Apappa Lagos Geotechnical Design

NOTRE DAME UNIVERSITY – LOUAIZE
DEPARTMENT OF CIVIL AND ENVIRONMENTAL
ENGINEERING
APAPPA LAGOS GEOTECHNICAL DESIGN
An Engineering Design II Report
SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL
ENGINEERING
In partial fulfillment of the requirements for the
Degree of
Bachelor of Engineering
By
Karim Taher
Zouk Mosbeh, Lebanon
2015

i
APAPPA LAGOS PROJECT GEOTECHNICAL DESIGN
An Engineering Design II
APPROVED FOR THE
DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING
BY
Mr. Michel Bouchedid, MCE, PE, MBA
Advisor
Dr. Naji Khoury, PE
Committee Member
Dr. Sophia Ghanimeh
Committee Member
Dr. Jacques Harb, PE
Chair of CEE Department

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SENIOR DESIGN REPORT CHECKLIST
Learning objective State how/where in the project the CLO is met
CLO 1 Implement an engineering project design
1.1. Identify a need/define a problem
Design the foundation and shoring system for
a building to be built on soft soils with high
water table
1.2. State objectives
Provide multiple foundation design
alternatives for the building and recommend
the most economical one
1.3. Collect information
From existing geotechnical report
1.4. Identify constraints
Poor soil conditions at the surface and high
water table
1.5. Identify adopted codes, standards, or
rules of practice
American Concrete Institute (ACI-318) and
British Standard Institute (BSI/1989)
1.6. Analyze the problem using acquired
engineering knowledge
Problem analysis includes raft foundation at
multiple levels, deep foundation, and shoring
system
1.7. Synthesize and propose a solution
Recommended solution includes a 9 meter
excavation with a shoring system
CLO 2 Develop skills needed to function within a design team
3. Team work statement
Project completed by one person
CLO 3 Produce a technical design report, a technical presentation and engineering
drawings
4.1. Technical report (hard and soft copies)
Completed
4.2. Oral presentation (soft copy)
Completed
4.3. Technical engineering drawings
Completed

iii
ACKNOWLEDGMENTS
I would like to express my sincere gratitude to my advisor Mr. Michel Bouchedid, P.E. and Mr.
Nabil Houssayni for their guidance and continuous support to complete this study and prepare
this report. Besides my advisor and my friend, I would like to thank Rasha Joumaa and my
family for their moral support throughout the course of my engineering degree and my life in
general.

iv
ABSTRACT
One of the most important objectives of engineering is optimization. In this project, several
design alternatives will be considered in order to choose the most optimal design. The design
evaluation for the different alternatives will include a cost analysis in addition to an evaluation of
the practicality of the design and its constructability.
The project consists of a 12 story building that will be constructed in Lagos, Nigeria. One of the
main challenges facing the owner is the poor bearing capacity of the soil at the surface and the
high water table.
A local geotechnical company who prepared a geotechnical report for this project recommended
that the building be supported on drilled piles extending into harder soils. The drilled piles option
provides sufficient bearing support for the building. However, this alternative is uneconomical.
Another alternative consists of excavating 9 meters below ground surface to build underground
basements, thus building the foundation on harder soils. The 9 meters excavation alternative
requires the construction of a temporary shoring system along with a dewatering system to avoid
damaging the surrounding environment including other buildings and roads. The cost of the
alternative with basements is more economical because the basements can be sold. Also, the
shoring system is less costly than the pile foundation as discussed in the report.
As a summary, this report describes the problem that a developer in Nigeria has with the soil
conditions at his project site, provides the soil parameters to be used in the design, and discusses
different alternatives for foundation design and recommends the most economical alternative for
the developer.

v
CONTENTS
SENIOR DESIGN REPORT CHECKLIST..........................................................................................................3
ACKNOWLEDGMENTS........................................................................................................................................4
ABSTRACT ...............................................................................................................................................................5
A. INTRODUCTION............................................................................................................................................1
B. GOAL AND METHODOLOGY.....................................................................................................................3
B.1. OBJECTIVES ...............................................................................................................................................3
B.2. ASSUMPTIONS.......................................................................................................................................3
B.3. CODES, STANDARDS AND RULES OF PRACTICE.........................................................................4
B.4. PURPOSE OF THIS PROJECT................................................................................................................4
B.5. SCOPE OF THE PROJECT.......................................................................................................................4
B.6. LOCATION OF THE PROJECT ..............................................................................................................5
B.7. SUMMARY OF THE GEOTECHNICAL REPORT..............................................................................5
C. RESULTS AND ANALYSIS....................................................................................................................... 10
C.1. SOIL PROPERTIES CALCULATION ................................................................................................. 10
C.2. CHECK FOR BEARING CAPACITY ................................................................................................... 15
C.3 SHORING SYSTEM DESIGN................................................................................................................. 19
C.4. DEWATERING SYSTEM ...................................................................................................................... 42
C.5. PILE FOUNDATION DESIGN ............................................................................................................. 43
C.6. COST ANALYSIS..................................................................................................................................... 62
D. CONCLUSION AND RECONMMENDATIONS.................................................................................... 64
D.1. CONCLUSION.......................................................................................................................................... 64
D.2. LIMITATIONS......................................................................................................................................... 64
D.3. CONSTRUCTION RECOMMENDATIONS ...................................................................................... 65
E. REFERENCES............................................................................................................................................... 66
F. APPENDIX .................................................................................................................................................... 68

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List of Figures
Figure 1. Map of Lagos (Extracted from Google Earth, August 2015)..............................................5
Figure 2. Completed Boreholes Layout (Extracted from the Geotechnical Report by Basol
Associates Ltd., 2014) .........................................................................................................................................6
Figure 3. Distribution of the Measured SPT Blow Counts with Depth .......................................... 11
Figure 4. Triaxial Compression Test Mohr Circle Diagram (Extracted from Basol Associates
Ltd., 2014)............................................................................................................................................................. 13
Figure 5. Load Eccentricities along x and y Directions........................................................................ 17
Figure 6. Checking Column Pressure on Soil........................................................................................... 18
Figure 7. Diaphragm Wall Supported by Ground Anchors (Extracted from the Internet for
Illustration) .......................................................................................................................................................... 19
Figure 8. Ground Anchor Detailing ............................................................................................................. 20
Figure 9. Anchor Free Length According to the Assumed Failure Surface.................................. 27
Figure 10. Drawing the Model on PLAXIS................................................................................................. 27
Figure 11. PLAXIS Mesh Generation........................................................................................................... 28
Figure 12. Water Table Definition............................................................................................................... 28
Figure 13. Water Pressure Shadings .......................................................................................................... 29
Figure 14. Layer 3 Defined as a Dry Cluster ............................................................................................ 29
Figure 15. Initial Stress Definition............................................................................................................... 29
Figure 16. Load Definition.............................................................................................................................. 30
Figure 17. Plate Definition.............................................................................................................................. 30
Figure 18. Excavating First 3 Meters.......................................................................................................... 31
Figure 19. Activating First Row of Anchors............................................................................................. 31
Figure 20. Excavating Second 3 Meters..................................................................................................... 32
Figure 21. Activating Second Row of Anchors........................................................................................ 32
Figure 22. Excavating Last 3 Meters........................................................................................................... 33
Figure 23. Phi/C Reduction............................................................................................................................ 33
Figure 24. Run Calculation ............................................................................................................................. 34
Figure 25. Total Displacement of the Shoring System......................................................................... 34
Figure 26. Total Horizontal Displacement of the Shoring System.................................................. 35
Figure 27. Total Vertical Displacement of the Shoring System........................................................ 35
Figure 28. Plate Horizontal Displacement................................................................................................ 36
Figure 29. Plate Vertical Displacement...................................................................................................... 37
Figure 30. Axial Forces on the Plate............................................................................................................ 37
Figure 31. Shear Forces on the Plate.......................................................................................................... 38
Figure 32. Bending Moment on the Plate ................................................................................................. 38
Figure 33. Anchor 1 Horizontal Displacement ....................................................................................... 39
Figure 34. Anchor 2 Horizontal Displacement ....................................................................................... 39
Figure 35. Reinforced Concrete Beam Stress in the Ultimate State (Deep Excavation, Theory
and Practice)........................................................................................................................................................ 41
Figure 36. Open Sumps Method for Dewatering.................................................................................... 43
Figure 37. Ultimate Load-Carrying of Pile................................................................................................ 45
Figure 38. Variation of Nq* with L/D (Extracted from Das 2007b, after Coyle and Costello)
................................................................................................................................................................................... 48

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Figure 39. Unit Frictional Resistance in Sand (Extracted from Das, 2007b) .............................. 50
Figure 40. Variation of K with L/D (Extracted from Das 2007b, after Coyle and Costello,
1981)....................................................................................................................................................................... 51
Figure 41. Estimation of Frictional Resistance using the λ Method............................................... 55
Figure 42. Pile Reinforcement 45 cm Diameter..................................................................................... 58
Figure 45. Pile Distribution under Raft Foundation............................................................................. 61
Figure 46. Architectural Design.................................................................................................................... 70
Figure 47. Building Section ............................................................................................................................ 71
Figure 48. Parking Lots.................................................................................................................................... 72
Figure 49. Borehole No. 1 ............................................................................................................................... 73
Figure 50. Borehole No. 1 (continued) ...................................................................................................... 74
Figure 51. Borehole No. 2 ............................................................................................................................... 75
Figure 52. Borehole No. 2 (continued) ...................................................................................................... 76

