Presentation on subsoil investigation and foundation recomendation

1. UNIVERSITY OF NIGERIA
DEPARTMENT OF GEOLOGY
SIWES SEMINAR PRESENTATON ON:
GEOTECHINCAL ASSESSMENT
(SUBSOIL INVESTIGATION)
BY:
BASSEY DANIEL KUFRE
2010/170012
SUPERVISOR: MR. I. OKONKWO

2. OUTLINE
• COMPANY PROFILE
• ACTIVITIES UNDERTAKEN
• SUBSOIL INVESTIGATION
 METHODOLOGY
 TEST RESULTS
 RESULT ANALYSIS
 INTERPRETATION AND RECOMENDATION
• SKILLS ACQUIRED
• CHALLENGES
• CONCLUSION

3. COMPANY PROFILE
 KDF KONSULT LIMITED is a geotechnical and engineering company
with head office at No. 3, Balogun Street, Ikeja, Lagos State.
 KDF KONSULT LIMITED is a leading service provider in:
 Geotechnical assessment (subsoil investigation)
 Mining
 Dredging
 Water and environmental engineering
 Soil stabilization
 Foundation design
 Geophysical/geological and hydrographic investigation

4. SUBSOIL INVESTIGATION
APPARATUS
 There are several methods of subsoil investigation or soil testing.
They are:
 Cone Penetration Test (CPT)
 Standard Penetration Test (SPT)
 Vane Shear Test (VST)
 Pressuremeter Test (PMT)
 Flat Plate Dilatometer Test (DMT)

5. SUBSOIL INVESTIGATION
APPARATUS
CONE PENETRATION TEST (2.5 TON CAPACITY)
 This is done using a DUTCH CONE PENETROMETER.
The apparatus consists of:
 Sounding rods
 Push/pull adaptor
 Spiral anchor
 Handle and T-piece
 Mantle cone
 Wrenches set
 Testometer

6. SUBSOIL INVESTIGATION
APPARATUS
 The apparatus consists of a cylindrical
probe of 1000mm2 cross sectional area,
and a conic head of apex angle of 60o
attached to a rod enclosed by an outer
sleeve.
CONE
1M ROD

7. SUBSOIL INVESTIGATION
PROCEDURE
 The probe is forced down through the soil at a steady rate of about
20mm/s in the closed position by exerting pressure manually for a 2.5 Ton
capacity machine or hydraulic pressure (for larger capacity machines).
 The cone penetrometer is used to estimate soil bearing capacity and
settlement of foundations.
 The results from CPT can be correlated with lab test results and
other field tests (usually Standard Penetrometer Tests) to build
empirical relationship for soil strength and deformation parameters.

8. SUBSOIL INVESTIGATION

9. SUBSOIL INVESTIGATION
TEST RESULTS
 The resistance offered by the soil to the penetration of the cone is measured.
 This is called Cone Resistance Value (or Qc Value).
 A low Qc value indicates soft or weak soil strata and thus poor geotechnical
quality while a high Qc value is indicative of good geotechnical property.
 The groundwater level/condition can also be assessed during testing.
 Test is aborted when the machine anchor legs pull from the ground as this
indicates that the rod can penetrate no further.

10. SUBSOIL INVESTIGATION
TEST RESULTS
Generally,
For clay:
Qc value Remark
• 0 – 2
• 2 – 4
• 4 – 10
• 10 – 20
• >20
Very soft
Soft
Firm
Stiff
Stiff to hard
For sand:
Qc value Remark
• 0 – 40
• 40 – 100
• >100
Loose sand
Medium dense
Dense

11. SUBSOIL INVESTIGATION
TEST RESULTS
0 0
5 0.25
10 0.5
10 0.75
13 1
11 1.25
10 1.5
14 1.75
17 2
23 2.25
21 2.5
29 2.75
35 3
43 3.25
56 3.5
70 3.75
81 4
100 4.25
112 4.5
131 4.75
152 5
DEPTH (m)
Qc VALUE
(kgf/cm2)
SOIL PROFILE
DEPTH(m) DESCRIPTION
0 – 0.75
0.75 – 2.0
2.0 – 5.0
Dark-brown
cohesionless soil
Firm to stiff
cohesive soil
Stiff to very stiff
cohesive soil

