Piling Platform Design
Ziauddin Ahmed
Geotechnique Pty Ltd
March 3, 2022
Ziauddin Ahmed (Geotechnique Pty Ltd)
Piling Platform Design
March 3, 2022
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Table of Contents I
1
2
3
4
5
Introduction
Overturned Rigs
Loads on Piling Rig
Ground Pressure Variation
Pressure Distribution of Footings
Eccentric Loading
Eccentricity in both Directions
Equivalent Uniformly Distributed Load
Loading Cases
Ground Pressure Calculation
Bearing Capacity
Terzaghi’s Bearing Capacity Formula
Bearing Capacity Factors
Groundwater Effects
Examples of Bearing Capacity Calculation
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Table of Contents II
Two-Layer System
Meyerhof’s Bearing Capacity - Failure Surface
Upper Layer Contribution
Geogrid Reinforcement Contribution
6
Platform Thickness Design Calculation Procedure
Clay Subgrade
Sand Subgrade
Example Calculation - Soft Clay Subgrade
Summary of Platform Design
7
Questions
8
References
9
Appendices
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Introduction
Introduction
Piling rigs exert considerable pressure on the supporting ground.
Piling rigs can overturn or fall if the ground has low allowable bearing
capacity.
This type of problem mostly occurs in soft natural clays or soft/loose
and wet uncontrolled fill where the allowable bearing capacity is
generally low. Piling rigs can also overturn or fall if taken close to
unstable slopes.
Design of piling platform thickness might be required where the
ground is not suitable to support the maximum pressure exerted by
the rig. A granular platform may also be required to provide an
all-weather surface.
This presentation briefly describes variation in ground pressure during
the operation of the rig and the design of piling platform thickness.
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Introduction
Overturned Rigs
Overturned Rigs Supported on Soft/Loose Material I
Figure 1: Overturned Rig
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Introduction
Overturned Rigs
Overturned Rigs Supported on Soft/Loose Material II
Figure 2: Overturned Rig
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Introduction
Overturned Rigs
Overturned Rigs Supported on Soft/Loose Material III
Figure 3: Overturned Rig
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Loads on Piling Rig
Loads on Piling Rig
Figure 4: Various Loads on Pile Driving Rig
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Loads on Piling Rig
Ground Pressure Variation
Ground Pressure Variation
Ground pressure varies during the operation of the rig. An example of ground
pressure variation during the rotation of the rig mast is shown below:
Figure 5: Variation in Ground Pressure at different Jib Positions
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Pressure Distribution of Footings
Eccentric Loading
Pressure Distribution of Footing under Eccentric Loading I
As the resultant of various loads on the rig will not pass through the centre
of the tracks, the pressure distribution will be non-uniform. The pressure
distribution under eccentric loading Coduto et al. (2016) will generally be
as below.
Figure 6: Pressure Distribution under Eccentric Loading/Moment
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Pressure Distribution of Footings
Eccentric Loading
Pressure Distribution of Footing under Eccentric Loading II
Where ’B’ is footing width and ’e’ is eccentricity from the centre. Pressure
qmax and qmin are given Gere & Goodno (2013) by:
Pey
P
+
B
I
P
Pey
= −
B
I
qmax =
qmin
Taking y =
B
2,
moment of inertia, I , for 1m length of footing will be
6Pe
P
6e
P
1+
qmax = + 2 =
B
B
B
B
P
6Pe
P
6e
qmin = − 2 =
1−
B
B
B
B
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1×B 3
12 .
