction or a combination of these methods. In every case, hole excavation, concrete placement,
and all other aspects of shaft construction shall be performed in conformance with the provisions of
this Specification and the Construction Specification.
10.8.1.5. Downdrag
Downdrag loads shall be evaluated, as specified in Article 10.7.1.4.
For end bearing shafts where downdrag is a strength limit state issue, the load factors for the downdrag
load shall be the reciprocal of the resistance factor used for the method of estimating the shaft
resistance, as specified in Table 10.5.5-3.
71
Specification for Bridge Design
10.8.1.6. Group Spacing
The center-to-center spacing of drilled shafts should be the greater of 3.0 diameters or the spacing
required to avoid interaction between adjacent shafts.
If closer spacing is required, the sequence of construction shall be specified in the contract documents,
and the interaction effects between adjacent shafts shall be evaluated.
10.8.1.7. Batter Shafts
Batter shafts should be avoided. Where increased lateral resistance is needed, consideration should be
given to increasing the shaft diameter or increasing the number of shafts.
10.8.1.8. Groundwater Table And Buoyancy
The provisions of Article 10.7.1.7 shall apply as applicable.
10.8.1.9. Uplift
The provisions of Article 10.7.1.9 shall apply as applicable.
Shafts designed for expansive soil shall extend to a depth into moisture-stable soils sufficient to
provide adequate anchorage to resist uplift. Sufficient clearance should be provided between the
ground surface and underside of caps or beams connecting shafts to preclude the application of uplift
loads at the shaft/cap connection due to swelling ground conditions.
10.8.2. Movement at the Service Limit State
10.8.2.1. General
The provisions of Article 10.7.2.1 shall apply as applicable. The Service Load Combination in Table
3.4.1-1 shall be used as appropriate.
In estimating service limit state settlements of drilled shafts in clay, only permanent loads shall be
considered. Transient loads shall be added to the permanent loads when estimating settlement of shafts
in granular soil.
10.8.2.2. Criteria For Horizontal Movement
The provisions of Article 10.7.2.2 shall apply as applicable.
10.8.2.3. Settlement
10.8.2.3.1. General
The settlement of a drilled shaft foundation involving either single-drilled shafts and groups of drilled
shafts shall not exceed the movement criteria selected in accordance with Article 10.6.2.2.
10.8.2.3.2. Settlement of Single-Drilled Shaft
The settlement of single-drilled shafts shall be estimated in consideration of:
72
Specification for Bridge Design

Short-term settlement,

Consolidation settlement if constructed in cohesive soils, and

Axial compression of the drilled shaft.
10.8.2.3.3. Group Settlement
The provisions of Article 10.7.2.3 shall apply as applicable.
10.8.2.4.Lateral Displacement
The provisions of Article 10.7.2.4 shall apply as applicable.
10.8.3. Resistance at the Strength Limit State
10.8.3.1. General
The strength limit state of Article 10.7.3.1 shall apply.
10.8.3.2. Axial loading of drilled shafts
The provisions of Article 10.7.3.2 and Figure 10.5.4.3 shall apply as applicable.
10.8.3.3. Semiempirical Estimates Of Drilled Shaft Resistance
In Cohesive Soils
Semiempirical methods may be used to estimate the resistance of drilled shafts in cohesive soils.
Drilled shafts in cohesive soils should be designed by total and effective stress methods for undrained
and drained loading conditions, respectively.
Shafts in cohesionless soils should be designed by effective stress methods for drained loading
conditions or by empirical methods based on in-situ test results.
The resistance factors for side resistance and tip resistance shall be taken as specified in Table 10.5.5-3.
10.8.3.3.1. Shaft Resistance Using the -Method
The nominal unit side resistance, in MPa, for shafts in cohesive soil loaded under undrained loading
conditions may be taken as:
qs =
 Su
where:
Su
=
mean undrained shear strength (MPa)

=
adhesion factor (DIM)
(10.8.3.3.1-1)
73
Specification for Bridge Design
The following portion of a drilled shaft, illustrated in Figure 1, shall not be taken to contribute to the
development of resistance through skin friction:

At least the top 1500 mm of any shaft;

For straight shafts, a bottom length of the shaft taken as the shaft diameter;

Periphery of belled ends, if used; and

Distance above a belled end taken as equal to the shaft diameter.
Values of  for contributing portions of shafts excavated dry in open or cased holes shall be as
specified in Table 1.
Table 10.8.3.3.1-1 - Values
of  for Determination of
Side Resistance in Cohesive
Soil (Reese and O’Neill 1988)