12. SUBSOIL INVESTIGATION
TEST RESULTS (SPT)
DEPTH (m) N-VALUE U4 SAMPLE
0.00 – 0.75 -- --
0.75 – 6.00 -- Retrieved at
3.00m
6.00 – 12.75 14 – 16 Abortive
12.75 – 16.50 20 – 32 N/A
16.50 – 20.00 20 – 32 N/A
GEOTECHNICAL ENGINEERING PARAMETERS

13. SUBSOIL INVESTIGATION
TEST RESULTS (SPT)
 The sampler is driven in three
successive 150mm (450mm) into
the soil before retrieval.
 The “N” value is taken as the
number of blows required to drive
the sampler the last 300mm
through the soil.

14. SUBSOIL INVESTIGATION
TEST RESULTS ANALYSIS
From the test results shown, the following information can be obtained:
Depth (m) Geotechnical Properties
0.00 to –.0.75 Moderate geotechnical properties, moderate shear
strength and moderate compressibility potential.
0.75 to –2.00 Moderate to good geotechnical properties, moderate
to high shear strength and low compressibility
potential.
2.00 to –5.00 Good geotechnical properties, high shear strength
and low compressibility potential

15. SUBSOIL INVESTIGATION
TEST RESULTS ANALYSIS
BEARING CAPACITY ANALYSIS
ULTIMATE BEARING CAPACITY
qult = CNc + ΨDNq + 0.5BΨNΨ
NOTE:
For pure clay,
Φ = 0
Nc = 5.14
Nq = 1
NΨ = 0
Thus, for the test above, the equation
becomes:
qult = 5.14Cu + ΨD
For pure sand,
C = 0
Where;
C = cohesive strength of soil
D = depth of foundation
B = width of foundation
ΨD = overburden pressure
Ψ = unit weight of soil
Nc = BC factor (cohesion)
Nq = BC factor (surcharge and friction)
NΨ = BC factor (self weight and friction)
*BC = Bearing Capacity

16. SUBSOIL INVESTIGATION
TEST RESULTS ANALYSIS
ALLOWABLE BEARING CAPACITY
Qa = Qult / FS
*FS = Factor of Safety
SETTLEMENT ANALYSIS
Settlement for the calculated Allowable Bearing
Capacity must not exceed 50mm.
S = 1.1Mv x 0.55qn x D
Where;
S = Total Settlement
Mv = volume of compressibility potential
qn = net foundation base pressure
D = depth of foundation

17. SUBSOIL INVESTIGATION
TEST RESULTS ANALYSIS
The table below shows the permissible settlement as per I.S. Code:
SOIL TYPE PERMISSIBLE TOTAL
SETTLEMENT
PERMISSIBLE DIFFERENTIAL
SETTLEMENT
ISOLATED
FOOTINGS
RAFT FOOTINGS ISOLATED FOOTINGS RAFT FOOTINGS
Sand 4.0cm 4.cm to 6.5cm 2.5cm 2.5cm
Clay 6.5cm 6.5 to 10.0cm 4.0cm 4.0cm

18. SUBSOIL INVESTIGATION
TEST RESULTS INTERPRETATION
 From the test result and analysis presented above, Shallow Foundation
(Stiffened Raft Slab) is considered adequate for the proposed development.
 The Stiffened Raft Slab foundation design is a quite simple and common
slab Foundation design, can be used on most classes of soil, and helps to
Minimize differential settlement as it spreads structural load evenly.

19. SKILLS ACQUIRED
After my internship with KDF KONSULT LIMITED, :
 i can effectively carry out soil testing using a Dutch Cone Penetrometer.
 i can effectively carry out soil testing using a Standard Penetrometer.
 i can accurately give recommendation on foundation design.

20. CHALLENGES
Work place procedures/routine.
Poor welfare of internship students.
Restriction from some information.
Time constraint.

21. CONCLUSION
 The SIWES programme has made it possible to apply the theoretical
knowledge in real work situations especially as it concern geotechnical
assessment and engineering geology in general.
 I was also able to develop good work ethics and cooperation.

22. THANK
YOU