/ No of QuestionsDate of Examination

No. of Pages

THE INSTITUTE OF ENGINEERS, SRILANKAPART 11EXAMINATIONS - JUNE 2012

205-ENGINEERING GEOLOGY AND SOIL MECHANICS

Answer five questions including question 01 Time allowed: 3 hours

INSTRUCTIONS TO CANDIDATES

This paper contains 7 questions on 6 pages (including this page).

Answer five questions selecting at least two from each section including question 01

This examination accounts for 100% of the subject assessment. The marks assigned for eachquestion and sections there of are indicated in square brackets.

This is a closed book examination.

It is an offence to he in possession of unauthorized material during the examination

Only approved calculators are permitted .programmable calculators are not allowed.

Assume reasonable values for any data not given in or with the examination paper. Clearly statesuch assumptions made on the script.

1

Section A Geology

Question 01

The part of the lower surface (A) and upper surface (B) ofa shale layer are shown in the givenmap. FF is a fault with a down throw of 50 meters in the north. A plane of unconformity wasindicated by UU line and M and N are two bore holes.

I. Calculate the hade of the fault[3 marks]

II. Complete the outcrops of the shale layer on the south and north side of the fault.[12marks]

III. Describe the type of faulting using a sketch diagram.[5 Marks]

Question 02

Write short notes on thefollowing;

b) Unconformityc) Shales and slatesd) Chemical sedimente) Mechanical weatheringf) Sedimentary rocks

[4x5 Marks]

Question 03

(a) Explain favorable geological conditions for

I. Locating an industrial rock quarryII. Locating a major dam site

III. Locating a major reservoir[4x3 Marks]

(b) Describe the following with illustrations;

I. Sand dunesII. Unconformity

[4x2 Marks]

2

Section B- Soil Mechanics

Question 04

a) Explain in detail the use of the plasticity chart in defining a soil. (AUnified Soil Classificationchart is provided for reference).

[3 Marks]

b) Sieve analysis test was conducted for a soil sample of 450 grams. Following results wereobtained:

Sieve 8 14 28 35 48 100 200 pannumber

Diameter 2.362 1.168 0.580 0.417 0.295 0.147 0.074

Weight 75.2 85.2 100 54.2 45.2 34.0 30.0 26.2[g]

I. Plot the grain size curve on semi-log paper[7 Marks]

II. Clasify the soil using the unified soil classification.[10 Marks]

Question 05

a) Falling head permeability test was conducted in the laboratory for a sample of soil compactedto the appropriate density. Sample was saturated prior to the test and the data obtained in thetest are given in table Q-5-1. Estimate the coefficient of permeability.

Diameter of the soil sample = 100.0 mm.

Length of the soil sample =127.8 mm.

Diameter of the stand pipe =5.0 mm.

Table Q-5-1.

Time(min) Head Difference(mm)

0 981

20 957

40 942

3

60 924

80 900

[6Marks]

b) Briefly discusses the following1. properties and the utility of the flow net2. seepage force

[4x2Marks]

d) State the basic principle of flow nets describing the trial sketching method of obtaining aflow net with particular reference to a homogenous earth dam

[6 Marks]

Question 06

a) A perfectly dry sand sample completely fills a cylinder. Determine the void ratio, e, of the sandin terms of the volume of the cylinder, V; the specific gravity of the soil grains Gs; the unitweight of water Ow; and the dry weight of the sand enclosed in the cylinder, Ws

[5 Marks]

[5 Marks]

b) An undisturbed specimen of clay is taken from a sampling tube the volume of which is 0.014rrr'. The weight of the specimen is 245 N and the moisture content is 22.1 %. Calculate the dryunit weight. If the specific gravity of the particles is 2.67, find the void ratio and the percentagesaturation.

c) Following results were obtained from Proctor compaction test carried out on a soil. Obtain anestimate of the optimum moisture content and maximum dry unit weight. Draw the line of zero airvoids relating dry unit weight moisture content. Assume the specific gravity as 2.75.

Moisture content (%) Bulk unit weight (kN/m3)

8.4 17.5

9.0 19.8

10.2 20.9

12.4 22.2

15.2 20.6

17.2 20.3

4

[10 MarksQuestion 07

(a) Figure Q7.a shows the flow lines in a soil layer under an impermeable concrete dam with animpermeable cut-off wall at its upstream end. The soil is underlain by a relatively impermeablerock. Draw a square flow net using only these flow lines and hence calculate the flow under the damfor the case when the soil is homogeneous and isotropic with equal vertical and horizontalpermeabilities. Take the permeability as k = 5.0 X 104 m/sec, and the retained water height as 9.25m.

[8 Marks]

(b) If the cut-off wall was at the downstream rather than the upstream end of the dam, what wouldhappen to the flow net and hence the flow. (Hint. You do not need to draw anything)

[4 Marks]

(c) Figure Q7.b shows the flow lines for the same situation but with cut-off walls at both ends ofthe dam. Complete the flow net and hence calculate the flow. For this case determine the upthrustdue to the water pressures on the base of the dam. (Hint: Consider the symmetry before drawingthe flow net and calculating the upthrust. Note also that the base of the dam is 1.2 m below the soilsurface)

[8 Marks]

5

10.

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Figure Q7.a

3D.

Figure Q7.b

6

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