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KENCH SURVEYS LIMITED
GEOTECHNICAL INVESTIGATION REPORT
ON THE
HARBOUR SITE
FOR
JOLOMI ENGINEERING SERVICES LIMITED
AT MUSHESHE FISH YARD,
OFF ENERHEN ROAD,
WARRI
Client: Consultants:Jolomi Engineering Services Limited, Kench Surveys LimitedWarri, Warri.Delta State Delta State
August 2010
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CONTENT
NOTATIONS iii
EXECUTIVE SUMMARY iv
1.0 INTRODUCTION 1
2.0 SCOPE OF WORK 1
3.0 SITE DESCRIPTION AND GEOLOGY 2
4.0 FIELD WORK 3
5.0 LABORATORY TESTS 5
6.0 SOIL STRATIGRAPHY 6
7.0 ENGINEERING PROPERTIES OF THE SOILS 7
8.0 DISCUSSIONS 9
9.0 BEARING CAPACITY CALCULATIONS Shallow Foundation 10
10.0 BEARING CAPACITY CALCULATIONS Pile Foundation 12
11.0 DESIGN LENGTH OF SHEET PILE 16
12.0 RECOMMENDATION 18
13.0 CONCLUSIONS 19
14.0 LIMITATIONS 20
References 21
APPENDICES
APPENDIX A: Site Plan
APPENDIX B: Borehole Logs
APPENDIX C: Index Summary
APPENDIX D: Atterberg Limits
APPENDIX E: Triaxial Shear Strength
APPENDIX F: Direct Shear Strength
APPENDIX G: Consolidation Results
APPENDIX H:Particle Size Distriution
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NOTATIONS
B width of raft foundation
b half the width of raft foundation in the calculation of settlementvalues
BS British Standard
c - undrained cohesion of the soil
Cv - coefficients of consolidation
f - unit skin friction
H - Thickness of strata under consideration = 2B
I - Influence factor from Bousinesqs chart
K - coefficient of lateral earth pressure
mv - coefficient of volume compressibility
Nq - bearing capacity factor
Po - effective overburden pressure of the soil at the point, kPa
q - unit end bearing capacity for driven piles
Qall - allowable bearing capacity for raft foundation for a safety factor of 3
Qs - safe bearing capacity for a limiting maximum settlement of 50mm for raftfoundation
Qu - ultimate bearing capacity for raft foundation
Sc - consolidation settlement
Si - immediate settlement
St - Total settlement = Immediate settlement + consolidation settlement
= Si + Sc
Soed - One dimensional consolidation calculated from laboratory oedometer test
Su - undrained shear strength of the cohesive soil
v - vertical stress, at the point under consideration, beneath the corner of arectangular foundation
4x v - vertical stress, at the point under consideration, beneath the centre of arectangular foundation
SPT - Standard Penetration Test
- pile bearing capacity factor = 0.5-0.50 for < 1.0 & 0.5-0.25 for >
1.0 - unit weight of soil
- ratio of undrained shear strength to overburden pressure = Su/Po
- friction angle between the soil and pile wall
- Applied pressure at point under consideration
- angle of friction taking as zero for undrained condition of the soil
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EXECUTIVE SUMMARY
Kench Surveys Limited was commissioned by Jolomi Engineering Surveys Limited to
carry out a geotechnical investigation at the site for its proposed administrative office,warehouse, jetty, harbour and slipway at its property site in Musheshe Fish yard, off
Enerhen road, Effurun near Warri in Delta State. The investigation is to obtain soil
parameters for the foundation design of the proposed facilities at the site. The scope
of the investigation, which was, carried out on August 22 and 23, 2010 includes the
exploration of two (2) number boreholes using the cable percussive drilling method.
All explorations were to a maximum depth of 20m below the existing ground level.
The stratigraphy reveals a stratum of loose to dense sand on the entire site overlaid
by a 4.5m thick layer of soft to firm clay at the approach of the site and a 4.0m thick
layer of clayey peat towards the waterfront.
