Soil Bearing Capacity
For Foundation design the Soil Bearing Capacity is very essential. Soil Bearing capacity is the term explained as, the soil strength or the soil capable enough to carry certain load. SBC of soil can be find out by using the test called Standard perpetration test (SPT) using SBC number the strength is to be determined. After find out the Soil Bearing capacity the report to be prepared and submitted to design department for foundation design.
The following report is the sample copy of soil bearing capacity report.
For Foundation design the Soil Bearing Capacity is very essential. Soil Bearing capacity is the term explained as, the soil strength or the soil capable enough to carry certain load. SBC of soil can be find out by using the test called Standard perpetration test (SPT) using SBC number the strength is to be determined. After find out the Soil Bearing capacity the report to be prepared and submitted to design department for foundation design.
The following report is the sample copy of soil bearing capacity report.
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1. INTRODUCTION
1.1. PURPOSE AND SCOPE
Geo-technical site investigation work
for. “PROPOSED CONSTRUCTIONOF R.C.C
ROOF GROUND INDUSTRIAL GODOWN BUILDING S.F. No: 158/2B & 158/2C OF
AVINASHI VILLAGE, TIRUPUT-DT.” The primary purpose of our investigation
is to obtain data to develop foundation design recommendations for the above
work. At, first instance, Visit to site and chose spot for SPT. Client’s
representatives choose a no of location and selected the locations of SPT. To
accomplish these purposes, the following tasks were performed:
1. Detailed soil borings (Not required for this
site) were done up to stratum to explore the sub surface stratigraphy and
obtain soil samples for testing.
2. Field and laboratory tests
were conducted to evaluate the index and engineering properties of the soils
3. Engineering analysis were performed to
develop foundation design information for proposed structure
1.2. SITE ADDRESS:
S.F.
No: 158/2B & 158/2C OF AVINASHI VILLAGE, TIRUPUT-DT.
1.3. THE STRUCTURE
As per the client information the Industrial
godown building (G+1) for the above mentioned site.
2. FIELD INVESTIGATIONS
2.1. ROTARY BORING
Rotary drilling technique was adapted
using Calyx machine in this field. In this method, boring is effected by the
cutting action of a rotating bit that is kept in firm contact with the bottom
of the hole. The bit is attached to the lower end of a hollow drill rod that
is rotated by a suitable chuck. Drilling mud (usually Bentonite) is
continuously forced down the hollow drill rods. The mud returning upwards
though the annular space between the drill rods and the side of the hold
bring the cutting to the surface.
2.2. STANDARD PENETRATION TEST
It is now most commonly used in site test.
The test measures the penetration resistance of the split spoon sampler, when
it is driven into the soil, at the bottom of a borehole in a standard manner.
The N-value, which is the number of blow required to achieve 300mm
penetration of the soil, indicates the relative density of sand or gravel,
the consistency of other soil such as silts or clays and the strength of weak
rocks.
The test is described in IS 2131 - 1981.
The split spoon sampler is attached to stiff drill rod and lowered to the
bottom of the bore hold. A standard blow consists of dropping a mass of
63.5kg free fall through 750 mm on to an anvil at the top of the rods and
ensuing that this amount of dynamic energy is transferred to the sampler as
much as possible.
The number of blows required to achieve
each 150mm penetration is recorded for a fall penetration of 450mm. The
initial 150mm penetration is referred to as seating drive and the blows
required for this penetration are not considered as this zone is in disturbed
soil. The next 300mm of penetration is referred to as the test drive and the
number of blows required to achieve this fully is termed the penetration resistance
or N-value.
The total number of blows (N)
required, to advance the spoon into the bore, for another two successive 15cm
(a total of 30 cm) is recorded as a measure of the soil relative density or
consistency as given in Table.
CO – RELATION FOR SATURATED SAND/NON – PLASTIC SILT
CO – RELATION FOR SATURATED CLAY/PLASTIC SILT
Rock samples were extracted by Rotary
drilling technique using double tube core barrel of 76mm diameter, filter
with a diamond bit. The extracted cores for every run, not exceeding 1.0
meter were arranged in the core boxes and the T.C.R as well as R.Q.D values
were measured. The appropriate estimation of the properties of the
encountered rock strata can be obtained by referring to the borehole logs and
the following description
The fieldwork was carried out under the
close supervision of our engineer in accordance with Indian Standard
mentioned earlier.
