INTERVIEW Q&A for Geo-Technical Investigation and Geological Materials and Ground Water

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.   

 

 

  Atterberg limits test

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.

 The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density.