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Question 1
ప్రశ్న 1
A foundation excavation in saturated sand needs groundwater lowering and lateral support. Which statement correctly differentiates dewatering from shoring or bracing?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Dewatering is used to control the groundwater level, inflow or hydraulic pressure relevant to excavation. Shoring and bracing provide mechanical support to excavation faces or retaining walls. Lowering groundwater can reduce some water pressures but does not eliminate earth pressures. Conversely, a retaining wall does not necessarily prevent groundwater from entering the excavation. A safe excavation may require both systems working together under a coordinated construction sequence.
వివరణ:
Question 2
ప్రశ్న 2
A shallow pit is excavated in stable, coarse gravel, with a small quantity of seepage and no evidence of soil-particle migration. Which groundwater-control method is a reasonable first option, subject to discharge and base-stability checks?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Sump pumping collects water that has already entered the excavation. It can be appropriate for small, shallow excavations in sufficiently stable coarse soils. Drainage ditches direct the inflow to a sump from which a pump removes it. Filters or other collection details can limit movement of soil particles into the pump. Where inflow threatens slope or base stability, a groundwater-lowering system outside the excavation may be preferable.
వివరణ:
Question 3
ప్రశ్న 3
During direct sump pumping from a sandy foundation excavation, the discharged water becomes increasingly turbid and sand boils appear near the excavation floor. What is the most appropriate response?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Turbid discharge can indicate that soil particles are being removed with the groundwater. Sand boils may indicate excessive upward hydraulic gradients near an excavation base. Uncontrolled removal of soil can undermine foundations or excavation support. The response should include assessment of seepage paths and suitable filtration or pressure-control measures. Simply increasing pumping can aggravate the instability instead of correcting it.
వివరణ:
Question 4
ప్రశ్న 4
In a conventional vacuum-assisted wellpoint dewatering system installed around a trench, which pairing of components and functions is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Wellpoints are relatively small screened intake points placed in the ground around an excavation. Risers convey collected groundwater from these points to a header system. A pump, often with appropriate vacuum equipment, removes the water and sustains drawdown. A suitable filter pack helps prevent fine soil from entering and clogging the intake. Sheet piling, struts and other separate members provide excavation support when needed.
వివరణ:
Question 5
ప్రశ్న 5
A contractor claims that one ground-level suction-type wellpoint stage can lower groundwater by any required depth if a sufficiently powerful motor is installed. Which assessment is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A suction pump cannot lift water through an unlimited vertical distance. Atmospheric pressure provides an upper physical limit, while friction, leakage and practical vacuum losses reduce attainable suction lift. Ordinary single-stage wellpoints are therefore suited to a limited lowering range. Multiple stages may be used when excavation geometry and ground conditions permit. Deep wells or eductor systems may be more appropriate where a large drawdown is required.
వివరణ:
Question 6
ప్రశ్న 6
A deep trench in permeable sand requires groundwater lowering beyond the practical lift of one conventional suction-wellpoint stage, but space exists for staged excavation and installation. Which approach is technically appropriate?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A multistage wellpoint arrangement can provide greater total lowering than one suction stage. Successive wellpoint levels are introduced as excavation proceeds and working platforms become available. Each stage must operate within its practical suction limits. The excavation-support system must remain effective throughout the changing construction stages. Seepage, piping and adjacent-ground effects require assessment before the system is adopted.
వివరణ:
Question 7
ప్రశ్న 7
At a site with a horizontal ground surface, the initial groundwater table is 1.0 m below ground level. The proposed excavation base is 5.0 m below ground level, and the design requires groundwater at least 0.8 m below that base. What minimum lowering of the groundwater table from its initial position is required?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The required groundwater position is 5.0 + 0.8 = 5.8 m below ground level. Initially the groundwater table is at 1.0 m below the same datum. Required drawdown is the difference between final and initial groundwater depths. It is therefore 5.8 - 1.0 = 4.8 m. This is a level difference and does not by itself establish the pumping rate or the number of wells required.
