Islamic University of Gaza Faculty of Engineering Civil Engineering Department Soil Mechanics Lab ECIV 3151 Final Exam 2016/2017

Transcription

1 Islamic University of Gaza Faculty of Engineering Civil Engineering Department Soil Mechanics Lab ECIV 3151 Final Exam 2016/2017 Instructors: Dr. Jehad T. Hamad Engr. Yasser M. Almadhoun Examination Date: Time Allowed: 80 Minutes Student Name: Student ID.:... Mark:..... / 100 Problem No. 1: (30 points) State whether the following statements are True (T) or False (F): 1. [ ] Hydraulic conductivity of sandy soils is less than that of clayey soils. 2. [ ] Both types of soil specimens, whether disturbed or undisturbed, are used for testing purposes in the permeability test, whether it is a constant-head method or falling-head method. 3. [ ] Both liquid limit and plastic limit tests are determined using either disturbed or undisturbed soil specimens. 4. [ ] When the water content is beyond than that of the optimum, the compacted density falls off due to the formation of air voids. 5. [ ] The term soil consistency refers to the soil's response to stress. 6. [ ] To make a soil more dense, it requires removing as much of the porosity as possible. This is called densification. 7. [ ] Coefficient of permeability of soil decreases with the increase in temperature. 8. [ ] The clay specimen in one-dimensional consolidation test is regarded as laterally unrestrained and axially drained with two-path drainage. 9. [ ] Modified proctor test is used to attain a higher density of soil at a lower water content in virtue of offering a bigger amount of energy. 10. [ ] In the compaction Proctor test, the number of trials required for testing is governed by the weight of water adopted to add to the soil at each time. 11. [ ] For any soil type, porosity and degree of saturation may exceed 100%, whereas water content and void ratio cannot exceed 100%. 12. [ ] The soil density climbs with increasing water content till reach the optimum after which the soil density begins to decline. 13. [ ] Direct shear test is performed on a sand specimen which is considered consolidated drained during the test, while unconfined compression test is performed on a clay specimen which is considered consolidated undrained during the test. 14. [ ] Unconfined compression test is a UU triaxial compression test, except that the confining pressure is zero. 15. [ ] Compaction describes the process in which a soil mass is getting densified while consolidation describes the process in which a soil mass is getting squeezed. 16. [ ] The ratio of the weight of a given volume of soil solids to the weight of an equal volume of distilled water at the given temperature is known as void ratio. 17. [ ] When drainage is permitted under initially applied normal stress only and full primary consolidation is allowed to take place, the test is known as consolidated undrained test. Page 1 of 8

2 18. [ ] In a liquid limit test, the moisture content at 15 blows was 25% and that at 30 blows was 10%. The liquid limit of the soil, is 20%. 19. [ ] The ratio of the volume of voids to the volume of soil solids in a given soil mass is known as porosity. 20. [ ] When the plastic limit is equal to or greater than the liquid limit, then the plasticity index is zero. Problem No. 2: (18 points) ASTM D2216 Unconfined Compression Test was done on a specimen of clay whose mean length is 75 mm and mean diameter is 35 mm. The readings obtained from the test were as demonstrated in the table below. Piston Pressure, P (N) Vertical Deformation, δv (mm) Vertical Strain, εv (%) Corrected Area, A' (cm 2 ) Major Principal Stress, σ1 (kpa) Determine the following: a. (9 points) Fill in the table above. b. (2 points) Draw the stress-strain diagram for the tested soil sample above. c. (3 points) Determine the major and minor principal stresses at failure. d. (2 points) Draw Mohr-Coulomb circle showing the envelop failure surface. e. (2 points) Determine the unconfined compression strength and undrained cohesion. Page 2 of 8

3 Problem No. 3: (8 points) A sample of fine-grained soil that passes #40 sieve was tested for determining its liquid limit by ASTM D4318 Casagrande Test Method. The measurements obtained from the test were as given in the table under. Item Test 1 Test 2 Test 3 Mass of moist soil, in grams Mass of dry soil, in grams Number of blows, N Mass of pore water, in grams Water content, in percent Liquid limit, in percent Determine the following: a. (3 points) Fill in the table above. b. (2 points) Draw the flow curve for the tested soil sample. c. (2 points) What is the liquid limit of the tested soil sample? d. (1 points) If the plastic limit for the same soil sample tested above is 8%, what is the value for the placidity index? Page 3 of 8

4 Problem No. 4: (10 points) Permeability Test was done for both types of soils at an atmospheric temperature of 20 degrees Celsius: a. (4 points) ASTM D2216 Constant-Head Permeability Test Method was done for a specimen of sand. A volume of 220 cm 3 of water was collected in 1.5 minutes when water was permitted to drain through 20-cm sand specimen whose mean diameter is 60 mm under a water column of 1.7 m. Calculate the standard hydraulic conductivity for this tested sand specimen. b. (4 points) Falling-Head Permeability Test Method was done for a specimen of clay. Water dropped from a height of 90 cm to 85 cm during 200 minutes when permitted to drain from 2.1-mm manometer tube through 20-cm clay specimen whose mean diameter is 60 mm. Calculate the standard hydraulic conductivity for this tested clay specimen. c. (2 points) Why the soil specimen need to be totally immersed in water in the Permeability Test? Page 4 of 8

5 Problem No. 5: (14 points) ASTM D427 Mechanical Sieve Analysis Test was performed for a soil sample in order to determine its gradation on all screens. The measurements obtained from the test were as given in the table below. Sieving Sieve No. (#) Opening (mm) Sieve Mass Before Test (gm) Sieve Mass After Test (gm) Retained Mass (gm) Percent Retained Cumulative Percent Retained Cumulative Percent Passing Pan Total Soil Mass (gm) Determine the following: a. (9 points) Fill in the table above? b. (2 points) Draw the gradation ogive for the tested soil? c. (3 points) What are the proportions of gravel, sand and fines existing in the soil in accordance with the USCS? Page 5 of 8

6 Problem No. 6: (20 points) A) (9 points) What are the types of failure possible to take place across the clay specimen in ASTM D2166 Unconfined Compression Strength? Show their corresponding stress-strain diagrams and indicate at which the values for their unconfined compression strength are determined? Page 6 of 8

7 B) (11 points) ASTM D2435 One-Dimensional Consolidation Test was performed on a clay specimen. The deformation-square-root-of-time curve is given below and the line AB is as shown as under. If the height of the brass ring is 2 cm, calculate the coefficient of consolidation using Taylor s Method at 50% average degree of consolidation. Page 7 of 8

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