GEOTECHNICAL INVESTIGATION REPORT ON CONSTRUCTION OF OVERHEAD
TANK AT HILL CITY, PERNAMITTA, ONGOLE, OF ANDHRA PRADESH.
NAME OF THE COMPANY: M/s AUGUST INFRA,
VISAKHAPATNAM,
ANDHRA PRADESH.
CLIENT: M/S PAANYA PROPERTIES
Location of Site: HILL CITY, PERNAMITTA,
ONGOLE,
ANDHRA PRADESH.
Soil Investigation By: M/s PRUDHVI CONSULTANTS,
GUNTUR-2
1. INTRODUCTION
M/s August infra Visakhapatnam, Andhra Pradesh, requested to conduct necessary soil tests
on soil samples collected by M/S Prudhvi Consultants and to recommend suitable foundation
and bearing capacity of soil for proposed construction of Overhead tank at Hill city, pernamitta,
Ongole, District of Andhra Pradesh through Prudhvi Conultants Guntur.
The client chose the test location and depth of investigation. Boreholes were subjected to
standard penetration tests (SPT). Soil samples from disturbed and undisturbed boreholes were
collected for laboratory testing. The index properties and Engineering properties of the soil
were performed in the laboratory to determine the safe pressure on the encountered strata.
2. SCOPE OF WORK
The following is the scope of work for M/S. Prudhvi Consultants, Guntur. Soil boring at One
(1) location
 Collection of Undisturbed / Disturbed samples from the bore hole
 Observing the water table, if encountered
 Conducting standard penetration test (SPT) at 1m /1.50 m depth intervals as per IS Code
2131-1981
The following is the scope of work of M/S Quality Laboratory Services, Soil investigation and
testing department
 Testing of soil sample in the laboratory
 Preparation of technical report, recommendation of suitable foundations and the
Safe Bearing Capacity of soil.
3 SUMMARY
The details of the soil investigation conducted along with their results, analysis of the results,
recommendations for type of foundation and allowable bearing pressure at founding level
thereof has been presented in this report in the form of tabular columns. All the Laboratory
tests were conducted as per relevant Indian Standard codes.
The geotechnical investigations have indicated that the soil consists of Blackish- Reddish Stiff
Clay. Water table was not encountered till the termination depth during the period of field
investigation.
Subsurface conditions encountered during construction may vary somewhat from the
conditions encountered during the site investigation. In case significant variations are
encountered during construction, we request to be notified so that our engineers may review
the recommendations in this report in light of these variations.
Considering the type of structures involved and the subsoil characteristics as determined from
the geotechnical investigations, the following are the various options for the choice of
foundation.
Shallow foundations and Deep foundation in the form of
 Isolated Square footing
 Combined footing
 Raft Foundation
 Under-reamed pile foundation
 The actual size of foundations and type of foundations will be based on type of
structure, loading conditions, spacing of columns etc.
The depth of foundation should satisfy the following requirements.
 It should rest on ground of adequate bearing capacity and safe from settlement
considerations also
 It should have adequate embedded length so as to resist the overturning moments due
to horizontal forces.
4. FIELD INVESTIGATION PROCEDURE
The subsoil investigation was carried out to determine:
 Nature of substratum and engineering properties of soil which may affect the mode of
construction of the proposed work.
 Location of water table and possible effects on foundations.
 Field investigation procedure
The following methods were adopted for sub-soil investigations as per IS: 1892- 1979. Two
soil investigation bores of 150 mm diameter up to a depth of 6 meters were proposed and drilled
within the proposed structure location. Boring was done using combination of shell and rotary
methods with casing pipe to depending upon the type of strata met with in the bore hole location
using hand boring machine. Bore holes of 150 mm diameter with casing pipe were drilled to
facilitate collection of Undisturbed and Disturbed soil samples and to conduct Standard
Penetration Tests. Standard Penetration Tests (SPT) were conducted at every meter intervals
within each bore. These tests were conducted as per IS: 2131-1981. Number of disturbed but
representative soil samples were collected from the auger cuttings sand bailers for
identification and for conducting laboratory tests. Total of 4 bore holes were advanced up to a
depth of 6 meters below the existing ground level. A Strata is considered to be hard, when the
standard penetration test value, N i.e. the number of blows required for 300 mm penetration of
the SPT spoon beyond a seating penetration of 150 mm in the strata is more than 50 ( Clause
3.3.3 of IS: 2131-1981). If the penetration of the spoon is less than 300 mm more than 50 blows,
the N value is written as N>50. The depth of water table at the end of boring is observed. All
the results obtained from the field operations are shown in the tabular forms
5. LABORATORY TESTS
For classification of soil and obtaining engineering properties of soil, the following laboratory
tests are conducted as per relevant IS codes of practice detailed below.
