**GTU previous question papers **

**GUJARAT TECHNOLOGICAL UNIVERSITY**

**B. E. Sem. – V – Examination – June- 2011**

** ****Subject Name: Geotechnical Engineering – I**

**Instructions:**

**1. Attempt all questions.**

**2. Make suitable assumptions wherever necessary.**

**3. Figures to the right indicate full marks.**

**Q.1 (a) **1) Differentiate Physical weathering and Chemical weathering.

2) Differentiate Flocculated structure and Honeycombed structure.

3) Define phase diagram and draw phase diagrams in terms of void ratio ‘e’

and porosity ‘n’.

**(b) **An undisturbed soil sample has total weight of 2 0 gm, volume of 1200cc,

water content = 11 % and specific gravity G = 2.68. Compute (i) void ratio

(ii) porosity (iii) degree of saturation (iv) water content to make sample fully

saturated & (v) effective unit weight of the soil sample.

**Q.2 (a) **1) Classify the given soil sample:-

G = 20 %│% N : 10 20 30 60 90 100

S = 78 %│

f = %│(Dmm): 1.28 2.98 3. 4.80 4.92 5.25

2) Differentiate between coarse grained soils (CGS) and fine grained soils

(FGS). A FGS has liquid limit of 65 % and plastic limit of 23 %. Classify the same.

**(b) **1) Define the term ‘Soil Structure’ and briefly explain the commonly

observed soil structures.

2) Describe any one field identification test.

** ****OR**

**(b) **1) Define Toughness Index, Activity, Sensitivity and Thixotropy.

2) In a 10m thick sand deposit, ground water table (GWT) lies at 4.0m

depth below the GL. Sand deposit has γt = 18 kN/m3 & γsat = 20 kN/m3.

Compute effective stress values at the depths of 2.0m, 4.0m and 6.0m below the GL.

**Q.3 (a) **1) Explain the factors affecting permeability of soils.

2) Define ‘Critical Hydraulic Gradient’ and briefly explain ‘Quick Sand’ condition.

** ****(b) **The following data were recorded while performing the compaction test:-

Water content (%): 10 14 20 25

Bulk density (kN/m3): 17.7 19.8 21.0 21.8 21.6

Plot the MDD-OMC curve and obtain the optimum water content and

maximum dry density. Calculate the water content necessary to completely

saturate the sample at its maximum dry density, assuming no change in the

volume. Also plot zero air voids curve. Take G = 2.68

** ****OR**

**Q.3 (a) **A Falling Head permeameter accommodates a soil sample 6cm high and

50cm2 in cross sectional area. The permeability of the sample is expected to

be 1 x 10-4 cm/sec. If it is desired that the head in the Stand pipe should fall

from 30 cm to 10 cm in 40 minutes, determine the size of the standpipe

which should be used. If on the same soil sample a constant head of 200cm

is maintained for 2 hours then how much quantity of water will flow?

** ****(b) **1) Briefly explain the factors affecting compaction.

2) During field compaction process, how the compacted density and the

moisture content can be checked?

** ****Q.4 (a) **1) Briefly explain Coulomb’s, Mohr’s and Mohr-Coulomb’s failure

theories.

2) State merits and demerits of ‘Direct Shear Test’ and ‘Triaxial

Compression Test’.

** ****(b) **Determine the shearing strength parameters from the Direct Shear Test

results given below. The proving ring constant is 0.5 kg/Div.

Sr. No. Normal Stress (kg/cm2 ) Shear Force (kg**)**

1. 1.0 100

2. 2.0 150

3. 3.0 220

What would be shearing strength at the normal stress of 15 kg/cm2?

** ****OR**

**Q.4 (a) **1) Explain importance of ‘Unconfined Compression Test’ & ‘Laboratory

Vane Shear Test’.

2) Name and briefly explain the shear tests which may be performed based on the different drainage conditions.

**Q.4 (b) **From the Undrained Triaxial test results given below, determine the total

shear strength parameters c & φ by plotting conventional failure envelope or

modified failure envelope**. **Also state that at normal stress of 500 kPa, what

would be the shear strength?

Sr. No. Cell Pressure

(kPa)

Deviator Stress

(kPa)

1 100 180

2 200 320

3 300 50 0

**Q.5 (a) **Define the term ‘Consolidation’ and explain the same with the help of

Terzaghi’s Spring Analogy concept. State the assumptions used in

Terzaghi’s one dimensional consolidation theory.

**(b) **A 2.0 m x 2.0 m size footing placed at 2.0 m depth below the ground level

(GL) is transmitting net pressure intensity of 200 kPa. The ground water

table lies at 2.0 m depth below the GL. Using the data given below, divide

the clay stratum in three parts and compute the settlement due to

consolidation:-

(i) Top layer : 2.0 m thick sand, γt = 18 kN/m3

(ii) Middle layer : 3.0 m thick NC clay, γsat = 20.1 kN/m3,

γd = 16.0 kN/m3, Liquid Limit = 80 % & G = 2.7

(iii) Bottom layer : sand

** ****OR**

**Q.5 (a) **Define the terms coefficient of compressibility, coefficient of volume

compressibility, compression index and coefficient of consolidation. Explain

the ‘square-root time fitting method’ for determination of coefficient of consolidation.

**(b) **1) Define the term ‘pre-consolidation pressure’ and briefly explain the

method for determination of the same.

2) During consolidation test, the void ratio is determined to decrease from

0.95 to 0.55 under the stress increment of 1.0 kg/cm2 to 2.5 kg/cm2.

Compute coefficient of compressibility, coefficient of volume

compressibility & compression index.