FOUNDATION ENGINEERING

1. CIVIL ENGINEERING DEPARTMENT
SUBJECT : FOUNDATION ENGINEERING(2180609)
TOPIC: SUB-SOIL EXPLORATION AND METHODS OF IT.
NAME OF STUDENT ENROLLMENT NO. SEMESTER
ZALA SURPALSINH I 150600106063 8
GOVERNMENT
ENGINEERING COLLEGE,
GODHRA

2. SOURCES FOR THIS TOPIC
• IS : 1892-1979(Indian Standard CODE OF PRACTICE
FOR SUBSURFACE INVESTIGATION FOR
FOUNDATIONS)
• SOURCE USED TO MAKE THIS PPT
a. Book : foundation engineering (ATUL
PRAKASHAN)
b. Google

3. INTRODUCTION
• DEFINITION: SITE INVESTIGATION: Procedure of
obtaining information about surface & sub-surface
conditions at the site of proposed construction.
• Cost of site investigation & sub-soil exploration will
be less than 1% of the total cost of the entire
project.

4. STEPS FOR SOIL EXPLORATION
1. Planning of a programme of soil exploration.
2. Collection of soil samples.
3. Conducting in-situ tests. e.g. standard penetration
test.
4. Collection of ground water sample.
5. Conducting tests on soil and water samples.
6. Preparation of drawing chart.
7. Analysis of data collected.
8. Preparation of site investigation report.

5. OBJECTIVES OF EXPLORATION
• To select foundation for given structure.
• To select construction techniques.
• To determine safe depth of foundation.
• To determine bearing capacity of soil.
• To investigate safety of existing structures and
suggests remedial measures.

6. PLANNING A SUB-SOIL EXPLORATION
PROGRAMME
• TWO IMPORTANT ASPECTS OF PLANNING
1. Depth of exploration
2. Lateral extent of explanations.

7. 1.Depth of exploration
• It depends upon
a. Type of structure
b. intensity of loading
c. shape and disposition of loaded area
d. soil profile
e. Physical properties of soil

8. • The depth of foundation should be at least equal to
to the significant depth.
• DEFINITION : significant depth : The depth upto
which the stress increament due to superimposed
loads can produce significant settlement and
shear stress is known as the significant depth.

9. Sr.No. Types of foundation Depth of exploration
1 Isolated spread
footings
1.5B,
B= Width
2 Raft footings 1.5B
3 Pile foundation 1.5B, B= Width
of pile group
4 Adjacent footings with
clear spacing
less than twice the
width
1.5L
L= Length of footing
5 Road cuts Equal to the bottom
width of the cut
6 Fill 2m below the ground
level or equal to
height of the fill
whichever is higher.

10. 2.Lateral extent of explorations
UNIT NO OR SPACING OF BORE HOLES
Small &less important buildings 1 at centre may suffice.
Compact buildings ( covering an
area of 0.4 hectares)
At least 5 ( 1 at centre & 4 at
corner).
Large multistoreyed buildings At all important locations, spacing
should be 10 to 30m.
Highways Along centre line, spacing should
be 150 to 300m.
Concrete dams Spacing generally varies between
40 to 80m.

11. STAGES IN SUB-SOIL EXPLORATION
Reconnaissance
Preliminary explorations
Detailed investigations

12. Reconnaissance
• Geotechnical engineer
makes a visit to the site
for careful visual
inspection.
• Geotechnical engineer
should study soil maps,
aerial photographs of an
existing buildings.
• INFORMATION OBTAINED
DURING THIS STAGE
General topography of the site
Type of vegetation at site
Drainage pattern existing at site
Location of high flood marks
Evidence of landscape slides
Settlement cracks in existing
structures at site

13. Preliminary explorations
• Tests are connected with
cone penetratometers
and sounding rods for
strength and
compressibility of soils.
• Geophysical methods are
used for locating
boundaries of different
strata. E.g.electrical
resistivity method.
AIM
1. To determine depth, thickness,
composition of each soil stratum at
the site.
2. To determine depth of bed rock
and ground water table.

14. Detailed explorations
AIM
To determine engineering properties of soils in different strata.
ACTIVITIES
Extensive boring programme, sampling, testing of samples in
laboratory.
Field tests ( vane shear tests, plate load tests, permeability tests ) are
conducted to determine properties of soil in natural state.

15. METHODS OF SUB-SOIL
EXPLORATION
Direct methods
(IS 4453 : 2009)
• Pits and trenches
• Drifts and shafts
Semi-direct methods
• Borings
Indirect methods
• Sounding or
penetration tests
• Geophysical
methods

16. PITS AND TRENCHES
• Pits are dug manually but mechanical equipment
may also be used.
• Pits are normally of the shape of an inverted
frustum of a pyramid. The top of the pit is usually a
square of size 3 m x 3 m and its bottom is also a
square of 1.2 m x1.2 m providing sufficient space.

17. DRIFTS AND SHAFTS
• DEFINITION: DRIFTS: Horizontal tunnel made in the hill
side to determine nature and structure of geological
formation.
• Drifts are also known as adits.
• DEFINITION: SHAFTS: Large vertical holes made in the
geological formation.
• These may be rectangular or circular in section.

19. AUGER BORING
• An auger is a tool used for drilling bore hole into
the ground.
Hand operated augers Mechanical augers
Used for depths upto 6m. Used for depths upto 12m.
Used in cohesive and soft soils. Used in cohesive, soft and gravelly
soils.
E.g. post hole auger, helical auger. E.g. power augers.

20. WASH BORING
• Fast and simple method
• Not used in gravel and boulders and rocky strata.
1. Short depth hole is
drilled by auger
2. Casing pipe is pused into
hole & driven with aid of
power
3.Water jet pressure is
forced through screw bit
which loosens soil.
4. Resulting soil-water slurry
come upwards.

21. PERCUSSION DRILLING
• Used for making holes in rock formations.
• Procedure:
1. Heavy drilling bit called ' churn bit' alternatively
raised and dropped in the vertical hole.
2. material in the hole gets pulverized due to repeated
blows.
3. water added to the hole to facilitate the breaking of
stiff soil or rock.
4. Water forms slurry with pulverized material which
removed by bailer at intervals.

22. ELECTRIC RESISTIVITY METHOD
• Soil resistivity is a measure of how much the soil resists
the flow of electricity.
• Each soil has its own resistivity depending upon water
content, compaction, and composition.

23. • A direct voltage is imposed between the two outer
electrodes and the potential drop is measured
between the inner electrodes.
• The mean resistivity is given by the following
formula:
• where, p=
mean resistivity ( ohm.cm ) , D=
distance between electrodes ( cm ) E =
potential drop between inner electrodes ( V ) I =
current flowing between outer electrodes ( A)

24. Thank you