From analysis, using the average shear strength value of 23kPa for a soft to firm
clay, the allowable bearing capacity for a rectangular footing founded at a depth of
1.0m below the ground level is observed to be between 45 and 65kPa, for a breadth-
length (B/L) aspect ratio between 0.1 and 1.0.
Individual pad footings founded at a minimum depth of 1.0m below the existing
ground level is recommended to support the administrative building. The warehouse
should be founded also on raft foundations founded at the same depth. The jetty
should be supported on driven concrete piles to check corrosion while the harbour
should be heldin by steel sheet piles. and harbour building. Settlements from the
pile foundations are not expected to exceed 50mm. However, pile load test should
be carried out on all piles driven to confirm their working loads.
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1.0 INTRODUCTION
Jolomi Engineering Services Limited is proposing the construction of administrative
building and a warehouse on their site at the Mosheshe Fish Yard, off Enerhen road,
Effurun, near Warri in Delta State. At the water front, the construction of a jetty and
an harbour are being proposed also. Kench Surveys Limited was contracted by
Jolomi Engineering Services Limited to carry out a geotechnical investigation on the
site for these facilities. The investigation is to obtain soil parameters for the
foundation design of the proposed facilities at this site. The scope of the
investigation, which was, carried out on August 22 and 23, 2010 includes the
exploration of two (2) number boreholes using the cable percussive drilling method.
All boreholes explorations were to a maximum depth of 20m below the existing
ground level.
2.0 SCOPE OF WORK
The detailed work scope for the investigation is as presented below:
(i) Carry out two (2) number soil boring at the designated locations to a
maximum depth of 20m below the existing ground level.
(ii) Perform Standard Penetration Test on cohesionless material encountered in
the borehole.
(iii) Perform standard laboratory tests on soil samples obtained from (i) above
and determine relevant soil properties.
(iv) Submit of a detailed report including:
(a) An assessment of the sub-soil conditions for the proposed project and
suggested soil improvement where necessary.
(b) Engineering properties of the soils encountered and their effects on the
project.
(c) Assessment of the suitability of the soil and recommendation of
appropriate foundation type and design parameters.
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3.0 SITE DESCRIPTION AND GEOLOGY
The project site is situated within the Musheshe Fish yard off Enerhen road in
Enerhen Community of Delta State Part of the site towards the water front is
occasionally flooded by virtue of the fact that the entire area was a Swamp forest in
Delta State. Delta State is one of the nine states of the Niger Delta region of Nigeria.
The local geology of the location is composed of sediments which are characteristic
of several depositional environments as the River Niger empties her load into the
Atlantic ocean. The tidal swamp forest covers a substantial area of the delta
coastline, with the exception of the zone adjacent to the river plains, where they are
overlain by recent deposits of river mouth sediments. The growth of plants on the
surfaces of this sediment aided the slowing down of the Niger River flow which
encouraged further plant growth. Slowly these sediment deposits had displaced
portions of the river water to give way to what we now have as the Enerhen
community, on which this site lies.
At the time of this investigation, the entire project site was bare and empty.
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4.0 FIELD WORK
The investigation comprised mainly drilling two (2) geotechnical boreholes.
Appendix A shows the location of the test points. The field work for the investigation
was carried out between August 22 and 23, 2010.
The boreholes were advanced using a cable percussion boring rig.
4.1 Boring
The boreholes were drilled by the shell and auger cable percussive method, using a
manual drilling rig. The manual drilling rig is fitted with a free fall auger. The auger is
lifted to a height of about 1.0m above ground level. At this height it is allowed to free-
fall under gravity to advance the boring. As the auger falls it cuts through the soil
such that the cut soil material is retained inside it by means of a non-return flap valve
(commonly called the clark) at its lower end. The auger is then brought to the
surface where the soil retained in it is emptied out and samples taken. To prevent
collapse of the borehole wall, the hole is lined with 100mm diameter steel casings
(commonly called shells).
