Test 25 - Design and Stability of Gravity Dams

Question 1 ప్రశ్న 1

Which statement best summarizes the principal static-stability requirements of a gravity dam?

A The dam need only be heavy enough to prevent flotation; sliding and foundation stresses are secondary B The dam should be safe against sliding, should not develop unacceptable tensile or compressive stresses, and should maintain overall rotational equilibrium under the governing load combinations C Only the upstream face stress is relevant because the foundation does not participate in stability D A gravity dam is considered safe whenever its crest width exceeds one-third of its height

Question 2 ప్రశ్న 2

For a rectangular base of width B subjected to a resultant vertical force with linear base-pressure distribution, what condition keeps the entire base in compression?

A The resultant must lie outside the base B The eccentricity must be greater than B/2 C The resultant must lie within the middle third, so that |e| does not exceed B/6 D The resultant must pass exactly through the downstream toe

Question 3 ప్రశ్న 3

A 24 m wide gravity-dam base has its resultant intersecting the base 15 m from the upstream heel. What is the eccentricity of the resultant relative to the base centre?

A 1 m toward the heel B 3 m toward the downstream toe C 6 m toward the downstream toe D 9 m toward the heel

Question 4 ప్రశ్న 4

For a base width B carrying a net vertical force V, if the resultant has eccentricity e toward the downstream toe and the entire base remains in compression, which expressions give the toe and heel pressures under the usual linear-distribution assumption?

A p_toe = V/B(1 + 6e/B) and p_heel = V/B(1 - 6e/B) B p_toe = V/B(1 - 6e/B) and p_heel = V/B(1 + 6e/B) C p_toe = p_heel = 6Ve/B² for every eccentricity D p_toe = V/e and p_heel = V/(B-e)

Question 5 ప్రశ్న 5

A 20 m wide gravity-dam base carries a net vertical force of 12,000 kN/m. The resultant is 2 m toward the downstream toe from the base centre. Assuming full contact and linear pressure distribution, what are the toe and heel pressures?

A 720 kPa at the toe and 480 kPa at the heel B 960 kPa at the toe and 240 kPa at the heel C 1200 kPa at the toe and zero at the heel D 600 kPa at both the toe and heel

Question 6 ప్రశ్న 6

If the resultant on a rectangular gravity-dam base is located exactly at the middle-third limit toward the downstream toe, what is the corresponding idealized linear base-pressure condition?

A The toe pressure is zero and the heel pressure is twice the average pressure B The toe and heel pressures are equal C The heel pressure is zero and the toe pressure is twice the average pressure D Both toe and heel pressures are tensile

Question 7 ప్రశ్న 7

What does the ordinary full-contact linear pressure formula indicate when the resultant moves beyond the middle third toward the downstream toe?

A It predicts tensile stress at the heel, showing that the no-tension full-contact assumption is no longer satisfied B It predicts uniform compression over the whole base C It predicts zero pressure at the toe while the heel remains compressed D It proves that uplift pressure must be zero

Question 8 ప్రశ్న 8

The algebraic moment of all applied loads about the downstream toe is 96,000 kN·m per metre in the resisting sense, and the net vertical downward force is 12,000 kN/m. Where does the resultant intersect the base, measured from the downstream toe?

A 4 m B 6 m C 8 m D 12 m

Question 9 ప్రశ్న 9

In a simplified textbook overturning check, the sum of resisting moments about the downstream toe is 180,000 kN·m/m and the sum of overturning moments is 90,000 kN·m/m. What is the conventional factor of safety against overturning by the moment-ratio definition?

A 0.50 B 1.00 C 1.50 D 2.00

Question 10 ప్రశ్న 10

Which statement most accurately reflects current IS 6512-based gravity-dam assessment regarding overturning?

A A single universal overturning factor of safety is the only required stability check B Overturning is ignored because gravity dams cannot rotate C Overturning safety is assessed through the resultant and stress state together with sliding and foundation criteria; a standalone moment-ratio check is not the sole code criterion D Overturning safety depends only on crest width

Question 11 ప్రశ్న 11

In the shear-friction concept used for sliding assessment, what does the sliding safety measure fundamentally compare?

A The total available shear resistance along the potential sliding plane with the forces tending to cause sliding B The overturning moment with the dam crest width C The hydrostatic force with the wave force only D The foundation bearing capacity with reservoir volume

Question 12 ప్రశ్న 12

For a simplified friction-only sliding calculation, a dam has 14,000 kN/m downward load before uplift, 2,000 kN/m uplift, coefficient of friction 0.70, and 6,000 kN/m horizontal driving force. What is the sliding factor of safety under the stated assumptions?

A 0.98 B 1.20 C 1.40 D 1.63

Question 13 ప్రశ్న 13

A 15 m wide dam base is checked by a simplified shear-friction expression. Net compressive normal force is 8,000 kN/m, coefficient of friction is 0.60, cohesion is 100 kPa over the full 15 m base width per metre length, and horizontal driving force is 3,500 kN/m. What is the factor of safety?

A 1.20 B 1.50 C 1.80 D 2.10

Question 14 ప్రశ్న 14

A simplified gravity-dam sliding check has a downward structural load of 12,000 kN/m, horizontal driving force of 4,000 kN/m and friction coefficient 0.60. If uplift increases from zero to 3,000 kN/m, what happens to the friction-only factor of safety?

