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

Question

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.

Answer 1

given that,

Average blow count $=26$

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

standard penetration value (N)$=52$

factor of safety(fs)$=3$

length of file $=8m=8000mm$

allowable load$=?$

Qu$=400NA_b+2\bar{N}A_s$

where,

$A_b-$ gross sectional area

i.e $A_b=\frac{\pi}{4}\times d^ 2$

$=\frac{\pi}{4}(300)^2$

$=70685.8mm^2$ (Q)$0.07068$

$A_s=$ lateral surface area

i.e, $A_s=\pi\times$ dia of file $\times$ length of file

$=\pi \times d\times l$

$=\pi\times300\times8000$

$=\pi\times2400000$

$=7539822.37mm^2$ (Q) $7.54m^2$

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

Qu$=14705.6+392.08$

allowabe load$=\frac{Qu}{0.5}$

$=1509.77/3$

$=502.25KN$