Soil sampling, storage and transportation of soil samples

1. Sampling
Types, Criteria for undisturbed samples,
Transport and preservation of samples
1

2. Soil sampling
Soil sampling is the process of collection
of samples of soil in order to determine the
engineering properties of soil required for
the proper design of foundation
 Assessment of water table is also considered
to be a part of soil exploration

3. Types of Samples
Samples
Disturbed
Sample
Non -
Representative
Sample
Representative
sample
Undisturbed
sample

4. Disturbed Sample
The samples in which the natural
structure of the soil got disturbed
either partly or fully during sampling
are called disturbed samples
They are further classified as
a) Non Representative Sample
b) Representative Sample

5. Non -representative Sample
 Non-representative samples consist of
mixture of materials from various soil or
rock strata or are samples from which
some mineral constituents have been
lost or got mixed up.
 These are suitable only for providing
qualitative information such as major
changes in subsurface strata.
Example:
Soil sample from Auger and wash boring

6. Representative samples
 Representative samples are those in
which all the constituent minerals are
retained but only the structure of the
soil got disturbed
 There are changes in water content
also
 These samples are used in the
determination of physical properties
like atterberg limits and specific gravity

7. Undisturbed sample
 Undisturbed samples are those which
are subjected to minimum
disturbances.
 Purely undisturbed sample is an ideal
condition because all the samples will
get disturbed to some extent even
though precise equipments are used
 These samples are used in strength
and consolidation test
Example:
Tube sample and Chunk sample

8. Obtaining chunk sample
 A cylindrical container open at both
the ends is used for sampling.
 The soil is trimmed to shape at the
bottom of the test pit
 One end of container is closed and
inverted over the soil chunk and the
soil sample is removed using spatula
 This method is suitable for cohesive
soil.

9. Obtaining chunk sample or hand
craved sample

10. Criteria for undisturbed sample
Area ratio
Ar= Maximum cross-sectional area of the cutting edge X 100
/Area of the soil sample
Ar = (D2
2- D1
2)/D1
2 X100
The area ratio for undisturbed sample must be 10% or less
than 10%
Inside Clearance:
It allows elastic expansion of the sample and reduces
frictional drag
Ci = (D3-D1)/D1 X100
For undisturbed sample, it should be in the range of 0.5 to 3%
Outside clearance:
Co =(D2 – D4)/D4 X 100
For undisturbed sample, It should lie between 0 to 2%

11. Soil Sampler

12. 4. Inside wall Friction:
The inside wall should be smooth and oil is
generally applied to reduce friction
5. Design of Non return Valve:
The sampler must have a large orifice to allow
quick escaping of air, water or slurry. It should
close immediately when the sampler is with
drawn
6. Method of applying force:
The rate of advancement and method of
application of force controls the sample
disturbance. The sampler must be pushed not
driven

14. Types of samplers
 Split spoon sampler
 Scraper bucket sampler
 Shelby tubes and thin walled samplers
 Piston sampler
 Denison sampler

15. Preservation and transportation
of samples (IS 1892 -1979)
Disturbed Samples of Soil –
 Immediately after being taken from the bore hole or trial
pit, the sample should be placed in a cloth bag or tin
preferably in a glass jar of at least 0.5 kg capacity, and it
should fill this container with a minimum of air space.
 The container should have an air-tight cover. In this way
the natural water content of the sample can be
maintained for one or two weeks without appreciable
change.
 The containers should be numbered and a label should
be placed immediately under the cover in a container.
 The containers should be carefully packed in a wooden
box with saw dust or other suitable material, to prevent
damage during transit.
 They should be stored if possible in a cool room.

16. Undisturbed Samples of Soil - :
 Immediately after being taken from the boring or
trial pit, the ends of the sample should be cut and
removed to a depth of about 2.5 cm ( or more in
the top to cover any obviously disturbed soil).
 Several layers of molten wax should then be
applied to each end to give a plug about 2.5 cm
thick.
 If the sample is very porous, a layer of waxed
paper should first be placed over the ends of the
sample.
 Any space left between the end of the liner or
tube and the top of the wax should be tightly
packed with saw dust or other suitable material;
and a close-fitting lid or screwed cap be placed
on each end of the tube or liner.

17.  The lids should, if necessary, be held in
position by adhesive tape. If the
longitudinal joint of the liner is not air-
tight, this should be waxed and protected
by adhesive tape in the same way as the
lid.
 Samples which are not retained in a
tube should be wholly covered with
several layers of molten paraffin wax
immediately after being removed from
the sampling tool, and then placed in a
suitable metal container, being tightly
packed in the container with saw dust or
other suitable material.

18.  If the sample is very porous, it may be
necessary to cover it with waxed paper
before applying the molten wax
 The number of the sample should be
painted on the outside of the container,
and the top or bottom of the sample
should be indicated.
 The liner or containers should be placed
in a stout wooden box, preferably with
separate partitions, and packed with saw
dust, paper, etc, to prevent damage
during transit.
 It is desirable to test the undisturbed
samples within two weeks of sampling
 If possible the sample is stored in cool
dry place.

19. Planning of an excavation
programme
 Planning depends on type and
importance of the structure
 Depth, extent, thickness , composition
of each strata and the depth of water
table are required to be determined
 Trained persons having knowledge on
geology and geotechnical engineering
are necessary.
 Spacing and depth are the two
important aspects of a boring
programme

20. Spacing of boring
 It is impossible to determine the
spacing of borings before an
investigation begins, since it depends
on the uniformity of the soil deposit.
 It is related to the type, size and
weight of the proposed structure,
variation of strata and availability of
funds
 Spacing is decreased if additional data
are required and increased if the
strata is uniform

21. Spacing of boring

22. Depth of boring
 Boring is performed upto the depth that could consolidate
significantly under the load of the structure
 In case of important structures like dams, bridges etc, boring
is done upto the depth of rock
 Settlement will not occur if the additional load imposed by the
structure is 10% of the initial stress in the soil due to self-
weight.
 Critical depths of borings for buildings are about 3.5 m and
6.5 m for single- and two-storey buildings.
 For dams and embankments, the depth ranges between half
the height to twice the height depending upon the foundation
soil.

23.  In any case, the depth to which seasonal
variations affect the soil should be regarded
as the minimum depth for the exploration of
the sites.
 But, where industrial processes affect the
soil characteristics, this depth may be more.
 The presence of fast-growing and water-
seeking trees also contributes to the
weathering processes

24. Depth of Exploration

25. Boring log
 Information on subsurface conditions obtained from the
boring operation is typically presented in the form of a boring
record, commonly known as “boring log”.
 It consists of
1. Description or classification of various soil and rock
type
2. Ground water table details
3.Test data in case of ‘lab log’
 Comparison is generally made between the data obtained
from adjacent borings in order to predict the nature of
variation in the strata
 A site plan showing the location of borehole is enclosed along
with the boring log

26. A typical boring log

27. Report writing
The site investigation report
should contain the discussion of the
results of exploration programme.
The main findings of the
investigation should be brief but
should clearly state the salient points

28. A soil exploration report generally consists of the
following
1. Introduction
2. Description of the proposed structure
3. Location and geological condition of the site
4. Methods of exploration
5. Number of borings, their depth and location
6. General description of sub-soil condition as
obtained from the SPT and cone test
7. Details and results of the laboratory test
conducted
8. Depth of ground water table and its fluctuations
9. Discussions of the results
10. Recommendation about allowable bearing
pressure, depth and type of foundation
11. Conclusions and limitations of the
investigations .