Civil Engineering Reference
In-Depth Information
4.
Flysh claystone:
The Flysh claystone is located at a depth of 10.5 m below ground sur-
face. This material is also not susceptible to liquefaction.
The standard penetration data shown in Fig. 9.38 are uncorrected
N
values. Assume a
hammer efficiency
E
m
of 0.6 and a boring diameter of 100 mm, and the length of drill rods
is equal to the depth of the SPT test below ground surface.
The design earthquake conditions are a peak ground acceleration
a
max
of 0.25
g,
magni-
tude of 7.5, and the distance from the site to the fault is 37 km. Using the standard pene-
tration test data, determine the factor of safety against liquefaction versus depth. Also
determine if a flow slide is likely for a sloping ground condition.
Answer:
The sand layer
will liquefy during the design earthquake and a flow slide is likely.
Strain-Softening Soil
9.12
A site consists of a slope that has a height
H
of 40 ft, and the slope inclination is
2:1 (horizontal:vertical). At a depth of 20 ft below the toe of slope, there is a dense mate-
rial (i.e.,
D
20 ft). Assume that all the soil above this depth, including the slope itself, con-
sists of uniform clay that has a total unit weight
t
of 125 lb/ft
3
. Also assume that the
unconfined compression test data shown in Fig. 9.39 are representative of the uniform clay.
Using the Taylor chart shown in Fig. 9.40, calculate the static factor of safety of the slope
using a total stress analysis. It is anticipated that during its design life, the slope will be sub-
jected to strong ground shaking which would likely reduce the clay's shear strength to its
strain-softened state. Calculate the factor of safety of the slope for this earthquake condition
using a total stress analysis. Is a massive shear failure of the slope likely during the earth-
quake?
Answer:
Static factor of safety
1.89. For earthquake conditions, factor of safety
0.66, and yes, a massive shear failure of the slope is likely during the earthquake.
