4. A foundation is a lower part of a building structure
that transfers its load to the soil (earth) and the
structure must distribute the load equally within
tolerable limits.
Super structure
sub structure
5. Foundation engineering is
the branch of Geotechnical
engineering which deals
with Soil mechanics,
structural engineering,
project serviceability
requirements.
6. What are the types of
foundation??
There are generally 2 types of
foundations for constructing
structures like houses , buildings
etc.
Shallow foundation(D/B<1)
Deep foundation(D/B>1)
10. The portion of earth’s surface
consisting of disintegrated rock
and humus.
These are formed by the process
of weathering of parent rock
The weathering of rocks might
be due to mechanical
disintegration and chemical
decomposition
11. What is soil exploration?
Soil exploration consists of determining the profile of
the natural soil deposits at the site, taking the soil
samples and determining the engineering properties of
soils using laboratory tests as well as in-situ testing
methods.
14. Cohesive and Non-cohesive soils
Cohesive soil: Cohesive soils are a type of soil that
stick to each other. Cohesive soils are the silts and
clays, or fine-grained soils.
Non- Cohesive / Cohesionless soils: A cohesionless
coil (non-cohesive) soil are soils that do not adhere
to each other and rely on friction. These soils are
the sands and gravels, or coarse-grained soils
15. U-1 Soil exploration
What is the need of soil exploration?
• To determine the type of foundation for the proposed
project at the site.
• To determine the proper bearing capacity of the soil
• To determine how deep the foundation should be taken
• Ultimately, it is the subsoil that provides the ultimate
support for the structures.
16.
17. Test pits /trail pits
Trial pits are a simple and economical method of
soil exploration to shallow depths. In this method
of exploration, a square pit is excavated and soil
samples are collected at required depth.
Method of excavation
Pits can be excavated manually with crowbars by
local labor. Small tractor-mounted mechanical
excavators can also be used, if locally available,
which makes the exploration faster and
economical.
18. Size of the pits
The size of the excavation depends primarily on the
space required for efficient excavation and sample
collection and on economic limits. Test pits normally
are square or circular in plan, of size 1.2-3 m. Test
trenches usually are 1-2 m wide and may be extended
to any length, as required, to reveal soil conditions
along a specific line.
In general, test trenches are relatively shallow,
whereas test pits may be deep. It is common to limit
even test pit depths to a minimum, as the cost
increases with depth. Deeper excavations are justified
in countries where labor is inexpensive.
19. Advantages:
The method is simple and fast.
Test pits are one of the most
economical means of soil exploration
to shallow depths.
20. Trenches
Trenches are usually employed to expose steep
dipping bedrock buried below shallow
overburden,
These are normally dug across the strike of the
rocks or mineral zone being tested.
Excavation can be either by hand, mechanical
digger, or by bulldozer on sloping ground.
Excavated depths of up to 4 m are common.
21. Semi direct methods
Boring
Making or drilling bore holes into the ground for
obtaining soil or rock samples from specific depth.
Types of boring
1. Auger boring
2. Wash boring
3. Rotary drilling
4. Percussion drilling
22. Auger boring
This method is fast and economical, using simple,
light, flexible and inexpensive instruments for large
to small holes.
It is very suitable for soft to stiff cohesive soils and
also can be used to determine ground water table.
Soil removed by this is disturbed but it is better
than wash boring, percussion or rotary drilling.
This method of boring is not suitable for very hard
or cemented soils, very soft soils, as then the flow
into the hole can occur.
This method is also not suitable for fully saturated
cohesionless soil.
Augers
Augers
23. Wash boring
It is a popular method due to the use of limited equipments.
The advantage of this is the use of inexpensive and easily portable handling and
drilling equipments.
Here first an open hole is formed on the ground so that the soil sampling or rock
drilling operation can be done below the hole.
The hole is advanced by chopping and twisting action of the light bit. Cutting is
done by forced water and water jet under pressure through the rods operated
inside the hole.
In India the “Dheki” operation is used, i.e., a pipe of 5cm diameter is held
vertically and filled with water using horizontal lever arrangement and by the
process of suction and application of pressure, soil slurry comes out of the tube
24. Just by noting the change of colour of soil coming
out with the change of soil character can be
identified by any experienced person.
It gives completely disturbed sample and is not
suitable for very soft soil, fine to medium grained
cohesionless soil and in cemented soil.
25.
26. Rotary drilling
Rotary drilling method of boring is useful in case of highly resistant strata.
It is related to finding out the rock strata and also to access the quality of
rocks from cracks, fissures and joints.
It can conveniently be used in sands and silts also. Here, the bore holes
are advanced in depth by rotary percussion method which is similar to
wash boring technique.
