CHAPTER 3
DEEP FOUNDATION
INTRODUCTION
• It is a foundation system that transfers loads
to a deeper and competent soil layer.
• Structural members made of steel, concrete or
timber
• Deep and cost more than shallow foundation
• Necessary to ensure structural safety
Conditions require pile foundations
• When one or more
upper soil layers are
highly compressible and
too weak to support
• the load transmitted by
the superstructure,
piles are used to
transmit the load to
underlying bedrock or a
stronger soil layer,
Conditions require pile foundations
• When bedrock is not
encountered at a
reasonable depth below
the ground surface.
• The resistance to the
applied structural load
is derived mainly from
the frictional resistance
Conditions require pile foundations
• When subjected to
horizontal forces.
• Earth-retaining structures
and foundations of tall
structures that are
subjected to high wind or
to earthquake forces.
Conditions require pile foundations
• Expansive and collapsible soils
may be present at the site
• These soils may extend to a
great depth below the ground
surface
• If shallow foundations are
used in such circumstances,
the structure may suffer
considerable damage
Conditions require pile foundations
• The foundations of some
structures, such as
transmission towers, offshore
platforms, and basement mats
below the water table, are
subjected to uplifting forces.
• Piles are sometimes used for
these foundations to resist the
uplifting force.
Conditions require pile foundations
• Bridge abutments and
piers are usually
constructed over pile
foundations to avoid
the loss of bearing
capacity that a shallow
foundation might suffer
because of soil erosion
at the ground surface.
STEEL PILES (pg 393)
• pipe piles or rolled
steel H-section piles.
Wide-flange and Isection steel beams
can also be used.
• Usual length: 15 m
to 60 m (50 ft to 200
ft)
• Usual load: 300 kN
to 1200 kN (67 kip to
265 kip)
STEEL PILES
Advantages:
a. Easy to handle with
respect to cutoff and
extension to the desired
length
b. Can stand high driving
stresses
c. Can penetrate hard layers
such as dense gravel and
soft rock
d. High load-carrying
capacity
Disadvantages:
a. Relatively costly
b. High level of noise during
pile driving
c. Subject to corrosion
d. H-piles may be damaged
or deflected from the
vertical during driving
through hard layers or past
major obstructions
CONCRETE PILES (pg 396)
• Precast piles or cast-in-situ piles
• Usual length: 10 m to 15 m (30 ft to 50 ft)
• Usual load: 300 kN to 3000 kN (67 kip to 675 kip)
• Advantages:
a. Can be subjected to hard driving
b. Corrosion resistant
c. Can be easily combined with a concrete superstructure
CONCRETE PILES (pg 396)
• Disadvantages:
a. Difficult to achieve
proper cutoff
b. Difficult to
transport
Timber Piles
• Class A piles carry heavy loads. The minimum
diameter of the butt should be 356 mm (14 in.).
• Class B piles are used to carry medium loads.
The minimum butt diameter should be 305 to
330 mm (12 to 13 in.).
• Class C piles are used in temporary construction
work. They can be used permanently for
structures when the entire pile is below the
water table. The minimum butt diameter should
be 305 mm (12 in.).
Timber piles
Composite Piles
• The upper and lower
portions of composite
piles are made of
different materials
• Steel-and-concrete piles
consist of a lower
portion of steel and an
upper portion of castin-place concrete.
Continuous Flight Auger (CFA) Piles
Friction Pile
• Load Bearing Resistance derived mainly
from skin friction
End Bearing Pile
• Load Bearing Resistance derived mainly from base
Eqn for Estimating Pile Capacity
Meyerhof
Vesic
Sand
Sand
Clay (φ=0)
Clay (φ=0)
Coyle &
Castello
Sand
Meyerhof’s Method (sand)
Meyerhof’s Method (clay, φ = 0)
Vesic’s Method (Sand)
Table 9.7 (pg 418)
Vesic’s Method (clay, φ = 0)
Coyle & Castello (Sand)
Frictional Resistance (Qs)
Sand
Clay
λ
α
β
Qs in Sand
Coyle & Castello
Qs in Clay
Qs in Clay
Qs in Clay
Point Bearing Capacity of Piles Resting
on Rock
Pile Load Test
Pile Load Test
• 3 types of testing
– Load controlled test
– Constant rate of penetration test
– Cyclic loading
• Elapse time is important depend on type of soil
• Arbitrary settlement limits that the pile is
considered to have failed when the pile head has
moved 10 percent of the pile end diameter or the
gross settlement of 1.5 in. (38 mm) and net
settlement of 0.75 in. (19 mm) occurs under two
times the design load. (JKR standard)
Ultimate load from Pile Load Test
Elastic Settlement of Piles
Pile-Driving Formulas
Pile-Driving Formulas
•
•
•
•
•
Table 9.17 (pg 471)
Modified EN formula
Danish formula
Janbu’s formula
Please example 9.17
Negative Skin Friction
GROUP EFFICIENCY
A pile cap constructed
over a pile group;
either contact with
ground or above the
ground
GROUP EFFICIENCY
• If the spacing too close
stresses transmitted by
the piles will overlap,
reduce the capacity.
• In practice, center to
center spacing, d is 2.5D
but ordinary situation
about 3D to 3.5D
GROUP EFFICIENCY
GROUP EFFICIENCY, 
• If  > 1, act as single
pile
•
• If  < 1, act as group
pile
GROUP EFFICIENCY, 
Ultimate Capacity of Group Piles in
Saturated Clay
Ultimate Capacity of Group Piles in
Saturated Clay
Ultimate Capacity of Group Piles in
Saturated Clay
Example
• The section of 4 x 4
group pile in a layered
saturated clay. The piles
are square in cross
section (356 mm x 356
mm). The center-tocenter spacing, d of the
piles is 1 m. Determine
the allowable loadbearing capacity of the
pile group. Use FS = 3.
Consolidation Settlement of Group
Piles
Consolidation Settlement of Group
Piles
Consolidation Settlement of Group
Piles
Consolidation Settlement of Group
Piles
Consolidation Settlement of Group
Piles
Assignment