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Pressure Distribution of Footings
Eccentricity in both Directions
Eccentricity in both Length and Width Directions
When the resultant is eccentric in both x and y directions, the pressure
distribution will be as below:
Figure 7: Eccentricity in both Length and Width Directions
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Pressure Distribution of Footings
Equivalent Uniformly Distributed Load
Equivalent Uniformly Distributed Load
The above triangular and trapezoidal pressure distributions can be converted
into uniformly distributed load (UDL) by reducing the length and width of
the footing Coduto et al. (2016) as below:
Equivalent length, L′ = L − 2eL
Equivalent width, B ′ = B − 2eB
P + Wf
Equivalent pressure, qeq =
B ′ L′
Wf = Weight of footing
Figure 8: Equivalent Uniform Pressure
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Loading Cases
Loading Cases of Tracked Plants/Piling Rigs
The following loading cases Skinner (2004) are to be considered to determine
worst condition for platform thickness design.
Case 1 loading: This applies
to situation where the operator is unlikely to be able to
aid recovery from an imminent platform failure.
Standing
Travelling
Handling
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Case 2 loading: This applies to situation where the operator can control load safety by operating on the
machine. In this case the worst combination of loads and orientation of
the rig are considered to determine
maximum ground pressure.
Installing casing
Drilling
Extracting auger
Extracting casing
Travelling or slewing
Driving
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Loading Cases
Ground Pressure Calculation
Ground Pressure Calculation Excel Sheet
Federation of piling specialist (FPS, https://www.fps.org.uk/) has developed an excel sheet (Rig Track Pressure) to determine ground pressure
under tracked plants. A summary of the calculated ground pressure values
for various conditions of a tracked plant is shown below.
Figure 9: Summary of Calculated Ground Pressure Values
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Loading Cases
Ground Pressure Calculation
Bearing Capacity Calculation
Terzaghi assumed the following failure surface to derive the bearing capacity
formula.
Figure 10: Geometry of Failure Surface
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Bearing Capacity
Terzaghi’s Bearing Capacity Formula
Terzaghi’s Bearing Capacity Formula
Bearing Capacity Formula - Drained Condition
′
qn = c ′ Nc sc + σzD
Nq sq + 0.5γ ′ BNγ sγ
qn = nominal net bearing capacity
c ′ = effective cohesion
Nc , Nq , Nγ = Terzaghi’s bearing capacity factors f (ϕ′ )
ϕ′ = effective angle of friction; γ ′ = unit weight of soil above footing depth
′ = overburden pressure at footing depth (D)
σzD
sc , sq , sγ = shape factors
For undrained conditions ϕu = 0 and Nc = 5.7 (or 5.14), Nq = 1, Nγ = 0.
Bearing Capacity Formula - Undrained Condition
′
sq , cu = undrained cohesion
qn = cu Nc sc + σzD
′
At surface, qn = cu Nc sc as σzD
=0
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Bearing Capacity
Terzaghi’s Bearing Capacity Formula
Terzaghi’s Bearing Capacity Formulas - Granular Material
For granular material c ′ = 0. Therefore, the first term can be neglected:
Bearing Capacity Formula - Granular Material
′
qn = σzD
Nq sq + 0.5γ ′ BNγ sγ
′ = 0 and the bearing capacity formula can further be reduced
At surface σzD
to the last term
Bearing Capacity Formula - Granular Material & Footing at Surface
qn = 0.5γ ′ BNγ sγ
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Bearing Capacity
Bearing Capacity Factors
Terzaghi’s Bearing Capacity Factors
Nc
Nq
Nγ
120
Nc , N q , N γ
100
80
60
40
20
0
0
5
10
15
20
25
Friction Angle, ϕ degrees
30
35
40
Figure 11: Terzaghi’s Bearing Capacity Factors
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Bearing Capacity
Groundwater Effects
Effect of Groundwater on Bearing Capacity I
The following three cases are to considered for bearing capacity analyses:
Figure 12: Groundwater Cases for Bearing Capacity Analyses
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Bearing Capacity
Groundwater Effects
Effect of Groundwater on Bearing Capacity II
′ and
Presence of groundwater (Dw ) will effect the overburden pressure σzD
′
the unit weight γ in the last term of the formula.