వివరణ:
Question 8
ప్రశ్న 8
A dewatering scheme must continuously remove 52 L/s at the actual pumping head. Each identical installed pump can deliver 18 L/s at that head. The project requires the design inflow to be handled even with any ONE pump unavailable. What is the minimum number of installed pumps?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Three operating pumps deliver 3(18) = 54 L/s, which exceeds the design inflow of 52 L/s. Two operating pumps deliver only 36 L/s and are insufficient. One additional pump must be installed to satisfy the stated one-pump-unavailable requirement. The minimum installed number is therefore four pumps. Actual design must also address power supply, standby operation, sediment and changes in the required pumping head.
వివరణ:
Question 9
ప్రశ్న 9
An excavation extends well below the water table in thick, permeable sand and gravel. A relatively large groundwater inflow and significant drawdown are expected over a broad area. Which method is generally appropriate to evaluate?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Deep-well dewatering employs wells equipped with suitable pumps and intake screens. It can be well suited to relatively large flows in permeable strata and to deep excavations. The required spacing and well capacities depend on aquifer characteristics and the design drawdown. Pumping must be checked for effects on adjoining ground and structures. Excavation support and basal stability remain separate design requirements.
వివరణ:
Question 10
ప్రశ్న 10
A deep shaft passes through low-permeability silty soil, where groundwater inflow per intake is relatively small but the required lift is beyond a conventional suction-wellpoint stage. Which system merits particular consideration?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Jet-eductor systems can create suction at a wellpoint below the depth accessible to ordinary suction lifting. They use pressurized motive fluid and a return-flow arrangement. Such systems can be useful for deeper excavations in comparatively low-permeability materials where each intake yields a modest flow. Their operating efficiency and piping requirements must be considered. Eductors do not eliminate the need for ground support or management of basal hydraulic pressures.
వివరణ:
Question 11
ప్రశ్న 11
A project involves relatively low-permeability sandy silt with modest groundwater flow and a relatively shallow excavation. Which engineering assessment of vacuum-assisted wellpoints is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Vacuum can increase the effective hydraulic gradient toward a screened intake where the soil and installation permit it. This may assist drainage in some sandy silts and similar materials. The effect depends on maintaining an adequate seal and limiting entry of air. Low permeability can still restrict the water flow available from the soil. Design trials or field monitoring may be appropriate where the expected performance is uncertain.
వివరణ:
Question 12
ప్రశ్న 12
For a simplified groundwater-flow check feeding an excavation, use Darcy's law Q = kAi. Given k = 2.0 x 10^-4 m/s, effective flow area A = 15 m2 and hydraulic gradient i = 0.40, what is Q in litres per second? Assume Darcy flow under the stated conditions.
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Darcy's law gives the volumetric discharge as the product of permeability, flow area and hydraulic gradient. Substitution gives Q = (2.0 x 10^-4)(15)(0.40) m3/s. This equals 0.00120 m3/s. Multiplying by 1000 converts the rate to 1.20 L/s. The calculation represents the stated idealized flow path and not the total pumping requirement of an arbitrary excavation.
వివరణ:
Question 13
ప్రశ్న 13
An upward seepage path beneath an excavation base has head loss of 2.7 m over flow length 6.0 m. The assumed critical hydraulic gradient is 0.90. Using i = Delta h/L and FS = icritical/i, what is the calculated factor of safety against boiling?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The average upward hydraulic gradient is the head loss divided by the flow length. It is 2.7/6.0 = 0.45. The stated factor-of-safety definition divides the critical gradient by this working gradient. Thus FS = 0.90/0.45 = 2.00. Whether this margin is acceptable depends on the project's required safety level and the reliability of the seepage model.
వివరణ:
Question 14
ప్రశ్న 14
While dewatering an excavation in fine sand, water and sand begin to rise locally through the base as visible boils. Which explanation is most appropriate?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
An upward seepage gradient produces a force on the soil skeleton in the direction of flow. At sufficiently high gradients, effective stress and the soil's ability to retain particles can become dangerously low. Visible sand boils can indicate an internal erosion or boiling problem. The appropriate response includes reviewing piezometric heads, seepage paths and filtration or cutoff measures. Uncontrolled increases in pumping may increase the destabilizing hydraulic gradient.
వివరణ:
Question 15
ప్రశ్న 15
An excavation near an older building requires pumping from deep wells in compressible ground. Which effect on the neighbouring building should be investigated even if the excavation walls are well braced?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Groundwater lowering may extend beyond the limits of the excavation. A fall in pore pressure can increase effective stress in compressible soil. This may produce settlement, potentially affecting nearby shallow foundations and buried utilities. Structural excavation bracing does not necessarily prevent changes in groundwater pressure outside the wall. Monitoring and suitable groundwater-control or recharge measures may be needed to limit adverse effects.
