Deep Foundation Practice Questions

A $4 \times 4$ group pile, with each pile $20\ \text{m}$ long and $500\ \text{mm}$ in diameter, is installed in a square pattern in a clayey soil, as shown in the figure. The average unconfined compressive strength of the soil is $100\ \text{kN/m}^2$ , and the adhesion factor is $0.8$ . Neglect the bearing at the tip of the piles. For a group efficiency factor of $1.0$ , the centre to centre spacing(s) of the piles (in m) would be _______ (round off to two decimal places).

A reinforced concrete pile of $10 \mathrm{~m}$ length and $0.7 \mathrm{~m}$ diameter is embedded in a saturated pure clay with unit cohesion of $50 \mathrm{kPa}$ . If the adhesion factor is 0.5 , the net ultimate uplift pullout capacity (in kN) of the pile is _____. (rounded off to the nearest integer).

A circular pile of diameter $0.6 \mathrm{~m}$ and length $8 \mathrm{~m}$ was constructed in a cohesive soil stratum having the following properties: bulk unit weight $=$ $19 \mathrm{kN} / \mathrm{m}^{3}$ ; angle of internal friction $=0^{\circ}$ and cohesion $=25 \mathrm{kPa}$ . The allowable load the pile can carry with a factor of safety of 3 is ____ $\mathrm{kN}$ (round off to one decimal place). [Adopt: Adhesion factor, $\alpha=1.0$ and Bearing capacity factor, $\left.\mathrm{N}_{\mathrm{C}}=9.0\right]$

A group of 9 friction piles are arranged in a square grid maintaining equal spacing in all directions. Each pile is of diameter $300 \mathrm{~mm}$ and length $7 \mathrm{~m}$ . Assume that the soil is cohesionless with effective friction angle $\phi^{\prime}=32^{\circ}$ . What is the center-to-center spacing of the piles (in $\mathrm{m}$ ) for the pile group efficiency of $60 \%$ ?

A group of total 16 piles are arranged in a square grid format. The center-to- center spacing (s) between adjacent piles is 3 m. The diameter (d) and length of embedment of each pile are 1 m and 20 m, respectively. The design capacity of each pile is 1000 kN in the vertical downward direction. The pile group efficiency ( $\eta _g$ ) is given by $\eta _g=1-\frac{\theta }{90}\left[ \frac{(n-1)m+(m-1)n}{mn} \right]$ where m and n are number of rows and columns in the plan grid of pile arrangement, and $\theta =\tan ^{-1}\left ( \frac{d}{s} \right )$ . The design value of the pile group capacity (in kN) in the vertical downward direction is __________________. (round off to the nearest integer)

A reinforced concrete circular pile of 12 m length and 0.6 m diameter is embedded in stiff clay which has an undrained unit cohesion of 110 $kN/m^2$ . The adhesion factor is 0.5. The Net Ultimate Pullout (uplift) Load for the pile (in kN, round off to 1 decimal place) is _______

A timber pile of length 8 m and diameter 0.2 m is driven with a 20 kN drop hammer, falling freely from a height of 1.5 m. The total penetration of the pile in the last 5 blows is 40 mm. Use the Engineering News Record expression. Assumea factor of safety of 6 and empirical factor (allowing reduction in the theoretical set, due to energy losses) of 2.5cm. The safe load carrying capacity of the pile (in kN, round off to 2 decimal places) is _______

A group of nine piles in a 3 x 3 square pattern is embedded in a soil strata comprising dense sand underlying recently filled clay layer, as shown in the figure. The perimeter of an individual pile is 126 cm. The size of pile group is 240 cm x 240 cm. The recently filled clay has undrained shear strength of 15 kPa and unit weight of $16 kN/m^{3}$ The negative frictional load (in kN, up to two decimal places) acting on the pile group is______