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List of Tables
Table 1. Subsurface Profile Summary...........................................................................................................7
Table 2. Option A: 8 m Long Piles (Extracted from Basol Associates Ltd., 2014)........................8
Table 3. Option B: 32 m Long Piles (Extracted from Basol Associates Ltd., 2014) .....................9
Table 4. SPT N-Values for Boreholes 1 and 2.......................................................................................... 10
Table 5. Variation of NH, NB, NS and NR (Das, 2007b) ........................................................................... 12
Table 6. PLAXIS 2D Soil Data Input (Layer 1)......................................................................................... 22
Table 9. Diaphragm Wall Properties .......................................................................................................... 23
Table 10. Anchor Free Length Properties................................................................................................. 24
Table 11. Anchor Grouted Length Properties......................................................................................... 24
Table 12. Factor of Safety for Single Anchor (CICHE, 1998) ............................................................. 25
Table 13. Ultimate Frictional Strength of an Anchorage Body (Extracted from Deep
Excavation)........................................................................................................................................................... 26
Table 14. PLAXIS Outcomes Vs Acceptable Values............................................................................... 40
Table 15. Interpolated Value of Nq* Based on Meyerhof’s Theory ................................................ 46
Table 16. Summary of Point Bearing Pile Load Capacity at 8 m Depth ....................................... 49
Table 17. Summary of Point Bearing Pile Load Capacity at 32 m Depth...................................... 49
Table 18. Recommended Average Values for K (Das, 2007a) .......................................................... 51
Table 19. Summary of the Skin Friction Resistance at 8 m................................................................ 53
Table 20. Total Foundation Pile Capacity at 8 m ................................................................................... 54
Table 21. Variation of λ with Pile Embedment Length (Extracted From Deep Foundation,
Theory and Practice) ........................................................................................................................................ 55
Table 22. Variation of α (Interpolated Values Based on Terzaghi, Peck and Mesri, 1996)... 57
Table 23. Summary of the Skin Friction Resistance at 32 m............................................................. 57
Table 24. Total Foundation Pile Capacity at 32 m................................................................................. 58
Table 25. Foundation Piles Reinforcement.............................................................................................. 58
Table 26. Cost Analysis for the Shoring System Alternative............................................................. 62
Table 27. Cost Analysis for the Pile Foundations Alternative........................................................... 63
Table 28. Typical Floor Column Loads Exported from Etabs ........................................................... 68
Table 29. Maximum Pu for all Columns..................................................................................................... 69

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A. INTRODUCTION
I was introduced to this project, which is to be built in Lagos Nigeria, by a friend who was
working on the geotechnical design of the project’s deep foundations. The structure consists of a
12 story residential building to be built on poor soil conditions with a high water table. The local
geotechnical engineer in Lagos had recommended that the structure be supported on deep
foundation starting from ground surface with no underground basements. Since I had a strong
interest in completing my Senior II project with emphasis on geotechnical engineering, I thought
that this project would be a good candidate. After showing the project’s geotechnical report to
Mr. Bouchedid, he agreed to be my advisor on this project. However, he wanted me to check if
we can optimize the design in any way and make it more economical to the developer. Therefore,
the project was divided into three main alternatives:
1. Check the alternative of using raft foundations at different levels
2. Check the alternative of using drilled pile foundations if no basements are to be used
3. Design the shoring system for the raft foundation within a deep excavation alternative
The design is based on codes and regulations requested by the developer which will be further
described in Section B.3. The deep foundation alternative includes supporting the building on
drilled piles 8 or 32 m long. The raft foundation alternative consists of completing a 9 meter
excavation to build the foundation on harder soil. In this alternative, a shoring system will be
required.
The soil properties used in this report were obtained from the geotechnical report provided by a
local geotechnical engineer. The soil parameters that are not included in the geotechnical report
were estimated using the existing borehole logs which include SPT values. Once the soil
parameters are estimated, the bearing capacity for a raft foundation is checked at three levels

2
including 1.75 m, 4 m, and 9 m below ground surface. As is shown in subsequent sections of this
report, the allowable bearing capacity at 1.75 m and 4 m below ground surface is smaller than
the load applied by the building on the raft foundation. However, the allowable bearing capacity
at 9 m depth was found to be greater than the loads applied by the structure on the raft
foundation. The shoring system for the 9 m deep excavation consists of a diaphragm wall and
ground anchors.
The computer modeling is completed using the software PLAXIS 2D, which is a finite element
package intended for the two dimensional analysis of deformation and stability in geotechnical
engineering.
Since the local geotechnical engineer had recommended a deep foundation system and provided
pile capacity in the geotechnical report, an independent check was completed on pile capacities
using different methods to confirm the information provided in the report.
For both proposed alternatives, a cost analysis will be prepared to help the developer choose the
best alternative for his project. As is shown in the cost analysis section, the raft foundation at a
depth of 9 meters below ground surface using a diaphragm wall as a shoring system is more
economical than using a deep foundation system starting from ground surface with no
basements.

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B. GOAL AND METHODOLOGY
One of the most important goals of this project is to provide the developer multiple foundation
options for his project in order to help him choose the most economical one, which gives him the
highest return on his investment. In this project, the recommended solution to the soft soils
problem in the upper soil layer consists of adding two underground basements that can be sold
after the project is completed.
B.1. OBJECTIVES
The objectives of this project are as follows:
 Check the data provided in the existing geotechnical report.
 Estimate the soil properties needed for the design but not included in the existing
geotechnical report.
 Check the alternative of using raft foundations at different levels.
 Check the alternative of using drilled pile foundations if no basements are to be used.
 Design a shoring system for the deep excavation alternative.
 Complete a cost analysis for both alternatives.
 Recommend the best alternative for execution.
B.2. ASSUMPTIONS
All constraints and assumption are stated below:
 The soil parameters of the top 1.75 m of surficial soil which consists of fill and top soil were
not included in the geotechnical report.
 For the calculation of the SPT N60 value, the hammer type is not mentioned in the
geotechnical report, therefore it is assumed to be a Donut hammer.

4
 The allowable total settlement of a raft foundation resting on sand for a residential building
was assumed to be 50 mm as per ACI-318 recommendation.
B.3. CODES, STANDARDS AND RULES OF PRACTICE
The existing geotechnical report was completed according to the British Standard Institute (BSI)
to estimate the soil parameters. Therefore, the BSI will be used for analyzing the shoring system
and the drilled pile design.
The American Concrete Institute (ACI) code was used for the structural reinforcement for the
Diaphragm wall and for the tendons used for the ground anchors.
B.4. PURPOSE OF THIS PROJECT
The purpose of this report is to design the raft foundation, shoring system, and deep foundations
of a residential building in Lagos, Nigeria based on geotechnical information provided by a local
geotechnical firm in Lagos. The design that will be completed as part of this project will be
compared with the design recommendations provided in the geotechnical report to evaluate if the
project can be completed more efficiently while maintaining safety standards required by the
design codes.
B.5. SCOPE OF THE PROJECT
This report includes the design of a shoring system, a dewatering system, and the foundations of
a residential building consisting of 12 stories and 2 basements, located in Lagos, Nigeria.
As part of this design the required type, size, and length of drilled shafts will be determined
along with their reinforcements for the deep foundations. In addition, the shoring system, which
consists of a diaphragm wall and anchors, will be designed.
The possibility of a shallow foundation system consisting of spread footings or mat foundation
will be evaluated.

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B.6. LOCATION OF THE PROJECT
The project is located in Lagos, Nigeria, in the downtown area, at the location shown in a red
circle in Figure 1. The city of Lagos is the main city of the south-western part of Nigeria. Some
rivers, like Badagry Creek, flow parallel to the coast for some distance before exiting through the
sand bars to the sea. The two major urban islands of Lagos in the Lagos Lagoon are Lagos Island
and Victoria Island. These islands are separated from the mainland by the main channel draining
the lagoon into the Atlantic Ocean, which forms Lagos Harbour. The islands are separated from
each other by creeks of varying sizes and are connected to Lagos Island by bridges. The smaller
sections of some creeks have been sand filled and built over.
Figure 1. Map of Lagos (Extracted from Google Earth, August 2015)
B.7. SUMMARY OF THE GEOTECHNICAL REPORT
The soil report submitted by a local geotechnical firm in Lagos (Basol Associates Limited)
includes some of the important data needed for the design. Assumptions are made when needed
using codes and manuals, if the required information is not included in the report. The project
elevation is 15 meters above sea level.

