Unit 6 - Week 4: Geophysical Investigation - I - Nptel

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28/07/2020 Subsurface exploration importance and techniques involved - - Unit 6 - Week 4: Geophysical Investigation - I

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Unit 6 - Week 4:

Geophysical Investigation - I

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Prerequisite Assessment

Week 1:

Subsurface Exploration:

Need and Objectives

Week 2:

Geotechnical Investigations - I

Week 3:

Geotechnical Investigations - II

Week 4:

Geophysical Investigation - I

Lecture 1:

Seismic reflection method Lecture 2:

Seismic refraction method Lecture 3:

Electrical Resistivity Survey Quiz : Assignment 4 Lecture Note Assignment 4 solution

Due on 2019-03-27, 23:59 IST.

1 point 1)

1 point 2)

1 point 3)

Assignment 4

The due date for submitting this assignment has passed.

As per our records you have not submitted this assignment.

For better result, the spacing of current electrodes (Sc) and spacing between potential electrodes (Sp), in case of Schlumberger array should be maintained as

Sc ≥5Sp 2Sc ≥5Sp 2Sc ≤5Sp Sc =5Sp

No, the answer is incorrect.

Score: 0

Accepted Answers:

Sc ≥5Sp

In a Seismic refraction test, following data were recorded. The soil profile at the site is considered to be horizontal.

Distance (m) 0 5 10 20 40 60 80 100 120 Time (millisecond or ms) 0 11 23 49 63 68 75 83 90

Find out the distance from the source, where direct wave and refracted wave will reach simultaneously.

5.63m 10.37m 22.75m 38.23m

Score: 0

22.75m

Referring to Question 2, what would be the thickness of the surficial layer?

3.2m 5m 6.21m 9.87m

Score: 0

9.87m

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https://onlinecourses-archive.nptel.ac.in/noc19_ce10/unit?unit=24&assessment=28 2/3 Week 5:

Geophysical Investigation II

Week 6: Offshore investigation

Week 7: Offshore investigations II

Week 8: Dynamic Testing of Piles

Interaction session

1 point 4)

1 point 5)

1 point 6)

1 point 7)

1 point 8)

Referring to Question 2, if the obtained values of

V

₁ and

V

₂ are interchanged, what would be the thickness of surficial layer?

8m 9.32m Not applicable 12.12m

Score: 0

Not applicable

A loose deposit of sand is underlain by bedrock. During a seismic reflection survey, the

receiver marks the arrival time of directed and reflected waves as 50 ms and 300 ms respectively, as a result of impact loading at 45m from the receiver. The P wave velocity of the sand layer is (consider horizontal soil profile):

900 m/s 700 m/s 600m/s 500 m/s

Score: 0

900 m/s

Referring to Question 5, the thickness of sand layer would be:

80.1m 133.1m 190.1m 250.1m

Score: 0

133.1m

Referring to Question 5, assuming Poisson’s ratio of 0.3, the S wave velocity of sand layer would be:

374.33m/s 320.8 m/s 481.28 m/s 267.37 m/s

Score: 0

481.28 m/s

Current lines and equipotential lines intersect each other at 30º

60º 90º

Not possible to determine No, the answer is incorrect.

Score: 0

90º

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https://onlinecourses-archive.nptel.ac.in/noc19_ce10/unit?unit=24&assessment=28 3/3 1 point 9)

1 point 10)

In a Schlumberger array, the spacing between the current electrodes is ‘a’, spacing between the potential electrodes is ‘b’, voltage difference between the two potential electrodes is ‘v’ and current flowing between the two current electrodes is ‘i’. The apparent resistivity ‘r’ can be defined as

r=(πa^2 v)/(bi) r=(πa^2 v)/(4bi) r=(2πa^2 v)/(bi) r=(4πa^2 v)/(bi) No, the answer is incorrect.

Score: 0

r=(πa^2 v)/(4bi)

In seismic survey, beyond critical distance ………….types of wave will reach first at the geophone.

Direct wave Reflected wave Refracted wave None of the above No, the answer is incorrect.

Score: 0

Refracted wave

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