2. 2
Field Test (In-situ Test)
When it is difficult to obtain “undisturbed” samples.
In case of Cohesionless soils, Sensitive clays, etc.
Advantage:
Testing on natural soil under undisturbed
conditions
Disadvantage:
Testing conditions are not controlled
Time dependent phenomenon are difficult to
control due to large scale
Measurements/instrumentation is tricky and
rather a difficult task
In-situ shear strength tests
Standard Penetration Test (SPT)
Cone Penetration Test (CPT)
Dynamic Cone Penetration Test (DCPT)
Vane Shear Test (VST)
Dilatometer Test (DMT)
Pressure meter Test (PMT)
Settlement test
Plate Load Test
Field Test (In-situ Test)
3. 3
5
Common In Situ Testing Devices
In bore holes
DMTVST
SPT
CPT
PMT
DCPT
6
Standard Penetration Test
IS: 2131-1981
4. 4
7
Standard Penetration Test
Components
Drilling Equipment
Inner diameter of hole 100 to 150 mm
Casing may be used in case of soft/non-cohesive soils
Split spoon sampler IS:9640-1980
Drive weight assembly
Falling Weight = 63.5 Kg
Fall height = 75 cm
Others Lifting bail, Tongs, ropes, screw jack, etc.
Procedure
The bore hole is advanced to desired depth and bottom is cleaned.
Split spoon sampler is attached to a drill rod and rested on bore
hole bottom.
Driving mass is dropped onto the drill rod repeatedly and the
sampler is driven into soil for a distance of 450 mm. The number of
blow for each 150 mm penetration are recorded.
Procedure (Cont….)
N-value
First 150 mm penetration is considered as seating penetration
The number of blows for the last two 150 mm penetration are
added together and reported as N-value for the depth of bore
hole.
The split spoon sampler is recovered, and sample is
collected from split barrel so as to preserve moisture
content and sent to the laboratory for further analysis.
SPT is repeated at every 750 mm or 1500 mm interval
for larger depths.
Under the following conditions the penetration is
referred to as refusal and test is halted
a) 50 blows are required for any 150 mm penetration
b)100 blows are required for last 300 mm penetration
c) 10 successive blows produce no advancement
Standard Penetration Test
5. 5
Precautions during SPT
The ht. of free fall Must be 750 mm
The fall of hammer must be free, frictionless and vertical
Cutting shoe of the sampler must be free from wear & tear
The bottom of the bore hole must be cleaned to collect
undisturbed sample
When SPT is done in a sandy soil below water table , the
water level in the bore hole MUST be maintained higher
than the ground water level.
Otherwise: QUICK condition!!
Very Low N value
Correction for Overburden Pressure :
N' = Corrected value of
observed N
CN = Correction factor for
overburden pressure
' .NN C N
Peck, Hanson and Thornburn
(1974)
p' = Effective overburden pressure at a depth
corresponding to N-value measurement
SPT Corrections
6. 6
SPT Corrections
Correction for Dilatancy :
[ ]
Correction for Overburden Pressure : (Alternative)
Alternative -
If the stratum consists of fine sand and silt below water table, for N' > 15,
the dilatancy correction is applied as
SPT Hammer Energy Correction
Energy is dissipated in some fraction during the impact, and the
output energy is usually in the range of 50% to 80% of energy input.
For rope pully system with safety hammer
The N-value is standardized for 60 % energy output. For other
hammers, the N-value may be corrected in ratio of their energy
input
Although IS 2131-1981 is silent on this issue, the correction may be
applied as per the requirement of the project.
60%out
in
E
E
60
%
.
60
out inE E
N N
7. 7
SPT Test Data
No. of blows per 0.30m
Data from different bore holes
Interpretation from SPT: Cohesionless Soils
N'' f' Dr (%) consistency
0-4 25-30 0-15 very loose
4-10 27-32 15-35 loose
10-30 30-35 35-65 medium
30-50 35-40 65-85 dense
>50 38-43 85-100 very dense
8. 8
0.689
0.193
'
N
OCR
p
MN/m2
Interpretation from SPT: Cohesive Soils
N cu (kPa) consistency visual identification
0-2 0 - 12 very soft Thumb can penetrate > 25 mm
2-4 12-25 soft Thumb can penetrate 25 mm
4-8 25-50 medium Thumb penetrates with moderate effort
8-15 50-100 stiff Thumb will indent 8 mm
15-30 100-200 very stiff Can indent with thumb nail; not thumb
>30 >200 hard Cannot indent even with thumb nail
not corrected for overburden 6.25. in kPauc N
Mayne and Kemper (1988)
Cone Penetration Test (CPT)
IS: 4968 (Part –III)
9. 9
17
CPT Procedure
Push the sounding rod with cone into the ground for some specified
depth. Then push the cone with friction sleeve for another specified
depth (> 35 mm). Repeat the process with/without friction sleeve.