A heavy string of the drill rod is used for choking action. The broken rock
or soil fragments are removed by circulating water or drilling mud
pumped through the drill rods and bit up through the bore hole from which
it is collected in a settling tank for recirculation.
If the depth is small and the soil stable, water alone can be used. However,
drilling fluids are useful as they serve to stabilize the bore hole.
27. Drilling mud is slurry of bentonite in water.
The drilling fluid causes stabilizing effect to
the bore hole partly due to higher specific
gravity as compared with water and partly due
to formation of mud cake on the sides of the
hole.
As the stabilizing effect is imparted by these
drilling fluids no casing is required if drilling
fluid is used.
This method is suitable for boring holes of
diameter 10cm, or more preferably 15 to20cm
in most of the rocks.
It is uneconomical for holes less than 10cm
diameter. The depth of various strata can be
detected by inspection of cuttings.
Rotary drilling
28. Percussion drilling
In case of hard soils or soft rock, auger boring or wash boring cannot
be employed. For such strata, percussion drilling is usually adopted.
Here advancement of hole is done by alternatively lifting and
dropping a heavy drilling bit which is attached to the lower end of
the drilling bit which is attached to the cable.
Addition of sand increases the cutting action of the drilling bit in
clays. Whereas, when coarse cohesionless soil is encountered, clay
might have to be added to increase the carrying capacity of slurry.
After the carrying capacity of the soil is reached, churn bit is
removed and the slurry is removed using bailers and sand pumps.
Change in soil character is identified by the composition of the
outgoing slurry.
The stroke of bit varies according to the ground condition. Generally,
it is 45-100cm in depth with rate of 35-60 drops/min.
Percussion drilling
29.
30. Sub surface exploration-
The purpose of conducting a subsurface exploration is to
describe the geometry of the soil, rock, and water
beneath the surface.
Also, to determine the relevant engineering characteristics
of the earth materials using field tests and/or laboratory
tests.
31. Planning For Subsurface Exploration
The planning of the site exploration program involves location and depth of
borings, test pits or other methods to be used, and methods of sampling and
tests to be carried out.
The purpose of the exploration program is to determine, within practical
limits, the stratification and engineering properties of the soils underlying the
site.
The principal properties of interest will be the strength, deformation, and
hydraulic characteristics.
The program should be planned so that the maximum amount of information
can be obtained at minimum cost.
In the earlier stages of an investigation, the information available is often
inadequate to allow a firm and detailed plan to be made. The investigation is
therefore performed in the following phases
32. Completely familiar with the kind of information required from the
investigation.
Knowledge of type, size and importance of the project.
Preparation of layout plan of the project,
Preparation of borehole layout plan which includes number and spacing of
boreholes, depth and frequency of sampling.
Selection of proper drilling and sampling equipment.
Selection of personnel to supervise the field investigation.
Marking on the layout plan any additional types of soil investigation.
Preparation of guidelines for laboratory testing of collected samples.
To obtain the most useful information at minimum cost and
effort, proper planning of subsurface investigation programme is
essential.
33. Stage of Subsoil Investigation:
Different stages of sub-soil investigation of a major civil Engineering project are
mentioned below:
Reconnaissance study:
This may be in the form of a field trip to the site which can reveal information on the
type and behavior of adjacent sites and structures such as cracks, noticeable sags, and
possibly sticking doors andwindows.
The type of local existing structure may influence, to a considerable extent, the
exploration program and the best foundation type for the proposed adjacent structure.
Since nearby existing structures must be maintained, excavations or vibrations will
have to be carefully controlled.
Erosion inexisting cuts (or ditches) may also be observed. For highways, run off
patterns , as well as soil stratification to the depth of the erosion cut , may be observed.
Rock outcrops may give an indication ofthe presence or the depth of bedrock
35. Samples
Disturbed sample is a sample in which soil structure is
significantly or completely disturbed and the moisture content
may also differ from in-situ value.
The particle size distribution of in-situ soil is preserved. These
samples are required for identification and classification tests.
Undisturbed sample is a sample which retains as closely as
practicable, the true in-situ structure and moisture content of
soil.
These samples are required for shear strength, permeability and
consolidation tests.
36. The structure of the soil is disturbed to the considerable degree by the
action of the boring tools orthe excavation equipments.
The disturbances can be classified in following basic types:
Change in the stress condition
Change in the water content and the void ratio
Disturbance of the soil structure
Chemical changes,
Mixing and segregation of soil constituents
The causes of the disturbances are listed below:
Method of advancing the borehole
Mechanism used to advance the sampler
Dimension and type of sampler Procedure
followed in sampling and boring.
37. Field tests
1) Standard Penetration test(SPT)
2) Dynamic core penetration test(DCPT)
3) Static core penetration Test(CPT)
