A multistory building with a basement is to be constructed. The top $4 \mathrm{~m}$ consists of loose silt, below which dense sand layer is present up to a great depth. Ground water table is at the surface. The foundation consists of the basement slab of $6 \mathrm{~m}$ width which will rest on the top of dense sand as shown in the figure. For dense sand, saturated unit weight $=20 \mathrm{kN} / \mathrm{m}^{3},$ and bearing capacity factors $\mathrm{N}_{\mathrm{q}}=40$ and $\mathrm{N}_{\gamma}=45 .$ For loose silt, saturated unit weight $=18 \mathrm{kN} / \mathrm{m}^{3}, \mathrm{~N}_{\mathrm{q}}=15$ and $\mathrm{N}_{\gamma}=20 .$ Effective cohesion $\mathrm{c}^{\prime}$ is zero for both soils. Unit weight of water is $10 \mathrm{kN} / \mathrm{m}^{3}$. Neglect shape factor and depth factor. Average elastic modulus $E$ and Poisson's ratio $\mu$ of dense sand is $60 \times 10^{3} \mathrm{kN} / \mathrm{m}^{2}$ and 0.3 respectively.

The foundation slab is subjected to vertical downward stresses equal to net safe bearing capacity derived in the above question. Using influence factor $\mathrm{I}_{\mathrm{f}}=2.0$, and neglecting embedment depth and rigidity corrections, the immediate settlement of the dense sand layer will be:

(A) $58 \mathrm{~mm}$

(B) $111 \mathrm{~mm}$

(C) $126 \mathrm{~mm}$

(D) $179 \mathrm{~mm}$

A multistory building with a basement is to be constructed. The top $4 \mathrm{~m}$ consists of loose silt, below which dense sand layer is present up to a great depth. Ground water table is at the surface. The foundation consists of the basement slab of $6 \mathrm{~m}$ width which will rest on the top of dense sand as shown in the figure. For dense sand, saturated unit weight $=20 \mathrm{kN} / \mathrm{m}^{3},$ and bearing capacity factors $\mathrm{N}_{\mathrm{q}}=40$ and $\mathrm{N}_{\gamma}=45 .$ For loose silt, saturated unit weight $=18 \mathrm{kN} / \mathrm{m}^{3}, \mathrm{~N}_{\mathrm{q}}=15$ and $\mathrm{N}_{\gamma}=20 .$ Effective cohesion $\mathrm{c}^{\prime}$ is zero for both soils. Unit weight of water is $10 \mathrm{kN} / \mathrm{m}^{3}$. Neglect shape factor and depth factor. Average elastic modulus $E$ and Poisson's ratio $\mu$ of dense sand is $60 \times 10^{3} \mathrm{kN} / \mathrm{m}^{2}$ and 0.3 respectively.

The foundation slab is subjected to vertical downward stresses equal to net safe bearing capacity derived in the above question. Using influence factor $\mathrm{I}_{\mathrm{f}}=2.0$, and neglecting embedment depth and rigidity corrections, the immediate settlement of the dense sand layer will be:

(A) $58 \mathrm{~mm}$

(B) $111 \mathrm{~mm}$

(C) $126 \mathrm{~mm}$

(D) $179 \mathrm{~mm}$

1 Answer

127 votes

$58 \mathrm{~mm}$

$111 \mathrm{~mm}$

$126 \mathrm{~mm}$

$179 \mathrm{~mm}$

127 votes

127