SOIL MECHANICS AND
FOUNDATION ENGINEERING-II
(CE 311)
SAMPLERS AND SAMPLING
TECHNIQUES
 Generally Samples are collected from bore holes at depth
intervals of 1.5m and whenever there is change of soil type
observed.
 The SAMPLES obtained are varying in the degree of
DISTURBANCE they suffer in the process of sampling.
TYPES OF SOIL SAMPLES
 UNDISTURBED SAMPLES:
 In which care is taken to cause minimal disturbance to the
density, structure and water content of the soil.
 Obtained by carefully designed SAMPLERS.
 Can be tested in the LAB to determine both the physical and
engineering properties.
 DISTURBED SAMPLES:
 In which care is taken to ensure that at least the composition of
the soil remains unaltered.
 Obtained by more rugged but relatively crude.
 Can be used to determine mineralogy, grain size distribution and
Liquid Limit and Plastic Limits.
TYPES OF SOIL SAMPLES
(Contd.)
 DISTURBED NON-REPRESENTATIVE SAMPLES:
 These are not obtained by samplers but are recovered during
drilling operation.
 They give broad idea of the soil type but can not be used for
laboratory testing.
TYPE OF SOIL SAMPLERS
 PISTON SAMPLERS
 FOIL SAMPLERS
 OPEN DRIVE SAMPLERS
PISTON SAMPLERS
 thin-walled metal tubes which contain a piston at the tip
 pushed into the bottom of a borehole, with the piston
remaining at the surface of the soil while the tube slides past it
 Used for undisturbed samples from soft soils, but are difficult
to advance in sands and stiff clays, and can be damaged if
gravel is encountered
 Livingstone corer is a commonly used piston sampler
FOIL SAMPLERS
 Primarily used for sampling of
cohesive soils
 Uniquely adapted for sampling of
thinly stratified soil and for very soft
and semi-liquids soils which
frequently occur at harbour bottom
OPEN DRIVE SAMPLERS
 Called open drive because at the leading end, it is open and
soil enters through it.
 Cutting edge at leading end
 Pushing sampler into the ground displaces the soil of equal
volume of the metal of the sampler.
 Thicker the volume of metal, greater shall be the disturbance.
 Area Ratio (Ar) represents the ratio of soil volume that has to
be displaced to the sampled volume.
 The displacement of soil either in the sample or outside
 OUTSIDE DISTURBANCE is always better
Types of OPEN DRIVE Samplers
 THIN WALL SAMPLERS
 THICK WALL SAMPLERS
 COMPOSITE SAMPLERS
 SAMPLER WITH CORE CATCHER
THIN WALL SAMPLERS
 Made up of SEAMLES steel tube and cutting edge is and
integral part.
 Used when least disturbance needed i.e. undisturbed
samples are obtained
 Area ratio is 10%
 After sampling, the barrel is separated from the head
 Then both ends are dipped in molten wax
 Placed along length in the laboratory
 Cut along its length to give minimum disturbance
THICK WALL SAMPLERS
 Most Common type of samplers known as SPLIT SPOON
SAMPLER
 It splits into two halves longitudinally
 The soil sample obtained is DISTURBED but Representative
COMPOSIT SAMPLERS
 It is also thick wall sampler
 Its barrel is so shaped that a number of liners fit in it.
 After the sampling operation, the liners are pushed out of the
barrel; the soil remains in the barrel
 Samples obtained are DISTURBED Representative
IN-SITU FIELD TESTING
 PENETRATION TESTS
 Standard Penetration Test
 Static Cone Penetration Test
 GROUND WATER OBSERVATIONS
 PERMEABILITY TESTS
STANDARD PENETRATION TEST
(SPT)
 Split spoon sampler is driven by the impact of a hammer
under standardized test conditions
 We measure number of blows required to achieve a standard
amount of penetration.
 Sample obtained is UNDISTURBED
 Constant energy imparted by each blow is that of 650 N
weight falling freely from a height of 750 mm.
 The blow count (N) noted down
 Where N is number of blows required to push the split spoon
sampler from a penetration depth of 150 mm – 450 mm.
Factors affecting SPT N Values
 Efficiency of Mechanism
 Diameter of borehole
 The size of the rod to which split spoon sampler is attached
 Location of the water table
 etc.
 BUT the CODES OF PRACTICE do not give correction due
to above factors
Correction to the N-value
 As per the practice, the CODES give following TWO factors
for which correction in the N-values should be made.
 These are influence of DILATENCY and of OVERBURDEN
 OVERBURDEN CORRECTION:
 A soil have same c & f will exhibit
more strength if it is located deep
in the ground.
N´=CN Nobs
Correction to the N-value
 DILATENCY CORRECTION:
 In saturated condition, the impact load gives undrained
conditions and develops pore water pressure.
 In loose soil, N´ value < 15, positive pore pressure develops
thus effective stress decreases: NO CORRECTION IS
APPLIED
 In dense soil, N´ value >15, negative pore pressure develops
thus effective stress increases: CORRECTION IS APPLIED
𝑁´´ = 15
(𝑁´−15)
+
2
Problems
1. An SPT was conducted at a depth of 2m in a sand deposit
with a unit weight of 20kN/m3. The water table at this site
was 1m below ground level. The N value was observed to
be 5. What would be corrected N value?
2. At the site in Problem 1, the SPT conducted at 15m below
ground surface gives N observed as 21. What would be
the corrected N-value.
3. At a site the soil has a unit weight of 18 kN/m3 and the
water table is at a depth of 6m. The observed N-values at
the site were as follows:
Depth (m)
Nobs
3
9
6
8
9
17
12
19
15
25
Determine the magnitude and corrected N-values i.e. N“.
STATIC CONE PENETRATION
TEST (SCPT)
 MECHANICAL CONE
 ELECTRICAL CONE
Electrical Static Cone Penetration
Test (ESCPT)
 The consists of pushing a standard sized cone having
diameter of 35.6 mm with a taper angle 60° into the soil at a
rate of 10 to 20 mm/sec
 As cone penetrates into the ground, the cone tip resistance,
qC and the friction one the sleeve, fC is vey useful for the
design of foundations especially piles
Comparison of the SPT and ESCPT
PARAMETER
SPT
ESCPT
Impact
Static
Dynamic
Static
Frequency of measurement
At intervals
Continuous
Conducted in the Bore Hole
Yes
No
Affected by disturbance caused
Yes
No
Skill required to conduct test
Low
High
More for Shallow
Foundation
More for Deep
Foundation
Nature of load
Resistance Measured
Utility of Data
Presenting Results of
Site Investigations
 FOUR PARTS:
1. The Project: Nature of Civil Engineering Work
2. Results of Site Investigation: Nature of the site, the soil
profile and the properties of the soil.
3. Possible Solution and Analysis: which describes
alternative solutions that you have considered and the
analysis you conducted to characterize merits of each
alternative.
4. Recommendations: which presents the solution you
propose with details of required design parameters.