Pushing rate = 1 cm/s
Mantle tube is push simultaneously such that it is always above the
cone and friction sleeve.
Tip Load, Qc = Load from pressure gauge reading + Wt. of cone +
Wt. of connecting sounding rods
Tip resistance
With friction sleeve add its self weight as well Qt = Qc + Qf
Frictional resistance
Friction Ratio
c
c
c
Q
q
A
x-sectional area off cone = 10 cm2
surface area of friction sleeve
t c
f
f
Q Q
q
A
f
r
c
q
f
q
Typical range
0%
10%
Cohesive
Granular
CPT Results
& Soil
Classification
10. 10
Typical
CPT Data
0 2 4 6 8 10 12 14
CPT Cone Resistance, qc1
(MPa)
Mean
Mean-SD
Mean+SD
0 10 20 30
SPT Blow Count, N1(60)
(Blows/300 mm)
0 20 40 60 80 100
Relative Density, Dr
(%)
From CPT
From SPT
Interpreted
Soil Profile
0
1
2
3
4
5
6
7
8
9
10
DepthBelowExcavatedSurface(m)
Interbedded
Fine Sand
and
Silty Sand
(SP-SM)
Fine Silty
Sand
(SM)
Gray Silty
Clay (CL)
Sand (SP)
Fine Sand
w/ Shells
(SP)
12. 12
Dynamic Cone Penetration Test (DCPT)
Components:
1) Cone (dia = 50 mm)
~usually made of steel
IS: 4968 (Part – I, II)
SPT
DCPT
Hollow (split spoon)
Solid (no samples)
2) Driving rods/drill
rods
~marked at every 100 mm
DCPT Procedure
Cone – drill rod – driving head assembly is installed
vertically on the ground and hammer is dropped from
standard height repeatedly
The blow counts are recorded for every 100 mm penetration.
A sum of three consecutive values i.e. 300 mm is noted as the
dynamic cone resistance, Ncd at that depth.
The cone is driven up to refusal or the project specified depth.
In the end, the drill rod is withdrawn. The cone is left in the
ground if unthreaded or recovered if threaded.
No sample recovered
Fast testing – less project cost / cover large area in due time
Use of bentonite slurry is optional, which is used to reduce
friction on the driving rods.
• Modified cone is used in this case: diameter = 62.5 mm
13. 13
For clays, and mainly for soft clays.
Measure torque required to quickly
shear the vane pushed into soft clay.
torque undrained shear strength cu
Typical d = 20-100 mm.
25
Vane Shear Test (VST)
vane
undrained
bore hole
soft clay
measuring (torque)
head
vane
h2d
d
Vane Shear Test
Test in Progress Failure surface
2
2.
. . .
1
3.
u
T
c
D H
D
H
3
0.273u
T
c
D
Interpretation:
Undrained shear
strength -
For H = 2.D
14. 14
27
60 mm dia.
Flexible
membrane
Insert DMT using SPT
drilling equipment to the
desired depth and pressure
the cell
Measure pressure when the
membrane is flushed with
plate and when it enters
ground by 1.1 mm.
Decrease the pressure &
measure the pressure when
membrane is again flushed
with plate.
Determined:
Elastic Modulus
Soil Type and state
Dilatometer Test (DMT)
Pressure meter
Test (PMT)
Determined:
Elastic Young Mod, E
Shear Mod, G
Undrained shear strength, Su
15. 15
29
Pressure meter Test (PMT)
Measurements:
1. Fluid Pressure
2. Fluid volume change
Plate Load Test
This test is used to estimate the
Elastic Modulus and Bearing
Capacity of soils which are not
easily sampled.
Bearing Capacity Estimation: The
load is applied such that the rate of
penetration remains constant. A
load-settlement curve is produced.
Equations have been developed to
obtain undrained shear strength
from ultimate bearing capacity.