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Boreholes:
The subsurface investigations involved exploratory borings using a Pilcon Wayfarer Shell and
Auger cable percussion drilling rig. Boring logs summarizing the results of the exploration are
included in the Appendix. In addition to the borings, Dutch cone penetrometer Testing (DCPT)
was performed using a 10 ton rig. A total of two borings and four DCPTs were completed at the
project site as shown in Figure 3. Laboratory testing of samples recovered from the boreholes
was completed.
Figure 2. Completed Boreholes Layout (Extracted from the Geotechnical Report by Basol Associates Ltd.,
2014)
The shell and auger cable percussion boring was drilled to about 40 m in depth. Each of the four
DCPTs was pushed to a depth of about 6.2 m below the existing ground surface where it

7
encountered refusal; this is because of the inability of the DCPT machine to penetrate through
gravel and concrete rubble present in the upper layer.
During the drilling program, samples were recovered at regular intervals of 0.75 m, while
standard penetration tests (SPT) were carried out at alternative intervals of 1.5 m. The subsurface
profile is summarized in Table1.
Table 1. Subsurface Profile Summary
Depth Range (m) Description of Sub-soil Encountered
0 to 1.5 Loose, wet, dark grey, silty SAND with fine to coarse gravel, concrete rubble and
plant roots (top soil/old fill)
1.5 to 13 Medium dense, becoming dense, dark/yellowish brown/grey silty SAND with fine
to coarse gravel, wet.
13 to 26 Firm to stiff, yellowish brown/grey, mottled silty, Sand CLAY with fine gravel, dry.
26 to 40 Medium dense/dense, dark grey/grey silty SAND with fine to coarse gravel, wet
Groundwater Conditions
Groundwater was encountered within the drilled boreholes and in the DCPT tests at about 1 m
below the existing ground surface. It should be noted that the investigation was carried out
during the dry season. Thus, the water level would be higher and the site would potentially be
prone to flooding at the peak of the wet season in view of the geology and topography of the area
and site.
Bearing Capacity and Settlements
Based on the in-situ and laboratory test results on samples obtained from the borings, a general
safe (allowable) bearing capacity value of 105 kN/m2
was recommended in the report for rigid,

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well reinforced square or circular footings placed at a minimum depth of 1.75 meters below the
existing ground level, with a factor of safety of 3.
Shallow Foundations Recommendations
Soil parameters were obtained from available boring records, in-situ field data, and laboratory
test results obtained from the subsoil samples recovered during drilling and from results of the
DCPT results. The proposed building imposes approximately 180 kN/m2
of load which is higher
than the allowable bearing capacity at ground surface. Therefore, a raft foundation at ground
surface is not recommended for the proposed building.
However, shallow foundations in the form of spread footings placed at depths up to 1 m could be
adopted for ancillary structures made up of gates, generator houses, upon filling or compacting
the existing ground to densify the loose sand.
Deep Foundations Recommendations
Since ground improvement techniques to improve the allowable bearing capacity at ground
surface is not an option due to its high cost, deep foundation design in the form of drilled piles
may be the best alternative if no basements are to be built. Pile foundations would minimize
settlement of the proposed development and allow construction to commence immediately.
The following pile working loads were included in the geotechnical report as a guide based on
data obtained from the borings and DCPT results for bored cast-in-place piles:
Table 2. Option A: 8 m Long Piles (Extracted from Basol Associates Ltd., 2014)
Pile Type Pile Length
(m)
Safe Working Load
(kN)
Factor of Safety
45 cm Bored cast-in-place pile 8 560 3
60 cm Bored cast-in-place pile 8 1,010 3

9
Settlement of the proposed building on piles with the above quoted Safe Working Loads (SWL)
for Option A is expected to be minimal since the proposed piles will terminate within a medium
dense to dense sand, knowing that the first five meters of the second layer are medium dense,
then for the remaining part of the second layer, the sand will become dense.
Table 3. Option B: 32 m Long Piles (Extracted from Basol Associates Ltd., 2014)
Pile Type Pile Length
(m)
Safe Working Load
(kN)
Factor of Safety
Settlement of the proposed building on piles with the above quoted (SWL) for Option B is
expected to be minimal since the proposed piles will terminate within dense soils. These values
will be independently verified using different methods summarized in subsequent sections.

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C. RESULTS AND ANALYSIS
C.1. SOIL PROPERTIES CALCULATION
All soil properties were determined according to ASTM, using the Standard Penetration Test that
was completed in accordance with B.S 1377:1975, Test 19. A split barrel thick-walled sampler
“split spoon” of about 35 mm internal diameter is driven 450 mm into the soil by repeated blows
from a trip hammer weighing 65 kg and free falling 760 mm. Note that the ground surface at the
project site is considered to be flat since no information was provided regarding the grade of the
site.
Table 4. SPT N-Values for Boreholes 1 and 2
BH1 BH2
Depth
(m)
SPT N-Value
Depth
(m)
SPT N-Value
Layer 1
0 0 0 0
-1.5 10 -1.5 12
Layer 2
-2.5 16 -2.5 15
-4 22 -4 20
-6 24 -5.5 22
-7 27 -7.5 25
-8.5 30 -8.5 28
-10 30 -10 30
-11.5 38 -12 33
-13 12 -13 12
Layer 3
-14.5 10 -14.5 12
-16 11 -17.5 11
-17.5 12 -22 12
-19 12 -23.5 14
-20.5 12 -25 18
-22 12 -26.5 22
-25 10 -28 24
-26 15 -30 24
Layer 4
-28 20 -31.5 25
-29.5 22 -32.5 25
-31 25 -34 27
-32.5 25 -36 33
-35 27 -37.5 35
-36 30
-37.5 33
-38.5 35

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Figure 3. Distribution of the Measured SPT Blow Counts with Depth
SPT N60 Correction
The standard of practice is to express the SPT N-values to an average energy ration of 60%
(N60). Correcting the field data for the SPT N-value is as follows:
N60 =
N×(NH)×(NB)×(NS)×(NR)
60
(Eq.1)
N60 = SPT N-value to an average energy ratio of 60%
N = Field SPT N-value
NH = Hammer efficiency
NB = Borehole diameter correction factor
NS = Sampler correction factor
NR = Rod length correction factor

12
Table 5. Variation of NH, NB, NS and NR (Das, 2007b)
Variation of NH
Variation of NH
Country
Hammer
Type
Hammer Release
NH
(%)
Japan
Donut Free Fall 78
Donut Rope and Pulley 67
U.S
Safety Rope and Pulley 60
Argentina Donut Rope and Pulley 45
China
Donut Free Fall 60
Variation of NB
Variation of NB
Diameter
(mm)
NB
60-120 1
150 1.05
200 1.15
Variation of NS
Variation of Ns
Variable Ns
Standard Sampler 1
With Liner for Dense Sand and Clay 0.8
With Liner for Loose Sand 0.9
Variation of NR
Variation of NR
Rod Length
(mm)
NR
>10 1
60-100 0.95
400-600 0.85
0-400 0.75
Example calculation
 Layer 1 (0 to 1.5m): Disregarded because it consists of old fill
 Layer 2 (1.5 to 13m): Average N-Value = 24  N60 =
24×45×1.05×1×0.75
60
= 14.175
 Layer 3 (13 to 26m): Average N-Value = 14.437  N60 = 8.52
 Layer 4 (26 to 40m): Average N-Value = 27.84  N60 = 16.443

13
Friction Angle
The angle of internal friction (friction angle) is a measure of the ability of a unit of rock or soil to
withstand a shear stress. It is the angle (), measured between the normal force (N) and resultant
force (R), that is attained when failure just occurs in response to a shearing stress (S).
Peck, Hanson and Thornburn (1974) give a correlation between SPT N60 value and the friction
angle which can be approximated as follows (Wolff, 1989):
’ = 27.1 + 0.3N60 – 0.00054(N60)2
(Eq.2)
Example calculation
 Layer 1 (0 to 1.5 m): Disregarded because it consists of old fill
 Layer 2 (1.5 to 13 m): ’ = 27.1 + 0.3x14.175–0.00054 x (14.175)2
= 31.34o
 Layer 3 (13 to 26 m): Based on Triaxial test in geotechnical report, ’ = 5o
 Layer 4 (26 to 40 m): ’ = 27.1 + 0.3x16.443– 0.00054 x (16.443)2
= 31.73o
Figure 4. Triaxial Compression Test Mohr Circle Diagram (Extracted from Basol Associates Ltd., 2014)

14
Modulus of Elasticity (Es)
Young's modulus (ES) describes tensile elasticity, or the tendency of an object to deform along
an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress
to tensile strain. It is often referred to simply as the elastic modulus.
The modulus of elasticity is important in estimating the elastic settlement of foundations. The
first order of estimation was given by Kulhawy and Mayne (1990) as follows:
𝐸𝑠
𝑃𝑎
= ∝ 𝑁60 (Eq.3)
Pa: Atmospheric pressure = 100 kN/m2
α: constant
For our project, an approximated value using the classification of soil will be used as follows:
 Layer 1 (0 to 1.5 m) Es = 12000 kN/m2
 Layer 2 (1.5 to 13 m) Es = 45000 kN/m2
 Layer 3 (13 to 26 m) Es = 40000 kN/m2
 Layer 4 (26 to 40 m) Es = 45000 kN/m2
Cohesion
Cohesion is the component of shear strength of a rock or soil that is independent of internal
particle friction. In soils, true cohesion is caused by electrostatic forces in stiff overconsolidated
clays (which may be lost through weathering), it was estimated using the triaxial test and
reported in the geotechnical report as follows:
 Layer 1 (0 to 1.5 m): not considered because it consist of old fill
 Layer 2 (1.5 to 13 m): Assumed Cu = 0 kN/m2
for silty Sand (no Triaxial test data
available)
 Layer 3 (13 to 26 m): Cu = 68 kN/m2

