Test 29 - Pile Groups and Pile Load Tests

Question 1 ప్రశ్న 1

A heavily loaded foundation is supported by a closely spaced group of piles connected through a common pile cap. Which statement best explains why the group's geotechnical capacity and settlement should not automatically be obtained by multiplying the performance of one isolated pile by the number of piles?

A The pile cap eliminates all soil-pile interaction and makes settlement independent of pile spacing. B Stress and deformation zones around neighbouring piles can interact, affecting group resistance and settlement. C Every pile in a group necessarily loses its entire toe resistance. D A pile group transfers its entire load directly to the ground surface through the pile cap.

Question 2 ప్రశ్న 2

For a group of n identical piles, each having ultimate axial compression resistance Qu, the ultimate resistance of the group is Qug. Which expression correctly defines the conventional pile-group efficiency eta?

A eta = nQu/Qug. B eta = Qug + nQu. C eta = Qug/Qu, independent of the number of piles. D eta = Qug/(nQu).

Question 3 ప్రశ్న 3

Eight identical piles each have an ultimate axial compression resistance of 400 kN when considered individually. The assessed ultimate axial compression resistance of their group is 2560 kN. What is the group efficiency?

A 0.80. B 0.64. C 1.00. D 1.25.

Question 4 ప్రశ్న 4

A square pile group contains nine identical piles. The ultimate compression resistance of each isolated pile is 500 kN, and the specified group efficiency is 0.75. Assuming the efficiency method governs and no separate block-failure limit is imposed in this exercise, what is the ultimate group resistance?

A 3750 kN. B 4500 kN. C 3375 kN. D 3000 kN.

Question 5 ప్రశ్న 5

A pile group contains six identical piles with individual ultimate compression resistance of 800 kN each. The adopted efficiency is 0.80, and a factor of safety of 2.5 is applied to the resulting group ultimate resistance. Assume block failure and settlement do not govern. What is the allowable axial compression resistance of the group?

A 1920 kN. B 1536 kN. C 3840 kN. D 1200 kN.

Question 6 ప్రశ్న 6

Which statement about pile-group efficiency in different ground conditions is technically most appropriate?

A Group efficiency must always equal 1.0 regardless of pile installation and spacing. B Group efficiency can never exceed 1.0 in any soil. C Group efficiency depends only on the structural strength of the pile cap. D Group efficiency may be below unity where group interaction reduces resistance, while installation-induced improvement in some granular soils may produce different behaviour; the adopted value must be justified.

Question 7 ప్రశ్న 7

A closely spaced group of piles is embedded in soft cohesive soil. Which statement correctly describes an idealized block-failure mechanism?

A The piles and intervening soil may move approximately as a single block, with shear resistance along its external perimeter and bearing resistance beneath its base. B Every pile must fail independently through its own isolated cylindrical shaft surface. C Block resistance depends only on the compressive strength of the concrete pile cap. D The failure mechanism involves tension failure of reinforcement without any soil shear or base resistance.

Question 8 ప్రశ్న 8

Six circular piles are arranged in three columns and two rows at equal centre-to-centre spacing of 1.20 m in both directions. Each pile has diameter 0.40 m. Using the outer-to-outer dimensions of the pile arrangement for a rectangular block-failure model, what are the block length and width?

A 3.60 m and 2.40 m. B 2.40 m and 1.20 m. C 2.80 m and 1.60 m. D 3.20 m and 2.00 m.

Question 9 ప్రశ్న 9

A two-by-two pile group is idealized as a rectangular soil-pile block measuring 2 m by 2 m in plan and extending 10 m through uniform clay. Use the explicitly specified ultimate block-resistance equation Qblock = P L cu,side + A Nc cu,base, where P is block perimeter, A is block base area, cu,side = 25 kPa, cu,base = 30 kPa and Nc = 9. Neglect other resistance contributions. What is the ultimate block resistance?

