Question $4(15$ marks$)$

Table B$3$ below, shows the boring log at a site where a multistorey shopping centre would be

constructed. Soil classification and the standard penetration number, N$60,$ are provided in the

boring log$.$ All columns of the building are supported by square footings that must be placed at a

depth of $1\mathrm{.}5m.$ Additionally, the settlement $($elastic$)$ of each footing must be restricted to $20mm.$

Since the column loads at different location can vary, a design chart is helpful for quick estimation

of footing size required to support a given load.

a$.$ Prepare a chart by plotting the variation of maximum allowable column loads with footing

sizes, $B=1m,1\mathrm{.}5m,2m,$ and $3m.$ Use a factor of safety of $3.$

b$.$ If the gross column load from the structure is $250kN,$ how would you use this chart to select

a footing size?

c$.$ For the footing size determined in Part $($b$),$ what would be the net allowable column load

if you use Terzaghi's bearing$-$capacity equation? For the well$-$graded sand, assume that

$\frac{O}{{?}^{\text{'}}}=33$ and $=17k\frac{N}{m}3.$ Use Fs $=3$

Table B$3$ Boring Log