15
 Layer 4 (26 to 40 m): Assumed Cu = 0 kN/m2
because silty Sand (no Triaxial test data
available)
C.2. CHECK FOR BEARING CAPACITY
Initially, a bearing capacity check of the soil in the first layer at a depth of 1.75 m is determined
to check whether the soil can handle the column loads.
Bearing Capacity under Mat Foundation
The net allowable bearing capacity for mats constructed over granular deposits can be adequately
determined from the standard penetration resistance number using the following approximated
equation:
𝑞 𝑛𝑒𝑡, 𝑎𝑙𝑙 =
𝑁60
0.08
× 𝐹𝑑 ×
𝑆𝑒
25
(Eq.4)
Where
N60 = Standard Resistance Number
Fd = 1 +
0.33𝐷𝑓
𝐵
must be ≤ 1.33
Se = Settlement (mm) assumed to be 50 mm for sand
B = Width of the Mat (m)
Option 1: Bearing Capacity at 1.75 m Depth
N60 (z=1.75m) = 10.5 ==> Fd = 1 +
0.33×1.75
23.5
= 1.0245 < 1.33
==> 𝑞 𝑛𝑒𝑡, 𝑎𝑙𝑙 =
10.5
0.08
× 1.0245 ×
50
25
= 268.93 kN/m2
Following the conventional rigid method of mat foundation design procedure:
q =
𝑄
𝐴
±
𝑀𝑦𝑋
𝐼𝑦
±
𝑀𝑥𝑌
𝐼𝑥
(Eq. 5)
Where
A = area of the mat (m2
)

16
Ix = moment of inertia about the x-axis
Iy = moment of inertia about the y-axis
Ex = Load eccentricity in the x direction = x’ -B/2
Ey = Load eccentricity in the y direction = y’ -L/2
Mx = Qey moment of the column loads about the x-axis
My = Qex moment of the column loads about the y-axis
Q = Total Column Loads
A = 23.5× 36.25 = 851.875 m2
Ix =
1
12
BL3
=
1
12
(23.5) (36.25)3
= 93284.7 m4
Iy =
1
12
LB3
=
1
12
(36.25) (23.5)3
= 39203.9 m4
Q = 6x2009 + 3392x4 + 4129x4 + 1828x5 + 6366x7 + 6572x4 + 6235x2 + 4598x3 + 4340x1 +
5762x1 + 4197x4 + 11800x2
Q = 198876 kN

17
Figure 5. Load Eccentricities along x and y Directions
ex= x’ −
𝐵
2
x’ = 17.3507 m
ex = 17.35 –
23.5
2
= 5.6 m
ey= y’ −
𝐿
2
Y’ = 11.593 m
ey= 11.593 –
35.25
2
= −6.03 m
q = 233.45 ± 28.4x ± 12.85y
Column C7 at the left edge will apply the highest point pressure on the soil as follows:

18
Figure 6. Checking Column Pressure on Soil
q = 233.45 + 28.4×11.5 + 12.85×15.52 = 759.482 kN/m2
> qnet,all  not acceptable
Therefore a mat foundation at 1.75 m depth is not adequate.
Option 2: Bearing Capacity at 4 m Depth
After getting inadequate results from the preceding option, the bearing capacity is checked at 4
meters depth which is equivalent to adding a basement level to the structure.
N60 (z=4m) = 21 ==> Fd = 1 +
0.33×4
23.5
= 1.056 < 1.33
 𝑞 𝑛𝑒𝑡, 𝑎𝑙𝑙 =
21
0.08
× 1.056 ×
50
25
= 554.48 kN/m2
< 759.482
This option is also not adequate; therefore the depth is increased by another 4 m which is
equivalent to adding another basement level to the structure.
Option 3: Bearing Capacity at 9 m Depth
N60 (z=9m) = 28 ==> Fd = 1 +
0.33×8
23.5
= 1.112 < 1.33
 𝑞 𝑛𝑒𝑡, 𝑎𝑙𝑙 =
28
0.08
× 1.112 ×
50
25
= 778.63 kN/m2
> 759.48  OK

19
Therefore, increasing the depth of the raft to 9 meters below ground surface will be adequate for
the soil bearing capacity to handle all column loads under the mat foundation. However, by
adding two basement levels to the structure, a shoring system should be constructed to maintain
stability of the excavation.
C.3 SHORING SYSTEM DESIGN
This section includes the design of the shoring system which consists of a diaphragm wall
supported by anchors. This system will provide slope stability for the excavation. The wall and
anchors must interact and work together in order to resist earth pressure loads and surcharges
developing during and after construction. In addition, they should restrict deformations to
acceptable values. As the wall deflects toward the excavation under lateral loading, the anchor
stretches and initiates the load transfer to the fixed zone. The fixity imposed on the anchorage by
the soil restrains further wall deflection.
Figure 7. Diaphragm Wall Supported by Ground Anchors (Extracted from the Internet for Illustration)

20
Ground Anchors
A ground anchor normally consists of:
 A high tensile steel cable or bar, called the tendon, one end of which is held securely in
the soil by a mass of cement grout.
 The other end of the tendon is anchored against a bearing plate on the structural unit to be
supported
In general we can consider that an anchor consists of two parts:
 The fixed anchor length: the grouted length of tendon, through which force is transmitted
to the surrounding soil.
 The free anchor length: the length of tendon between the fixed anchor and the bearing
plate
Figure 8. Ground Anchor Detailing

21
Design Parameters and Process
The proposed solution was to increase the depth of excavation to provide adequate bearing
capacity under the mat foundation. Assuming the height of the proposed two basements is 3.5
meters each, with a 25 cm slab thickness, the excavation should extend from ground surface to 9
meters depth. This assumes that the mat foundation thickness is about 1.5 m.
After checking several sections and embedment depths, a 16 meters long diaphragm wall,
including 7 m embedment depth below the bottom of the excavation, and 40 cm thickness is
recommended for this project. A diaphragm wall is recommended instead of drilled secant piles
due to the high water table of the site and a full saturation of the second layer (silty sand), in
addition to the presence of concrete construction rubble in the top layer.
As was mentioned earlier, the top soil layer consists of fully saturated silty sand underlain by dry
sandy clay. Therefore it is recommended that test pits be dug inside the footprint of the
excavation to dewater the site once the D-wall is constructed. This D-wall will prevent the water
to seep into the site from outside while the water level inside the excavation will be lowered
using water pumps inside the test pits.
PLAXIS 2D Modeling
A two-dimensional finite element program PLAXIS 2D has been used to model a D-wall
supporting an excavation.
In a plane strain model all stresses are calculated along the three axes (x,y,z) but deformations
and strains are calculated in the 2D (x,z) plane.

22
The following soil parameters are used in the design
Table 6. PLAXIS 2D Soil Data Input (Layer 1)
Identification Fill
Material model Mohr-Coulomb
Material type Drained
General properties
unsat(kN/m3
) 14
sat(kN/m3
) 14
Permeability
Kx(m/day) 1
Ky(m/day) 1
Stiffness
Elasticity modulus Eref
(kN/m2
)
12000
Poisson’s Ratio

0.3
strength
Cref
(kN/m2)
1

(o
)
28
Interface (Adhesion
Coefficient)
Rinter 0.67
Identification Silty Sand
General properties
unsat(kN/m3
) 17
sat(kN/m3
) 17
Permeability
Kx(m/day) 1
Ky(m/day) 1
Stiffness
(kN/m2
)
45000
Poisson’s Ratio

0.3
strength
Cref
(kN/m2
)
1

(o
)
30.27
Interface (Adhesion
Coefficient)
Rinter 0.67

23
Identification Sandy Clay
General properties
unsat(kN/m3
) 14
sat(kN/m3
) 17
Permeability
Kx(m/day) 1
Ky(m/day) 1
Stiffness
(kN/m2
)
40000
Poisson’s Ratio

0.3
Strength
Cref
(KN/m2
)
68

(o
)
5
Interface (Adhesion
Coefficient)
Rinter 0.67
Once the soil layer parameters are entered, the plate parameters, which in our case is the D-wall,
are entered as follows:
Table 9. Diaphragm Wall Properties
EA
(kN/m)
8x106
EI
(kNm2
/m)
1.067x105
Thickness
(m)
0.4
Weight
(kN/m/m)
10
Poisson’s Ratio 0.18
Calculation
EA = 8x106 kN/m
EI = 1.067x105 kNm2/m
Weight = 0.4x25 = 10 kN/m/m
Poisson’s ratio of concrete = 0.18

24
Then the node to node anchor which is the free length of the anchor is defined as follows:
Table 10. Anchor Free Length Properties
EA
(kN/m)
135000
Lspacing
(m)
2
Material Type Elastic
Calculation
As specified in the BSI/1989 code the minimum horizontal spacing between two anchors should
be less than 3 m and greater than 1 m. In our case, the deflection was acceptable with a
horizontal spacing of 2 m.
The number of tendons used in our design is 5 strands having a diameter of 12.9 mm and a
modulus of elasticity 29,000 (steel 1860 type).
EA = 27000x5 = 135000 kN/m
Finally the geogrid which is the anchor grouted length should be defined as follows:
Table 11. Anchor Grouted Length Properties
EA
(kN/m)
2.65x104
Material Type Elastic
Calculation:
Egeogrid = 1.5x107 𝜋0.152
4
= 2.65x104
kN/m
Where the diameter of the grouted length is 15 cm.
The ultimate anchorage force Tu, for a friction type anchor can be calculated by the following
equation:
Tu = πDbLaτult
(Eq. 6)