Figure 10.8.3.3.1-1 - Explanation of
Portions of Drilled Shafts Not
Considered in Computing Side Resistance
(Reese and O'Neill 1988)
10.8.3.3.2. Tip Resistance
For axially loaded shafts in cohesive soil, the nominal unit tip resistance of drilled shafts, in MPa, may
be taken as:
qp = NcSu  4.0
(10.8.3.3.2-1)
Nc = 6[1 + 0.2 (Z/D)]  9
(10.8.3.3.2-2)
for which:
where:
D
=
diameter of drilled shaft (mm)
Z
=
penetration of shaft (mm)
74
Su
Specification for Bridge Design
=
undrained shear strength (MPa)
75
Specification for Bridge Design
The value of Su shall be determined from the results of in-situ and/or laboratory testing of undisturbed
samples obtained within a depth of 2.0 diameters below the tip of the shaft. If the soil within 2.0
diameters of the tip has Su < 0.024 MPa, the value of N0 shall be reduced by one-third.
For drilled shafts in clays with Su > 0.096 MPa with D > 1900 mm, and for which shaft settlements
will not be evaluated, the value of qp shall be reduced to qpr, as follows:
qpr =
qp Fr
(10.8.3.3.2-3)
for which:
Fr =
760
 1.0
12.0aDp  760b
a = 0.0071 + 0.0021
b = 1.45
(10.8.3.3.2-4)
Z
 0.015
Dp
2.0 S u with 0.5  b  1.5
(10.8.3.3.2-5)
(10.8.3.3.2-6)
where:
Dp
=
tip diameter (mm)
10.8.3.4.
Estimation
Cohesionless Soils
Of
Drilled-Shaft
Resistance
In
10.8.3.4.1. General
The nominal bearing resistance of drilled shafts in cohesionless soils shall be estimated using
applicable methods identified herein or other regionally accepted methods complying with Article
10.1. The factored resistance should be determined using any available experience with similar
conditions.
10.8.3.4.2. Shaft Resistance
The nominal resistance of drilled shafts in sand may be determined using any of the five methods
specified in Table 1. Higher values may be used only if verified by load tests.
Side resistance of drilled shafts in sand may be estimated using:

The friction angle,  f , or

The SPT blow count, N.
76
Specification for Bridge Design
The following notation shall apply to Table 1:
N
=
uncorrected SPT blow count (Blows/300 mm)
 v/
=
vertical effective stress (MPa)
f
=
friction angle of sand (DEG)
K
=
load transfer factor (DIM)
Db
=
embedment of drilled shaft in sand bearing layer (mm)

=
load transfer coefficient (DIM)
z
=
depth below ground (mm)
The friction angle of sands may be correlated to the SPT blow count or the cone resistance. Where site
specific data are not available, the values in Table 2 may be used for preliminary design.
Table 10.8.3.4.2-1 - Summary of Procedures for Estimating
Side
Resistance, qs, MPa, in Sand
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Specification for Bridge Design
Table 10.8.3.4.2-2- Friction Angles of Sands
10.8.3.4.3. Tip Resistance
The nominal tip resistance may be calculated using the procedures specified in Table 1, for which the
following notation applies:
Ncorr =
SPT blow count corrected for overburden pressure (Blows/300 mm)
=
[0.77 log10 (1.92/  'v )] N
N
=
uncorrected SPT blow count (Blows/mm)
D
=
diameter of drilled shaft (mm)
Dp
=
tip diameter of drilled shaft (mm)
Db
=
embedment of drilled shaft in sand bearing layer (mm)

=
vertical effective stress (MPa)
'
v
For base diameters greater than 1270 mm, qp should be reduced as follows:
qpr =
1270
qp
Dp
(10.8.3.4.3-1)
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Specification for Bridge Design
Table 10.8.3.4.3-1 - Summary of Procedures for Estimating Tip
Resistance, qp, MPa,
of Drilled Shafts in Sand
10.8.3.5. Axial Resistance In Rock
In determining the axial resistance of drilled shafts with rock sockets, the side resistance from
overlying soil deposits may be ignored.
If the rock is degradable, use of special construction procedures, larger socket dimensions, or reduced
socket resistance shall be considered.
The resistance factors for drilled shafts socketed in rock shall be taken as specified in Table 10.5.5-3.
10.8.3.6. Load Test
When used, load tests shall be conducted using shafts constructed in a manner and of dimensions and
materials identical to those planned for the production shafts.
The factored resistance for axial compressive capacity, axial uplift capacity, or lateral capacity shall be
taken as specified in Table 10.5.5-3.
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Specification for Bridge Design
10.8.3.7. Uplift Resistance
10.8.3.7.1. General
Uplift resistance shall be considered when upward loads act on the drilled shafts. Drilled shafts
subjected to uplift forces shall be investigated for resistance to pull out for their structural strength and
for the strength of their connection to supported components.
10.8.3.7.2. Uplift Resistance of a Single-Drilled Shaft
The uplift resistance of a single straight-sided drilled shaft may be estimated in a manner similar to
that for determining side resistance for drilled shafts in compression, as specified in Articles 10.8.3.3
and 10.8.3.4. In determining the uplift resistance of a belled shaft, the side resistance above the bell
may be neglected, and it can be assumed that the bell behaves as an anchor.
The resistance factor for the uplift capacity of drilled shafts shall be taken as specified in Table 10.5.5-3.
The factored uplift capacity of a belled drilled shaft in a cohesive soil, Qr, may be determined as:
QR =  Qn =  Qsbell
(10.8.3.7.2-1)
Qsbell = qsbell Au
(10.8.3.7.2-2)
for which:
where:
qsbell =
Nu Su (MPa)
Au
=
 (Dp2 - D2)/4 (mm2)
Nu
=
uplift adhesion factor (DIM)
Dp
=
diameter of the bell (mm)
Db
=
depth of embedment in the founding layer (mm)
D
=
shaft diameter (mm)
Su
=
undrained shear strength averaged over a distance of 2.0 bell diameters (2Dp) above the
base (MPa)

