SHEET NO. 6
SHEET
NO. 6
1) What are the
conditions necessary for Darcy’s law to be applicable to the flow of water through the soil ?
2) Explain the meaning
of the term ‘‘ Seepage pressure’’.
3) Write short
notes on Quicksand Conditions,
4) Define the
coefficient of permeability of soils.
5) Define the discharge velocity and the seepage
velocity. Drive the relationship between the two velocities in terms of soil`s
porosity.
6) Why is the capillary rise greater for fine-grained soils than for coarse-grained soils?
7) What are
the factors affecting the permeability of soils?
8) Compare between the constant head and variable head
permeability tests.
9) Describe clearly with a neat sketch of how you
will determine the coefficient of permeability of a clay sample in the
laboratory and derive the expression used to compute the permeability
coefficient. Mention the various precautions, you suggest, to improve the
reliability of the test results.
10)Stating
the basic principles of flow nets describe the trial sketching method of
obtaining a flow net with particular reference to a homogeneous earth dam.
11)Estimate
the coefficient of permeability for uniform sand with D10 = 0.18 mm.
12)Differentiate
between ‘Constant Head type’ and ‘Variable Head type’ parameters. Are both of
them required in the laboratory? If so, why?
13)Estimate the coefficient of permeability for sand with D10 = 0.18 mm.
14)Define
‘permeability’ and explain how would you determine it in the field.
15)A
permeability test is conducted on a horizontally placed soil sample 25 cm long
and 100 cm2 in the cross-section area. The total head at one end of the
sample is maintained at a value of 90 cm and that at the other end at 15 cm.
The flow through the specimen is found to be 1.0 Litre in 10 min.. Evaluate
the coefficient of permeability k in cm/sec.
16)A
constant head permeability test was run on a sand sample 25 cm long and 30 cm2
in area. Under a head of 40 cm the discharge was found 200 cm3 in
116 sec. The specific gravity of sand was 2.65 and its dry weight was 1320 gm.
Determine the coefficient of permeability k, discharge velocity vd
and seepage velocity vs.
17) A constant head permeability test is
performed on a coarse sand soil 12 cm long and 7.3 cm in diameter. Under a head
of 100 cm 5 litres of water are collected in 1 min and 12 sec.. Determine the
coefficient of permeability of the tested soil. How much water per hour would
pass through the mass of soil if the soil is 60 cm long and 100 cm2in
cross-section under a constant head of 20 cm.
18)A
canal and drain run parallel. The water level in the canal is 1.7 m higher than
that in the drain. A 1.5m thick sand layer lying between layers of impervious
clay connects both the canal and drain below their water levels. The sides of
the connected canal and drain are 45 ms apart. Calculate the loss of
water through the sand layer from the canal to the drain per day per Kilometer
if k of sand is 0.006 cm/sec.
19)In a
variable head permeability test on a clayey silt sample, the following results
were obtained :
sample length 120 mm,
sample diameter 80 mm,
initial head 1100 mm,
final head 420 mm
time for fall in head 6 min,
standpipe diameter 4 mm
Determine
from first principals the coefficient of permeability k.
20)a- A sample was found to be in 3 layers 20 mm, 60 mm and 40 mm thick.
Each of permeability 0.003 mm/sec., 0.0005 mm/sec. and 0.0017 mm/sec.
respectively. Find the ratio (kh /kv).
b-
Excavation is being carried out on soil with porosity n =0.35 and specific
gravity Gs =2.65. Define what is meant by a critical hydraulic
gradient and evaluate it for this soil.
21)The following data relate to a pump-out test: Diameter of well = 24 cm. The thickness of confined aquifer = 27 m. The radius of circle of influence = 333m. Drawdown during
the test = 4.5 m. Discharge = 0.9 m3/s. What is the permeability of the aquifer
?
22)The water table is lowered from a depth of 3 m
to a depth of 6 m in a deposit of silt. The silt remains saturated even after
the water table is lowered. What would be the increase in the effective stress
at a depth of 3 m and at 10 m on account of lowering of the water table?
Assume the water content as 27% and grain specific gravity 2.67.
23)Fig. (2) shows a constant head
permeability test. Where the cross-section of soil sample is circular and
discharge is 200 mm3/sec. It is required to determine;
·
The hydraulic gradient for soil 1 and
soil 2.
·
The coefficient hydraulic
conductivity in soil 1 and soil 2.
·
The pore water pressure at the
boundary surface between the two soils.
·
The seepage force for soil 1 and soil
2.
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