safe bearing capacity of soil

1. regdno:-
f20012001002
f20012001001
l20012001003
f20012001025
TOPIC:- Safe bearing capacity
name:-
Akash kumar panda
A.sritam patro
gOURGopal jena
etishree nayak
guidedby:- Er.Deeptirani mishra

2. TITLE AND CONTENTLAYOUT WITH LIST
Introduction
Literaturereview
soil
bearingcapacityof soil
Requirementsof SaFEbearingcapacity
objective
Methodology
FACTORSAFFECTINGSAFEBEARING
Reference
A D D A F O O T E R 2

3. INTRODUCTION
The safe bearing capacity of soil field test is performed to verify the soil’s ability to
support loads.Let’s consider an example of a small plastic chair. The small plastic
chair made for children and can support a capacity of 10 kg. Suppose, if an adult has
sat down, the chair will be broken. The same case is applied to the soil.
The bearing capacity of soil may be explained as the capacity of the soil to hold the loads
transferring from the foundation
A D D A F O O T E R 3

4. Foundation design consists of two
distinct parts: the ultimate bearing
capacity of the soil under the
foundation, and the tolerable
settlement that the footing can
undergo without affecting the
superstructure
They investigated the ultimate bearing
capacity of footings on a sand layer
overlying a clay layer in order to
study its influence on the ultimate
bearing capacity of footings
Hamzah M. Beakawi Al-
Hashemi
Oda and Win
A D D A F O O T E R 4
LITERATURE REVIEW

5. He analyzed the bearing
capacity of a strip footing
resting on two layers of
clay. He assumed that the
cohesive soils in both layers
are consolidated
approximately to the same
degree. In order to determine
the ultimate bearing capacity
of the foundation, he assumed
that the failure surface at the
ultimate load is cylindrical,
where the curve lies at the
edge of the footing.
Button (1953)
A D D A F O O T E R 5
LITERATURE REVIEW

6. Foundation design
consists of two distinct
parts: the ultimate
bearing capacity of the
soil under the
foundation, and the
tolerable settlement
that the footing can
undergo without
affecting the
superstructure
Hamzah M. Beakawi Al-
Hashemi(1999)
A D D A F O O T E R 6
LITERATURE REVIEW

7. WHAT IS SOIL AND WHAT IS ITS USE IN CIVILENGINEERINGWORLD
The soil is a mixture that contains minerals, organic matter, and living organisms.
But broadly speaking, soil can refer to any loose sediment.
Soil is a natural material with mechanical properties that allows it to be handled by
construction equipment designed for handling soil.
A D D A F O O T E R 7

8. BEARING CAPACITY OF SOIL
1. Introduction
The bearing capacity of soil may be explained as the capacity of the soil to hold
the loads transferring from the foundation. The pressure that the soil can easily
resist against load is called allowable bearing pressure.
A D D A F O O T E R 8

9. TYPESOF BEARINGCAPACITYOF SOIL
3. Types of Bearing Capacity
The capacity of Soil Following are some types of bearing capacity of soil:-
1. Ultimate bearing capacity (qu)
2. Net ultimate bearing capacity (qnu)
3. Net safe bearing capacity (qns)
4. Gross safe bearing capacity (qs)
Ultimate Ultimate bearing capacity (qu)
Ultimate bearing capacity (qu)
bearing capacity (qu)
Ultimate bearing capacity (qu)
A D D A F O O T E R 9

10. 1. ULTIMATEBEARINGCAPACITY
The gross pressure at the base of the foundation at which soil fails is called
ultimate bearing capacity.
It helps us to know how much pressure can a structure bear till its failure
A D D A F O O T E R 10

11. 2. NET ULTIMATEBEARINGCAPACITY
By neglecting the overburden pressure from ultimate bearing capacity we will get
net ultimate bearing capacity.
A D D A F O O T E R 11

12. 3. NET SAFE BEARING CAPACITY
By considering only shear failure, net ultimate bearing capacity is divided by
certain factor of safety will give the net safe bearing capacity.
Qns = qnu/ F
Where F = factor of safety = 3 (usual value)
A D D A F O O T E R 12

13. 4. GROSS SAFE BEARING CAPACITY
When ultimate bearing capacity is divided by factor of safety it will give
gross safe bearing capacity.
Gross SBC means, adding additional soil bearing capacity with net bearing
capacity. This additional bearing capacity density of filling material above the
footing
A D D A F O O T E R 13

14. REQUIREMENT OF SAFE BEARING CAPACITY
 The first test to be carried out before construction is the soil’s safe
bearing capacity. It is a preliminary test that must be carried out before
the construction of any structure.
 It is recommended that the safe bearing capacity of the ground be tested
at all points of the foot.
 The safe bearing capacity of the soil is enough at one part of the building,
but not the other part. It is recommended to check the SBC of soil at all
footing positions to overcome the Soil Liquefaction. And the perfect type
of footings is chosen by checking the Safe bearing capacity of the soil
A D D A F O O T E R 14

