Test 38 - Engineering Geology for Dams and Reservoirs

Question 1 ప్రశ్న 1

A new dam and its reservoir are proposed in a valley containing folded sedimentary rocks, a mapped fault and old landslide deposits. Which investigation approach gives the most defensible initial geological basis for site selection?

A Select the narrowest valley section without examining the reservoir basin or the abutments. B Integrate geological and structural mapping of the dam axis, foundations, abutments and reservoir rim with targeted drilling, groundwater observations and appropriate field testing. C Determine site suitability solely from the compressive strength of a fresh hand specimen. D Assume that all geological discontinuities are sealed once the reservoir is filled.

Question 2 ప్రశ్న 2

Two potential dam axes are compared. Site P is a very narrow gorge but intersects an extensive sheared and highly fractured foundation zone, whereas Site Q is somewhat wider with comparatively sound, well-investigated bedrock. Which preliminary decision is most appropriate?

A Site P must be selected because gorge width alone determines geological suitability. B Site Q must be rejected because competent bedrock is unnecessary at a dam site. C Both sites are geologically equivalent because the reservoir level is the same. D Compare the additional treatment, stability, seepage and construction risks at P against the greater structural quantities at Q rather than selecting on valley width alone.

Question 3 ప్రశ్న 3

A borehole beneath a proposed concrete dam indicates high intact-rock compressive strength, but mapping shows persistent clay-filled joints and an unfavorable shear plane. Which conclusion is correct?

A Strong intact specimens do not establish a sound rock-mass foundation; discontinuity orientation, shear strength, persistence and groundwater require independent assessment. B The foundation has unlimited shear resistance because intact-rock strength is high. C All clay-filled discontinuities are harmless once covered with concrete. D Joint mapping is unnecessary when core specimens are strong.

Question 4 ప్రశ్న 4

A 1.00 m diamond-drill core run beneath a proposed dam consists of SOUND pieces 20, 8, 15, 7, 16, 9 and 25 cm long, separated by NATURAL discontinuities. Using RQD = 100 x (sum of sound pieces at least 10 cm long)/(total core-run length), what is the RQD?

A 100%. B 64%. C 76%. D 85%.

Question 5 ప్రశ్న 5

A dam-axis borehole is drilled from ground reduced level (RL) 312 m. The log shows 7 m of soil overburden followed by 5 m of highly weathered rock, beneath which relatively sound rock begins. What is the RL of the top of relatively sound rock, and how should the result be used?

A RL 307 m; accept it as the founding level without any further investigation. B RL 300 m; use it as one investigated point in mapping the rockhead and weathering profile. C RL 305 m; treat the entire weathered layer as sound rock. D RL 295 m; assume it is the same at both abutments.

Question 6 ప్రశ్న 6

At a dam abutment, a persistent clay-coated bedding plane dips outward toward the valley and could daylight beneath a rock wedge loaded by the proposed structure. Which assessment is most appropriate?

A The bedding plane is safe because every inclined bed has high cohesion. B Outward-dipping bedding cannot daylight in a valley slope. C The dip direction alone proves that failure will certainly occur. D Assess potential kinematic release, discontinuity shear resistance, water pressure and supporting rock geometry before deciding on excavation or reinforcement.

Question 7 ప్రశ్న 7

A candidate dam foundation contains persistent bedding planes dipping into the hillside, away from the main downstream sliding direction. Which interpretation best reflects good engineering judgement?

A The site must be rejected solely because bedding is inclined. B The bedding orientation guarantees zero seepage and unlimited bearing resistance. C This orientation may be less unfavorable for one sliding mechanism, but rock wedges, other joint sets, seepage and foundation deformation must still be evaluated. D No geological mapping is needed because all bedding planes have the same shear strength.

Question 8 ప్రశ్న 8

A proposed dam axis directly crosses a fault with evidence of geologically recent surface displacement. Which investigation and site-selection response is most appropriate?

A Evaluate fault activity and potential surface rupture with suitable geological and seismotectonic studies, and consider avoiding the crossing because a sound intact-rock specimen does not remove rupture hazard. B Ignore the fault because reservoir water will permanently lock both sides together. C Treat the fault solely as a shallow surface-drainage issue with no foundation consequences. D Assume any grout curtain prevents future tectonic displacement across the fault.

Question 9 ప్రశ్న 9

A rock foundation contains a crushed fault zone with clay-rich gouge adjacent to open fractured rock. Which statement about its engineering behavior is most defensible?

