Civil Engineering Reference
In-Depth Information
FIGURE 11.22
Bearing capacity factors
N
,
N
q
and
N
c
which do not include allowance
for punching shear failure. [Note: for punching shear of loose sands or soft clays, the value of
tan
1
(0.67 tan
to be used in this figure
) and the cohesion used in the bearing capacity
equation
0.67
c
]. (
Reproduced from NAVFAC DM-7.2, 1982.
)
Q
all
acceptable for seismic loading conditions?
Answer:
Q
all
36 kips. A one-third
increase should not be recommended for seismic loading conditions because the soil has
a very high sensitivity
S
t
making it susceptible to strain softening.
11.7
Assume a pile having a diameter of 1 ft and a length of 30 ft will be driven into
a cohesive soil deposit that has the shear strength properties shown in Fig. 9.39. Determine
the allowable pile capacity using the peak undrained shear strength shown in Fig. 9.39
and a factor of safety of 3. It is anticipated that the site will be subjected to significant
earthquake shaking that will weaken the cohesive soil. Using the fully softened undrained
shear strength, calculate the allowable pile capacity for the seismic loading conditions
using a factor of safety of 3.
Answer:
Static
Q
all
27 kips, seismic
Q
all
17 kips.
