Optional FE Review:
Geotechnical engineering
Chris Rehmann
Geotechnical engineering
A.
B.
C.
D.
E.
F.
G.
H.
I.
Geology
Index properties and soil classifications
Phase relations (air-water-solid)
Laboratory and field tests
Effective stress (buoyancy)
Stability of retaining walls (e.g., active pressure/passive pressure)
Shear strength
Bearing capacity (cohesive and noncohesive)
Foundation types (e.g., spread footings, deep foundations, wall footings,
mats)
J. Consolidation and differential settlement
K. Seepage/flow nets
L. Slope stability (e.g., fills, embankments, cuts, dams)
M. Soil stabilization (e.g., chemical additives, geosynthetics)
N. Drainage systems
O. Erosion control
Soil classification: Example 1
A.
B.
C.
D.
Well-graded gravel
Well-graded sand
Poorly-graded sand
Silty sand
Percent finer
A soil sample has the grain size distribution shown
below. According to the Unified Soil Classification
System, it is a
100
90
80
70
60
50
40
30
20
10
0
0.001
0.01
0.1
Diameter (mm)
1
10
Soil classification: Example 2
A soil sample has a liquid limit of 79% and a plastic limit
of 46%. The plasticity chart indicates that the soil could
be
A.
B.
C.
D.
High plasticity silt
Low plasticity silt
High plasticity clay
Low plasticity clay
Phase relations: L&W #3.2a
A cubic foot of soil in its natural state weighs 113 lb;
after being dried it weighs 96 lb. The specific gravity of
the soil solids is 2.70. The water content is most nearly
A.
B.
C.
D.
18%
43%
63%
76%
L&W = Lambe and Whitman (1969), Soil Mechanics
Phase relations: L&W #3.2b
A cubic foot of soil in its natural state weighs 113 lb;
after being dried it weighs 96 lb. The specific gravity of
the soil solids is 2.70. The degree of saturation is most
nearly
A.
B.
C.
D.
18%
43%
63%
76%
L&W = Lambe and Whitman (1969), Soil Mechanics
Phase relations: L&W #3.2c
A cubic foot of soil in its natural state weighs 113 lb;
after being dried it weighs 96 lb. The specific gravity of
the soil solids is 2.70. The void ratio is most nearly
A.
B.
C.
D.
18%
43%
63%
76%
L&W = Lambe and Whitman (1969), Soil Mechanics
Phase relations: L&W #3.2d
A cubic foot of soil in its natural state weighs 113 lb;
after being dried it weighs 96 lb. The specific gravity of
the soil solids is 2.70. The porosity is most nearly
A.
B.
C.
D.
18%
43%
63%
76%
L&W = Lambe and Whitman (1969), Soil Mechanics
Phase relations: Example 2
A soil sample has a specific gravity of soil solids of 2.65,
a water content of 15%, and porosity of 31%. The
degree of saturation is most nearly
A.
B.
C.
D.
15%
25%
45%
88%
Phase relations: L&W #3.1
A soil sample has a void ratio of 0.76, specific gravity of
2.74, and a degree of saturation of 85%. The total unit
weight of the soil is most nearly
A.
B.
C.
D.
62.4 lb/ft3
120 lb/ft3
124 lb/ft3
171 lb/ft3
Laboratory tests: L&W #8.7a
The major principal stress on the element below is
most nearly
A.
B.
C.
D.
16.0 psi
21.5 psi
53.5 psi
75.0 psi
25 psi
30º
10
10
50 psi
Laboratory tests: L&W #8.7b
The minor principal stress on the element below is
most nearly
A.
B.
C.
D.
16.0 psi
21.5 psi
25.0 psi
53.5 psi
25 psi
30º
10
10
50 psi
Laboratory tests: L&W #8.7c
The maximum shear stress on the element below is
most nearly
A.
B.
C.
D.
10.0 psi
16.0 psi
21.5 psi
53.5 psi
25 psi
30º
10
10
50 psi
Laboratory tests: 1.30 #2.7b
A triaxial sample of loose sand with K0 = 0.5 is first
consolidated along the K0 line until s1 = 4 kg/cm2 and
then failed by decreasing s3 and keeping s1 constant. If
the sand has a friction angle of 30º, then the minor
principal stress at failure will be most nearly
A.
B.
C.
D.
1.3 kg/cm2
2.0 kg/cm2
2.7 kg/cm2
4.0 kg/cm2
Laboratory tests: Example 3
A sample of sand is placed in a constant-head permeameter. If the flow through the permeameter is 2 x 10-7
m3/s, the hydraulic conductivity of the sand is most
nearly
A.
B.
C.
D.
1.8 x 10-5 m/s
2.7 x 10-5 m/s
6.7 x 10-5 m/s
2.8 x 10-1 m/s
Laboratory tests: Example 4
A falling head permeameter test is run on a soil sample of length
8 cm and cross-sectional area 70 cm2. The tube has a crosssectional 3.5 cm2. If it takes 24 seconds for the water level to fall
from point A to point B, then the hydraulic conductivity is most
nearly
A.
B.
C.
D.
2.6 x 10-3 cm/s
2.2 x 10-2 cm/s
2.7 x 10-2 cm/s
8.8 cm/s
Effective stress: Example 5
Soil with a total unit weight of 131 lb/ft3 is saturated to the
surface. The effective vertical stress 10 ft below the surface is
most nearly
A.
B.
C.
D.
13.1 lb/ft2
195.4 lb/ft2
686 lb/ft2
1310 lb/ft2
Retaining walls: L&W ex. 13.2
A 20-foot high wall retains sand with a total unit weight of 110
lb/ft3 and a friction angle of 30°. In the active condition, the
magnitude of the horizontal thrust (per unit length of wall) on
the wall is most nearly
A.
B.
C.
D.
7333 lb/ft
14,666 lb/ft
22,000 lb/ft
25,403 lb/ft
Bearing capacity: L&W ex. 14.2
A footing rests on dry sand with total unit weight of 120 lb/ft3
and friction angle of 30°. The ultimate bearing capacity
(expressed as force per unit length of wall) is most nearly
A.
B.
C.
D.
4157 lb/ft
18,000 lb/ft
41,570 lb/ft
54,000 lb/ft
10 ft
4 ft
Flow nets: U.W.-Platteville example
If the hydraulic conductivity is 0.04 ft/s, the flow per
unit width beneath the barrier (in ft2/s) is most nearly
A. 0.45
B. 0.53
C. 1.02
D. 1.49