2007 EC Mekelle University 2014/2015 GC
Ethiopian Institute of Technology – Mekelle
School of Civil Engineering
Geotechnical Engineering Graduate Program
Course: Advanced Soil Mechanics
Instructor: Dr. Tensay G
Assignment- 1
1. A permanent surcharge of (your age in months)/2 kN/m2 is to be applied on the ground
surface of the soil profile shown in Figure AS1. It is required to eliminate all of the primary
consolidation in (your age in years)/10 months. Estimate the total surcharge needed to
achieve the goal.
0.0 m
Sand
= 17.5 kN/m3
-1.5 m GWT
Sand
sat = 0.67 x your age in years kN/m3
-3.0 m
Clay
sat = 17.2 kN/m3
Cv = (your age in years)/250 cm-2/min
-6.0 m
Sand
sat = 0.75 x your age in years kN/m3
Figure AS1.
2. An oil storage tank that is circular in plan is to be constructed over a layer of sand, as shown
in Figure AS2. Calculate the following settlements due to the uniformly distributed load q of
the storage tank:
a. The elastic settlement below the center of he tank at z=0 and 3 m.
b. The elastic settlement at (i) z =1.5 m, s = 0; (ii) z = 1.5 m, s = 3 m.
Assume that the Poisson’s ratio is equal to your age in years/100, E = your age in
years MN/m2, B=6 m and q= 5x your age in years kN/m2
Assignment for Adv Soil Mechanics Page 1/4
Diameter
B
q
Sand - , , E
Figure AS2
3. For the soil profile shown in Figure AS3, the water level which was initially at the ground
surface dropped down to a depth of 4.0 m below the ground. The thickness of each of the
stratums is as shown in the figure. The clay stratum is over-consolidated with a
preconsolidation pressure of 75.0 kN/m2. Determine the total primary consolidation
settlement due to the draw-down of the water table. The laboratory consolidation data for an
undisturbed clay sample are as shown in the table below.
Void ratio, e 1.25 1.2 1.15 0.9
15 55 95 470
Effective pressure (kPa)
sat=21 kN/m3
4.0 m
d=19 kN/m3
5.0 m
Figure AS3
sat=18.5 kN/m3
sat=23 kN/m3
5.0 m
d=21 kN/m3
4. The plan area of a loaded rigid foundation is shown in Figure P4-a. If this combined load is
applied on the ground surface of the sand deposit profile shown in Figure AS4, calculate the
surface elastic settlement at points A (the diametrical center of the semi-circle) and B.
Assignment for Adv Soil Mechanics Page 2/4
4m
x
Uniformly distributed vertical
load, q2=(your age in months)/2
3m
kPa A
B Uniformly distributed
y vertical load, q1= q2 /2kPa
Figure P4-a
Material Property
Sand:
= 0.25
2.5 m
=18 kN/m2
E=2.5 Mpa
Rock:
= 0.45
z
=22 kN/m2
E=35 MPa
Figure AS4
5. A route for a proposed 8-m-wide highway crosses a region with a 4-m-thick saturated, soft,
normally consolidated clay (CH) above impermeable rock. Groundwater level is 1 m below
the surface. The geotechnical data available during the preliminary design stage consist of
Atterberg limits (LL = 2x your age in years % and PL = your age in years %) and the natural
water content (w = 56%). Based on experience, the geotechnical engineer estimated the
coefficient of consolidation at (your age in years)/3 m2 per year. To limit settlement, a 4-m-
high embankment will be constructed as a surcharge from fill of unit weight 16 kN/m3 as
shown in the figure below.
Assignment for Adv Soil Mechanics Page 3/4
(a) Estimate the compression and recompression indices.
(b) Estimate the total primary consolidation settlement under the center of the embankment.
(c) Plot a time–settlement curve under the center of the embankment.
(d) How many years will it take for 50% consolidation to occur?
(e) Explain how you would speed up the consolidation.
(f) Estimate the rebound (heave) when the surcharge is removed.
(g) Sketch a settlement profile along the base of the embankment. Would the settlement be
uniform along the base? Explain your answer.
6. A covered steel with unit weight of 2xyour age in years kN/m3 tank, (your age in years)/2 m
in diameter x 10 m high and with 20-mm wall thickness, is filled with liquid (unit weight = 9
kN/m3) up to a height of 9.9 m. The tank sits on a concrete (unit weight = 25 kN/m3)
foundation, 15 m in diameter x 0.6 m thick. The foundation rests on the surface of a 5-m-thick
soft, normally consolidated clay above a thick layer of gravel. The geotechnical data of the
clay are: Cc = 0.560, Cr = 0.079, Cv = (your age in years)/3 m2/year, and w = (your age in
years)%. Groundwater level is 0.5 m below the surface. Assume the foundation is flexible.
a) Calculate the primary consolidation settlement at the center of the tank.
b) Calculate the differential consolidation settlement between the center and the edge of the
tank.
c) Calculate the time for 50% consolidation to occur.
d) The tank was loaded to half its capacity and kept there for 2 years. Calculate the
settlement. The tank was then drained; calculate the rebound.
Due date: Before Dec 31, 2014
Assignment for Adv Soil Mechanics Page 4/4