Case 1 (Dw ≤ D)
′
γ ′ = γb = γ − γw , σzD
= γDw + γ ′ (D − Dw )
Case 2 (D < Dw < D + B)
Dw − D
′
′
γ = γ − γw 1 −
, σzD
= γD
B
Case 3 (Dw ≥ D + B): no groundwater correction is required
′
γ ′ = γ, σzD
= γD
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Bearing Capacity
Examples of Bearing Capacity Calculation
Example Calculation for Undrained Condition
Calculating Bearing Capacity
Given data :
Undrained cohesion, cu = 120 kPa
Unit weight, γ = 18 kN/m3
Footing depth, D = 400 mm
Footing width, B = 700 mm
Factor of safety = 3.0
Overburden pressure at footing depth,
′
σzD
= 0.4 × 18 = 7.2 kPa
ϕu = 0, Nc = 5.7, Nq = 1, Nγ = 0 (Figure 11)
Taking sc = 1.0
Figure 13: Footing on Clay
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′
qn = cu Nc sc + σzD
= 120 × 5.7 × 1 + 7.2 (sc = 1)
= 691 kPa
691
qall =
= 230 kPa
3.0
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Bearing Capacity
Examples of Bearing Capacity Calculation
Example Calculation for Footing on Sand
Calculating Bearing Capacity
Given data :
Friction angle, ϕ′ = 30°
Effective cohesion, c ′ = 0
Unit weight, γ = 18 kN/m3
Footing depth, D = 400 mm
Footing width, B = 700 mm
Factor of safety = 3.0
Overburden pressure at footing depth,
′
σzD
= 0.4 × 18 = 7.2 kPa
For ϕ′ = 30°
Nc = 37.2, Nq = 22.5, Nγ = 20.1 (Figure 11)
Taking sc = sq = sγ = 1.0
Figure 14: Footing on Sand
Ziauddin Ahmed (Geotechnique Pty Ltd)
′
qn = c ′ Nc sc + σzD
Nq sq + 0.5γ ′ BNγ sγ
= 0 + 7.2 × 22.5 + 0.5 × 18 × 0.7 × 20.1
= 289 kPa
289
qall =
= 96 kPa
3.0
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Bearing Capacity
Two-Layer System
Bearing Capacity for Two-Layer System
If the above calculated bearing capacity is less than the maximum ground
pressure value for either Loading Case 1 or 2, then a piling platform should be
provided. Suitable material for constructing the platform would be granular
material such as crushed sandstone, recycled gravel or crushed rock. The
platform can further be reinforced with a layer of geogrid. The thickness of
the platform will depend on the maximum ground pressure of the rig, the
bearing capacity of the ground and the material properties of the platform.
Two-layer bearing capacity formula suggested by Meyerhof (1974) can be
used to determine the thickness of the piling platform. Meyerhof assumed
that the footing will punch through the upper firm/dense layer into the
bottom soft/loose layer.
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Bearing Capacity
Two-Layer System
Meyerhof’s Bearing Capacity - Failure Surface
Meyerhof assumed the following failure surface for deriving the bearing capacity formula for the two-layer system.
Applied Load, p
Granular Layer
ϕ′p & γp
Punching
shear, δ
0.5γp Kp D 2
D
cu Nc sc
Clay Subgrade, cu
B
with dimension L perpendicular
to the paper
Figure 15: Failure Surface for Two-Layer System
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Bearing Capacity
Two-Layer System
Upper Layer Contribution I
Contribution to the total bearing capacity by the piling platform is from
the frictional force on the failure surface, which is equal to 0.5γp Kp D 2 ×
tan (δ).
Bearing capacity formulas for a two-layer system with the footing at
the surface are shown below:
Undrained Condition
qn = cu Nc sc +
γp D 2
B
Kp tan (δp ) sp
Granular Material
′
qn = 0.5γ BNγ sγ +
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γp D 2
B
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Kp tan (δp ) sp
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Bearing Capacity
Two-Layer System
Upper Layer Contribution II
Where δp is coefficient of friction and can be taken as 32 ϕ′p and Kp is
coefficient of passive pressure. Subscript ’p’ stands for piling platform.