A It increases from 1.80 to 2.25 B It decreases from 1.80 to 1.35 C It remains 1.80 because uplift is vertical D It decreases from 3.00 to 0.75

Question 15 ప్రశ్న 15

For otherwise unchanged loading, what is the usual stability effect of reducing foundation uplift through effective drainage?

A It reduces effective normal force and normally lowers sliding resistance B It increases hydrostatic thrust on the upstream face C It increases effective downward force and can improve sliding stability, although the specified residual uplift must still be included D It necessarily moves the resultant outside the base

Question 16 ప్రశ్న 16

A gravity-dam base is 30 m wide. To satisfy the elementary middle-third criterion, between which distances from the upstream heel should the resultant intersect the base?

A 0 m and 10 m B 5 m and 25 m C 10 m and 20 m D 15 m and 30 m

Question 17 ప్రశ్న 17

A dam base 18 m wide carries a net vertical force of 9,000 kN/m. Its resultant has an eccentricity of 1.5 m toward the downstream toe. What are the toe and heel pressures under a linear full-contact distribution?

A 750 kPa at the toe and 250 kPa at the heel B 600 kPa at the toe and 400 kPa at the heel C 1000 kPa at the toe and zero at the heel D 500 kPa at both edges

Question 18 ప్రశ్న 18

On a 24 m wide base, the computed linear pressures are 750 kPa at the downstream toe and 250 kPa at the upstream heel. What is the eccentricity of the resultant toward the toe?

A 1 m B 2 m C 3 m D 4 m

Question 19 ప్రశ్న 19

A no-tension contact analysis finds that the resultant intersects the base 4 m from the downstream toe and the compressed base pressure is triangular with maximum pressure at the toe. What width of the base remains in compression?

A 4 m B 8 m C 12 m D 16 m

Question 20 ప్రశ్న 20

In the triangular no-tension pressure condition of a compressed contact width of 12 m, the net vertical compressive force is 6,000 kN/m. What is the maximum base pressure at the downstream toe?

A 500 kPa B 750 kPa C 1000 kPa D 1500 kPa

Question 21 ప్రశ్న 21

Which description best represents the elementary gravity-dam profile used in introductory design theory?

A It is an idealized profile developed from a limited set of forces and stress conditions, commonly represented by a triangular section before practical crest width, uplift, seismic and other requirements are added B It is the final construction profile and therefore requires no modification for spillways, roadways or earthquake effects C It is always a rectangular section because hydrostatic pressure is uniform D It is derived without considering the self-weight of the dam

Question 22 ప్రశ్న 22

Consider an idealized triangular gravity-dam profile with a vertical upstream face. Water depth is 20 m, concrete unit weight is 24 kN/m³ and water unit weight is 9.81 kN/m³. Neglect uplift, tail-water and all loads other than self-weight and hydrostatic pressure. What base width makes the full-reservoir resultant pass through the downstream-side middle-third limit?

A Approximately 8.18 m B Approximately 12.79 m C Approximately 16.63 m D Approximately 24.47 m

Question 23 ప్రశ్న 23

A triangular gravity dam has a vertical upstream face, height 20 m and base width 12 m. Take gamma_c = 24 kN/m³ and gamma_w = 9.81 kN/m³, with full reservoir to the crest and no uplift or tail-water. Which conclusion follows from the stated idealized loads?

A The resultant lies approximately 3.46 m from the downstream toe, outside the middle third toward the toe, so the full-contact linear analysis predicts heel tension B The resultant lies exactly at the base centre and produces uniform pressure C The resultant lies 8 m from the toe, so the heel pressure is twice the toe pressure D The resultant lies outside the physical base on the upstream side

Question 24 ప్రశ్న 24

When the resultant of loading moves toward the downstream toe while the net vertical force and base width remain unchanged, what happens under the full-contact linear stress model?

A Toe compression decreases and heel compression increases B Toe and heel pressures remain equal C Toe compression increases and heel pressure decreases, potentially reaching tension if the resultant moves beyond the kern D Both edge pressures decrease by the same amount

Question 25 ప్రశ్న 25

A 20 m wide dam base has the following simplified loads per metre length: weight 16,000 kN acting at the base centre, uplift 4,000 kN acting 8 m from the upstream heel, and a downstream horizontal water force of 5,000 kN acting 6 m above the base. Take the friction coefficient as 0.65 and neglect all other forces. Which set of results is correct?

A Net vertical force = 12,000 kN; resultant 6.83 m from the toe; e = 3.17 m toward the toe; toe/heel pressures ≈ 1170/30 kPa; friction-only sliding factor ≈ 1.56 B Net vertical force = 20,000 kN; resultant at the centre; toe/heel pressures = 1000/1000 kPa; sliding factor = 2.60 C Net vertical force = 12,000 kN; resultant 13.17 m from the toe; e = 3.17 m toward the heel; toe/heel pressures ≈ 30/1170 kPa; sliding factor ≈ 0.65 D Net vertical force = 16,000 kN; resultant 6.83 m from the toe; toe pressure = 600 kPa; sliding factor = 1.00

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