Essay on Geotech Exam Autumn 2005

Submitted By Zee-Raul
Words: 1000
Pages: 4

Cover Type A

THIS PAPER MAY BE REMOVED FROM THE EXAM CENTRE.

_______________________

_________________________________________

AUTUMN SEMESTER, 2005

SUBJECT NAME

:

GEOTECHNICAL ENGINEERING

SUBJECT NO.

:

48360

DAY/DATE

:

THURSDAY 16th JUNE 2005

TIME ALLOWED :

3.00 hours plus 10 min. reading time

START/END TIME :

18.00 – 21:10

NOTES/INSTRUCTIONS TO CANDIDATES:




There are 6 questions in this exam and you should attempt all questions.
Questions are worth different marks. The value of each question is given.
This is an OPEN BOOK exam- any aids may be used.

QUESTION 1
(20 marks)
An eccentrically loaded long strip footing which has a width of 3 m carries an inclined line load of P (kN per meter run). The load is applied 1 m from one side of the footing as shown in Figure 1. The inclination angle of the load is 10 degrees. The base of the footing is 1.2 m below the surface and the water table is located at the level of the base. The soil is a loose sand having a unit weight of γt = 16 kN/m3 and a friction angle of φ’ = 35o. The friction angle and the adhesion between the footing base and soil can be taken as δ = 20o and ca = 0, respectively.
Use Hansen’s theory of bearing capacity and the effective width concept to find the value of the line load P that ensures a factor of safety of 2.5.

10o

1.2m

P
1m
3m
Figure 1

QUESTION 2
(15 marks)
A plate loading test is carried out on a sandy site as shown in Figure 2. The sand deposit beneath the plate is deep and no ground water exists. The unit weight of the sand is γt = 20 kN/m3. The load on the plate is increased until bearing failure occurs at a load of
Fu = 9.1 kN.
A 1.2m×1.2m square footing is going to be constructed on the site so that its base will be
0.5 m below the ground level. Use Terzaghi’s bearing capacity theory and determine the ultimate load, Pu, that would be required to cause bearing failure of this footing. You may assume the soil is a cohesionless sand and backfigure its friction angle from the result of the plate test.

F

Pu

Plate size:
300mm×300mm

0.5m

Figure 2

1

1.2m×1.2m

QUESTION 3
(15 marks)
A 6 m long circular concrete pile of diameter 0.6m is to be cast-in-situ in a deep layer of clay. The clay has an undrained cohesion of cu=100kPa.
a) Calculate the allowable bearing capacity of the pile assuming a factor of safety of 3.
b) Use an appropriate Young’s modulus for the clay and calculate the settlement of the bored pile when it is loaded to 200 kN. You may assume that the Young’s modulus of the concrete pile is 20GPa.

QUESTION 4
(20 marks)
Figure 3 shows a section of an anchored retaining wall embedded 1.5 m into a saturated stiff clay. The soil behind the wall is a sandy soil. The following properties of the soils are known: Sand γt = 15 kN/m3, c′= 0, φ′ = 30o,
Clay
γt = 20 kN/m3, cu = 25kPa, φu = 0o
The water table is 0.65m below the surface of the clay layer as shown in Figure 3. The short term stability of the wall is going to be considered in an undrained analysis.
a) Use Rankin’s theory of lateral earth pressure and determine the active and passive total horizontal pressure at different points on the wall (points 1 to 6 in Figure 3)
b) Use a global factor of safety of F = 1.7 for the passive earth pressure and for the anchor and determine the design tension force for the anchor, Td, per meter run of the wall.
1

1m

Td
Sand

4m

0.65m

2
3

5

Water table

1.5m

Clay
4

6

Figure 3

2

QUESTION 5…