A 2000 kN. B 3080 kN. C 3600 kN. D 1080 kN.

Question 10 ప్రశ్న 10

A nine-pile group has an individual-pile resistance sum of 4500 kN and an assessed efficiency of 0.85. A separate block-failure analysis gives an ultimate resistance of 3500 kN. If the design exercise adopts the smaller ultimate resistance and applies factor of safety 2.5, what is the allowable group compression resistance?

A 1530 kN. B 1800 kN. C 3825 kN. D 1400 kN.

Question 11 ప్రశ్న 11

Circular piles have diameter 0.45 m and are placed at centre-to-centre spacing of 1.35 m. What is the spacing-to-diameter ratio s/d?

A 3.0. B 2.5. C 3.5. D 4.0.

Question 12 ప్రశ్న 12

A designer proposes increasing the spacing between piles in a closely spaced group in soft clay. Which assessment of this change is most technically appropriate?

A Increasing spacing always doubles pile-group capacity regardless of the soil profile. B Increasing spacing has no effect on pile-cap size or construction. C Greater spacing can reduce some interaction effects, but the resulting cap dimensions, structural forces, cost and settlement must also be evaluated. D Increasing spacing eliminates all risk of negative skin friction.

Question 13 ప్రశ్న 13

An isolated pile and a closely spaced pile group are subjected to the same average working load per pile in a deposit containing a deep compressible clay layer. Why might settlement of the pile group be considerably greater?

A The pile cap prevents stress transmission to the underlying clay. B The group influences a larger volume of soil, and overlapping stress zones can produce significant compression of deeper layers. C Every individual pile in a group necessarily becomes shorter under load. D Settlement of a pile group depends exclusively on pile concrete strength.

Question 14 ప్రశ్న 14

A pile group transfers loading to a compressible soil layer of thickness 3 m. The estimated average increase in effective vertical stress within the layer is 40 kPa, and the representative coefficient of volume compressibility is mv = 5.0 x 10^-4 kPa^-1. Using the simplified one-dimensional settlement equation S = mv DeltaSigma' H, what is the eventual settlement contribution of the layer?

A 20 mm. B 40 mm. C 80 mm. D 60 mm.

Question 15 ప్రశ్న 15

A pile group satisfies an assessed allowable axial compression-resistance limit, but its predicted differential settlement exceeds the specified structural serviceability tolerance. What is the correct engineering decision?

A The design must be revised or otherwise justified because satisfying axial resistance alone does not establish acceptable settlement performance. B The foundation is automatically satisfactory because the piles have sufficient ultimate strength. C The settlement calculation must be ignored whenever a pile cap is provided. D The allowable differential settlement is always equal to the pile diameter.

Question 16 ప్రశ్న 16

Which statement correctly describes the principal structural function of a reinforced-concrete pile cap supporting several columns or a heavily loaded structural member?

A It provides geotechnical shaft friction along the full embedded length of each pile. B It prevents the piles from receiving any bending or shear forces. C It transfers the supported structural actions to the piles and may redistribute forces according to pile layout, cap stiffness and support conditions. D It always carries its entire vertical load through direct bearing on the soil beneath the cap.

Question 17 ప్రశ్న 17

A rigid pile cap carries a centrally applied vertical service load of 2400 kN. It connects six identical vertical piles having equal axial stiffness and symmetrically arranged positions. Neglect pile-cap self-weight and soil contact beneath the cap. What is the axial reaction in each pile under the stated equal-load-sharing model?

A 300 kN. B 400 kN. C 600 kN. D 800 kN.

Question 18 ప్రశ్న 18

Four identical vertical piles support a rigid cap at plan coordinates x = +1 m and x = -1 m, with two piles at each x-coordinate. A downward load of 2400 kN acts at the group centroid together with a moment of 400 kN m that INCREASES compression in piles at positive x. For this exercise, use R_i = P/4 + M x_i/(sum x_j²), with sum x_j² = 4 m². What is the compressive reaction in EACH pile at x = +1 m?

