SOILS AND FOUNDATIONS A 36 inch diameter drilled shaft is placed 34-feet deep in
ID: 1714312 • Letter: S
Question
SOILS AND FOUNDATIONS
A 36 inch diameter drilled shaft is placed 34-feet deep in clay. The clay from the ground down to 18 feet deep has cu = 1,200 #/ft2 and = 102 #/ft3. The lower layer to the bottom has cu = 1,800 #/ft2 and = 112#/ft3. The soil’s angle of internal friction is 30°. For the skin friction, use *= 0.4. The concrete used has a compressive strength of 4,400 psi at 28 day testing. If the county Factor of Safety to be used is 2, what is the working load for this drilled shaft?
38 kips
90 kips
142 kips
194 kips
252 kips
a.38 kips
b.90 kips
c.142 kips
d.194 kips
e.252 kips
Explanation / Answer
for 30o internal friction Nc= 24
teap bearing=Nc*cu*A= 24*1.8*3.14*1.5^2= 305 kips
Shaft bearing = D(Cu1L1+Cu2L2) = 0.4*3.14*3(1.2*18+1.8*16)=190 kips
total= 305+190=495 kips
allowable load= total/FOS= 495/2=247kips
nearest answer= 252 kips
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