Test 37 - Engineering Geology for Tunnels

Question 1 ప్రశ్న 1

A water-conveyance tunnel is proposed through a hill where a regional fault, alternating sandstone and shale, and variable groundwater conditions are expected. Which investigation programme provides the most reliable geological basis for comparing possible alignments?

A Select the shortest alignment using topographic maps alone, because subsurface structures cannot be investigated before excavation. B Integrate surface geological and structural mapping, targeted boreholes, groundwater observations and suitable geophysics into a longitudinal geological model. C Use the compressive strength of a single fresh sandstone specimen to characterize the entire alignment. D Defer all mapping until the tunnel is completed because drilling cannot help predict tunnelling conditions.

Question 2 ప్రశ్న 2

Two proposed tunnel routes pass through the same nominal rock formation. Route X is supported only by a few widely spaced boreholes, while Route Y has geological mapping, cores, water-pressure measurements and a correlated longitudinal section. Which conclusion is most defensible?

A Route X is better characterized because fewer data eliminate geological variability. B Neither route needs investigation once the general name of the rock formation is known. C A longitudinal geological section directly guarantees identical rock conditions at every tunnel chainage. D Route Y has a stronger basis for predicting changes in lithology, discontinuities and groundwater, although uncertainty remains between observations.

Question 3 ప్రశ్న 3

A proposed tunnel passes through a massive, relatively unweathered rock unit and then through strongly fractured, altered rock of the same mineral composition. Which assessment best explains why excavation behaviour may change?

A Rock-mass performance depends on jointing, alteration and groundwater as well as the intact mineral composition and strength. B Identical mineral composition guarantees identical stand-up time and support requirements. C Fractures always increase intact rock tensile strength and therefore remove roof-collapse risk. D Weathering affects rock colour only and cannot influence tunnelling stability.

Question 4 ప్రశ్న 4

A tunnel will intersect a thick shale interval containing clay minerals that deteriorate after repeated wetting and drying. Which geological hazard and construction response are most appropriate?

A Strongly improved durability merely from leaving the exposed shale unprotected for several weeks. B The absence of any deformation risk because all sedimentary rocks remain stable when wetted. C Slaking and loss of exposed-rock integrity; investigate moisture sensitivity and provide timely suitable support and water control. D A requirement to apply blasting energy exclusively to groundwater rather than to the rock.

Question 5 ప్రశ్న 5

Two straight tunnel alignments are being compared in thinly bedded weak rock. Alignment P follows a persistent, clay-coated bedding weakness for a long distance, while Alignment Q crosses the same bedding at a high angle. What is the best preliminary engineering judgement?

A Alignment P is always safer because a tunnel must follow a bedding plane to remain stable. B Alignment Q may reduce prolonged exposure to the weak horizon, but joint orientation, stresses, cover and groundwater must still govern the final choice. C Both alignments necessarily experience the same wall and roof failure mechanism regardless of bedding orientation. D Alignment Q is impossible because a tunnel cannot cross sedimentary bedding.

Question 6 ప్రశ్న 6

The crown of a shallow rock tunnel contains two persistent, intersecting joints whose geometry defines a rock wedge capable of moving into the opening. Which statement identifies the principal instability mechanism?

A The entire tunnel must fail by uniform compression of unjointed rock. B Only groundwater chemistry determines whether the wedge can fall. C A bedding plane cannot contribute to a roof fall when other joints are present. D Gravity-driven release of a discontinuity-bounded wedge is possible, depending on its orientation, confinement and shear resistance.

Question 7 ప్రశ్న 7

A rock tunnel exposes blocks bounded by persistent joint planes. Which rock-bolt arrangement most directly improves the stability of a potentially detachable roof block, assuming competent anchorage rock is available?

A Install suitably oriented bolts crossing the relevant discontinuities and anchored adequately into stable surrounding rock. B Install bolts entirely within the loose block without crossing any potential release surface. C Choose bolt orientation solely from the tunnel length without considering joint geometry. D Remove all block-support measures whenever the intact rock compressive strength is high.

Question 8 ప్రశ్న 8

A 1.00 m rock-core run produces SOUND pieces separated only by NATURAL fractures, having lengths of 21, 9, 7, 25, 5, 17 and 16 cm. Using RQD = 100 x (sum of lengths of sound pieces at least 10 cm long)/(total core-run length), what is the rock quality designation?