25
Where
Tu = Ultimate anchorage force = 500 kN/m
Db = Diameter of the fixed section = 15 cm
La = Length of the fixed section (grouted length)
τult = Average ultimate shear resistance strength per unit area between the fixed section and the
soil.
The factor of safety is chosen using the following table:
Table 12. Factor of Safety for Single Anchor (CICHE, 1998)
Classification
Tensile force
of tendon
Anchoring
Force
Bond Force
Of Tendon
temporary anchors whose working
period is not longer than 6 months
and which
do not affect public safety when
failing
1.4 2 2
temporary anchors whose
working period is not longer than 2
years and which do not affect
public safety when failing
1.6 2.5 2.5
Permanent or temporary anchors
which
are highly risky in rusting or which
affect public safety seriously due to
failure
2 3 3
 La-first, row =
500×2.5
𝜋×0.15×176.5
= 15 m
 La-second, row =
500×2.5
𝜋×0.15×196.5
= 13.5 m

26
Using the following table the factor of safety will be chosen:
Table 13. Ultimate Frictional Strength of an Anchorage Body (Extracted from Deep Excavation)
Type Of soil
τult
(kg/cm2
)
Rock
Hard Rock 15-25
Soft Rock 10--15
Weathered Rock 6--10
Mudstone 6--12
Gravel
N=10 1--2
N=20 1.7--2.5
N=30 2.5--3.5
N=40 3.5--4.5
N=50 4.5--7
Sand
N=10 1--1.4
N=20 1.8--2.2
N=30 2.3--2.7
N=40 2.9--3.5
N=50 3--4
τult (Sand Layer) = 176.5 kN/m2
τult (clay Layer) = 196.5 kN/m2
By drawing the assumed failure surface at
𝜋
4
+
𝜙
2
= 60o
, the free length of the anchor can be
determined. Two meters should be added to the free length as a safety for this assumption as
shown in Figure 9 below.

27
Figure 9. Anchor Free Length According to the Assumed Failure Surface
After entering all the input data, we start by drawing the model on PLAXIS as shown in Figure
10 below.
Figure 10. Drawing the Model on PLAXIS
As previously mentioned, PLAXIS 2D is a finite element software that works by dividing the
soil layers into small portions to calculate the stress at each node. The model was taken as a 15
node element in a plain strain model.

28
Figure 11. PLAXIS Mesh Generation
After generating meshes, the model should be updated with initial conditions such as water
pressure, water table and stresses.
Figure 12. Water Table Definition

29
Figure 13. Water Pressure Shadings
Knowing that the third layer is stiff clay, a dry cluster is defined, to reduce the upheaval pressure.
Figure 14. Layer 3 Defined as a Dry Cluster
Figure 15. Initial Stress Definition

30
Afterwards, the construction phases are defined; these phases are a projection of the real
execution process.
Phase 1, Defining Surrounding Loads: a setback of 3 meters exists between the adjacent parcel
and the excavation, therefore a 5 kN/m2
surcharge was used. A small building exists in the
adjacent property; therefore a 20 kN/m2
surcharge was used for the building.
Figure 16. Load Definition
Phase 2, Plate Definition: The plate consists of the 16 m long and 40 cm thick diaphragm wall,
therefore this phase includes drilling and pouring the diaphragm wall.
Figure 17. Plate Definition

31
Phase 3, Excavation Stage 1: This phase includes the excavation of the first 3 m and updating the
water table to that level.
Figure 18. Excavating First 3 Meters
Phase 4, Defining Row 1 of Anchors: This phase includes defining and activating the first row of
anchors, which includes a 100 kN/m force.
Figure 19. Activating First Row of Anchors

32
Phase 5 Excavation Stage 2: This phase includes excavating the second 3 m and updating the
water table to that level.
Figure 20. Excavating Second 3 Meters
Phase 6, Defining Row 2 of Anchors: This phase includes defining and activating the second
row of anchors, which includes a 100 kN/m force.
Figure 21. Activating Second Row of Anchors

33
Phase 7, Excavation Stage 3: This phase includes excavating the last 3 m and lowering the
water table to 11 meters below ground surface which is 2 meters below the bottom of the
excavation.
Figure 22. Excavating Last 3 Meters
Phase 8, Phi/C Reduction: This phase includes running the program to calculate the factors of
safety to ensure a global factor of safety greater or equal than 1.25.
Figure 23. Phi/C Reduction

34
Once all the phases are defined, we run the program as shown in Figure 24 below:
Figure 24. Run Calculation
After verifying that all stages are safe for construction, an output of the model will be generated
as shown in the following figures:
Figure 25. Total Displacement of the Shoring System

35
Figure 26. Total Horizontal Displacement of the Shoring System
Figure 27. Total Vertical Displacement of the Shoring System

36
Figure 28. Plate Horizontal Displacement

37
Figure 29. Plate Vertical Displacement
Figure 30. Axial Forces on the Plate

38
Figure 31. Shear Forces on the Plate
Figure 32. Bending Moment on the Plate

39
Figure 33. Anchor 1 Horizontal Displacement
Figure 34. Anchor 2 Horizontal Displacement

40
Table 14. PLAXIS Outcomes Vs Acceptable Values
Analyzed Values Acceptable Values
Total Horizontal Displacement 6.692 cm < 10 cm ==> O.K
Total Vertical Displacement 5.935 cm < 10 cm ==> O.K
Plate Horizontal Displacement 6.692 cm < 10 cm ==> O.K
Plate Vertical Displacement 722.28x10-8
cm < 10 cm ==> O.K
Axial Force on the Plate 300.6 kN/m < 700 kN/m ==> O.K
Shear Forces on the Plate 151.9 kN/m < 350 kN/m ==> O.K
Bending Moments on the Plate 221.44 kNm/m < 714 kNm/m ==> O.K
Anchor Total Displacement 4 cm < 8 cm ==> O.K
The acceptable values defined in Table 14 may differ from one project to another. This usually
depends on several factors including the owner, the consultant, the type of construction, and the
type of codes used.
Diaphragm Wall Design
The design of the diaphragm wall includes the wall thickness and reinforcements. The thickness
of the D-wall usually depends on the stress analysis, the deformation analysis, and the concrete
reinforcement.
The reinforcement design follows the load and resistance factor design (LRFD). The main items
of design include the vertical and horizontal reinforcements as well as the shear reinforcement.
Based on the bending moment and shear envelop obtained from the PLAXIS 2D analysis of the
plate and according to the ACI code the following section will give a detailed illustration and
calculation of the reinforcement for the diaphragm wall.
For Bending:
Mu =
𝐿𝑓×𝑀
𝛼
(Eq. 7)
Mn =
𝑀𝑢
𝜙
(Eq. 8)

41
For Shear:
Vu =
𝐿𝑓×𝑉
𝛼
(Eq. 9)
Vn =
𝑉𝑢
𝜙
(Eq. 10)
Where
Mu = Bending moment for design
Mn = Nominal bending moment
Vu = Shear for design
Vn = Nominal shear
M = Bending moment obtained from PLAXIS 2D analysis
V = Shear obtained from PLAXIS 2D analysis
Lf = Load resistance factor = 1.6 according to ACI (2008)
ϕ = Strength reduction factor = 0.9 for bending moment and 0.75 for shear
α = Short term magnified factor for allowable stress = 1
Vertical Reinforcements
Figure 35. Reinforced Concrete Beam Stress in the Ultimate State (Deep Excavation, Theory and Practice)

42
As shown in Figure 35, the nominal resistance bending moment of concrete is
MR =
1
𝜙
[𝑃𝑚𝑎𝑥 × 𝑓𝑦(1 − 0.59
𝑃𝑚𝑎𝑥×𝑓𝑦
𝑓′ 𝑐
)] 𝑏𝑑2
(Eq. 11)
Where
D = distance from extreme fiber to the centroid of the steel layer
Pmax = 0.75Pb
f’c = Compressive strength of concrete
fy = Steel yield strength
Pb = Reinforcements ratio =
0.85𝑓′ 𝑐
𝑓𝑦
β1 (
6120
6120+𝑓𝑦
) , β1 = 0.85 for f’c = 25 MPa
 MR=
1
0.9
[0.0365 × 420(1 − 0.59
0.0365×420
25
)] 1 × 0.272
= 792.486 kN-m
Mu = 1.6×221.44 = 354.304 < ϕMR= 713.3 kN-m, therefore only tension reinforcement should be
designed for.
C.4. DEWATERING SYSTEM
The dewatering system is proposed to be done using the open sumps method. This method
consists of collecting the ground water seeping into an excavation from pits typically excavated
near the perimeter as shown in Figure 36.
The open sump method is the most common and economical method of dewatering when
applicable.