Formulas for shape factors sc , sγ , sp are as below:
B
sc = 1.0 + 0.2
L
B
sγ = 1.0 − 0.3
L
B
sp = 1.0 +
L
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Bearing Capacity
Two-Layer System
Upper Layer Contribution III
Kp tan(δ)
10
Kp tan(δ) can be determined from Figure
16.
Kp × tan(δ)
8
6
4
2
30
32
34
36
38
40
Friction Angle, ϕ degrees
42
44
Figure 16: Kp × tan(δ)
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Bearing Capacity
Two-Layer System
Upper Layer Contribution IV
300
Nγ
275
250
225
200
175
Nγ
Nγ can be determined
from Figure 17. These
are based on Skinner
(2004).
150
125
100
75
50
25
0
30
32
34
36
38
40
Friction Angle, ϕ degrees
42
44
Figure 17: Nγ vs ϕ
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Bearing Capacity
Two-Layer System
Geogrid Reinforcement I
Geogrid can be provided under the granular platform to increase the bearing
capacity.
Applied Load, p
Granular Layer
ϕ′p & γp
0.5γp Kp D 2
Punching
shear, δ
Td
D
Geogrid Reinforcement
cu Nc sc
Clay Subgrade, cu
B
with dimension L perpendicular
to the paper
Figure 18: Failure Surface with Geogrid
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Bearing Capacity
Two-Layer System
Geogrid Reinforcement II
Tensile strength of the geogrid is assumed (based on tension membrane
theory) to contribute to the bearing capacity of the platform. Allowable
tensile strength of geogrid reinforcement,
Td =
Tult
2
Contribution to the increase in the bearing capacity is given by
Rg =
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2Td sp
B
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Bearing Capacity
Two-Layer System
Geogrid Reinforcement III
Bearing Capacity of Piling Platform with Geogrid Reinforcement
Undrained Condition
qn = cu Nc sc +
γp D 2
B
Kp tan (δp ) sp +
2Td sp
B
Granular Material
′
qn = 0.5γ BNγ sγ +
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γp D 2
B
Kp tan (δp ) sp +
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2Td sp
B
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Bearing Capacity
Two-Layer System
Geogrid Reinforcement IV
Geogrid works well in combination with geofabric, which acts as a separator
between the clayey subgrade and the granular platform material. It should
also be noted that considerable stretching will be required to mobilise the
full tensile strength of the geogrid. Therefore, a higher safety factor shall
be used in calculating Td .
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Platform Thickness Design Calculation Procedure
Clay Subgrade
Design Calculation Procedure - Clay Subgrade I
The design procedure is based on the method described in Skinner (2004).
Note: Notations used in the design procedure is slightly different from those
previously used
(a) Determine design parameters based on the ground conditions and platform material to be used.
cu undrained shear strength of clay
ϕ′p friction angle of platform material
γp unit weight of platform material
(b) Obtain maximum ground pressure and track dimensions for Case 1 and
Case 2 loading conditions.
q1k Case 1 loading
q2k Case 2 loading
Wd track width
L1 effective length of the track for Case 1 loading
L2 effective length of the track for Case 2 loading
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Platform Thickness Design Calculation Procedure
Clay Subgrade
Design Calculation Procedure - Clay Subgrade II
Apply loading factors to calculate design ground pressure values.
q1d = γq q1k = 2.0 × q1k
q2d = γq q2k = 1.5 × q1k
(c) Calculate bearing capacity and shape factors and punching shear coefficients
(d) Check support for subgrade alone. The design bearing capacity can be
calculated using Rd = cu Nc sc . If Rd < (q1d or q2d ) then a platform
will be required to support the plant.