15. General formula of Safe Bearing Capacity is,
Safe Bearing capacity of soil =
Ultimate Bearing Capacity
Cross Sectional Area*Factor Of Safety
A D D A F O O T E R 15
METHODOLOGY

16. OBJECTIVES
If more load is applied to the soil than its resistance, the soil begins to
shift or break, which leads to settlements.
In order to keep the structure safe, the safe bearing capacity is calculated
on the field at different points, and the foot selection is made
accordingly.
A D D A F O O T E R 16

17.  Labrotary Method
Plate Load Test
 Field Method
Drop Weight Method
A D D A F O O T E R 17
TESTSWE WILL DO !

18. PLATE LOADTEST
Plate load test is performed to determine the ultimate load bearing capacity of soil
over the in-situ conditions. The plate load test is mandatory in case of
designing foundation over the sandy and clayey soil. This test gives the
highest rate of accuracy determining the safe bearing capacity of soil in case of
shallow foundations.
This test determines the Ultimate Bearing capacity of Soil, Settlement of
foundation & Allowable bearing pressure of soil. Plate load test is suitable for
Cohesionless soil as in case of Cohesion soil the settlement takes place in longer
duration which this test is not suitable.
A D D A F O O T E R 18

19. APPARATUSFOR PLATE LOADTEST ON SOIL
Mild Steel plate
Hydraulic jack
Reaction beam or reaction truss
Dial gauges
Excavating tools
A D D A F O O T E R 19

20. PROCEDURE
Excavate test pit up to the desired depth. The pit size should be at least 5 times the size of the test
plate (Bp).
At the center of the pit, a small hole or depression is created. The size of the hole is the same as the
size of the steel plate. The bottom level of the hole should correspond to the level of the actual
foundation. The depth of the hole is created such that the ratio of the depth to width of the hole is
equal to the ratio of the actual depth to the actual width of the foundation.
A mild steel plate is used as a load-bearing plate whose thickness should be at least 25 mm thickness
and size may vary from 300 mm to 750 mm. The plate can be square or circular. Generally, a
square plate is used for square footing and a circular plate is used for circular footing.
A D D A F O O T E R 20

21. PROCEDURE
A column is placed at the center of the plate. The load is transferred to the plate through the
centrally placed column.
The load can be transferred to the column either by gravity loading method or by truss
method.
A D D A F O O T E R 21

22. PROCEDURE
For gravity loading method a platform is constructed over the column and load is applied to the
platform by means of sandbags or any other dead loads. The hydraulic jack is placed in between
column and loading platform for the application of gradual loading. This type of loading is called
reaction loading.
At least two dial gauges should be placed at diagonal corners of the plate to record the settlement.
The gauges are placed on a platform so that it does not settle with the plate.
Apply seating load of T/m2 and release before the actual loading starts.
The initial readings are noted.
A D D A F O O T E R 22

23. PROCEDURE
The load is then applied through the hydraulic jack and increased gradually. The increment is
generally one-fifth of the expected safe bearing capacity or one-tenth of the ultimate bearing
capacity or any other smaller value. The applied load is noted from the pressure gauge.
The settlement is observed for each increment and from dial gauge. After increasing the load-
settlement should be observed after 1, 10, 20 and 40 minutes or more untill the settlement upto 25
mm (For Foundation). The readings are noted in tabular form.
After completing the collection of data for a particular loading, the next load increment is applied and
readings are noted under new load. This increment and data collection is repeated until the
maximum load is applied. The maximum load is generally 1.5 times the expected ultimate load or
3 times of the expected allowable bearing pressure.
A D D A F O O T E R 23

24. OBSERVATION
Sl no. Time
(in min)
Load
(in tone)
1st Gauge
Settlement
(in mm)
2nd Gauge
Settlement
(in mm)
Average
Settlement
(in mm)
1 1 2 1.74 0.76 1.25
2 10 4.2 9.23 5.21 7.22
3 20 6.16 22.2 14.41 18.305
4 34 8.1 31.8 18.4 25.1
5 40 8.9 36.41 21.88 29.14
A D D A F O O T E R 24

25. CALCULATION
i)Area of the Plate:- 0.25*0.75 m^2
ii)Final and total load applied upto 25 mm settlement
=8800 kg
So, Ultimate Bearing Capacity= Total Load/Area of the plate
=8800/0.25*0.75
=46933.33 kg/m^2
Therefore Ultimate Bearing Capacity= 46933.33 kg/m^2
A D D A F O O T E R 25