A 91%. B 63%. C 79%. D 100%.

Question 9 ప్రశ్న 9

A borehole gives relatively high Rock Quality Designation (RQD), but mapping identifies a continuous clay-filled discontinuity oriented unfavorably above a proposed tunnel. Which interpretation is correct?

A High RQD proves that persistent weak discontinuities cannot affect tunnel stability. B RQD alone is insufficient; the orientation, persistence, filling and water pressure on the weak surface must also be evaluated. C The joint must be ignored because RQD measures the compressive strength of every rock block. D A high RQD proves that no geological investigation is necessary at the tunnel crown.

Question 10 ప్రశ్న 10

A tunnel approaches a mapped fault zone containing highly fractured rock, clay-rich gouge and locally elevated groundwater pressure. What is the most appropriate construction-planning response?

A Treat the fault zone as sound unjointed rock because the mineral name of the host formation is unchanged. B Increase advance length and delay support without investigation to pass the fault more quickly. C Assume fault gouge is always impermeable and cannot coexist with significant water inflow. D Use additional ahead-of-face investigation and prepare adaptable excavation, support and groundwater-control measures for the weak zone.

Question 11 ప్రశ్న 11

In plan view, a straight fault-damage zone is 10 m wide measured PERPENDICULAR to its parallel boundaries. A straight tunnel intersects the boundaries at an angle of 30 degrees to the fault trace. Assuming uniform zone width and sin(30 degrees) = 0.5, what distance along the tunnel lies within the zone?

A 5 m. B 10 m. C 15 m. D 20 m.

Question 12 ప్రశ్న 12

A tunnel route crosses a tightly folded sedimentary sequence, and the mapped hinge zone contains intense jointing and contrasting sandstone-shale beds. Which prediction is most defensible?

A Every fold hinge must be unfractured and stronger than the limbs. B Folded beds retain constant strike and dip throughout the tunnel alignment. C Bedding orientation and local rock-mass quality may vary markedly, requiring focused mapping of hinges, fractures and weaker layers. D Folding always prevents groundwater from entering tunnel excavations.

Question 13 ప్రశ్న 13

A tunnel is to pass through a synclinal sedimentary structure. Which statement about groundwater and tunnel stability is most appropriate?

A The mere presence of a syncline proves that the tunnel will be completely dry. B Fold geometry may influence the distribution of permeable beds and groundwater, but inflow must be evaluated from hydraulic heads and connected discontinuities. C Every syncline contains a single open underground river along its axis. D Synclinal beds cannot contain fractures or clay-rich weakness zones.

Question 14 ప్రశ్న 14

A groundwater-bearing joint at tunnel level is connected to a piezometric surface 10 m above the joint. For an idealized hydrostatic check, take the water unit weight as 10 kN/m3 and ignore flow losses. What is the gauge water pressure at the joint?

A 100 kPa. B 10 kPa. C 1000 kPa. D 0 kPa.

Question 15 ప్రశ్న 15

Ahead of a tunnel face, drilling intersects saturated, poorly cemented sand under appreciable hydraulic head. Which hazard and response should be considered most seriously?

A The sand must become self-supporting immediately after wetting, so no support is necessary. B Groundwater can only affect the final tunnel lining, never the excavation face. C The excavation will necessarily remain stable because its cover is greater than its radius. D Flowing or running ground and face instability may develop; examine groundwater pressure reduction, ground improvement and immediate face or peripheral support.

Question 16 ప్రశ్న 16

A tunnel portal is proposed beneath a steep hillside mantled by weathered rock and loose colluvium, while competent rock occurs farther inside the hill. What is the most appropriate preliminary design judgement?

A The portal will be safer than the deeper tunnel because it has less ground cover under every geological condition. B Portal stability can be evaluated entirely from the strength of deep unweathered rock. C Investigate cut-slope and shallow-cover stability, weathered material and drainage, and design suitable portal protection and early support. D A concrete portal structure eliminates the need to consider landslides and rockfalls above it.

Question 17 ప్రశ్న 17

A rock tunnel runs almost parallel to a persistent steep joint set that cuts across the planned sidewall. What should principally determine whether this orientation is unfavorable?

