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) $179 \mathrm{~mm}$

Question ID - 155923 :- 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) $179 \mathrm{~mm}$

3537

Answer Key : (A, B, C, D) -

$58 \mathrm{~mm}$
$111 \mathrm{~mm}$
$126 \mathrm{~mm}$
$179 \mathrm{~mm}$

Next Question :

Air at a stagnation temperature of $300 K$ (ratio of specific heats, $\gamma=1.4$ and specific gas constant $\mathrm{R}$ $=287 \mathrm{~J} / \mathrm{kgK}$ ) enters the impeller of a centrifugal compressor in axial direction. The stagnation pressure ratio between the diffuser outlet and impeller inlet is $4.0 .$ The impeller blade radius is 0.3 $\mathrm{m}$ and it is rotating at $15000 \mathrm{rev} / \mathrm{min} .$ If the slip factor $\sigma_{s}$ (Ratio of tangential component of air velocity at the blade tip to the blade tip speed) is $0.88,$ the overall efficiency (total-to-total) of the compressor (in \%) is__________