INTERVIEW QUESTIONS & ANSWERES
Geo-Technical Investigation and Geological Materials and Ground Water
Note: Below information is given as a general (Please reconfirm from your contractual requirements)
·
Soil Investigation general Testing
Method?
SPT (Standard Penetration Test)
·
Soil
Sampling Equipment?
Core Barrel
·
Diameter
of Samples (general)?
85. Mm and 93.mm
·
Groundwater
sampling Equipment?
Piezometer
·
Borehole
will be backfilled or not, If yes which material will be used?
After the testing and sampling, the
borehole entire depth will be backfilled by cement grout the same as the tremie method. (To know about the Tremie method, Pls. search with the same keyword in this blog)
·
Why
Bentonite not used as a drilling fluid?
Bentonite
slurry can cause smooth interface condition and affect the skin friction
·
Backfill
Material (Friction Fill) Requirement for MSE Wall construction?
1)
Backfill Density = 19 – 20 KN/m3
2)
Angle of internal friction =35.Degree
3)
Maximum Particle size =50mm
4)
Max. passing % of particle size = .075mm
< 15
5)
Uniformity Coefficient > 4
6)
Plastic Index < 6
7)
pH Value = 4.5 to 9
8)
Seismic Factor (a/g) = 0.1
·
Angle
of internal friction mean?
Angle of internal friction
(friction angle) A measure of the ability of a unit of
soil or rock to withstand a shear stress.
It is the angle (φ), measured between the normal force
(N) and resultant force (R), that is attained when failure just occurs in
response to a shearing stress (S). Its tangent (S/N) is the coefficient of
sliding friction. Its value is determined experimentally.
·
What
is Friction co-efficient Mu (μ)
μ = Frictional force / Normal Force
(Units Newton /Newton)
“μ” don’t have a units ……. N/N – Will
be cancelled
Note: Coefficient of Friction is Static (μs) and Kinetic (μk)
(μs) > (μk)
Because Static is non moved (Non
motioned), Where the Kinetic is Motioned
·
Uniformity
Coefficient and Curvature Co-Efficient of Soil?
Uniformity Coefficient Cu= D60/D10
Curvature Coefficient Cc=
(D30) ^2 / (D10) (D60)
Refer to Youtube Video for more info.: https://youtu.be/KRMAm7e8VL4
·
What
is D10 and D60 soil ?
A)
D10 is called as effective
particle size. This means that 10% percent of the particles are finer and
90% of the particles are coarser than D10. This is the size at
10% finer by weight.
B)
Similarly, D60 is the
particle size at which 60% of the particles are finer and 40% of the
particles are coarser than D60 size.
·
What
are the test will be conducted to the soils in general?
C)
FDT (Field Density Test)
D)
CBR (California Bearing Ratio)
E)
Plate Load Test
F)
Moisture Content Test. This is a very
important test for building construction. ...
G)
Specific Gravity Test. The specific gravity
of any substance is the ratio of density to the density of the water. ...
H)
Atterberg Limits Test. ...
I)
Proctor's Compaction Test.
·
Dry
Density (FDT) Test - Purpose and How?
The dry density of soil is the weight
of soil particles in a given volume of a sample. Its value depends on the void
ratio and the soil’s specific gravity. This value is used to classify soil as
dense, medium dense, or loose. The dry density test is done using one of three
methods: sand replacement, core cutter, or water displacement. Of these, the
sand replacement and core cutter methods are the more widely used.
Test
refer to ASTM D 1556
Short
notes of test as below
1) 150.mm
depth core will be cutted from the compacted formation. (150 depth hole)- (Weight of Wet sample from hole)
·
Cone
will be placed and dune sane will be filled (to find Volume of Hole)
2)
Moisture content will be check with rapid
test at site itself and with help of graph actual moisture value will be taken.
(To find Dry Density of sample)
3)
Wet
density of sample = Weight of wet sample from hole / Volume of the hole
4)
Dry Density of sample = Wet density of
sample / 1+ (moisture content in %) (i.e., Wet density =2.098 and moisture
content found 8.36% (Therefore = 2.098/
(1.0836)=1.936
5)
To check the relative degree of compaction
in % =
=
(Dry density of site sample) / (Laboratory MDD of sample) x100
I.e,
Say, 1.936 / 1.970 * 100 = 98.281%
Video
Refer: https://youtu.be/pyyvTOExjrE
·
What
is mean by CBR and Its Purpose?