26. CALCULATION
As we know that Safe Bearing Capacity= Ultimate Bearing Capacity/Factor of Safety
Here Factor of Safety is taken as 3
So SBC of that Soil is ,
=46933.33/3
=15644.44 kg/m^2
A D D A F O O T E R 26

27. DROPWEIGHT METHOD:-
Well, so many theories explained about how to find the safe bearing capacity of the
soil. Among them, Drop weight method is the easiest and reliable test.
This is a Field Procedure.
It is also Praticed in most of the site for getting general knowledge about the bearing capacity
of the soil of that construction site
As a pit is digged here so mostly during finding the SBC of the ground soil it is used (At the
Time of Foundation)
A D D A F O O T E R 27

28. PROCEDURE
Firstly Excavate a pit of required depth. So we had taken the depth as 2 metre
Then we have to take a square cube of known dimensions 0.15*0.15*0.15
Now drop the square-cube on the pit from the height from the normal ground level
Measure the impression made on the pit by square cube using the scale and then take it as D
(In our Test it is 0.02m)
Note the cross section area and the weight of the cube for calculation
Here we also need to find the resistance of the soil.s
A D D A F O O T E R 28

29. A D D A F O O T E R 29

30. CALCULATION
Reistance of Soil=M*H/d
Where w is the weight of the cube
H is depth of the pit
D is the measurement of the impression on soil by Cube
As we know that density of concrete cube of this dimension is 2400kg/m^2
So 0.15*0.15*0.15*2400*10*2/0.02=8100
Now Safe Bearing Capacity of that soil= R/A*FOS
=8100/0.15*0.15*3
=12000 kg/m^2
A D D A F O O T E R 30

31. FACTORS AFFECTING SAFE BEARING CAPACITY
Safe bearing capacity of a soil depends upon various factors as follows:
Type of soil structure – soil parameters like cohesion, friction, shear strength, etc.
has a direct impact on the bearing capacity of the soil. For cohesionless soil
and mixed types of soils, it increases proportionally with an increase in the
angle of friction. For cohesive soil, it varies linearly with the cohesion (C) value.
Water table and variations – water table near the foundation is found to adversely
affect the bearing capacity of the soil due to seepage and uplift problems.
However, water table at considerable depth below the base of foundation does
not have any significant impact on the bearing capacity of the soil
A D D A F O O T E R 31

32. FACTORS AFFECTINGSAFE BEARINGCAPACITY
Density of the soil – denser the soil greater will it’s bearing capacity.
Void ratio and porosity of soil – the presence of subsurface voids tends to decrease the bearing capacity of the soil.
Voids also allow seepage of the water that can further affect the soil strength.
A D D A F O O T E R 32

33. REFERENCE
1] Namdar, A., Nusrath, A., foundation numerical modeling and mitigation, Frattura
ed Integrità Strutturale, 12 (2010) 57-62; doi: 10.3221/IGF-ESIS.12.06.
[2] Namdar, A., Pelkoo, M. K., Numerical analysis of soil bearing capacity by
changing soil characteristics, Frattura ed Integrità Strutturale, 10 (2009) 37-41;
doi: 10.3221/IGF-ESIS.10.05.
[3] Galvín, P., Romero, Soil Dynamics and Earthquake Engineering, 57(2014) 10-14.
[4] Namdar, Numerical analysis of SBC, 7(6) (2012) 636-646.
A D D A F O O T E R 33

34. REFERENCE
Namdar, A., Pelkoo, M. K., Bearing capacity of mixed soil model, Frattura ed Integrità Strutturale, 7 (2009) 73-79; doi:
10.3221/IGF-ESIS.07.06.
De Beer, EE., Bearing capacity and settlement of shallow foundations on sand, In: Proceedings of symposium on bearing
capacity and settlement of shallow foundations. Duke University; (1965) 15-33.
Terzaghi, K., Theoretical soil mechanics, New York: John Wiley & Sons, (1943).
Meyerhof, G.G., Some recent research on the bearing capacity of foundations, Can Geotech J, 1(1) (1963) 16-26.
Vesic, A.S., Analysis of ultimate loads of shallow foundations, JSMFD, ASCE 99(1) (1973) 45-73.
Namdar, A., Nusrath, A., foundation numerical modeling and mitigation, Frattura ed Integrità
Strutturale, 12 (2010) 57-62; doi: 10.3221/IGF-ESIS.12.06.
Namdar, A., Pelkoo, M. K., Numerical analysis of soil bearing capacity by changing soil
characteristics, Frattura ed Integrità Strutturale, 10 (2009) 37-41; doi: 10.3221/IGF-
ESIS.10.05. Galvín, P., Romero, Soil Dynamics and Earthquake Engineering, 57(2014) 10-14. .
A D D A F O O T E R 34