1)
2)
3)
4)
5)
Grain size analysis ( as per IS 2720 (part-4)-1985)
Liquid and plastic limit tests (as per IS 2720 ( part-5)-1985)
In- situ density and Natural Moisture content tests
Free swell index test (as per IS 2720 ( part-40)-1977)
Unconfined Compressive Strength test (as per IS 2720 ( part-10)-1991)
6. REFERENCES
IS 6403: Code of practice for Determination of Bearing Capacity of foundation
IS 1498: Classification and Identification of soil
IS 2911: (part 3), C.O.P for Design and construction of Under-reamed pile foundations.
IS 1904: C.O.P for Design and construction of foundations in soils.
IS 2720: Code of practice for carrying out various laboratory tests on soils
IS 8009: (Part I):1976 Code of practice for calculation of settlements of Shallow
foundations
IS 8009: (Part II): 1980 Code of practice for calculation of settlement of deep foundations
7. SAFE BEARING CAPACITY
Calculation of Safe Bearing capacity Based on shear as per IS 6403
As per clause 5.2.2.1 of IS 6403
Qnu = C*Nc*Sc*Dc*Ic+ Ƴ*Df (Nq-1) Sq Dq Iq + 0.5 B Ƴ NƳ SƳ DƳ IƳ Wʹ
Where
Qnu is the net ultimate bearing capacity of soil
Sc, Sq, SƳ are the shape factors as per Table 2 of IS 6403
Dc, Dq , DƳ are the depth corrections factors as per 5.1.2.2 of IS 6403
Ic, Iq , IƳs are the inclination factors as per 5.1.2.3 of IS 6403
Wʹ is the effect of water table as per 5.1.2.4 of IS 6403
Nc, Nq, NƳ are obtained from the Table1 of IS 6403
Qns = Qnu/ FS
SBC is determined for foundation width of 2m and Depth of 3m using a factor of safety of 3.0
against shear failure. Water table correction factor Wʹ is considered as 0.5 to account for ground
saturation effect.
Calculation Allowable bearing capacity of under-reamed pile as per IS 2911 part-3 1980
Qu= Ap*Nc* Cp+ Aa*Nc* C'a+ Ca'*As' + α*Ca*As
Where,
Qu is the Ultimate bearing capacity of pile (kN)
Ap is Cross-sectional area of pile m2
Nc is the bearing capacity factor (generally taken as 9 for clays)
Cp is the Cohesion at the pile tip (kPa)
Aa is π/4(Du2-D2) in m2
Ca’ is the Average cohesion of soil around the under-reamed bulbs (kPa)
Ca is average cohesion of the soil along the pile stem (kPa)
As is the surface area of stem (m2)
As’ is the surface area of the cylinder circumscribing the under reamed pile (m2)
Qa is the allowable bearing capacity of under-reamed pile (kN).
Qa = Qu/ factor of safety
As per IS 2911 Part-3 1980 the factor of safety is generally considered as 2.5 in compression
and 3 in uplift.