California Bearing Ratio
Purpose
of CBR test?
(The Californian Bearing Ratio
(CBR) test is a penetration test
used to evaluate the subgrade strength of roads and pavements. The results
of these tests are used with the curves to determine the thickness of pavement
and its component layers)
Penetration in mm at how much load
Two penetration value will be check
2.5.mm depth and 5mm depth, Therefore how much the weight required to penetrate
in 2.5mm and 5mm.
Video Refer : https://youtu.be/fCmMW73rP64
·
Plate
Load Test
The Plate Bearing
Test (or Plate Loading Test) is an insitu load bearing
test of soil used for determining
the ultimate bearing capacity of the ground and the likely settlement
under a given load. ... A factor of safety is applied to give the
safe bearing capacity of soil.
Reference standard : BS
1377 Part.9
·
Moisture
Content Test purpose and how the test will be?
This is a very important test for
building construction. The moisture content of the soil is determined using
several methods, including the oven-drying method, calcium carbide method,
torsion balance method, Pycnometer method, sand bath method, radiation method,
and alcohol method. The most common method is the oven-drying method, which
involves weighing the sample soil, drying it in an oven at a 110 degrees
Celsius (+/- 5 degrees), and weighing it again. The difference in the before
and after weights is the weight of water in the soil.
Short
notes of Rapid test method at site as follows (Calcium Carbide Method or Speedy
Test Method):-
1) Fill the wet soil sample into the
apparatus
2) Put the weight metal balls for
mixing
3) Put calcium carbide into the
apparatus and close
4) Shake as stated
5) Calcium carbide reaction with water
will produce colorless flammable gas, (which is C2H2)
6) Pressure gauge available with the
apparatus will show the moisture content in percentage (Gas converted into
Moisture content in %)
Video Refer: - https://youtu.be/xfQwcBI4YTA?list=TLPQMTcwNTIwMjADw7KXMmLHuQ
·
What
is specific Gravity
The specific gravity is normally
defined as the ratio between the weight of a given volume of material and weight
of an equal volume of water.
1. Cubic meter concrete weight =
25.Kn/m3 (Which is 2549.Kg/m3)
1. Cubic meter water weight (4.degree
Celsius) = 9.806.Kn/m3 (Which is 1000.Kg/m3, standard at 4 degree C)
25 / 9.806 = 2.549.. (No units,
because Kn/3 / Kn/3……. Will be cancelled, So no units)
Therefore specific gravity
of concrete is 2.549. (Non units value)
Note: Specific
gravity can be used to determine if an object will sink or float on water. The specific gravity of water is equal to One.
1) If
an object or liquid has a specific gravity greaterthen one, it will sink.
2) If the specific gravity of an object or a
liquid is less than one, it will float.
B)
Atterberg limits is a basic measure of
the critical water content of fine-grained soils. These tests include
shrinkage limit, plastic
limit, and liquid limit, which are outlined in ASTM D4318. Depending on
the water content of a soil, it may appear in four states: solid,
semi-solid, plastic and liquid.
C)
The Atterberg limits can
be used to distinguish between silt and clay, and to distinguish
between different types of silts (Fine sand) and clays.
The water content at which the soils
changes from one state to the other are known as
consistency limits or Atterberg's limit.
D) Distinctions in soil are used in assessing the soils that are to have structures built on them. Soils when wet retain water, and some expand in volume. The amount of expansion is related to the ability of the soil to take in water and its structural make-up (the type of atoms present). These tests are mainly used on clayey or silty soils since these are the soils that expand and shrink due to moisture content. Clays and silts react with the water and thus change sizes and have varying shear strengths. Thus these tests are used widely in the preliminary stages of designing any structure to ensure that the soil will have the correct amount of shear strength and not too much change in volume as it expands and shrinks with different moisture contents.
·
Proctor's
Compaction Test.
