CVEN 365
Sections 300, 301, and 303
Summer 2005
Assignment No. 6
(Textbook: Craig’s Soil Mechanics, 7th Edition, R. F. Craig)
Problem No. 1.
Work Prob. No. 7.2 in your textbook. Note that the laboratory data gives both the
loading and unloading (or rebound) test results.
Problem No. 2.
Work Prob. No. 7.4 in your textbook.
Problem No. 3.
Work Prob. No. 7.6 in your textbook.
1
Problem 04. (Consolidation and Settlement)
Two nearby building sites are occupied by a building that was completed 10 years ago
and a vacant lot where a new building is to be built. They are in a place known for its
geological irregularity. The new building is to be 15 stories high and the building will
apply pressure to the soil surface of 105 kPa. It will have 1.5 times the load of the old
building at Site No.1, where the settlement up to the present time is 0.2 m.
2
The void ratio of the normally consolidated clay at Site No.1 is 0.8 and that at Site No.2
is 0.6 and their measured permeabilities are found to vary as the square of the void ratios.
The unit weight of the sand is 17.3 kN/m3 and of the clay is 18.9 kN/m3 at both sites. The
compression index of the clay at Site No.1 is 0.41 and at Site No.2 is 0.29. Answer the
following questions:
a. What is the initial effective stress at the middle of the clay layer at each site?
b. What is the change of effective stress in the middle of the clay layer at each site
due to the building load?
c. What is the maximum settlement that will occur in Site No.1 and in Site No.2?
d. What is the percent of the total settlement that has occurred to the present time at
Site No.1?
e. What is the current dimensionless time constant, T, for the building at Site No.1.
(See Table 6.2, pg.179 in your text)
f. What is the coefficient of consolidation, cv, of the clay at Site No.1?
g. Assuming that the av of the clay is the same at both sites, how long will it take the
building at Site No.2 to settle 60 percent of its total settlement?
Problem No. 5 (Expansive Clay)
of 2
m2
A clay is made up of disk-shaped particles with an average specific surface area
. What matric suction will this soil develop at a water content of 30% and
g
temperature of 25C.? The surface tension is 73
1.
2.
3.
4.
dyne
.
cm
______________________ kPa
______________________ psi
______________________ cm
______________________ pF
3
Problem No. 6
Given:
Soil borings on this site have produced the following information on the soils
beneath the foundation:
Liquid Limit
Plastic Limit
% - #200
% - 2
Vertical Strain
=
=
=
=
=
45%
23%
75%
38%
50% of total volume strain
Find.
Plasticity Index
Soil zone No. (I through VI) where the soil plots
Soil compression index for 100% fine clay
Soil compression index for the soil beneath the foundation
The change of pF at the edge of the foundation
The volume strain in the soil in the active zone (top 6 feet) (shrinkage)
The vertical shrinkage strain of the soil at the edge of the foundation
The vertical shrinkage at the edge of the foundation
4