(e) Calculate the bearing resistance of the platform using equation Rp =
0.5γp Wd Nγp sγ . The bearing resistance of the platform shall be greater
than 1.6q1k and 1.2q2k . The platform material should also be stronger
than the subgrade material (i.e. 0.5γp Wd Nγp sγ > cu Nc sc ).
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Platform Thickness Design Calculation Procedure
Clay Subgrade
Design Calculation Procedure - Clay Subgrade III
(f) Calculate platform thickness using the following equations:
Loading Case 1 :
D1 =
1.6q1k − cu Nc sc1
Wd ×
γp Kp tan (δp ) sp1
12
1.2q2k − cu Nc sc2
γp Kp tan (δp ) sp2
12
Loading Case 2 :
D2 =
Wd ×
Use the larger of D1 and D2 to construct the platform.
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Platform Thickness Design Calculation Procedure
Clay Subgrade
Design Calculation Procedure - Clay Subgrade IV
(g) Geogrid can be used to reduce platform thickness. The following equations can be used to determine the thickness with geogrid reinforcement:
Loading Case 1 :
D1 =
1.6q1k − cu Nc sc1 − (2.0Td /Wd )
Wd ×
γp Kp tan (δp ) sp1
12
1.2q2k − cu Nc sc2 − (2.0Td /Wd )
γp Kp tan (δp ) sp2
12
Loading Case 2 :
D2 =
Wd ×
Use the larger of D1 and D2 to construct the platform.
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Platform Thickness Design Calculation Procedure
Clay Subgrade
Design Calculation Procedure - Clay Subgrade V
In any case, the designed platform should satisfy the following conditions; ignoring the effect of reinforcement.
Rd > q1d and q2d
q1d = 1.25q1k
q2d = 1.05q1k
Rd = cu Nc sc + γp D 2 /Wd Kp tan (δp ) sp
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Platform Thickness Design Calculation Procedure
Sand Subgrade
Design Calculation Procedure - Sand Subgrade I
(a) Determine design parameters based on ground conditions and platform
material to be used.
ϕ′s friction angle of sand subgrade
γs′ unit weight of sand subgrade
ϕ′p friction angle of platform material
γp unit weight of platform material
(b) Obtain maximum ground pressure and track dimensions for Case 1 and
Case 2 loading conditions.
q1k Case 1 loading
q2k Case 2 loading
Wd track width
L1 effective length of the track for Case 1 loading
L2 effective length of the track for Case 2 loading
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Platform Thickness Design Calculation Procedure
Sand Subgrade
Design Calculation Procedure - Sand Subgrade II
Apply loading factors to calculate design ground pressure values.
q1d = γq q1k = 2.0 × q1k
q2d = γq q2k = 1.5 × q1k
(c) Calculate bearing capacity and shape factors and punching shear coefficients
(d) Check support for subgrade alone. The design bearing capacity can
be calculated using bearing capacity equation Rd = 0.5γs′ Wd Nγs sγ . If
Rd < (q1d or q2d ) then a platform will be required to support the
plant.
(e) Check support for platform material. Calculate the bearing resistance
of the platform using equation Rd = 0.5γp Wd Nγp sγ . The bearing resistance shall be greater than 1.6q1k and 1.2q2k . The platform material
should also be stronger than the subgrade material.
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Platform Thickness Design Calculation Procedure
Sand Subgrade
Design Calculation Procedure - Sand Subgrade III
(f) Calculate platform thickness using the following equations:
Loading Case 1 :
D1 =
1.6q1k − 0.5γs′ Wd Nγs sγ1
Wd ×
γp Kp tan (δp ) sp1
12
1.2q2k − 0.5γs′ Wd Nγs sγ2
γp Kp tan (δp ) sp2
12
Loading Case 2 :
D2 =
Wd ×
Use the larger of D1 and D2 to construct the platform.