2.3. SAMPLING
Soil samples were collected through Split
spoon and rock core sample were collected through single tube core barrel.
3. LABORATARY TESTS
The operations to be performed in the
laboratory depend upon the type of the nature of data required for the
problem at hand. In case of cohesionless material, like sand, the laboratory
tests are usually minimum and the design parameters are worked out from field
test data such as form SPT- N value, Core resistance and plate load test
data.
In the case of cohesive soils, the
programme of laboratory testing can vary from carrying out simple tests such
as unconfined tests to comprehensive study of soil behaviour using triaxial
shear tests and consolidation tests.
Following laboratory tests are conducted.
For Cohesionless soil
a) Specific gravity
b) Sieve analysis
c) Direct shear test
For Cohesive soil
a) Specific gravity
b) Natural moisture content
c) Atterberg’s limits
d) Sieve Analysis
4. FOUNDATION ANALYSIS
4.1 Safe Bearing Capacity
The bearing capacity of granular soil
depends upon the unit weight and angle of internal friction of the soil.
These two properties of granular soils are determined by standard penetration
tests.
The allowable bearing pressure based on
tolerable settlement has been established empirically by Terzaghi and Peck,
1948 and may be expressed by the equation.
Safe
bearing capacity = 1.40(N”-3) x ((B+0.3)/2B)2 xW’ x Rd x s
Where,
N” = Corrected N value
B = Width of Foundation = constant 1
W’ = Water table correction = constant
0.5
Rd = Depth of Foundation = constant 2
s
= Tolerable settlement = 25 mm
5. DESIGN CRITERIA
5.1 Design of Foundations
As per the clients information the PROPOSED CONSTRUCTIONOF R.C.C ROOF GROUND
INDUSTRIAL GODOWN BUILDING S.F. No: 158/2B & 158/2C OF AVINASHI VILLAGE,
TIRUPUT-DT. The design of foundation depends upon the founding strata,
loading intensity at the foundation level and configuration at loading
points.
For the above conditions, pile foundations are
recommended for the proposed structure shown in the following recommendation.
5.2 Depth of Foundation
Minimum depth of foundations is governed
by the following factors:
·
Top
loose zone.
·
Adequate
depth of soil above founding level, to ensure mobilization of full safe
bearing capacity.
·
Adequate
depth of soil strata below founding level of requisite strength to mobilize
the safe bearing capacity and at the same time restricts the total and differential
settlements within the allowable limits.
·
The
type and depth of foundation shall be decided by the design engineer.
6. FOUNDATION RECOMMENDATIONS
·
The
engineering properties of soil and SPT N value are to be considered for the
foundation recommendation
The site for PROPOSED CONSTRUCTIONOF R.C.C ROOF GROUND INDUSTRIAL GODOWN BUILDING
S.F. No: 158/2B & 158/2C OF AVINASHI VILLAGE, TIRUPUT-DT. The
borehole investigation was conducted and SBC was determined.
7. PRECAUTIONS
Entire report should be
studied before implementing the recommendations. Loose pockets of soil, if
encountered shall be removed and backfilled with a levelling course of
concrete shall be laid and construction of foundations with IS CODE
recommends can be taken up subsequently.
8. LIMITATIONS
The soil investigations have
been carried out at locations in the site chosen by the client so as to
represent the entire site. The recommendations provided in this report are
hence valid only for these test locations. However, if there is any change in
sub soil conditions and properties at places between or beyond chosen test
locations, JAI SHRIRAM ENGINEERING COLLEGE may be contacted for further
advice.
With passage of time, the recommendations may vary
due to manmade and natural environmental changes.
GEOTECHNICAL
INVESTIGATOR
9. REFERENCES
1. IS: 6403-1981
2. IS:
2911-(part1/sec-2 0-1979)
3. IS: 2131-1980
4. IS: 8009
(Part-1) 1976
5. IS: 2720 for
all laboratory tests
6. Wayne CTEng(1992)Foundation
design,13th reprint, Prentice - Hall of India Pvt.Ltd.,
7. Bowles
J.E,(1982) Foundation Analysis and design ,3rd edition, Mc Graw Hill
International Book Co.
8.
Tomlinson M.J. (1995) Foundation Design and Construction, 6th edition, Longman
Group.
ANNEXURE
– I
SOIL
TEST RESULTS
SM
– SILTY SAND, S - SAND, SBC is based on SPT Result.
*NP – Non Plastic, N/A – Not Applicable
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