4.1.1 Collecting Undisturbed Samples
Undisturbed samples were taken at approximately 1.0m intervals of depths in clays
and silts. This is done by driving thin-walled tube into the soil, using a U4 bomber to
its full length of 0.45m or otherwise penetration refusal. The tube is then pulled to the
surface, removed from the sampling hammer, labelled and waxed top and bottom to
prevent loss of natural moisture from the soil.
4.1.2 Collecting Disturbed Sample
Representative disturbed samples were taken at regular intervals of 1.0m depth, and
also when a change in soil type was observed. The samples were used for a detailed
and systematic description of the soil in each stratum in terms of its visual properties
and for laboratory analysis. The borehole log obtained is presented in Appendix B. A
large number of disturbed samples were taken for examination and laboratory
analysis.
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4.2 Groundwater Conditions
Field measurements of ground water showed that the ground water was observed at
a depth of 4.50m below the existing ground surface, at the time of the field work.
5.0 LABORATORY TESTS
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Detailed laboratory investigations are being carried out on representative samples
obtained from the borehole for the classification tests and other tests. All tests are
being carried out in accordance with BS1377:1990 Methods of test for soil for civil
engineering purposes. Brief comments on the tests are given below:
Classification
Atterberg consistency limit tests were carried out on the cohesive samples. The
results show that the samples are low to medium plasticity silty clay. The particle size
distributions of a number of representative samples of the cohesionless soils were
determined by sieve analysis. The results disclosed that the samples are
predominantly, fine to medium dense sand with occasional gravels as shown in
Appendix D.
Undrained Shear Strength
This type of test is usually performed on undisturbed samples of cohesive soils. Depending
on the consistency of the cohesive material, the test specimen is prepared by trimming the
sample or by pushing a mould into the sample. A latex membrane with thickness of
approximately 0.2mm is placed around the specimen. A lateral confining pressure of
600kPa to 1000 kPa is maintained during axial compression loading of the specimen.
Consolidation and drainage of pore water during testing is not allowed.
The test is deformation controlled (strain rate of 60%/h), single stage, and stopped when
an axial strain of 15% is achieved.
The deviator stress is calculated from the measured load assuming that the specimen
deforms as a right cylinder.
The presentation of test results includes a plot of a Mohr circle. The undrained shear
strength, Cu, is taken as the point of intercession of a common tangent to the semi-circles
and the ordinate of the chart.
6.0 SOIL SRATIGRAPHY
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The soil stratigraphy encountered on the project site as observed from the explored
boreholes are as presented in Appendix B - borehole logs. The stratigraphy reveals
a stratum of loose to dense sand overlain by a 4.0m thick layer of soft to firm clay
around borehole 1 and a 4.0m thick layer of clayey peat around borehole 2. The
sand stratum is observed, in the entire site, to the maximum 20.0m depth of the
investigation.
The soil profile is as presented below.
Table 1:The profile is as presented in table 1 below.
Stratum No. DescriptionAverage depth
(m)
1
CLAY, soft to firm, dark reddish
brown (in borehole 1)
PEAT, clayey, very soft, blackish grey
(in borehole 2)
0 - 4.0
2SAND, loose to dense, occasionally
clayey, light grey to whitish grey4.0 - 20
7.0 ENGINEERING PROPERTIES OF THE SOIL
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The engineering properties of the formation encountered during the investigation are
as summarised below.
7.1 THE SOFT TO FIRM CLAY
This surface soft to firm clay is characterized by moderate compressibility and,moderate moisture content. This clay stratum is encountered from the ground level
to a depth of 4.0m below the existing ground level.
The variation in the engineering properties is as presented below:
Min Max Mean
Moisture content (%) 47 47 47
Bulk unit weight (kN/m3) 19.20 21.60 20.40
Dry unit weight (kN/m3) 13.06 14.69 13.88
Liquid limit (%) 49 53 51
Plastic limit (%) 20 24 22
Plasticity index (%) 29 29 29
Liquidity index 0.80 0.94 0.87
Consistency index 0.20 0.06 0.13
Undrained strength (kPa) 23 23 23
7.2 THE CLAYEY PEAT
This surface, very soft clayey peat observed close to the water front is characterized
by very high compressibility and moderate moisture content. This peat is fibrous and
possesses no engineering property of significance. That it is fibrous confirms the fact
that the settlement cannot be predicted. Under any imposed stress, the organic
fibres will continually decompose and reduce in volume. This reduction in volume will
give rise to large unpredicted settlements. It is recommended that about 2.0m thick
of this material be removed and replaced with clean river sand. This will reduce the
overall settlement that would have resulted from the entire mass.