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Platform Thickness Design Calculation Procedure
Example Calculation - Soft Clay Subgrade
Example Calculation - Soft Clay Subgrade I
Subgrade Properties
Undrained cohesion, cu = 24 kPa
Calculating Bearing Capacity of Subgrade
Platform Properties
Friction angle, ϕ′p = 40°
Unit weight, γp′ = 20 kN/m3
Rd = cu Nc sc
= 24 × 5.14 × 1.04 = 128 kPa
Plant Details
Width, Wd = 0.7 m
Effective lengths, L1 = 3.6 m & L2 = 3.1 m
Calculate design loading for Case 1 & Case 2
Loading Details
Loading Case 1, q1k = 140 kPa
Loading Case 2, q2k = 190 kPa
q1d = 2.0 × q1k = 2.0 × 140 = 280 kPa
q2d = 1.5 × q2k = 1.5 × 190 = 285 kPa
q1d > Rd
Geogrid Details
Ultimate tensile strength, Tult = 30 kN/m
q2d > Rd
Nc = 5.14 (we previously used 5.7)
Nγ p = 109 (from Figure 17)
Kp tan(δ) = 5.5 (Figure 16)
sc 1 = 1 + 0.2(Wd /L) = 1 + 0.2(0.7/3.6) = 1.04
sc 2 = 1 + 0.2(0.7/3.1) = 1.05
sγ1 = 1 − 0.3(Wd /L) = 1 − 0.3(0.7/3.6) = 0.94
sγ2 = 1 − 0.3(0.7/3.1) = 0.93
sp1 = 1 + (Wd /L) = 1 + (0.7/3.6) = 1.19
sp2 = 1 + (0.7/3.1) = 1.23
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As design loading values are higher than the above
calculated subgrade bearing resistance, a piling
platform will be required.
Check if the platform material is stronger than
subgrade: 0.5Wd γp′ Nγ p = 0.5 × 0.7 × 20 × 109
= 717 kPa. As Rd < 717 kPa, the chosen platform
material is stronger than the subgrade.
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Platform Thickness Design Calculation Procedure
Example Calculation - Soft Clay Subgrade
Example Calculation - Soft Clay Subgrade II
Check if the bearing capacity of the platform material
is higher than the design loading values.
Calculating design loadings for Case 1 & 2:
=
q1d = 1.6 × q1k = 1.6 × 140 = 224 kPa
0.7 ×
1.6 × 140 − 128
20 × 5.5 × 1.19
1
2
= 0.71 m
q2d = 1.2 × q2k = 1.2 × 190 = 228 kPa
q1d < 717 kPa
Case 2 Loading q2d = 1.2q2k
q2d < 717 kPa
D1 =
Considering the above, the chosen platform material
is stronger and suitable to provide the required
bearing capacity.
