presentation about subsoil exploration, its advantages and different methods of soil exploration.

2. Subject Teacher
 Honorable Sir,

3. Participants
1.Ghulam Murtajiz ( G L ) L-14CE-54
2. Muhammad Tashfeen L-14CE-45
3.Kamran Khan L-14CE-14
4.Shankar Lal L-14CE-40
5.Khalil ur Rehman L-14CE-55

4. Objectives;
IMPORTANCE OF SUBSOIL EXPLORATION
&
BORING METHODS
Prepared by; Engr Khalil Dawar L-14CE-55

5. What is Soil?
 To a Civil Engineer: It is a material that can be;
 built on: foundations of buildings, bridges
 built in: basements, culverts, tunnels
 built with: embankments, roads, dams
 supported: retaining walls

7. Subsoil
 Soil is divided into different layers known as horizons.
 B horizon are commonly referred to as the subsoil.
 Subsurface horizon formed below an O, A and/or E horizon
and above the C layer.
 B - horizons have material (usually iron but also humus, clay,
carbonates, etc.)

9. Subsoil Exploration
 The process of identifying the Subsoil layer deposit and their
physical characteristics is generally referred as Subsoil
exploration.

10. Importance
 Selecting the type and depth of foundation suitable for the
given site.
 Evaluating the load bearing capacity of soil.

11.  Estimating the probable settlement of a structure.
 Determining the location of the water table.
 Determine an adequate and economic foundation design.

13.  Determine the suitability of the site for the proposed project.
 Selection of appropriate construction equipment (especially
for excavation and foundations).

15. Methods of soil Exploration

16. Exploration methods
Direct Methods Semi Direct In Direct Methods
Test pits,Trial
pits,Trenches
Borings
•Auger
•Wash Boring
•Percussion
drilling
•Rotary Drilling
Sounding or
penetration
Tests and
Geophysical
methods

17. Boring
Drilling a hole into the soil strata up to specified depth is
known as boring.
1. Auger boring
2.Wash boring
3. Percussion drilling
4. Rotary drilling

18. Auger Boring
 Drilling is made using a device called Soil Auger.
 Hand operated (up to 3 to 5m) and Power driven (Greater than
5m).
 When the auger gets filled with soil sample, it is taken out and
the soil sample collected.
 Suitable in all soils above GWT but only in
 cohesive soil below GWT.

19. Hand operated Auger
Good foe soil exploration for
highways and small structures.

20. Power driven Augers

22. Wash Boring:
 In this method, a casing about 2 to 3 m (6 to 10 ft) long is
driven into the ground.
 The soil inside the casing then is removed by means of a
chopping bit that is attached to a drilling rod.
 Water is forced through the drilling rod, and it goes out at a
very high velocity through the holes at the bottom .
 The water and the chopped soil particles rise upward in the
drill hole and overflow.

23. Wash Boring:

25.  Rotary method is similar to wash boring technique.
 Rotary drilling method of boring is useful in case of highly
resistant strata.
 A heavy string of the drill rod is used for choking action.
 The broken rock or soil fragments are removed by circulating
water or pumped through the drill rods and bit up through the
bore hole from which it is collected in a settling tank.
Rotary Drilling

27. Percussion Drilling
 Grinding the soil by repeated lifting and dropping of heavy
chisels or drilling bits.
 By moving the rope or cable up and down, the cutting or
hammering bit loosens the soil or consolidated rock in the
borehole,
 Water is added to form slurry of cuttings.
 percussion drilling is generally used up to depths of 25 meters

29. Geo-Physical Methods
 These soil exploration methods are based on principle
That
 physical properties like electrical conductivity, elasticity or
seismicity, magnetic susceptibility, density etc. vary for
different types of soils.

30. Seismic Refraction Method
 Based on the principle that sound waves travel with different
velocities in different types of soil.
 In this method shock waves (or sound waves of vibration) are
created.
 Sound waves travel down in the sub-soil strata and get
refracted after striking a hard rock surface below.
 The refracted or radiated shock waves are picked up by the
vibration detector (also known as geophone)

31.  It is possible to evaluate the depth of various strata in the sub-
soil and different materials such as clay, gravel, silt rock, hard
rock etc.

32. Type of
Rock/Soil
Granite Sand
Stone
Shale Hard
clay
Loose
gravel
(wet)
Loose
sand
(wet)
Loose
sand
(dry)
Velocity
(m/sec)
4000
to
6000
1500
to
3000
1300
to
3000
600
to
1500
500
to
1000
500
to
1500
250
to
600

34. Electrical Resistivity Method
 This soil exploration method is based on the principle
 That each soil has different electrical resistivity, depending
upon the type of soil, its water content, compaction and
composition.
 Saturated soil has lower electrical resistivity as compared to
loose dry gravel or solid rock.

35.  In this method 4 electrodes are driven in the ground at equal
distance apart and in a straight line.
 A current is passed between the two outer electrodes and the
potential drop between the inner electrodes is measured by
use of potentiometer.
 Thus knowing the values of change in mean resistivity of sub-
soil strata at site, it is possible to establish the nature and
distribution of different type of soils in the formation.

36. The mean resistivity is calculated by the following formula:
P = 2 π D (E/I)
 Where,
 P = mean resistivity (ohm.cm)
D = distance between electrodes (cm)
E =potential drop between inner electrodes (volts)
I = current flowing between outer electrodes (amperes)