SUB SOIL PROFILE INFORMATION
BORE HOLE 1
Site Location
ONGOLE
Bore Hole No
1
Depth of GWT
Not Encountered
Depth of Bore Hole
6.0 m
Date of Drilling
8/07/2022
Type of Boring
Rotary
Ending of Drilling
09/07/2022
Diameter of Boring
150 mm dia
Depth (m)
Soil Strata
1.0 to 6.0
Blackish
Silty Clay
Blackish
Silty Clay
Reddish
Silty Clay
Reddish
Silty Clay
Reddish
Silty Clay
Reddish
Silty Clay
Sample
Depth (m)
Type
Penetration
15-30 cm 30-45cm
0-15 cm
N
1.0-1.45
SPT
2
2
4
6
2.0-2.45
SPT
3
4
5
9
3.0-3.45
SPT
5
5
6
11
4.0-4.45
SPT
6
8
11
19
5.0-5.45
SPT
4
8
11
19
6.0-6.45
SPT
9
11
15
26
WL (%)
WP (%)
IP (%)
FSI (%)
Gravel (%)
Sand (%)
Silt & Clay
Recorded N
SPT
Ƴd KN/m2
3
NMC (%)
SPT
Ø
2
Blackish
Clay
Blackish
Clay
Reddish
Clay
UCS KN/m2
SPT
ISC
Type of Sample
1
VIS
Depth below GL (m)
ENGINEERING PROPERTIES OF SUBSOIL AT BH-2 LOCATION
MH-CH
100
0
44.43
17.9
63
39
24
50
0
2
98
6
MH-CH
100
0
46.97
18.2
65
36
29
50
0
3
97
9
MH-CH
120
0
34.34
17.5
66
32
34
50
1
3
96
11
4
SPT
5
SPT
6
SPT
Reddish
Clay
Reddish
Clay
Reddish
Clay
MH-CH
130
0
32.52
19.0
51
30
21
40
1
3
96
19
MI-CI
135
0
27.25
18.8
49
28
21
50
2
4
94
19
MI-CI
160
0
19.62
19.0
43
24
19
50
2
6
92
26
9. RECOMMENDATIONS AND KEY POINTS
 The foundation soil at the proposed location of construction of Overhead tank at
Ongole, Andhra Pradesh represented by 1 bore holes i.e., BH- 1 consisted of Reddish
Clay with stiff consistency.
 No ground water table encountered within the depth of exploration.
 Considering the prevailing sub soil conditions at the proposed location of construction
of the structures, the following recommendations and key points are made for
foundation design.
1. The recommended depth of foundation is 3.0m from the ground level in case of isolated
square foundation.
2. The recommended allowable bearing pressure at a depth of 2.0 m & 3.0m from the
ground level is 80 kN/m2 &110 kN/m2 respectively.
3. Under-reamed pile foundation is also recommended for this soil location and structure.
4. The recommended capacity of under-reamed pile foundations are tabulated below
Dia of
Dia of
Length of pile
Safe load for double
Safe load increase per 0.3
stem (m)
Bulb (m)
below cap (m)
under-reamed pile (kN)
m length (m) (kN)
0.3
0.375
0.4
0.45
0.5
0.75
0.94
1.00
1.125
1.25
3.5
3.75
4
4.5
5
179.65
311.47
382.82
488.41
546.56
5.09
6.26
8.14
9.89
11.18
KEY POINTS
1. The foundation soil should be well compacted prior to foundation laying and the
foundation are to be laid on 100 to 200 mm thick lean concrete (1:4:8) in case of shallow
foundation.
2. Sufficient spacing must be provided between footings to avoid over stress in adjacent
footing.
3. The above recommendations are based on the field and laboratory tests conducted on
the soil and our experience in this regard. If the actual subsoil conditions during
excavation for the foundation differ from the observations reported here, the design
experts/consultants should be referred for suggestion, further investigations.
4. A proper drainage should be provided with suitable finished surface slope, drains and
out falls in order to maintain a low and stable water regime in the site.
5. Back filling shall be done in a layers of thickness, and compacted thoroughly. this can
be achieved with suitable compaction equipment’s and the excavated soil is not suitable
for the back filling purpose. (Back filling of the foundation should be done with the
selected soil having Plasticity Index, PI < 6 and Cu > 2, preferably gravel which will
be composed of well graded, coarse siliceous grains sharp and gritty touch and free
from direct and other deleterious matter.)
6. The entire depth of foundation should not be excavated at a time and should be
excavated in stages with proper supports to avoid collapsing the soil.
7. When soil needs to be excavated for footings proper protection measures need to be
taken to prevent damage to the adjacent structure.
8. Soil samples received for testing, water table conditions and other site details furnished
by the M/s Quality Laboratory Services. Laboratory is only responsible for the results
obtained by testing on given soil samples and the Safe Bearing Capacity recommend as
well.
Prepared By
For Quality Laboratory Services
CH V S Chirajneevi
Authorized Signatory
(M.Tech Geotech)