Modulus Estimation: The load is
applied to the plate in increments of one
fifth of the design load. Time-settlement
and load-settlement curves are then
produced to estimate modulus of soil
from the test results.
16. 16
ROCK TESTING
Rock Testing
Unconfined Compression Test
Brazilian Test
Point Load Test
Direct Shear Test
Slake Durability Test
Schmidt Rebound Hardness Test
Sound Velocity Test
In-situ stress measurements in rocks
17. 17
Core cutting &
grinding machine:
Cutting and grinding
cylindrical rock specimens
core size: EX to NX
Polishing & Lapping machine
Core drilling machine:
Rock core preparation
For regular and irregular
Samples.
core size: EX to 100mm
Specimen Preparation Equipments for
Rock Testing
Rock Core sizes:
EX = 21.46 mm
AX = 30.10 mm
BX = 42.04 mm
NX = 54.74 mm
More: 35mm, 50mm,
75mm, 100 mm
Rock Samples
Granite:
High stiffness
High strength
Very brittle
Limestone:
Medium stiffness
Medium strength
Medium brittleness
Shale:
Low stiffness
Low strength
Ductile
18. 18
Unconfined Compression Test
This test is performed to obtain
the unconfined compressive
strength (UCS) of intact rock
cores (slenderness ratio = 2).
UCS is the maximum stress that
that rock specimen can sustain.
Rock specimen is kept in a
loading frame, and if required
heated to the desired test
temperature.
Axial load is continuously
increased on the specimen until
peak load and failure are
obtained.
Brazilian test: Tensile strength of Rock
Brazilian test is performed to obtain the
tensile strength of rock mass.
Tensile strength of rock is imp to know
for drilling, blasting of rocks, failure of
roof and floor of tunnels, chambers &
underground roadways; often weak
rocks fail in tension exhibiting splitting
mode of failure.
In this test, a disc/cylinder is subjected
to a line load, and fracture should
initiate at the centre and progress
towards periphery. If opposite, the test
is discarded as considered that it did
not fail in tension.
19. 19
Point Load Test: compress. strength of irregular rock sp.
When regular cores could not be obtained;
only irregular pieces are available from
the rock excavation, Point load test is
performed to obtain the compressive
strength of rock mass.
The roughly chiseled spherical mass with
dia. ranging between 30-50 mm is tested
between two hard conical tips in a rigid
frame.
Direct Shear Test:
Normal stress versus Shear stress response of rock mass
It measures peak and residual direct shear strength as a function of
stress normal to the sheared plane.
It can be used for testing for both: core & lump specimens.
Shear box size: 300mm x 300mm x 100mm
20. 20
Triaxial Shear Test:
shear strength parameters (c, f) of rock mass
Triaxial cells for testing rocks are
designed to withstand a confining
pressure 150 Kg/cm2.
Mostly triaxial tests on rock
specimens are performed under no
volume change conditions.
Stress-strain curve is obtained using
deviator stress and axial strain. The
modulus and failure deviator stress
are estimated. Shear strength
parameters (c & f ) are calculated
adopting similar methods as in soils
If the strain gauges are attached to
measure the lateral strain, poisson’s
ratio (n) also can be obtained.
Slake Durability Test:
Resistance of rock mass to disintegration during wetting-drying
Rock fragments of known
weight placed in rotating drum
apparatus, and rock pieces
(approx 10 pieces, each 40-60gm
weight) are circulated through
wet and dry cycles.
Re-weigh the rock fragments to
determine the slake durability
index (SDI).
Mostly, this test allows the rock
mass to get exposed up to two
cycles of wetting and drying.
21. 21
Schmidt Test: Hardness of rock
Schmidt test is performed
to determine the rebound
hardness of rock.
The plunger of the hammer
is pressed against the
specimen and the height of
rebound of the plunger on
a scale is taken as the
measure of hardness.
Sound Velocity Test: P & S-wave velocity of rocks
It is non-destructive test and performed to determine the
velocity of elastic wave propagation through rock in the
laboratory.
slenderness ratio used for the test is usually 3. Test can be
conducted on dry, moist or saturated specimens.
A transmitter and a receiver are attached at sides of rock
specimen (a thin layer of grease is applied on the
specimen’s ends to have proper contact with transducers).
The energy transmission between the transducers
(transmitter and receiver) is used to determine the
velocities of P and S wave.
