POKHARA UNIVERSITY
Level: Bachelor
Semester – Fall
Programme: BE
Course: Foundation Engineering
Year
: 2005
Full Marks: 100
Time
: 3hrs.
Candidates are required to give their answers in their own words as far
as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
1. a)
Pick up the right answer
4
1.1 In a soft clay soil vertical cut can be made, theoretically without any
lateral support, if the depth doesn't exceed
i.
2cu/
iii. 4cu /
ii.
cu/4
iv. 8cu /
1.2 In a board cast in situ pile, in sand, the load carrying capacity when
compared to the driven pile of similar dimension
i.
Will be smaller
iii. Can be smaller or larger
ii.
Will be larger
iv. Will almost be the same
1.3 Select the incorrect statement
i.
Bearing capacity of a soil depends upon the amount and the
direction of load.
ii.
Bearing capacity of a soil depends upon types of soil.
iii.
Bearing capacity of a soil depends upon shape and size of
footing.
iv.
Bearing capacity of a soil independent of rate of loading.
1.4 Undisturbed samples are obtained by
i.
Direct excavation
iii. Thick wall sampler
ii.
Thin wall sampler
iv. Augers
b)
State whether the following statements are true or false and also
justify the answer.
i.
The elastic theory approach estimates the soil pressure on the side
and the base under the design loads.
ii.
Inside clearance is provided to minimize friction during the driving
8
and withdrawal of a sampler.
iii.
Lowering of ground water table in the sand soil results in an
appreciable increasing the settlement of the foundation.
iv.
Active earth pressure decrease on submergence of back fill soil
following the rise of water table.
c)
Fill in the blanks in the following statements, giving calculation
steps where necessary: -
i.
A footing 1.2m wide with its base at 1 m depth on sand soil settles
20mm when the water table is at 2m depth from ground surface if
the water table rises to be the level of base footing, the settlement is
likely to be ………m.
ii.
The observed N value at 12 m depth in a fully submerged coarse
sand deposit with sat = 20 kN/m3 is 45. The N value corrected for
overburden pressure = ………….(Use Peck et.al)
iii.
In a 16 pile group the load carrying capacity of a pile is individual
action is 250 kN. If the efficiency of the pile group is 0.8, the load
shared by one pile in group action is ……..kN.
iv.
The differential settlement in raft foundation is approximately
……… of the total settlement.
2. a)
What do you understand by site investigation? What are the
different purposes for which the site investigation is made?
7
b)
Compute area of a sampling tube if its outside diameter is 100mm
and inside diameters is 94mm. In what types of soil this is used. The
tube is pushed into firm clay at the bottom of the borehole to a
distance of 550mm. The length of the recovered sample is 530mm.
Determine the recovery ratio. If the lower end of the tube is reamed
so that the inside diameter of the cutting edge is 1.25% less than the
inside diameter of the tube. Describe how the recovery ratio is
affected.
9
3. a)
Describe the Culmann's Graphical method for the solution of the
passive earth pressure problem whenthere is friction between soil
and wall and back of wall is not vertical.
7
b)
Find the factor of safety against overturning and sliding for the
retaining wall shown in figure. Use Rankine's theory. soil =
19.8kN/m3, conc = 22kN/m3, 'backfill = 350 below base,
9
8
4. a)
Determine the minimum depth of cantilever sheet pile shown in the
figure (factor of safety = 1). Assume groundwater table to be located
deep.
10
b)
Describe how do you account the effect of water table in Terzaghi's
general bearing capacity equation.
6
5. a)
A square footiung (1.5m1.5m) is located at a depth of 1m. The
footing is subjected to an eccentric load of 400kN, with an
eccentricity of 0.2m along one of the symmetrical axes. Determine
factor of safety against bearing failure. Use Merhof's equation. Take
 = 21kN/m3, C = 100kN/m2,  =0, Nc = 5.14, Nq = 1, Nr =0.
8
b)
A building has to be supported on a RC raft foundation of dimension
12m18m. The subsoil is clay with unconfined compressive strength
of 0.15kg/cm2. The pressure on the soil due to the wt. of the building
and loads that that it will carry will be 15t/m2 at the base of the raft.
If the unit wt. of the excavated soil is 1.8t/m3, at what depth should
db the bottom of the raft be placed to provide a factor of safety of 3
against shear failure.
8
Explain different methods for the installation of piles.
6
6. a)
b)
A group of nine piles, 8m long, is used as the foundation for a
column. The piles are 30cm diameter with center to center spacing
90cm. The subsoil consists of clay with unconfined compressive
strength of 180kN/m2. Estimate the safe load
10
7. a)
What are the situations where a well foundation is more suitable
than other types of foundation? Write the uses of various component
of well foundation?
5
b)
A machine weighting 600 kN is mounted on a concrete foundation
block resting on a soil layer. The area of the foundation block is 25
m2 and its weight is 1000kN. The system is subjected to vertical
linear vibration. The coefficient of elastic uniform compression for
the soil is 11104 kNm3. Calculate the natural frequent of the
system.
6