43
Figure 36. Open Sumps Method for Dewatering
C.5. PILE FOUNDATION DESIGN
Piles are structural members of timber, concrete, and/or steel that are used to transmit surface
loads to lower levels in the soil mass. This transfer may be by vertical distribution of the load
along the pile shaft or a direct application of the load to a lower stratum through the pile point. A
vertical distribution of the load is made using a friction or floating pile and a direct load
application is made by a point pile. This distinction is purely one of convenience since all piles
carry load as a combination of side resistance and point bearing except when the pile penetrates
an extremely soft soil to a solid base. Piles are commonly used for the following purposes:
 To carry the superstructure loads into or through a soil stratum. Both vertical and lateral
loads may be involved
 To resist uplift, or overturning forces, such as for basement mats below the water table or
to support tower legs subjected to overturning from lateral loads such as wind
 To compact loose, cohesionless deposits through a combination of pile volume
displacement and driving vibrations. These piles may be pulled out of the ground later

44
 To control settlements when spread footings or a mat is on a marginal soil or is underlain
by a highly compressible stratum
 To stiffen the soil beneath machine foundations to control both amplitudes of vibration
and the natural frequency of the system
 As an additional safety factor beneath bridge abutments and/or piers, particularly if scour
is a potential problem
 In offshore construction to transmit loads above the water surface through the water and
into the underlying soil. This case is one in which partially embedded piling is subjected
to vertical (and buckling) as well as lateral loads
Cast-in-Place Piles
A cast-in-place pile is formed by drilling a hole in the ground and filling it with concrete. The
hole may be drilled, or formed by driving a shell or casing into the ground.
The casing may be driven using a mandrel, after which withdrawal of the mandrel empties the
casing. The casing may also be driven with a driving tip on the point, providing a shell that is
ready for filling with concrete immediately. The casing may also be driven open-end, where the
soil entrapped inside the casing can be jetted out after the driving is completed. Various methods
with slightly different end results are available and patented.
Estimation of Pile Load Capacity at 8 m Depth
The ultimate load-carrying capacity Qu of a pile is given by the following equation:
Qu = Qp + Qs (Eq. 12)
Where
Qp = Load-carrying capacity of the pile point
Qs = Frictional resistance or skin friction derived from the soil-pile interface.

45
Figure 37. Ultimate Load-Carrying of Pile
Point Bearing Capacity
There are many methods to estimate the point bearing capacity of a pile. In this report, it will be
discussed and calculated using the methods of Meyerhof, Vesic and Coyle-Costello. The average
of these three methods will be used for design.
After calculating the total point bearing capacity, the factor of safety should be used to obtain the
total allowable load per each pile, or
Qall =
𝑄𝑢
𝐹𝑆
(Eq. 13)
Typically for residential buildings, F.S. = 3
Meyerhof’s Method
In general, the point load capacity in sand increases with depth of embedment. However, beyond
the critical embedment ratio, (LB/D)cr, the value of Qp remains constant.
For the case of piles in sand, where c = 0, the following equation applies:
Qp = (Ap)(q’)(Nq*) (Eq. 14)

46
Where
Ap = Area of the pile
q = Effective vertical stress at the level of the pile tip = ’L
Nq* = Bearing capacity factor
The pile capacity will be investigated for the following diameters: 45 cm, 60 cm, and 80 cm.
= 30o
 from table 15, Nq* = 56.7
Table 15. Interpolated Value of Nq* Based on Meyerhof’s Theory
Soil Friction Angle Nq*
20 12.4
21 13.8
22 15.5
23 17.9
24 21.4
25 26
26 29.5
27 34
28 39.7
29 46.5
30 56.7
31 68.2
32 81
33 96
34 115
35 143
36 168
37 194
38 231
39 276
40 346
Qp (D = 45 cm) = 0.159x14x8x56.7 = 1226 kN  Qu =
1226
3
= 336 kN
Qp (D = 60 cm) = 0.282x14x8x56.7 = 2178 kN  Qu =
2178
3
= 598 kN
Qp (D = 80 cm) = 0.5x14x8x56.7 = 3873 kN  Qu =
3873
3
= 1063 kN

47
Vesic’s Method
Vesic (1977) proposed a method for estimating the pile point bearing capacity based on the
theory of expansion of cavities. According to this theory and the basis of effective stress
parameters, the following expression shall be used:
Qp = (Ap)( o’)(NϬ*) (Eq. 15)
Where
 o’= Mean effective normal ground stress at the level of pile point =
1+2𝐾0
3
xq
Ko = Earth pressure coefficient at rest = 1 −sin
NϬ* = Bearing capacity factor
 o’ = [
1+2( 1 − sin Ѻ)
3
]xq’ = [
1+2( 1 − sin 30)
3
]x14x8 = 74.66 kN/m2
(Es)(Pa)(m) = 100 x 450 (medium dense soil) = 45000 kN/m2
Poisson’s ratio (s) = 0.3
The rigidity index Ir =
𝐸𝑠
2(1+𝑢𝑠)𝑞𝑡𝑎𝑛Ѻ
=
45000
2(1 + 0.3)14×8×𝑡𝑎𝑛30
= 267.65
 The modified rigidity index =
267.65
1+220.425×0.011475
= 75.82
 NϬ* = 45
Qp (D = 45 cm) = (0.159)( 74.66)(45) = 650 kNQu =
650
3
= 177 kN
Qp (D = 60 cm) = (0.282)( 74.66)(45) = 1150 kNQu =
1150
3
= 316 kN
Qp (D = 80 cm) = (0.5)( 74.66)(45) = 2040 kNQu =
2040
3
= 560 kN
Coyle Costello Method
Coyle and Costello (1981) analyzed 24 large scale field load test of driven piles in sand and these
results gave the following equation:

48
Qp = (Ap)(q)(Nq*) (Eq. 16)
Where
Ap = Area of the pile
q = Effective vertical stress at the level of the pile tip = L
Nq* = Bearing capacity factor
Figure 38. Variation of Nq* with L/D (Extracted from Das 2007b, after Coyle and Costello)
Qp (D = 45 cm) = (0.159)( 14)(18)(30) = 1460 kN  Qu =
1460
3
= 402 kN
Qp (D = 60 cm) = (0.282)( 14)(18)(28) = 2423 kN  Qu =
2423
3
= 665 kN
Qp (D = 80 cm)= (0.5)( 14)(18)(25) = 3845 kN  Qu =
3845
3
= 1056 kN

49
Table 16. Summary of Point Bearing Pile Load Capacity at 8 m Depth
Pile Diameter
(cm)
Meyerhof
(kN)
Vesic
(kN)
Coyle Costello
(kN)
Factor of Safety Average
(kN)
45 336 177 402 3 305
60 598 316 665 3 527
80 1063 560 1056 3 893
Table 17. Summary of Point Bearing Pile Load Capacity at 32 m Depth
Pile Diameter
(cm)
Meyerhof
(kN)
Vesic
(kN)
Coyle Costello
(kN)
Factor of Safety Average
(kN)
45 1635 215 435 3 760
60 2900 383 665 3 1316
80 5140 680 998 3 2225
Frictional Skin Resistance
The frictional skin resistance of a pile can be calculated using the following equation:
Qs = ∑ 𝑃∆𝐿𝑓 (Eq. 17)
Where
P= Perimeter of the pile
∆L= Incremental pile length
f = Unit frictional resistance at any depth
The unit frictional resistance “f”, is hard to estimate. There are many ways to do so. In this report
several methods will be evaluated. Several important factors must be kept in mind:
 The nature of the pile, knowing that the process of calculation for driven piles differs
from drilled piles. The vibration caused during pile driving helps densify the soil around
the pile thus increasing the friction angle of the sand

50
 It has been shown that the nature of variation of “f” in the field is approximately as
shown in Figure 39 below. It increases with depth more or less linearly to a depth L’ and
remains constant thereafter. The magnitude of the critical depth L’ may be 15 to 20 times
the pile diameter.
Figure 39. Unit Frictional Resistance in Sand (Extracted from Das, 2007b)
L’ will be estimated as 15 diameter of the pile, thus L’ = 15D
 At similar depths bored piles will have a lower skin friction compared with driven piles
For Z = 0 to L’
 f = Ko’tan
Where
K = effective earth pressure

51
 o’ = Effective vertical stress
= Soil pile friction
For Z = L’ to L use f = L’
Table 18. Recommended Average Values for K (Das, 2007a)
Bored Pile Ko = 1 –sinϕ
Low-Displacement Pile Ko = 1 -sinϕ to Ko = 1.4(1 - sinϕ)
High-Displacement Pile Ko = 1 -sinϕ to Ko = 1.8(1 - sinϕ)
The values of should be in the range of 0.5ϕ to 0.8ϕ
Coyle and Costello Method
Qs = (Ko’tan)pL
The earth pressure coefficient K will be deducted from the figure below:
Figure 40. Variation of K with L/D (Extracted from Das 2007b, after Coyle and Costello, 1981)

52
For L = 8 m and D = 45 cm  K = 0.9
For L = 8 m and D = 60 cm  K = 0.8
For L = 8 m and D = 60 cm  K = 0.78
o’ = [
1+2( 1 − sin Ѻ)
3
]xq = [
1+2( 1 − sin 30)
3
]x17x8 = 90.67 kN/m2
= 0.8= 0.8×30 = 24
P (D = 45 cm) = 1.41
 Qs = (0.9×90.67×tan24)×1.41×8 = 409 kN
 For F.S. = 3 use Qs (D = 45 cm) = 136 kN
P (D = 60 cm) = 1.88
 Qs = (0.8×90.67×tan24)×1.88×8 = 485 kN
P (D = 80 cm) = 2.51
 Qs = (0.78×90.67×tan24)×2.51×8 = 632 kN
Meyerhof Method
Meyerhof (1976) indicated that “f” for driven piles may be estimated using the standard
penetration number N60 as follows:
f = 0.02PaN60 for high-displacement piles (Eq. 18)
f = 0.01PaN60 for low-displacement piles (Eq. 19)
Where
Pa = Atmospheric pressure = 100 kN/m2

