Answer to Question #196907 in Civil and Environmental Engineering for Kelly

Question #196907

A 8m thick layer of medium sand overlies a deep deposit of dense gravel. A series of standard penetration tests carried out through the depth of the sand has established that the average blow count is 26. Further tests show that the gravel has a standard penetration value of N = 52 in the region of the interface with the sand. A precast pile of diameter 300mm is to be driven down through the sand and to penetrate sufficiently into the gravel to give good end bearing. Adopting a safety factor of 3.0, determine the allowable load that the pile will be able to carry.



1
Expert's answer
2021-05-24T17:25:01-0400

given that,

Average blow count =26=26

diameter of forecast file =300mm=0.3m=300mm=0.3m

standard penetration value (N)=52=52

factor of safety(fs)=3=3

length of file =8m=8000mm=8m=8000mm

allowable load=?=?

Qu=400NAb+2NˉAs=400NA_b+2\bar{N}A_s

where,

AbA_b- gross sectional area

i.e Ab=π4×d2A_b=\frac{\pi}{4}\times d^ 2

=π4(300)2=\frac{\pi}{4}(300)^2

=70685.8mm2=70685.8mm^2 (Q)0.070680.07068

As=A_s= lateral surface area

i.e, As=π×A_s=\pi\times dia of file ×\times length of file

=π×d×l=\pi \times d\times l

=π×300×8000=\pi\times300\times8000

=π×2400000=\pi\times2400000

=7539822.37mm2=7539822.37mm^2 (Q) 7.54m27.54m^2

Qu=(400)(52)(0.0707)+(2)(26)(7.54)=(400)(52)(0.0707)+(2)(26)(7.54)

Qu=14705.6+392.08=14705.6+392.08

allowabe load=Qu0.5=\frac{Qu}{0.5}

=1509.77/3=1509.77/3

=502.25KN=502.25KN


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