A 500 kN. B 600 kN. C 800 kN. D 700 kN.

Question 19 ప్రశ్న 19

A pile group passes through recently placed fill and consolidating clay that move downward relative to the pile shafts. Which interpretation of negative skin friction is correct?

A Downward relative soil movement may mobilize negative skin friction and dragload, increasing pile compression demands in affected portions of the shafts. B Negative skin friction always acts upward and increases usable positive shaft resistance. C Negative skin friction is another name for end-bearing resistance at the pile tip. D Negative skin friction cannot develop in a pile group connected by a rigid cap.

Question 20 ప్రశ్న 20

A rigid pile cap transfers a total structural downward load of 2000 kN to four identical piles. In a simplified axial-force assessment, each pile develops an additional downward dragload of 100 kN above the section being checked. Neglect other forces and assume equal structural load distribution. What is the SUM of axial compression forces in the four piles at that section?

A 1600 kN. B 2000 kN. C 2400 kN. D 2800 kN.

Question 21 ప్రశ్న 21

Under IS 2911 (Part 4):2013, which distinction between initial and routine pile-load tests is correct?

A An initial load test is restricted to structural concrete testing, whereas a routine test measures only groundwater levels. B An initial test is used to assess pile capacity and establish relevant performance criteria, while a routine test on a working pile checks its behaviour under the assigned load requirements. C A routine test must always be performed before the first pile is installed, while an initial test is performed only after the structure is completed. D Initial and routine tests are identical in purpose, selection and interpretation under every condition.

Question 22 ప్రశ్న 22

A pile-supported pumping station must resist vertical compression, horizontal forces and occasional uplift. Which statement correctly identifies the relevant load-testing categories covered by IS 2911 (Part 4):2013?

A Only vertical compression testing is relevant because all pile forces are treated as downward. B A concrete cube compression test alone establishes the lateral and uplift capacities of the completed pile. C A low-strain integrity test is a direct substitute for every pile-load test. D Vertical compression, lateral and pull-out tests address different modes of loading and should be selected according to the project's requirements.

Question 23 ప్రశ్న 23

A working pile of diameter 500 mm has a specified working axial compression load of 850 kN. For the ROUTINE vertical compression test covered by IS 2911 (Part 4):2013, take the required test load as at least 1.5 times the working load. What is the minimum required test load? If the recorded settlement at this load is 11 mm, it is below the stated 12 mm settlement criterion for piles of diameter up to 600 mm.

A 1275 kN; the recorded 11 mm settlement satisfies the stated displacement criterion at this load. B 850 kN; the recorded settlement is irrelevant. C 1700 kN; the recorded settlement necessarily indicates failure. D 2125 kN; the recorded settlement must be zero.

Question 24 ప్రశ్న 24

A low-strain pile-integrity test indicates no clear major discontinuity in a completed bored pile, but its geotechnical axial load capacity has not been verified. Which engineering conclusion is appropriate?

A The pile has automatically passed every axial compression and uplift capacity requirement. B Integrity testing establishes the exact ultimate toe and shaft resistances without any additional information. C An integrity result concerns indications of structural continuity and does not by itself establish geotechnical axial capacity or working-load settlement. D The pile can be assigned an unlimited working load because no major defect was detected.

Question 25 ప్రశ్న 25

An initial axial pile-load investigation is required to understand how positive shaft resistance and toe resistance contribute to the total response. Which statement best describes the relevant testing approaches under IS 2911 (Part 4):2013?

A A routine low-strain integrity test directly separates shaft and toe capacity without applying load. B A cyclic load-test method on a suitable initial test pile can help estimate shaft and toe contributions, while maintained-load testing provides load-settlement information relevant to working-load assessment. C A lateral pile-load test automatically determines the independent compression resistance at the pile toe. D A concrete slump test determines the precise proportion of geotechnical load carried by pile shaft friction.

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