53
At 8 m depth, N60 = 14.175
f = 0.01×100×14.175 = 14.175
P (D = 45 cm) = 1.41; F.S. = 3
 Qs (D = 45 cm) = 54 kN
P (D = 60 cm) = 1.88; F.S. = 3
 Qs (D = 60 cm) = 71 kN
P (D = 80 cm) = 2.51; F.S. = 3
 Qs (D = 80 cm) = 97 kN
Briaud’s Method
Briaud et al (1985) proposed another correlation for unit skin resistance using the standard
penetration resistance as follows:
f = 0.224Pa(N60)0.29
(Eq. 20)
At 8 m depth, (N60)avg = 14.175
f = 0.224×100×14.1750.29
= 48.32
P (D = 45 cm) = 1.41; F.S. = 3
 Qs (D=45cm) = 182 kN
P (D = 60 cm) = 1.88; F.S. = 3
 Qs (D = 60 cm) =243 kN
P (D = 80 cm) = 2.51; F.S. = 3
 Qs (D = 80 cm) = 324 kN
Table 19. Summary of the Skin Friction Resistance at 8 m
Diameter
(cm)
Coyle and Costello
(kN)
Meyerhof
(kN)
Briaud
(kN)
Average
(kN)
45 54 210 182 149
60 71 280 243 198
80 97 380 324 267

54
Table 20. Total Foundation Pile Capacity at 8 m
Pile Diameter
(cm)
Pile Length
(m)
Safe Working Load
(kN)
Factor of
Safety
45 8 454 3
60 8 725 3
80 8 1160 3
Frictional Skin Resistance for 32 m Depth Piles
Three main methods for obtaining and estimating the unit frictional resistance of a pile in the
clay are as follows:
λ Method
Vijayvergiya and Focht (1972) proposed the lambda method based on the assumption that the
displacement of soil caused by a pile results in a passive pressure at any depth and the average
unit skin resistance is:
favg = λ(o’ + 2Cu) (Eq. 21)
Where
o’= Mean effective vertical stress for the entire embedment length
Cu= Shear strength
1’ = [
1+2( 1 − sin Ѻ)
3
]xq = [
1+2( 1 − sin 30)
3
]x14x13 = 121.33 kN/m2
2’ = [
1+2( 1 − sin Ѻ)
3
]xq = [
1+2( 1 − sin 5)
3
]x14x13 = 171.41 kN/m2
’ = [
1+2( 1 − sin Ѻ)
3
]xq = [
1+2( 1 − sin 30)
3
]x14x6 = 56 kN/m2
From table 21, λ (at 13 m to26 m) = 0.1472

55
 favg =
𝐴1+𝐴2+𝐴3
32
= 127.84 KN/m2
 Qs (D = 45 cm) =
0.1472[ 127.84+2×68]×13×1.41
3
+ 171 (sand) = 408 kN
 Qs (D = 60 cm) =
0.1472[ 127.84+2×68]×13×1.88
3
+ 222 (sand) = 538 kN
 Qs (D = 80 cm) =
0.1472[ 127.84+2×68]×13×2.51
3
+ 331 (sand) = 752 kN
Table 21. Variation of λ with Pile Embedment Length (Extracted From Deep Foundation, Theory and
Practice)
Embedment Length
(m)

0 0.5
5 0.336
10 0.245
15 0.2
20 0.173
25 0.15
30 0.136
35 0.132
40 0.127
50 0.118
60 0.113
70 0.11
80 0.11
90 0.11
Figure 41. Estimation of Frictional Resistance using the λ Method

56
β Method
When piles are driven into a saturated clay layer of soil, the pore water pressure in the soil
around the pile increases. This excess pore water pressure in normally consolidated clays may
increase up to four to six times cu. However, the unit frictional resistance of the pile can be
determined on the basis of the effective stress parameters of the clay, thus the following equation
can be used:
f = βo’ (Eq.22)
o’= Vertical effective stress
β = Ktanϕ’
ϕ’ = Friction angle of the clay
K = Earth pressure coefficient = 1 - sinϕ’
Thus f = (1 - sinϕ’)(tanϕ’)o’ = 16.61
 Qs (D = 45cm) =
16.61×1.41×13
3
+ 171 (sand) = 273 kN
 Qs (D = 60cm) =
16.61×2.88×13
3
+ 222 (sand) = 430 kN
 Qs (D = 80cm) =
16.61×2.51×13
3
+ 331 (sand) = 512 kN
α Method
According to the α method, the unit skin resistance in clayey soils can be represented by the
following equation:
f = αCu
Where α is the empirical adhesion factor. The approximate value of α is shown in Table 22

57
Table 22. Variation of α (Interpolated Values Based on Terzaghi, Peck and Mesri, 1996)
𝑪𝒖
𝑷𝒂
α
≤0.1 1
0.2 0.92
0.3 0.82
0.4 0.74
0.6 0.62
0.8 0.54
1 0.48
1.2 0.42
1.4 0.4
1.6 0.38
1.8 0.36
2 0.35
2.4 0.34
2.8 0.34
Pa is the atmospheric pressure = 100 kN/m2
For Cu = 68 kN/m2
, thus α = 0.588
 Qs (D = 45cm)
= 0.588×1.41×68×13
3
+ 171 (sand) = 415 kN
 Qs (D = 60 cm) =
0.588×1.88×68×13
3
+ 222 (sand) = 548 kN
 Qs (D = 80 cm) =
0.588×2.51×68×13
3
+ 331 (sand) = 766 kN
Table 23. Summary of the Skin Friction Resistance at 32 m
Diameter
(cm)
α Method
(kN)
β Method
(kN)
λ Method
(kN)
Average
(kN)
45 415 273 408 366
60 548 430 538 506
80 766 512 752 677

58
Table 24. Total Foundation Pile Capacity at 32 m
Pile Diameter
(cm)
Pile Length
(m)
Safe Working Load
(kN)
Factor of
Safety
45 32 1326 3
60 32 1822 3
80 32 2902 3
Pile Foundation Structural Reinforcement
The following table summarizes the reinforcement for each of the drilled pile sections according
to the American concrete institute (ACI-318) also shown in the figures below.
Table 25. Foundation Piles Reinforcement
Column Diameter 45 cm 60 cm 80 cm
Area of Steel 3600 mm2
6000 mm2
8400 mm2
Reinforcement 12 at 20 mm 12 at 25 mm 12 at 30 mm
Figure 42. Pile Reinforcement 45 cm Diameter

59
Group Action in Piled Foundation
The supporting capacity of a group of vertically loaded piles can, in many situations, be
considerably less than the sum of the capacities of the individual piles comprising the group.
In all cases, the elastic and consolidation settlements of the group are greater than those of a
single pile carrying the same working load as that on each pile within the group. This is because
the zone of soil or rock which is stressed by the entire group extends to a much greater width and
depth than the zone beneath the single pile. Even when a pile group is bearing on rock the elastic

60
deformation of the body of rock within the stressed zone can be quite appreciable if the piles are
loaded to their maximum safe capacity.
Group action in piled foundations has resulted in many recorded cases of failure or excessive
settlement, even though loading tests made on a single pile have indicated satisfactory
performance.
The allowable loading on pile groups is sometimes determined by the so-called efficiency
formulae, in which the efficiency of the group is defined as the ratio of the average load per pile
when failure of the complete group occurs, to the load at failure of a single comparable pile.

61
Pile Distribution under Raft Foundation
When designing a raft or spread footings over piles, if a column needs more than one pile to
carry the structural loads, it is recommended that the piles be equally spaced such that their
combined center of gravity coincides with the center of gravity of the column they are
supporting. When piles groups are used, a minimum center to center spacing of three times the
pile diameters used. In order to minimize the amount of drilled piles to be completed on the
project, 32 m long piles are recommended for the deep foundations alternative. The following
figure shows the plan of the piles relative to the column location.
Figure 45. Pile Distribution under Raft Foundation

62
C.6. COST ANALYSIS
Tables 26 and 27 below summarize the cost of the deep foundation and shoring system
alternatives. These values are estimated based on the construction market in Lagos, Nigeria.
Based on this cost analysis, it is clear that the deep foundation alternative recommended by the
local geotechnical engineer in Lagos is less economical than the shoring system alternative.
However, the schedule for completing the deep foundation alternative will most likely be
significantly faster than the 9 meter deep raft with a shoring system and dewatering alternative.
Table 26. Cost Analysis for the Shoring System Alternative
Item Description Qty
Unit
Rate
Amount
U.S.$
Diaphragm
Wall
Constructing D-wall (30 MPA),
Drilling and
installation of reinforcement as
specified in the design
(16 m Depth)
1792 m2
$300/m2
537,600
Grouted
Tieback
Anchors
Drill and complete with all related
accessories and
material.
The anchors will penetrate the
D-Wall. No need for whaler beams.
1st row of anchors
 Spacing =2 m
 No. of strands = 5
 Angle of inclination = 20o
 Pull out force = 50 ton
56 anchors
26 m long
$100/lm 145,600
2nd
row of anchors
 Spacing = 2 m
 No. of strands = 5
 Angle of inclination = 20o
 Pull out force = 50 ton
56 anchors
23 m long
$100/lm 128,800
Excavation Excavation and disposal of soil 6801 $8/m3
54,405
Dewatering dewatering system 1 $10,000 10,000
Basements
Basement area that can be sold is
about 755 m2 2 $800/m2
- 604,000
Total $ 271,805

63
Table 27. Cost Analysis for the Pile Foundations Alternative
Item Description Qty Unit Rate
Amount
U.S.$
Deep
Piles
Pile construction (30 MPA)
complete with drilling, concrete,
reinforcement and all related work
as specified and as directed by the
engineer
60 cm Diameter 32 m long 22 $7933.6/pile
174,539.2
Drilling 32 m $230/m
Concrete 1.12 m3
$180/m3
Reinforcements 1.776 ton $750/Ton
80 cm Diameter at 32 m long 75 $11832.8/pile
887,460
Drilling 32 m $230/m
Concrete 16.08 m3
$180/m3
Reinforcements 2.1312 ton $750/Ton
Total $ 1,061,999.2

64
D. CONCLUSION AND RECONMMENDATIONS
D.1. CONCLUSION
The alternative with 2 basements and the D-wall shoring system is more economical than the
deep foundation alternative. However, it should be noted that the execution for each alternative is
quite different. The shoring system is more time consuming due to the excavation and
dewatering phases. However, if the schedule is not very tight, there is a larger profit to make in
selling the two basements in addition to the cheaper construction approach.
As a conclusion, this report demonstrates that a small engineering exercise can provide insight
for the owner to come up with the most economical solution for his project.
D.2. LIMITATIONS
Some of the limitations that should be noted are as follows:
 This analysis is based on limited soil exploration. It is possible that during construction
different soil conditions may be observed. In that case, the current design should be
revised and modified accordingly.
 Appropriate machinery should be used by the shoring contractor during construction to
obtain a satisfactory diaphragm wall system.