=
1
1.2q2k − cu Nc sc 2 2
Wd ×
γp Kp tan (δp ) sp 2
1
0.7 ×
Calculate Platform Thickness for each Loading Case
1.2 × 190 − 130
20 × 5.5 × 1.23
2
= 0.72 m
Case 1 Loading q1d = 1.6q1k
D1 =
Calculate Platform Thickness with Geogrid
Reinforcement
1
1.6q1k − cu Nc sc1 2
Wd ×
γp Kp tan (δp ) sp1
Ziauddin Ahmed (Geotechnique Pty Ltd)
Design tensile strength,
Piling Platform Design
Td =
Tult
2
=
30
= 15 kN/m
2
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Platform Thickness Design Calculation Procedure
Example Calculation - Soft Clay Subgrade
Example Calculation - Soft Clay Subgrade III
Calculate Platform Thickness with the effect of
Reinforcement ignored
Case 1 Loading q1d = 1.6q1k
Case 1 Loading q1d = 1.25q1k
1
1.6q1k − cu Nc sc 1 − (2.0Td /Wd ) 2
D1 = Wd ×
γp Kp tan (δp ) sp 1
(
)1
=
0.7 ×
1.6 × 140 − 128 − 2.0 ×
15
0.7
D1 =
2
20 × 5.5 × 1.19
=
1
1.25q1k − cu Nc sc 1 ) 2
Wd ×
γp Kp tan (δp ) sp 1
1
0.7 ×
= 0.53 m
1.25 × 140 − 128
20 × 5.5 × 1.19
2
= 0.51 m
Case 2 Loading q2d = 1.2q2k
D1 =
=
Case 2 Loading q2d = 1.05q2k
1
1.2q2k − cu Nc sc 2 − (2.0Td /Wd ) 2
Wd ×
γp Kp tan (δp ) sp 2
(
)1
0.7 ×
1.2 × 190 − 130 − 2.0 ×
15
0.7
2
=
20 × 5.5 × 1.23
= 0.53 m
Ziauddin Ahmed (Geotechnique Pty Ltd)
D1 =
1
1.05q2k − cu Nc sc 2 2
Wd ×
γp Kp tan (δp ) sp 2
1
0.7 ×
1.2 × 190 − 130
20 × 5.5 × 1.23
2
= 0.61 m
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Platform Thickness Design Calculation Procedure
Example Calculation - Soft Clay Subgrade
Summary of Platform Design
Summary of Design
Platform thickness without geogrid reinforcement : 0.72m
Platform thickness with geogrid reinforcement : 0.61m
Tensile strength of geogrid reinforcement : 30 kN/m
The above calculations can be easily done using Excel. An excel sheet has
been developed to determine platform thickness design. This is saved in K
drive Piling Platform Excel Sheet.
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March 3, 2022
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Questions
Any Questions!!!
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March 3, 2022
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References
References
Coduto, D. P., Kitch, W. A. & Yeung, M. R. (2016), Foundation design:
principles and practices, Prentice Hall USA.
Gere, J. M. & Goodno, B. (2013), Mechanics of Materials, 8th Eds, Cengage
Learning.
Meyerhof, G. (1974), ‘Ultimate bearing capacity of footings on sand layer
overlying clay’, Canadian Geotechnical Journal 11(2), 223–229.
Skinner, H. (2004), Working platforms for tracked plant: good practice
guide to the design, installation, maintenance and repair of groundsupported working platforms, BREbookshop.
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Appendices
Appendices I
Undrained shear strength of clay is half of unconfined compressive strength.
Mohr circle for unconfined compression test is shown below.
σ1 = 100 kPa
τ (kPa)
70
σ3 = 0 kPa
60
σ3 = 0 kPa
cu = 50 kPa
50
40
σ1 = 100 kPa
30
20
10
σ (kPa)
0
0
10 20 30 40 50 60 70 80 90 100
Figure 19: Mohr Circle for Unconfined Compression Test
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Appendices
Appendices II
Empirical correlation between DCP values and undrained shear strength of
clayey soils.
Table 1: Soil Consistency
Term
DCP
n
(Blows/100mm)
Very Soft
Soft
Firm
Stiff
Very Stiff
Hard
0−1
1−2
2−3
3−7
7 − 12
> 12
Undrained shear
strength,
cu
(kPa)
≤ 12
> 12 to ≤ 25
> 25 to ≤ 50
> 50 to ≤ 100
> 100 to ≤ 200
> 200
Design Shear
Strength, cud
(kPa)
−
20
40
80
−
−
The platform thickness design method shown in this presentation is applicable Skinner (2004) for clayey soils with shear strength between 20 and
80kPa.
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Appendices
Appendices III
Design values for granular platform material.
Table 2: Properties of Granular Material
Material Type
Friction Angle, ϕ◦
Unit Weight, γ
Crushed or Ripped Sandstone
35 to 40
20
Roadbase Gravel
40 to 45
21
kN/m3
The above values are possible when the material is compacted to ≥ 98%
Standard Density.
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