Test 24 - Forces Acting on Gravity Dams

Question 1 ప్రశ్న 1

Which group most appropriately represents the standard actions that may have to be considered in the stability analysis of a solid gravity dam?

A Only self-weight, hydrostatic pressure and foundation reaction B Dead load, reservoir and tail-water loads, uplift, earthquake forces, earth and silt pressures, ice, wind, wave and thermal loads as applicable C Only water pressure, sediment pressure and turbine reaction D Only permanent vertical forces because horizontal forces are resisted entirely by the foundation

Question 2 ప్రశ్న 2

For a vertical upstream face retaining water to a depth H, which statement correctly describes the static hydrostatic pressure resultant?

A Pressure is uniform with depth and the resultant acts at H/2 above the base B Pressure decreases linearly with depth and the resultant acts at 2H/3 above the base C Pressure increases linearly with depth, and the resultant acts at H/3 above the base D Pressure varies parabolically and the resultant always acts at the water surface

Question 3 ప్రశ్న 3

A gravity dam has a vertical upstream face retaining water to a depth of 30 m. Taking the unit weight of water as 9.81 kN/m³, what is the horizontal hydrostatic force per metre length of dam?

A 4414.5 kN/m B 2943.0 kN/m C 8829.0 kN/m D 1471.5 kN/m

Question 4 ప్రశ్న 4

For the 30 m water depth in the preceding type of situation, the hydrostatic force is 4414.5 kN/m and acts 10 m above the base. What is its overturning moment about the base level per metre length of dam?

A 13,243.5 kN·m/m B 22,072.5 kN·m/m C 132,435 kN·m/m D 44,145 kN·m/m

Question 5 ప్రశ్న 5

A vertical downstream face of a gravity dam is subjected to 6 m of tail-water. Taking gamma_w = 9.81 kN/m³, which result correctly gives the tail-water force and its line of action?

A 353.16 kN/m acting 3 m above the base B 176.58 kN/m acting 2 m above the base C 58.86 kN/m acting 6 m above the base D 176.58 kN/m acting 4 m above the base

Question 6 ప్రశ్న 6

A gravity dam has 30 m headwater and 6 m tail-water acting on vertical faces. Ignoring all other horizontal forces and taking gamma_w = 9.81 kN/m³, what is the net horizontal hydrostatic force?

A 4591.08 kN/m upstream B 4414.50 kN/m downstream C 4237.92 kN/m downstream D 176.58 kN/m upstream

Question 7 ప్రశ్న 7

A triangular gravity-dam section is 30 m high and 24 m wide at the base, with a vertical upstream face. If the unit weight of concrete is 24 kN/m³, what are the self-weight and its horizontal line of action from the upstream heel per metre length?

A 8640 kN/m acting 8 m from the heel B 17,280 kN/m acting 12 m from the heel C 8640 kN/m acting 16 m from the heel D 4320 kN/m acting 8 m from the heel

Question 8 ప్రశ్న 8

A gravity-dam section has a vertical upstream face, a top width of 6 m, a base width of 24 m and a height of 30 m. If concrete weighs 24 kN/m³, at what horizontal distance from the upstream heel does the self-weight resultant act?

A 6.0 m B 12.0 m C 10.0 m D 8.4 m

Question 9 ప్రశ్న 9

What is the principal effect of uplift pressure beneath a gravity dam on its static stability?

A It increases the effective downward normal force and therefore always improves sliding resistance B It acts upward, reducing the effective downward force and generally reducing resistance to sliding and overturning C It acts only horizontally and therefore has no influence on base stresses D It is present only during earthquakes and disappears during normal reservoir operation

Question 10 ప్రశ్న 10

A gravity dam has a base width of 20 m and an upstream water depth of 25 m, with no tail-water. If the undrained uplift pressure is assumed to decrease linearly from full reservoir pressure at the heel to zero at the toe, what is the uplift resultant per metre length?

A 4905 kN/m B 1962 kN/m C 2452.5 kN/m D 1226.25 kN/m

Question 11 ప్రశ్న 11

At the base of a dam, the uplift pressure corresponds to 24 m water head at the heel and 4 m head at the toe over a base width of 18 m. Assuming a linear pressure variation and gamma_w = 9.81 kN/m³, where does the uplift resultant act from the heel?

A Approximately 6.86 m from the heel B Exactly 9.00 m from the heel C Approximately 11.14 m from the heel D Exactly 6.00 m from the heel

Question 12 ప్రశ్న 12

What is the correct conceptual effect of a properly functioning foundation-drainage system beneath a gravity dam?

A It necessarily eliminates uplift pressure everywhere beneath the base B It converts the entire uplift force into a horizontal force C It increases reservoir pressure at the heel D It can reduce uplift near the drainage line, but uplift must still be included using the specified pressure distribution

Question 13 ప్రశ్న 13

Under the simplified silt-pressure criterion given in IS 6512:2019, the horizontal combined 'silt and water pressure' may be represented by an equivalent fluid having approximately what density?