65
D.3. CONSTRUCTION RECOMMENDATIONS
Some recommendations concerning the execution of the shoring system are as follows:
 The tieback anchor drilling machine is preferred to be of the type no 3 Bauer C6/C8.This
excavators has a high torque and can be fitted with many types of excavation heads.
 The diaphragm wall excavation machine is preferred to be either SoilMech or
Casagrande. These excavators have appropriate calibration instruments to prevent high
wall inclination.
 A tremmy pipe should be used for the diaphragm wall during the concrete pouring
process to avoid segregation of concrete.
 It is recommended to use bentonite slurry in order to stabilize side walls during
excavation.
 During the pouring of the diaphragm wall, the sand might undergo permeation due to the
concrete. As a result, when the excavation process begins, there should be an excavator
(helicopter) in order to break additional concrete without damaging the diaphragm wall.
 Since the water will remain present behind the diaphragm wall, there might be a high
probability of water leakage from the holes of the anchors. This unwanted water seepage
can be collected by a network of small water pipes to take the water to a sump pump and
dispose of it.

66
E.REFERENCES
 Basol Associates Limited (2014). Report on Subsoil Site Investigations of the Proposed
Development for Jubali Group, Apapa, Lagos, December 2014.
 Bowles, J. (1977). Foundation analysis and design (2d ed.). New York: McGraw-Hill.
 British standard Bs 8110-1: 1997 incorporating amendments Nos.1 and 2
 Budhu, M. (2011). Soil Mechanics and Foundations (3rd ed.). Hoboken: Wiley
Textbooks.
 Building code requirements for structural concrete: (ACI 318-99) ; and commentary
(ACI 318R-99). (1999). Farmington Hills, Mich.: American Concrete Institute.
 Coduto, D. (2001). Foundation design: Principles and practices (2nd ed.). Upper Saddle
River, N.J.: Prentice Hall.
 Construction Guides, Thomas Telford Pub.Co., London.
 Das, B. (2002). Soil mechanics laboratory manual (6th ed.). New York: Oxford
University Press.
 Das, B. (2007a). Principles of geotechnical engineering (7thEd.). Stamford, Washington:
Cengage Learning.
 Das, B. (2007b). Principles of foundation engineering (6thEd.). Boston: PWS-Kent Pub.
 Department of the army, U.S. army corps of engineers, Washington, Dc 20314-1000,
Bearing capacity of soils.
Design of pile foundation.

67
Settlement analysis.
 Geotechnical engineering circular no. 4, ground anchors and anchor system, U.S
department of transportation, office of bridge technology 400 seventh street, SW
Washington, DC 20590, June 1999
 Look, B. (2007). Handbook of geotechnical investigation and design tables. London:
Taylor & Francis.
 Mansur, C.I. and Kaufman, R.I. (1962) Dewatering, in Foundation Engineering
Ed.byG.A. Leonards pp.241-350, McGraw-Hill Book Co.
 Ou, Chang. (2006). Deep excavation: Theory and practice. London: Taylor &
Francis/Balkema.
 Powers, J.P. (1992), Construction Dewatering, 492p., 2nd ed. John Wiley and Sons Inc.
 Quinion, D.W. and Quinion, G.R.(1987), Control of Groundwater, ICE Works
 Somerville, S.H.(1986), Control of Groundwater for Temporary Works,
CIRIA(Construction Industry Research and Information Association) Report No.113.
 Teng, V.C.(1962) Foundation Design, 466 p., Ch.5, Prentice-Hall, IAC.,Englewood
Cliffs, N.J.
 Tomlinson, M., & Woodward, J. (n.d.). Pile design and construction practice (Sixth ed.).
 US Army Corps of Engineers engineer manual, Geotechnical Investigations.

68
F. APPENDIX
Table 28. Typical Floor Column Loads Exported from Etabs
TYP
SLS ULS
SW SIDL DL LL SUM DL LL SUM
80.6 36.4 C1 117 16.1 133.1 140.4 25.76 166.16
137.5 67.6 C2 205.1 30 235.1 246.12 48 294.12
175.8 89.4 C3 265.2 39.6 304.8 318.24 63.36 381.6
181.8 94.1 C4 275.9 42 317.9 331.08 67.2 398.28
240.3 124.5 C5 364.8 56.8 421.6 437.76 90.88 528.64
235 121.6 C6 356.6 55.5 412.1 427.92 88.8 516.72
156.5 76.1 C7 232.6 35.8 268.4 279.12 57.28 336.4
227.8 114.7 C8 342.5 47.9 390.4 411 76.64 487.64
178.7 87.6 C9 266.3 36 302.3 319.56 57.6 377.16
82.5 36.6 C10 119.1 19 138.1 142.92 30.4 173.32
169.8 86.9 C11 256.7 35.5 292.2 308.04 56.8 364.84
129 56.8 C12 185.8 35.5 221.3 222.96 56.8 279.76
91.3 42.82 C13 134.12 22.2 156.32 160.944 35.52 196.464
183.7 97.7 C14 281.4 39.4 320.8 337.68 63.04 400.72
135.4 62 C15 197.4 38 235.4 236.88 60.8 297.68
143.5 68.8 C16 212.3 33.5 245.8 254.76 53.6 308.36
170.4 88.7 C17 259.1 36.4 295.5 310.92 58.24 369.16
207 101.9 C18 308.9 41.6 350.5 370.68 66.56 437.24
91 38.3 C19 129.3 17.1 146.4 155.16 27.36 182.52
197.4 92.4 C20 289.8 43.9 333.7 347.76 70.24 418
206 96 C21 302 45.8 347.8 362.4 73.28 435.68
72.8 30.7 C22 103.5 13.1 116.6 124.2 20.96 145.16
68.4 28.9 C23 34.2 12.5 46.7 41.04 20 61.04

69
Table 29. Maximum Pu for all Columns
Analysis Etabs Max
WT2 WT1 TYP WT2 WT1 TYP WT2 WT1 TYP
C1 0.0 0.0 77.8 0.0 0.0 166.2 0.0 0.0 166.2
C2 0.0 0.0 284.7 0.0 0.0 294.1 0.0 0.0 336.8
C3 0.0 0.0 328.7 0.0 0.0 381.6 0.0 0.0 394.6
C4 0.0 0.0 348.3 0.0 0.0 398.3 0.0 0.0 427.5
C5 0.0 0.0 536.9 0.0 0.0 528.6 0.0 0.0 536.9
C6 0.0 0.0 525.0 0.0 0.0 516.7 0.0 0.0 525.0
C7 0.0 0.0 305.9 0.0 0.0 336.4 0.0 0.0 375.3
C8 0.0 323.7 532.4 0.0 510.0 487.6 0.0 510.0 532.4
C9 0.0 363.9 479.0 0.0 268.7 377.2 0.0 493.2 479.0
C10 0.0 0.0 146.2 0.0 0.0 173.3 0.0 0.0 173.3
C11 0.0 552.5 539.9 0.0 406.7 364.8 0.0 559.0 539.9
C12 194.0 552.5 190.9 289.0 204.1 279.8 289.0 557.6 279.8
C13 0.0 0.0 150.3 0.0 0.0 196.5 0.0 0.0 196.5
C14 0.0 633.1 555.4 0.0 444.6 400.7 0.0 633.1 555.4
C15 194.0 633.1 196.3 239.6 218.6 297.7 246.6 633.1 297.7
C16 0.0 0.0 164.4 0.0 0.0 308.4 0.0 0.0 308.4
C17 0.0 179.0 538.4 0.0 304.0 369.2 0.0 312.4 538.4
C18 0.0 427.8 499.1 0.0 539.2 437.2 0.0 559.0 499.1
C19 0.0 0.0 89.3 0.0 0.0 182.5 0.0 0.0 182.5
C20 0.0 0.0 417.6 0.0 0.0 418.0 0.0 0.0 418.0
C21 0.0 0.0 414.3 0.0 0.0 435.7 0.0 0.0 435.7
C22 0.0 0.0 138.7 0.0 0.0 145.2 0.0 0.0 163.6
C23 0.0 0.0 84.8 0.0 0.0 61.0 0.0 0.0 141.2

70
Figure 46. Architectural Design

71
Figure 47. Building Section

74
Figure 50. Borehole No. 1 (continued)

76
Figure 52. Borehole No. 2 (continued)

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