A The entire zone must be uniformly stronger and less deformable than the intact host rock. B Fault gouge may form a weak seam, while adjoining connected fractures can transmit water; permeability need not be uniform throughout the zone. C A fault zone can never affect differential deformation of the dam foundation. D Every fault is either completely watertight everywhere or freely permeable everywhere.

Question 10 ప్రశ్న 10

Two persistent joint sets intersect beneath a steep dam abutment and form a block with a potential release direction toward the excavated valley face. What geological hazard should be examined?

A Uniform vertical consolidation of an entirely unfractured rock mass. B Only chemical dissolution of the concrete dam crest. C Kinematically possible rock-wedge instability, subject to joint geometry, shear resistance, persistence and groundwater. D A guarantee that the rock block cannot move because joints occur in two sets.

Question 11 ప్రశ్న 11

Fresh rock beneath a proposed dam has sound laboratory strength, but open stress-relief joints occur along the steep valley wall near the abutment. Which consequence is most important?

A Stress-relief joints guarantee the abutment has zero water permeability. B They can affect only the rock colour and have no structural effect. C They always extend uniformly to bedrock depths regardless of the valley geometry. D They may reduce rock-mass integrity and provide connected seepage or block-release paths requiring mapping and testing.

Question 12 ప్రశ్న 12

Foundation excavation exposes local pockets of decomposed rock and narrow weak seams immediately beneath the planned contact surface. Which geological remedial approach is most appropriate?

A Remove unsuitable weathered material to an approved profile and use engineered local replacement, such as dental concrete where appropriate, with verification of the remaining foundation. B Cover all weak pockets with loose spoil because the dam weight will automatically stabilize them. C Retain every decomposed seam unchanged since it must have the same stiffness as fresh rock. D Rely solely on surface paint to restore the internal shear strength of the seams.

Question 13 ప్రశ్న 13

A dam-site investigation needs to assess seepage through fractured foundation rock. Which field information is most directly relevant to identifying potential seepage zones?

A The colour of aggregate stockpiles and the nominal dam height alone. B Depth-specific borehole water-pressure or packer tests, piezometric observations and discontinuity mapping interpreted together. C Only the compressive strength of dry intact specimens without logging fractures. D A regional rainfall total used as a direct substitute for foundation permeability measurements.

Question 14 ప్రశ్న 14

Foundation rock has connected water-bearing fractures that may transmit reservoir water beneath a dam. Which distinction between a grout curtain and foundation drainage is correct?

A Grout curtains necessarily remove every possible groundwater head, while drainage serves only aesthetic purposes. B Drain holes convert weak gouge into strong fresh granite without affecting groundwater. C A grout curtain is intended mainly to reduce hydraulic conductivity or seepage through treated paths, while drainage provides controlled pressure relief and collection; both require verification. D The two methods are identical and neither depends on geological connectivity.

Question 15 ప్రశ్న 15

A proposed rock foundation has relatively shallow fractured zones that reduce its mechanical stiffness, while a separate deep permeable fracture network poses a leakage risk. Which grouting distinction is most accurate?

A Consolidation grouting is exclusively for sediment removal from the upstream catchment. B A grout curtain is mainly intended to replace the entire rock foundation with concrete. C All shallow and deep grouting methods have identical targets regardless of geology. D Consolidation grouting is primarily directed at improving mechanical behavior in selected rock zones, while curtain grouting mainly targets hydraulic seepage control.

Question 16 ప్రశ్న 16

A water-pressure test shows considerable flow into very narrow rock fractures, but a proposed cement grout has particles too large to penetrate many of those apertures. What is the most defensible decision?

A Check groutability with suitable trials and consider alternative treatment materials or cutoff methods rather than assuming high water intake guarantees cement-grout penetration. B Increase grout pressure without any upper limit so that hydraulic jacking is unavoidable. C Assume all high-permeability fractures can always be sealed by the same cement mixture. D Ignore the test result because fracture width cannot influence grouting.

Question 17 ప్రశ్న 17

Part of a proposed reservoir rim consists of karstified limestone containing connected solution cavities that extend toward a nearby lower valley. Which geological concern is most important?

A Limestone cannot dissolve and therefore guarantees reservoir watertightness. B Only the dam body requires investigation because water cannot bypass the dam through the rim. C Reservoir leakage may follow solution channels around the dam, so the rim requires detailed hydrogeological investigation and possibly extensive cutoff treatment or a different site. D All cavities will seal spontaneously and permanently as soon as reservoir filling begins.