A 1000 kg/m³ B 1360 kg/m³ C 1925 kg/m³ D 2400 kg/m³

Question 14 ప్రశ్న 14

For a wave height hw = 2.0 m, IS 6512:2019 gives the approximate total wave force as Pw = 20hw² kN per metre length. If the reservoir still-water depth at the dam is 30 m, what is the approximate overturning moment of the wave force about the base, using the specified line of action 0.375hw above still-water level?

A 1200 kN·m/m B 2400 kN·m/m C 2460 kN·m/m D 4800 kN·m/m

Question 15 ప్రశ్న 15

According to the approximate wave-pressure representation used for solid gravity dams, where does the resultant wave force act relative to the still-water level?

A At a height of 0.375hw above the still-water level B Exactly at the still-water level C At a depth of hw below the still-water level D At a height of 2hw above the still-water level

Question 16 ప్రశ్న 16

Which statement about ice pressure on a gravity dam is most appropriate?

A Ice pressure is a vertical force acting through the foundation centroid B Ice pressure must be included with identical magnitude for every dam in every climate C Ice pressure replaces hydrostatic water pressure wherever ice forms D Where relevant, ice can exert a predominantly horizontal action near the reservoir surface and should be evaluated for applicable climatic conditions

Question 17 ప్రశ్న 17

Which statement best represents the treatment of direct wind pressure in IS 6512:2019 for a massive gravity dam?

A Wind pressure is always the largest horizontal action on the dam B Direct wind pressure exists but is seldom significant for the dam body and may generally be ignored, although wind is important in generating waves C Wind pressure must always be added numerically to hydrostatic pressure using the unit weight of water D Wind acts only on the foundation and never on the reservoir surface

Question 18 ప్రశ్న 18

In a simplified pseudo-static earthquake analysis, a dam monolith has a weight of 9000 kN per metre and a horizontal seismic coefficient of 0.10. If its centroid is 12 m above the base, what are the horizontal inertia force and its corresponding moment about the base?

A 90 kN and 1080 kN·m B 9000 kN and 108,000 kN·m C 900 kN and 10,800 kN·m D 90,000 kN and 1,080,000 kN·m

Question 19 ప్రశ్న 19

During earthquake analysis of a gravity dam with a reservoir, which statement correctly distinguishes dam inertia from hydrodynamic water effects?

A Earthquake shaking can produce inertia force in the dam body and an additional hydrodynamic pressure response of the reservoir water B Only the dam body responds to earthquake motion; reservoir water cannot exert any additional dynamic pressure C Hydrodynamic pressure permanently replaces the static hydrostatic pressure after an earthquake D Dam inertia is always vertical and hydrodynamic pressure is always zero

Question 20 ప్రశ్న 20

For a simplified force system, headwater thrust is 4000 kN/m downstream, tail-water thrust is 300 kN/m upstream, dam weight is 9000 kN/m downward and uplift is 1800 kN/m upward. Neglecting all other forces, what is the magnitude of the resultant applied force?

A 7200 kN/m B 10,000 kN/m C 5500 kN/m D Approximately 8095 kN/m

Question 21 ప్రశ్న 21

For a conventional gravity-dam section, take moments about the downstream toe and define clockwise moments as positive. Which sign assignment is generally correct for the four stated forces?

A Headwater negative, uplift negative, self-weight positive and tail-water positive B Headwater positive, uplift positive, self-weight negative and tail-water negative C All four forces produce positive moments D Headwater positive, uplift negative, self-weight positive and tail-water negative

Question 22 ప్రశ్న 22

Why should the beneficial effect of tail-water not be assessed only by subtracting its horizontal thrust from the upstream reservoir thrust?

A Because tail-water always acts in the same downstream direction as headwater B Because tail-water has no influence on any gravity-dam force C Because tail-water can provide an upstream stabilizing thrust while also contributing to uplift pressure toward the downstream toe D Because tail-water changes concrete self-weight to zero

Question 23 ప్రశ్న 23

Which loading description most appropriately represents the normal operating condition for a solid gravity dam?

A Dead load with full reservoir elevation, normal dry-weather tail-water, normal uplift, and applicable silt and ice effects B Dam completed with no reservoir, no tail-water and maximum earthquake C Maximum flood reservoir with all gates open but no uplift D Empty reservoir with maximum wave pressure and maximum silt pressure

Question 24 ప్రశ్న 24

Which combination correctly represents the flood-discharge loading condition specified for a solid gravity dam?

A Dam completed with an empty reservoir, no tail-water and no uplift B Full reservoir elevation with normal dry-weather tail-water and all flood effects omitted C Maximum flood pool elevation with the spillway gates closed, zero tail-water and zero uplift D Reservoir at maximum flood pool elevation, all spillway gates open, tail-water at flood elevation, normal uplift and applicable silt effects

Question 25 ప్రశ్న 25

Consider the following statements about forces acting on a gravity dam: I. Self-weight normally provides an important stabilizing downward action. II. Hydrostatic pressure on a vertical upstream face varies linearly with depth. III. Uplift generally reduces the effective downward force available for stability. IV. Tail-water thrust generally acts opposite to upstream reservoir thrust. Which option is correct?

A I and II only B II and III only C I, II, III and IV D I, III and IV only

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