A 0.5 m x 0.5 m square concrete pile is to be driven in a homogeneous clayey soil having undrained shear strength, $c_{u}$ = 50 kPa and unit weight, $\gamma = 18.0 kN/m^{3}$ . The design capacity of the pile is 500 kN. The adhesion factor $\alpha$ is given as 0.75. The length of the pile required for the above design load with a factor of safety of 2.0 is

Two identical concrete piles having the plan dimensions 50 cm x 50 cm are driven into a homogeneous sandy layer as shown in the figures. Consider the bearing capacity factor $N_{q}$ , for $\phi =30^{\circ}$ as 24 If $Q_{P1}$ and $Q_{P2}$ represent the ultimate point bearing resistance of the piles under dry and submerged conditions, respectively, which one of the following statements is correct?

It is proposed to drive H-piles up to a depth of 7 m at a construction site. The average surfacearea of the H-pile is 3 $m^{2}$ per meter length. The soil at the site is homogeneous sand, havingan effective friction angle of 32 $^{\circ}$ . The ground water table (GWT) is at a depth of 2 m below the ground surface. The unit weights of the soil above and below the GWT are 16 $kN/m^{3}$ and 19 $kN/m^{3}$ respectively. Assume the earth pressure coefficient, K= 1.0, and the angle of wall friction $\delta =23^{\circ}$ , The total axial frictional resistance (in kN, up to one decimal place) mobilized on the pile against the driving is _____

A pile of diameter 0.4 m is fully embedded in a clay stratum having 5 layers, each 5 m thick as shown in the figure below. Assume a constant unit weight of soil as 18 kN/ $m^{3}$ for all the layers. Using $\lambda$ -method ( $\lambda$ =0.15 for 25 m embedment length) and neglecting the end bearing component, the ultimate pile capacity (in kN) is ________.

The action of negative skin friction on the pile is to

A single vertical friction pile of diameter 500 mm and length 20 m is subjected to a vertical compressive load. The pile is embedded in a homogeneous sandy stratum where: angle of internal friction is $\phi=30^{\circ}$ , dry unit weight $(\gamma _{d})=20 kN/m^{3}$ and angle of wall friction is $\delta =2\varphi /3$ . Considering the coefficient of lateral earth pressure (K)=2.7 and the bearing capacity factor ( $N_q$ )=25, the ultimate bearing capacity of the pile (in kN) is________

Four columns of a building are to be located within a plot size of 10 m x 10 m. The expected load on each column is 4000 kN. Allowable bearing capacity of the soil deposit is 100 kN/ $m^{2}$ . The type of foundation best suited is

A singly under-reamed, 8 m long, RCC pile (shown in the figure) weighing 20 kN with 350 mm shaft diameter and 750 mm under-ream diameter is installed within stiff, saturated silty clay (undrained shear strength is 50 kPa, adhesion factor is 0.3, and the applicable bearing capacity factor is 9) to counteract the impact of soil swelling on a structure constructed above. Neglecting suction and the contribution of the under-ream to the adhesive shaft capacity, what would be the estimated ultimate tensile capacity (rounded off to the nearest integer value of kN) of the pile?

The ultimate load capacity of a 10 m long concrete pile of square cross section 500mm x 500 mm driven into a homogeneous clay layer having undrained cohesion value of 40 kPa is 700 kN. If the cross section of the pile is reduced to 250mm x 2500 mm and the length of the pile is increased to 20 m, the ultimate load capacity will be

A precast concrete pile is driven with a 50 kN hammer railing through a height of 1.0 m with an efficiency of 0.6. The set value observed is 4 mm per below and the combined temporary compression of the pile, cushion and the ground is 6 mm. As per Modified Hiley Formula, the ultimate resistance of the pile is

A pile of 0.50 m diameter and of length 10 m is embedded in a deposit of clay. The undrained strength parameters of the clay are cohesion = 60 kN/ $m^{2}$ and the angle of internal friction= 0. The skin friction capacity (kN) of the pile for an adhesion factor of 0.6, is