The variation in the engineering properties is as presented below:
Min Max Mean
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Moisture content (%) 89 94 92
Bulk unit weight (kN/m3) 19.22 21.46 20.34
Dry unit weight (kN/m3) 9.91 11.35 10.63
Liquid limit (%) 116 130 123
Plastic limit (%) 48 130 89
Plasticity index (%) 82 83 82
Liquidity index 0.50 0.74 0.62
Consistency index 0.50 0.26 0.38
Undrained strength (kPa) 8 8 8
7.3 LOOSE to DENSE SAND
The fine to coarse silty sand encountered immediately beneath the firm to stiff clay is
of medium dense to very dense sand. This sand formation presents an SPT N value
between 9 and 41. From the SPT values it is observed that the sand formation
increases in density with depth. This formation of sand is competent to support high
bearing pressures without excessive settlement.
The variation of the geotechnical parameters is as presented below:
Min Max Ave
Effective Particle Size, d10 (mm) 0.08 0.14 0.11
Mean Particle Size, d30 (mm) 0.09 0.27 0.17
Particle Size, d60 (mm) 0.16 0.60 0.30
Coefficient of Uniformity, Cu = d60/ d10 2.00 4.29 2.83
Coefficient of Curvature, Cc = d302/d10.d60 0.71 0.91 0.80
Angle of Frictional Resistance, 29 40 35
8.0 DISCUSSIONS
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The investigation was carried out with the aim of obtaining geotechnical parameters
for the administrative building, warehouse, jetty and harbour belonging to Jolomi
Engineering Services Limited on her property at the Musheshe Fish yard, Enerhen
near Warri. The 4m thick near surface soft to firm clay soil encountered toward the
entrance to the site is of moderate compressibility but the peat towards the water
front is of very high compressibility. This peat is characterized by very low shear
strength and high moisture content. This peat is fibrous and possesses no
engineering property of significance. The fibrous nature confirms the fact that the
settlement cannot be predicted. Under any imposed stress, the organic material will
decompose and reduce the entire volume of the mass. This reduction in volume will
give rise to large unpredicted settlements. As a result, it has to be removed to as
deep as 2.0m, and replaced with clean river sand, for the construction of the slipway.
This will minimize the overall settlement that would have resulted from the entire
mass.
The administrative building and the warehouse can be supported on raft foundations
directly on the formation. Settlements from these rafts should create no problems.
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9.0 BEARING CAPACITY CALCULATIONS Shallow Foundation(Administrative Building and Warehouse)
The ultimate bearing capacity, Qu, for shallow rectangular foundations on cohesive
soils, using consistency values of a soft to firm clay is given below as:
Qu = .Df. + 0.67c[1+0.3(B/L)]Nc
where = unit weight of soil at depth
Df = depth of foundation
c = shear strength of the soil
B = Foundation width
L = Foundation Length
Nc = Bearing Capacity factor
Below are bearing capacity charts for ultimate bearing capacity versus foundation
aspect ratios at various depth of foundation
Table 2: Values of Ultimate Bearing Capacity, kPa, for various foundation depth
Df B/L Ratio
(m) 0.1 0.2 0.5 1.0
0.5 111 114 123 138
1.0 120 123 132 147
1.5 129 131 140 155
2.0 137 140 149 164
Table 3: Values of Allowable Bearing Capacity, kPa, for various foundation depth
Df B/L Ratio
(m) 0.1 0.2 0.5 1.0
0.5 37 38 41 46
1.0 40 41 44 49
1.5 43 44 47 52
2.0 46 47 50 55
Below are the charts for both the ultimate and allowable bearing capacities
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Fig. 1: Ultimate Bearing Capacity Chart for foundations at different Breadth/Length ratios
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Fig. 2: Allowable Bearing Capacity Chart for foundations at different Breadth/Lengthratios
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9.1 SETTLEMENT Shallow Foundation
Total settlements for the allowable bearing capacity are within the limits of maximum
allowable settlement. Settlement of this formation under the administrative buildingwill not exceed the maximum allowable settlement were a raft on individual pad
foundation is used.
