Q21GATE 2007MCQ

What is the ultimate capacity in kN of the pile group shown in the figure assuming the group to fail as a single block ?

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📖 Explanation

The ultimate load capacity of the pile group by block failure,

\begin{aligned} Q_{u g}=& c_{u} N_{c} A_{b}+P_{b} L c_{u} \\ =& 40 \times 9 \times (1.2+0.4)^{2}+4 \\ & \times (1.2+0.4) \times 10 \times 40 \\ =& 3481.6 \mathrm{kN} \end{aligned}

Q22GATE 2006MCQ

For the soil profile shown in Figure below, the minimum number of precast concrete piles of 300 mm diameter required of safely carry the load for a given factor of safety of 2.5 (assuming 100% efficiency for the pile group) is equal to

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📖 Explanation

The ultimate load capacity of piles $=2.5 \times 5000=12,500 \mathrm{kN}$ The load capacity of single pile

\begin{aligned} =& c_{u} N_{c} A_{b}+\alpha \bar{c}_{u} A_{s} \\ =& 150 \times 9 \times \frac{\pi}{4} \times (0.3)^{2}+0.57 \times 100 \\ & \times 10 \times 0.3 \pi \\ =& 632.64 \mathrm{kN} \end{aligned}

$\therefore \quad$ Number of piles $=\frac{12500}{632.64}=19.75 \approx 20$

Q23GATE 2005MCQ

Negative skin friction in a soil is considered when the pile is constructed through

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Q24GATE 2004MCQ

A group of 16 piles of 10 m length and 0.5 m diameter is installed in a 10 m thick stiff clay layer underlain by rock. The pile-soil adhesion factor is 0.4; average shear strength of soil on the sides is 100 kPa; undrained shear strength of the soil at the base is also 100 kPa. Assuming 100% efficiency, the group side resistance is

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📖 Explanation

\begin{aligned} \eta &=\frac{Q_{u g}}{n Q_{u}} \;\;\;\;\;[\because \eta=100 \%] \\ Q_{u g} &=n Q_{u}=n \times \alpha c_{u} P L_{c} \\ &=16 \times 0.4 \times 100 \times \pi \times 0.5 \times 10 \\ &=10053.1 \mathrm{kN} \end{aligned}

Q25GATE 2003MCQ

For the $\left ( 3\times 3 \right )$ pile group shown in the figure, the settlement of pile group, in a normally consolidated clay stratum having properties as shown in the figure, will be

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📖 Explanation

Assume equivalent raft at a distance of $\frac{L}{3}=\frac{5}{3}$ from the bottom of the pipe and load dispersion at $2 \mathrm{H}: 1 \mathrm{V}$ Compressible layer thickness $=7-5+\frac{5}{3}=3.667 \mathrm{m}$ Average stress at the center of layer,

\begin{aligned} \bar{\sigma}_{0}=& \gamma_{\text {sub }} \times 5.17 \\ &=(20-10) \times 5.17 \\ &=51.7 \mathrm{kN} / \mathrm{m}^{2} \end{aligned}

Increased width of equivalent raft at depth $=1.2+\frac{\left(\frac{5}{3}+2\right)}{2}=3.03 \mathrm{m}$ Pressure increase due to load on pile,

\begin{aligned} \Delta \sigma &=\frac{500}{3.03^{2}}=54.34 \mathrm{kN} / \mathrm{m}^{2} \\ \Delta H &=\frac{C_{c} H_{0}}{1+e_{0}} \log \left(\frac{\bar{\sigma}_{0}+\Delta \sigma}{\bar{\sigma}_{0}}\right) \\ &=\frac{0.027 \times \frac{11}{3}}{1+1.05} \log \left(\frac{51.7+54.34}{51.7}\right) \\ &=15.07 \mathrm{mm} \end{aligned}

Q26GATE 2003MCQ

Match the items of List-I with List-II and select the correct answer.

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Q27GATE 2001MCQ

Identify the two TRUE statements from the following four statements. I. Negative skin friction is higher on floating piles than on end bearing piles. II. All other things being the same in footings on sand, the footing with smaller width will have lower settlement at the same net pressure. III. The void ratio of soils is always less than 1.0. IV. For determining the depth of embedment of anchored sheet piles, net moment at the anchor elevation is set to zero.

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