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IS 4453: 2009 METHODS OF SUBSURFACE EXPLORATION
1.
2. 1. Purpose of code
2. Applications
3. Exploration methods
4. Recording of information
5. Questions
6. Suggestions
3. Before the any construction we must know about
the behavior of soil for the upcoming loading on it
e.g. soil properties like bearing capacity of that
soil , soil type etc. It can be done by exploring the
subsurface.
This IS code 4453 gives the information about
direct methods of subsurface exploration i.e. open
test pit, trenches, drifts, shafts.
Knowledge of the nature, structure and
composition of the strata encountered is obtained
by Geological Investigations and Subsurface
Exploration.
4. For water resources projects, location and depth of
surface exploration by pits, trenches, drifts and
shaft is very important.
For exploring foundation of dams & prospecting
for embankment material or concrete aggregate,
open pits & trenches are generally employed to
obtain required information.
5. Following are the methods of subsurface
exploration-
1. Exploration by Pits
2. Exploration by Trenches
3. Exploration by Drifts or Tunnels
4. Exploration by Shafts
6. Pits are dug by hand tools or mechanical equipments,
they provide necessary working space for inspection of
strata
Its shape is inverted frustum of pyramid ; top of pit- 3m
x 3m; bottom of pit- 1.2m x 1.2m ;depth- 3m for soft
soil (with sloping cut walls), 6m for hard soil (no need
of sloped walls)
Shallow pits (less than 3m) do not require any lateral
support but deep pits and GWT arises then sheeting
(50mm thickness) and bracing is required
The excavated material should be kept round the pits
and its depth is marked at the end of change of
material. By this we can collect different samples later
on.
7. Trenches are continuous over a length and provide a
continuous exposure of the surface along a desired line.
They are best suited for sloped areas.
Instruction for pits and trenches-
1. Deep pits should be ventilated. It can be done by
pipes, canvass sheeting may also used to deflect wind
into the pits.
2. Test pits and trenches should be fenced or covered &
filled back again after the investigation
3. If GWT arises then suction pumps are used (upto
depth 4.5m) having dia. of pipe 10 mm more than
discharge opening of pump or we can use IC engine
with no gas in a pit
4. For UD samples a pillar of 40 cm x 40 cm is made at
centre of pit of representative soil strata.
5. Special care shall be taken to preserve natural water
content of samples.
9. Drifts are the horizontal tunnel made in hill sides to
determine nature and structure of soil strata
A rectangular section of minimum depth of 2.1 m ,
width 1.8 m , with some slope of floor (self draining)
In soft rock arches may be provided & for hard rock
bolts may used to hold together the jointed blocks of
rock.
For a tunnel it must have proper ventilation, lighting
& a proper transportation system.
10. Shafts may be rectangular or circular in section
depending upon investigation requirement and
ease of construction.
Shafts have minimum dimension of 2.4 m x 2.4 m
or dia. 2.4 m for easy movement to workers,
equipments.
Deep shafts should be ventilated, if GWT arises
then there should proper dewatering system, walls
should be strong or if it is weak then provide
supports. Shafts left open for inspection should be
provided with covers, grills or barricades for safety.
11. Besides proper supervision of the work, careful and systematic records
should be kept and made available at project site for consultation.
A recommended proforma for the recording of information obtained
from trial pits is given in Annex A. In some cases. where the strata are
irregular in shape. it may be necessary to carry out three-dimensional
logging
Geological logging and sampling of exploratory drifts should proceed
concurrently with the operation of excavation, after proper cleaning of
side walls and , crowns.
Before logging, the distances are usually marked along the spring line
(or centre line) of the drift, from a reference point which is usually taken
at the portal of the drift
For preparing a three-dimensional (3D) log of“ a circular shaft. the
depths should be marked from the ground level downwards. along four
lines (shown for one line in Fig. 5 ); the north-south ( or upstream-
downstream) and east-west (or right-left) diameters of the shaft
Plans and sections illustrating exploratory features should generally be
drawn to the scale of I : 1000. Geological logs should be drawn I : 100
scale
12.
13. Why subsurface explorations is necessary?
What are the different methods of subsurface exploration?
Are there any other methods of subsurface exploration? Explain
if any.
What are the different stages of subsurface exploration?
Discuss the safety recommendations as per is code 4453?
What are the different methods for providing ventilation during
the excavation work?
What are the different arrangements one should do for dealing
with problems of water , instability of slopes?
What are the factors affecting soil exploration?
What in meant by recording of information?
What are the different informations to be recorded before
investigations? How dos it help in analyzing the sub surface?
14. If one is assigned to do subsurface
exploration and geotechnical investigations,
he must refer the IS code 4453
He must do the preliminary survey before
execution of the project.