A The tunnel length alone, regardless of joint dip and persistence. B The joint attitude relative to tunnel surfaces, persistence, infill, friction, water and any release surfaces that could form unstable blocks. C The colour of the joint surface, without observing aperture or condition. D A rule that every joint plane parallel to a tunnel must always produce failure.

Question 18 ప్రశ్న 18

A tunnel investigation needs to determine whether closely jointed rock ahead of excavation is likely to transmit substantial groundwater. Which test or observation combination is most relevant?

A Use borehole packer or water-pressure testing where suitable, together with joint logging and groundwater-head monitoring. B Determine only the dry density of an unfractured hand specimen and infer all tunnel inflow. C Treat a single RQD value as a direct measurement of groundwater discharge. D Estimate water pressure solely from the colour of the tunnel lining.

Question 19 ప్రశ్న 19

While drilling ahead of the tunnel face, probe holes encounter unexpectedly high water pressure and heavily crushed material. What should the excavation team do with this new information?

A Ignore the probe results because the preconstruction geological section must be exact. B Continue with the original support class regardless of observed ground changes. C Advance unsupported through the zone to avoid the delay caused by monitoring. D Update the geological model and construction risk assessment, then adapt advance length, support and groundwater-control provisions as necessary.

Question 20 ప్రశ్న 20

A short circular rock-tunnel reach has nominal excavation diameter 6 m and length 20 m. Geological fracturing causes an estimated 10% ADDITIONAL excavation volume beyond the nominal circular profile, uniformly over this reach. Using pi = 3.14, what is the estimated EXTRA excavation volume due to overbreak?

A 565.2 m3. B 28.26 m3. C 56.52 m3. D 62.80 m3.

Question 21 ప్రశ్న 21

A tunnel encounters jointed but relatively competent rock with discrete unstable roof blocks and locally small loose fragments. Which statement about initial support functions is correct?

A Rock bolts are useful only for waterproofing and cannot reinforce discontinuity-bounded blocks. B Properly anchored rock bolts can restrain blocks, while suitably applied shotcrete can help support the excavation surface and retain smaller fragments. C Shotcrete automatically removes all water pressures behind a lining without drainage design. D Steel ribs are categorically prohibited whenever rock bolts are installed.

Question 22 ప్రశ్న 22

Which distinction between squeezing ground and rockburst is most appropriate for interpreting tunnel hazards?

A Squeezing involves substantial, often progressive inward deformation of weak ground under stress, whereas rockburst is a sudden, violent release of stored strain energy in stressed brittle rock. B Squeezing is always a chemical reaction, whereas rockburst is only groundwater boiling. C Both terms mean exactly the same slow clay-swelling process. D Rockburst is defined as the gradual sedimentation of sand at the tunnel invert.

Question 23 ప్రశ్న 23

Two tunnel segments show similar intact-rock compressive strengths, but the second segment has closely spaced joints, clay-filled shears and groundwater inflow. What is the best assessment of support needs?

A They must require identical support because intact strength is the only significant index. B The second segment can be assumed stable without support because water eliminates friction. C Rock-mass quality indices can always replace face mapping and engineering observations. D The second segment may require shorter advances and stronger or earlier support; evaluate discontinuities, groundwater and deformation in addition to intact strength.

Question 24 ప్రశ్న 24

Excavation of a tunnel through connected water-bearing fractures is predicted to lower groundwater head in nearby wells if sustained uncontrolled drainage occurs. Which action is most defensible?

A Ignore the potential impact because groundwater drained into a tunnel cannot affect surrounding wells. B Guarantee that sealing any one fracture will restore the entire preconstruction groundwater regime. C Assess possible drawdown and environmental effects, and evaluate pregrouting, drainage design and groundwater monitoring as appropriate. D Assume inflow can always be controlled by increasing tunnel overbreak.

Question 25 ప్రశ్న 25

A tunnel alternative is slightly longer but avoids an extensive crushed fault zone and unstable portal slope. The shorter route crosses both adverse features. Which selection principle is most appropriate?

A Always select the shortest route because length alone determines tunnel construction risk. B Compare alternatives using geological stability, groundwater, construction method, support needs, portal works, risk and cost instead of length alone. C Avoid geological investigation because alignment comparison cannot use subsurface information. D Assume faults cause no additional excavation difficulty unless they are presently active.

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