10.0 BEARING CAPACITY CALCULATIONS Pile Foundation(Jetty and Harbour)
The ultimate bearing capacity, Qu, of driven piles is determined by the equation
below:
Qu = q.Ab + f.As
where q = unit end bearing capacity = kPa
f = unit skin friction = kPa
Ab = gross base area of pile tip, m2
As = side surface area of pile, m2
10.1 End Bearing & Skin Friction in Cohesive Soils
For piles in cohesive soils,
The unit end bearing, q = 9. Su 9.1.1
The unit skin friction, f = .Su 9.1.2
Where, Su = undrained shear strength of the soil, kPa
10.2 End Bearing & Skin Friction in Cohesionless Soils
For piles in cohesionless soils,
The unit skin friction, f = K Po tan 9.2.1
The unit end bearing, q = po Nq 9.2.2
Where,
K = coefficient of lateral earth pressure
= friction angle between the soil and pile wall
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= 0.75 x (angle of frictional resistance)
Nq = bearing capacity factor
po = effective overburden pressure of the soil at the point, kPa
Chart of Ultimate Pile Capacity for Concrete Piles
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Fig. 3 Chart of Ultimate pile capacity for straight shaft steel pipe pile
Using a safety factor of 3 on the ultimate pile capacity, the chart for the allowable pile
capacity is as presented in figure 4 below.
Chart of Allowable Pile Capacity for Concrete Piles
Fig. 4 Chart of Allowable pile capacity for straight shaft steel pipe pile
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Table 4:Allowable Pile Capacity, kN for concrete pile at various depth (m)
Pile depth (m) 300mm diameter
pile
400mm diameter
pile
500mm diameter
pile
10 55 80 108
15 176 257 349
20 389 558 746
11.0 DESIGN LENGTH OF SHEET PILE
In cohesionless soil, C is zero.
The active and passive lateral earth pressure of soil can be written as
Ka=tan2(45- /2) is the active lateral earth pressure coefficient
Kp= tan2(45+ /2) is the passive lateral earth pressure coefficient, and
is internal friction angle.
is unit weight of soil, h is the height difference between the existing ground level
and the river-bed.
The lateral forces Pa is calculated as
Pa=Ka h2/2
Below the bottom of excavation, the sheet pile is subjected to active pressure on the
earth side and passive pressure on the side of the river-bed.
Where Kp is passive earth pressure coefficient. When the sheet pile rotates away
from the earth side, there are active pressure on the earth side and passive pressureon the river bed side.
Calculating embed depth D
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Once D is determined, the minimum embedded depth of entire sheet pile is equal to
h+D. Usually a factor of safety between 1.2 and 1.4 is applied to D, and the length of
sheet pile L is equal to h+D*FS. FS is factor of safety from 1.2 to 1.4.
Example 1: Design cantilever sheet pile in cohesionless soil.
