5. Standard Penetration Test”.
Generally used for cohesionless soils
To determine relative density , angle of
shearing resistance, UCC
A bore hole is made using drilling tools
After reaching the specified depth, the drilling
tool is replaced by a split spoon sampler to
collect soil sample.
The sampler is driven in to the ground by a
hammer of weight 65 kg falling from the
height of 750 mm at the rate of 30
blows/minute
6. First 150 mm penetration is taken as seating
drive and the no. of blows required for that
penetration is discarded
No of blows required for next 300mm
penetration after seating drive is taken as
standard penetration number (N)
No of blows greater than 50 are taken as
refusal and the test is discontinued
Corrections are applied to the observed N
value
7. Correction to N value
Of these, overburden correction is applied
first and to that corrected value, dilatancy
Correction is applied
9. Corrections to N value
Overburden Correction applied to N value
based on chart by Peck, et. al. (varies from 0.45
to 2)
No=CN * N
CN= Correction factor = 0.77 log (2000/po )
po =overburden pressure in kN/m2
N= observed SPT value
N’=No
11. Dilatancy Correction
Due to the presence of fine sand and silt
below the water table, negative pore
pressure develops which increases, the
observed N value. Hence correction Is
applied as follows.
If soil is saturated &
SPT(N’)>15 then used N’’=15+0.5(N’-15)
15. PLATE LOAD TEST
Reference: IS 1888-1982 method of load test on soils
• This test is used for
Conducting the load tests on soil.
Evaluation of bearing capacity and
settlement of soil.
This method assumes that down to the depth
of influence of stresses the soil strata is
reasonably uniform.
• .
16. Procedure:
A test pit having width equal to 5 times width
of test plate and depth equal to depth of
foundation is excavated.
A small depression equal to size of the plate
is made at the center of pit and the plate is
placed in it as shown in figure. Mild steel
plate of 30 - 75 cm size and 1.5 – 2.5 cm
thickness and are used.
The hydraulic jack is placed centrally over the
test plate
17. Procedure:
Three or four dial gauges fixed on the
periphery of bearing plate
A seating pressure of 0.07Kg/cm² is applied
on the plate and removed after 5-10 minutes
and set dial gauges reading to zero.
Load is applied on the plate in increments of
50 – 100 kN/m² or 1/5 of the expected
ultimate bearing capacity whichever is less
The applied load is measured by proving ring.
18. Procedure:
Settlement of plate is observed for each load
increment until the rate of settlement is not
more than 0.02 mm per minute.
Testing is continued till a settlement of 25
mm under normal condition or 50 mm in
dense sand, gravel or till failure occurs
whichever is earlier.
From the results of the test, a load settlement
curve is plotted as shown in figure.
22. Load settlement curve
When a load settlement
curve does not indicate
any marked breaking
point, tangents are drawn
to initial and final straight
parts of the curve. The
ultimate load is then
considered corresponding
to the point of intersection
of these tangents.
30. PROCURE
The cone is pushed in to the ground by static
pressure.
The pressure required to push the cone in to the
soil is measured by hydraulic gauges
This method is also used to measure the skin
friction values which is used to determine the
length of the piles.
In order to find out the cone resistance, the cone
alone is pushed
Later the cone and sleeve is pushed together to
find out the combined frictional and point
resistance of the cone.
31. Frictional resistance = Combined resistance
– Cone resistance
Cone penetration resistance is denoted as qc
in kN/m2.
The result of the test are plotted as variation
of cone resistance along the depth as shown
in figure.
32. Advantages
• Rapid test
• Economy
• identification of problem
soils
• Detailed & precise data
• Real time measurement
Disadvantages
• Soil sample not obtained
• Depth limited
• Normally can’t push through
gravel
• Requires special equipment
and skilled operator
Assessment of CPT
33. SIGNIFICANCE
Useful for determination of bearing capacity at
different depths.
Skin friction values required to be used for
determining the length of piles may be determined
by this test.
LIMITATIONS
The is unsuitable of gravelly soil
35. ENCI 579 35
Pressure meter test
The test is conducted in a predrilled borehole
Probe consisting of three cell, upper and lower prevents
middle cell from expanding vertically
Pressure from a gas is applied to the probe and any
volume change is measured by a volumeter
Each pressure increment is held for a fixed time, generally
1 minute
The pressure is increased till soil fails
Pressure verses change in volume is plotted
Soil is initially in elastic phase but enters a plastic phase at
high pressure
