Mid-term-exam-with-solutions.pdf

2nd semester 2013/2014 Instructors: Prof. Mohammed Awad Dr. Jehad Hamad T.A: Engr. Othman Tayeh Engr. Samia Nassar

Islamic University of Gaza Faculty of Engineering Civil Engineering department

Soil Mechanics ECIV 3351

Soil Mechanics ECIV 3351 Time Allowed: 75 minutes Mid-Term Exam 12/4/2014

Student Name

Q. No

Maximum mark

1

10

2

10

3

20

4

20

5

20

Total

80

ID

Mark

1

Notes

Mid-Term Exam

Soil Mechanics ECIV 3351

SHOW ALL WORK! This is close book exam: please enter answers with appropriate units. Partial credit will not be given unless steps are shown. Correct answers must have supporting calculation. All assumptions should be cited. Write answer logically, neatly, and legibly

Question (1): (10 points) The moist unit weight of a soil sample is 16.5KN/m3. Given that the w=15% and Gs=2.7, find: a) b) c) d)

Dry unit weight (ɤd). The porosity (n). The degree of saturation (S). The mass of water in Kg/m3 that must be added to reach full saturation.

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Mid-Term Exam

Soil Mechanics ECIV 3351

Question (2): (10 points) a) Show the saturation moisture content is

wsat=

)

where

b) A geotechnical laboratory reported these results of five samples taken from a single boring. Determine which are not correctly reported, if any, show your work: where Sample #1: w=30%, ɤd=14.9 KN/m3, ɤs=27 KN/m3,clay.

Sample #2: w=20%, ɤd=18 KN/m3, ɤs=27 KN/m3,silt.

Sample #3: w=10%, ɤd=16 KN/m3, ɤs=26 KN/m3,sand.

Sample #4: w=22%, ɤd=17.3 KN/m3, ɤs=28 KN/m3,silt.

Sample #5: w=22%, ɤd=18 KN/m3, ɤs=27 KN/m3,silt.

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Mid-Term Exam

Soil Mechanics ECIV 3351

Question (3): (20 points) Classify the following soils (a & b) using the unified soil classification system. (Give group Symbol & group Name). a) A clayey soil sample weights 1.5 N. Its clay fraction 0.34, gravel fraction 0.15, sand fraction 0.2, silt fraction 0.31. If its liquid limit is 60%, and its plastic limit is 26%.

b) The particle size distribution for a soil sample shown in the table below, with LL=30% and PL=18% Particle % Finer size (mm) than 6 100 4.75 95 2.36 84 1.3 60 0.6 30 0.2 10 0.075 8

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Mid-Term Exam

Soil Mechanics ECIV 3351

17 cm

Water

6 cm

E

Soil 5 K5

5 cm

5 cm

Soil 3 D K3

C

Soil 4 K4

5

Soil 2 K2

25 cm

Water

Question (4): (20 points) For the Figure shown below; 1.Find the Pressure head at the following points A – B – C – D – E. Assume 2.5k1 = k2 = 1.5 k3 = 2k4=3 k5 2. Find the flow rate. (Hint k1 = 3.5*10-2 cm/sec)

5 cm

B

Soil 1 K1

A

1.5 cm 1.5 cm

Mid-Term Exam

Soil Mechanics ECIV 3351

Question (5): (20 points) For the flow net shown below, if the coefficient of permeability of the soil below the dam is (5.2x10-3 cm/sec) and ɤsat = 18.2 kN/m3, find the following:

10 m

A- The rate of seepage (m3/sec /m). B- The uplift force underneath the dam. C- The effective stress at points L and N. D- The driving head at point M. 30 m Water table

Water table

6m

8m

8m

1m

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Mid-Term Exam

Soil Mechanics ECIV 3351

Useful formulas k H ( eq )

H 1  , k H ( eq )  (k H1 H1  k H 2 H 2  ...  k H n H n ) H H   H1   H 2        ...   n   k1   k 2   kn 

S.e=Gs w

q= k i A

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Soil Mechanics ECIV 3351

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