Given:
Depth of existing ground level to river bed, h = 6 m
Take depth of sheet pile below the river bed as D
Therefore (h + D) = depth between existing ground level and bottom of sheet pile
Unit weight of soil, = 19.8 9.81 = 9.99 say 10.0 kN/m3
Average Internal friction angle, = 30 degree
Requirement: Design length of a cantilever sheet pile
Solution:
Design length of sheet pile:
Calculate lateral earth pressure coefficients:
Ka = tan2 (45- /2) = 0.333
Kp = tan2 (45+ /2) = 3
The lateral earth pressure at bottom of excavation is
pa =0.5Ka (h+D)2 = 0.5*0.333*10.0*(6 + D)2 = 1.665(6 + D)2
pp =0.5KpD2 = 0.5*3.0*10.0* D2 = 15.0D2
Taking moment of these forces about the base of the wall, we have
Mo = pa * (h+D)/3 - pp * D/3 = 0
1.665(6 + D)2 *(h+D)/3 - 15.0D2 *( D/3) = 0
0.555(6 + D)3 - 5 D3 = 0
Solving for the depth D by trial and error, we have
D = 5.55m , say 6.0m
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Checking
pa = 1.665(6 + D)2 = 1.665*122 = 239 kN
pp = 15 * 62 = 540 kN
pa * (h+D)/3 = 239 * 4 = 956 kNm
pp * D/3 = 1080 kNm
Length of sheet pile = h + D = 6 + 6 = 12m
Using a safety factor of 1.4 for D
Total length of sheet pile 6 + 1.4 * 6 = 14.4m
Use pile length of 15m from the existing ground level.
12.0 RECOMMENDATIONS
Considering the imposed load from the administrative building, which is not expected
to be more than a one-storey high, and the moderate compressibility of the soft to
firm clay, it is recommended that the administrative building and the warehouse be
founded on raft foundations. Driven concrete piles are preferred for the jetty area to
check the problem of corrosion to steel pipe piles. Analysis has been carried out for
300mm, 400mm and 500mm diameter concrete piles in this report. Other sizes can
be provided upon request.
The minimum embedded depth for the sheet piles is 15.0m below the existing ground
level, that is about 9.0m below the river bed. Sheet piles are commonly of steel
which are susceptible to corrosion hence, adequate cathodic protection should be put
in place to minimize corrosion of the sheet piles.
13.0 CONCLUSION
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Kench Surveys Limited was requested by Jolomi Engineering Surveys Limited to
carry out a geotechnical investigation on a six storey building along Airport Road,
Warri in Delta State. The investigation was by means of two (2) number boreholes to
a maximum depth of 20m.
Field and laboratory investigations revealed a surface soft to firm clay spanning to a
depth of 4.0m below the existing ground level. Beneath the clay, the formation
presents a stratum of loose to dense to the final 20.0m depth of investigation.
Determination of ultimate bearing capacity using the average cohesion of a soft to
firm clay of 23kPa gave an ultimate bearing capacity of 120kPa for a rectangular
footing founded at a depth of 1.0m below the ground level. Using a safety factor of 3,
the allowable bearing capacity for this soil at this depth is observed to be about
40kPa.
Considering the moderate compressibility of the surface soft to firm clay, the
administrative building and the warehouse can be founded on a raft, but the jetty can
only be founded on piles. The sheet piles should be taken to a minimum depth of
15.0m below the existing ground level that is about 9.0m below the river bed. Driven
concrete piles are preferred for the jetty area to check the problem of corrosion to
steel pipe piles.
Settlement of the piles is not expected to be more than 25mm where the maximum
imposed load on the group is taken as half the total number of single piles in the
group multiplied by the allowable bearing capacity. However, pile load tests should
be carried out on all piles installed to confirm their work load.
14.0 LIMITATIONS
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This investigation is carried out in accordance with accepted geotechnical
engineering practice. The recommendations and conclusions reached in the report
are based on the data obtained from soil boring, and the laboratory analysis. It is not
anticipated that the soil conditions will vary significantly from those described.
However, should the soil conditions during actual construction vary, it would be
necessary to evaluate the engineering significance of such variations which could
result in further investigations and supplemental recommendations.
Suv. Chris Ojukoko
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References
1. Bowles, J. E, (1997); Foundation Analysis and Design, McGraw-Hill Companies
Inc.; 5th edition
2. Gopal, R. & Rao, A.S.R, (1991); Basic and Applied Soil Mechanics, pages 474
-545; New Age International Publishers; 2nd edition.
3. Murthy, V. N. S, (2007); Textbook of Soil Mechanics and Foundation
Engineering, page 630; CBS Publishers; 1st edition.
4. Tomlinson, M. J. (1994); Pile Design and Construction Practice; E & F N Spon; 4th
edition,
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