=
resistance factor specified in Table 10.5.5-3
If the soil above the founding stratum is expansive, Su should be averaged over the lesser of either
2.0Dp above the bottom of the base or over the depth of penetration of the drilled shaft in the founding
stratum.
The value of Nu may be assumed to vary linearly from 0.0 at Db/DP = 0.75 to a value of 8.0 at
Db/DP = 2.5, where Db is the depth below the founding stratum. The top of the founding stratum
should be taken at the base of zone of seasonal moisture change.
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Specification for Bridge Design
10.8.3.7.3. Group Uplift Resistance
The provisions of Article 10.7.3.7.3 shall apply. The resistance factors for uplift resistance of groups
of drilled shafts shall be taken as specified in Table 10.5.5-3.
10.8.3.8. Lateral Load
The design of laterally loaded drilled shafts shall account for the effects of interaction between the
shaft and ground, including the number of piers in the group.
The drilled shaft head shall be fixed into the cap.
10.8.3.9. GROUP CAPACITY
10.8.3.9.1. General
Possible reduction in resistance from group effects shall be considered.
10.8.3.9.2. Cohesive Soil
The provisions of Article 10.7.3.10.2 shall apply.
The resistance factor for the group capacity of an equivalent pier or block failure shall be taken as
specified in Table 10.5.5-3 and shall apply where the cap is or is not in contact with the ground.
The resistance factors for the group capacity calculated using the sum of the individual drilled shaft
capacities are the same as those for the single-drilled shaft capacities.
10.8.3.9.3. Cohesionless Soil
Regardless of cap contact with the ground, the individual capacity of each shaft shall be reduced by a
factor  for an isolated shaft taken as:

 = 0.65 for a center-to-center spacing of 2.5 diameters,

 = 1.0 for a center-to-center spacing of 6.0 diameters.

For intermediate spacings, the value of  may be determined by linear interpolation.
10.8.3.9.4. Group in Strong Soil Overlying Weaker Compressible Soil
The provisions of Article 10.7.3.10.4 shall apply.
10.8.4. Structural Design
10.8.4.1. General
The structural design of drilled shafts shall be in accordance with the provisions of Section 5 for the
design of reinforced concrete.
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Specification for Bridge Design
10.8.4.2. Buckling Of Drilled Shafts
The provisions of Article 10.7.4.2 shall apply.
10.8.5. Details for Drilled Shafts
10.8.5.1. General
All shafts shall be sized in 150 mm increments with a minimum shaft diameter of 450 mm. If the shaft
is to be manually inspected, the shaft diameter should not be less than 750 mm. The diameter of
columns supported by shafts should be smaller than the diameter of the drilled shaft.
10.8.5.2. Reinforcement
Where the potential for lateral loading is insignificant, drilled shafts may be reinforced for axial loads
only. Those portions of drilled shafts that are not supported laterally shall be designed as reinforced
concrete columns in accordance with Article 5.7.4. Reinforcing steel shall extend a minimum of 3000
mm below the plane where the soil provides fixity.
Where permanent steel casing is used and the shell is smooth pipe greater than 3.0 mm thick, it may be
considered to be load-carrying. Allowance should be made for corrosion.
10.8.5.3. Transverse Reinforcement
Transverse reinforcement shall be designed to resist loads due to fresh concrete flowing from inside
the cage to the side of the excavated hole. Transverse reinforcement may be constructed as hoops or
spiral steel.
Seismic provisions shall be in accordance with Article 5.13.4.6.
10.8.5.4. Concrete
The maximum aggregate size, slump, wet or dry placement, and necessary design strength should be
considered when specifying shaft concrete. The concrete selected should be capable of being placed
and adequately consolidated for the anticipated construction condition, and shaft details should be
specified. The maximum size aggregate shall be equal to or smaller than one-fifth the clear spacing of
the shaft reinforcing steel.
10.8.5.5. Reinforcement Into Superstructure
Sufficient reinforcement shall be provided at the junction of the shaft with the superstructure to make a
suitable connection. The embedment of the reinforcement into the cap shall comply with the provision
for cast-in-place piles in Section 5.
10.8.5.6. Enlarged Bases
Enlarged bases shall be designed to ensure that plain concrete is not overstressed. The enlarged base
shall slope at a side angle not greater than 30o from the vertical and have a bottom diameter not greater
than three times the diameter of the shaft. The thickness of the bottom edge of the enlarged base shall
not be less than 150mm.