MORE IN Geotechnical Engineering 1
VTU Civil Engineering (Semester 5)
Geotechnical Engineering 1
May 2016
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1(a) Critically define the terms void ratio, porosity and water content with phase diagram.
4 M
1(b) Derive the relation $$\gamma _{d}=\dfrac{G.\gamma w}{1+e}$$ with usual notations.
6 M
1(c) In an earthen embankment under construction, the bulk unit weight is 16.5kN/m3 at water content 11%. If the water content has to be increased to 50%, compute the quantity of water to be added per cubic meter of soil. Assume no change in void ratio. Also determine 'e' at this water content taking G = 2.65.
10 M

2(a) Define relative density of sand and list its importance in geotechnical engineering.
4 M
2(b) Describe consistency of soil. List and define consistency limits.
6 M
2(c) The following results are obtained by conducting liquid limit test on clayey soil in the laboratory:
 No. of blows (N) : 34 23 18 12 Water content (W%): 44.6 49.4 51.4 55.6

Plot flow curve. Determine Liquid limit, Toughness index. Assume plastic limit = 20%.
10 M

3(a) Explain with the help of typical particle size distribution curve, well graded, poorly graded and gap gtaded soil.
4 M
3(b) With the neat sketch, explain structure of clay minerals.
6 M
3(c) Following results are obtained from the laboratory tests conducted on two soil samples :
 Soil sample A B Liquid limit 85% 45% Plastic limit 50% 12%

Show the positions of these soils on plasticity chart and classify as per I.S. system.
10 M

4(a) Derive the relation between co-efficient of permeability and percolation with usual notations.
7 M
4(b) Explain Quick - sand phenomena and list its importance during construction.
5 M
4(c) A falling head permeater accommodates a soil sample of 6cm length and 500cm2 in area. The permeability of sample is expected to be 1 × 10-4 cm/sec. Head of water in the standpipe falls from 30cm to 10cm in 40 minutes. Determine the size of the stand pipe which should be used.
8 M

5(a) Explain sensitivity and thixotropy of clayey soil.
4 M
5(b) List the factors affecting shear strength of soil.
4 M
5(c) A direct shear test results are obtained as follows :
 Normal stress (kN/m2) : 100 200 300 Shear stress (kN/m2) : 130 185 240

Determine shear parameters graphically. Also draw Mohr's circle corresponding to second test result and report major and minor principal stresses.
12 M

6(a) List the factors affecting compaction of soil and explain any 2 in detail.
5 M
6(b) List and explain various types of field compaction equipments.
5 M
6(c) The results of standard compaction test conducted in the laboratory are tabulated as follows:
 Water content% : 5 10 14 20 25 Bulk density kN/m3 17.7 19.8 21 21.8 21.6

Find MDD and OMC with usual notaions by plotting comoaction curve. Also draw ZAVD -line assuming G = 2.65.
10 M

7(a) State the assumptions of one - dimensional Terzaghi's theory of consolidation. Also write standard / general differential one - dimensional consolidation equation with usual notation.
8 M
7(b) Explain with neat sketch, determination of co-efficient of consolidation by square - root of time fitting method.
6 M
7(c) A layer of soft clay is 6m thick and lies under newly constructed building. The weight of sand overlying the clayey layer produces a pressure of 260 kN/m2 and this new construction increases the pressure by 100kN/m2. If the compression index is 0.5, compute settlement of soil layer given water content 40% and G = 2.65.
6 M

8(a) Critically discuss limitations of direct shear test.
4 M
8(b) Explain Vane shear test with neat sketch along with relations.
6 M
8(c) A vane apparatus test. A torque of 45N-m was applied at which failure took place. Subsequently, vane instrument rotated rapidly, so as to get reolded soil sample. This remolded soil was sheared at a torque of 18 N-m. Then calculate sensitivity of clayey soil.
10 M

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