Question 18 ప్రశ్న 18

A reservoir basin contains thick gypsum-bearing strata and mapped sinkholes. Which conclusion is most defensible about leakage control and long-term geological behavior?

A Gypsum is less soluble than quartz, so dissolution can safely be ignored. B Gypsum dissolution may enlarge cavities and seepage routes; the site requires special investigation, and ordinary localized grouting cannot automatically guarantee long-term watertightness. C Sinkholes prove that groundwater pressure will always be zero. D A thin surface layer of soil guarantees isolation of all gypsum beds from reservoir water.

Question 19 ప్రశ్న 19

An otherwise favorable dam site impounds water close to a low saddle on the reservoir rim separating the basin from an adjacent valley. What additional investigation is particularly important?

A Determine only the compressive strength of concrete proposed for the dam crest. B Assume saddle topography proves the two valleys are hydraulically disconnected. C Check only the dam spillway gates because the rim is outside the engineering-geology scope. D Investigate saddle geology, permeable strata, buried channels and groundwater heads for possible leakage from the reservoir into the adjacent valley.

Question 20 ప్రశ్న 20

Exploration drilling reveals a buried gravel-filled palaeochannel crossing the dam foundation beneath a thin low-permeability cover. Which engineering-geology response is most appropriate?

A Map its continuity and hydraulic connection, investigate underseepage, and consider a properly designed cutoff and related drainage or filter measures. B Assume the gravel channel is impermeable because it is covered by clay. C Ignore the palaeochannel because it is not visible at the current ground surface. D Treat the channel only as a surface landscaping issue and omit subsurface tests.

Question 21 ప్రశ్న 21

A reservoir rim slope contains a persistent weak bedding surface and is partly supported by the reservoir water. The reservoir level is lowered rapidly, but pore pressures within the slope remain temporarily high. What condition requires particular attention?

A A guarantee that the rock slope becomes more stable because its submerged weight increases. B Reduced external water support combined with lagging internal pore pressure may worsen slope stability during rapid drawdown. C Complete elimination of seepage forces immediately upon lowering the reservoir. D Automatic strengthening of clay-filled bedding planes as soon as the water level falls.

Question 22 ప్రశ్న 22

Geological mapping identifies a large potentially unstable rockslide mass on a steep reservoir rim above deep water. Besides local slope failure, which additional reservoir-related consequence should be evaluated?

A The slide would necessarily decrease all wave heights by creating a new beach. B The landslide can be ignored because it is not directly below the dam. C Rapid entry of a large rock mass into the reservoir may displace water and create hazardous impulse waves, including risks to structures and people. D The only possible consequence is improved foundation-rock compressive strength.

Question 23 ప్రశ్న 23

A reservoir catchment contains extensive weathered shale and actively eroding slopes. Which engineering-geology assessment is most relevant to the future sedimentation problem?

A Sediment supply depends only on the concrete strength of the dam. B Weathered shale cannot contribute sediment because it is classified as rock. C Reservoir sedimentation will automatically cease after the first rainfall season. D Assess erodible lithologies, slope failures, sediment transport pathways and existing or future deposition using catchment mapping and sediment observations.

Question 24 ప్రశ్న 24

Before first reservoir filling, downstream springs and observation wells around the proposed basin are available for monitoring. Which programme best supports later detection and interpretation of reservoir-induced leakage?

A Record baseline spring discharge, groundwater levels and relevant water chemistry before impoundment, then monitor their changes alongside reservoir level and rainfall. B Ignore spring conditions until years after filling because baseline conditions are irrelevant. C Monitor only the dam crest settlement and assume it fully describes rim seepage. D Interpret every increase in downstream spring flow as dam leakage without comparing rainfall or other influences.

Question 25 ప్రశ్న 25

A dam site has localized weathered foundation pockets, a treatable fractured seepage zone and a reservoir rim with a separate, potentially connected karst pathway. Which overall geological recommendation is most defensible?

A Treat only the weathered pockets and assume all remote leakage paths are sealed. B Install one short grout hole at the dam axis and regard the entire reservoir as proven watertight. C Develop a site-wide geological model and evaluate local excavation or replacement, appropriate grout or cutoff and drainage works, plus independent assessment of rim leakage and monitoring before accepting the site. D Ignore groundwater conditions whenever the dam body is structurally strong.

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