వివరణ:
Question 16
ప్రశ్న 16
An excavation base consists of a 3.0 m thick saturated soil plug above a confined aquifer. For an idealized uplift-force comparison, the plug's saturated unit weight is 18 kN/m3, the upward artesian pressure at its base corresponds to 5.0 m water head with gamma_w = 10 kN/m3, and side resistance is neglected. Calculate FS = downward plug weight per unit area / upward water pressure, and compare it with the project's required FS of 1.30.
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The downward plug weight per unit area is 3.0(18) = 54 kPa. The upward artesian pressure at the base is 5.0(10) = 50 kPa. Their ratio is FS = 54/50 = 1.08. This is less than the specified required value of 1.30. The simplified check indicates insufficient margin and requires examination of pressure relief, cutoff, construction sequence or other stabilization measures.
వివరణ:
Question 17
ప్రశ్న 17
A foundation excavation is underlain by a pressurized confined aquifer, and the proposed excavation level creates a risk of hydraulic uplift of the intervening low-permeability layer. What groundwater-control measure is most directly relevant?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A confined aquifer can exert upward pressure on the strata above it. Removing overburden during excavation can reduce the downward forces resisting this pressure. Relief wells or a suitable aquifer pumping system may reduce the hazardous piezometric head. The required drawdown should be established by an uplift and seepage analysis. Monitoring is important because wall bracing alone does not remove artesian pressure beneath the excavation.
వివరణ:
Question 18
ప్రశ్న 18
A sheet-pile wall is installed around a deep urban excavation, with interlocks sealed to reduce inflow. Which statement best explains the relationship between the sheet-pile cutoff and structural bracing?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Interlocking sheet piles may provide both a retaining wall and some restriction of groundwater inflow. Their joints and embedment influence seepage through and beneath the enclosure. Lateral earth and water pressures can still require structural supports. Walers, struts or anchors resist loads and limit deformation according to the design. Cutoff and lateral support must therefore be evaluated as separate but interacting functions.
వివరణ:
Question 19
ప్రశ్న 19
Which description correctly distinguishes walers, struts and rakers in an internally braced excavation?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Walers collect lateral reaction from a wall or sheathing along its length. Struts carry compressive forces between opposing walls or other suitable supports. Rakers are inclined compression members that bear against a designed reaction block or support. The effectiveness of each member depends on connections, stability and construction sequence. None of these structural members alone substitutes for a groundwater-control system.
వివరణ:
Question 20
ప్రశ్న 20
A narrow trench can accommodate compression members spanning between opposing retaining walls, but a wider excavation has obstructions preventing straightforward cross-lot struts. Which alternative support arrangement is particularly relevant where suitable reaction foundations can be provided within the excavation?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Cross-lot struts transfer compressive forces between opposed excavation walls. Rakers can instead support a wall along an inclined load path to a prepared reaction location. They may suit excavation layouts in which full-width cross-lot struts are impractical. Their bases and connections must be designed for substantial concentrated forces. Their placement can obstruct excavation operations and must be coordinated with the construction sequence.
వివరణ:
Question 21
ప్రశ్న 21
An idealized vertical excavation-support wall carries a triangular lateral pressure distribution that varies from zero at its top to 60 kPa at its base over a height of 4.0 m. Neglect other loads. What are the resultant lateral force per metre of wall length and the height of its line of action above the base?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The resultant of a triangular pressure distribution equals its diagram area per metre of wall. It is 0.5(60)(4) = 120 kN/m. The resultant acts one-third of the triangle height above the side of maximum pressure. Since the pressure is greatest at the base, the distance above the base is 4/3 = 1.33 m. The stated result is an idealized lateral force and does not represent all loads in an actual braced excavation.
వివరణ:
Question 22
ప్రశ్న 22
A waler in a braced excavation receives a prescribed horizontal line load of 70 kN per metre along the wall. Identical struts are spaced 3.0 m apart, and for this exercise each interior strut carries the tributary load over its spacing with no other forces. What is the horizontal compression force in an interior strut?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The waler is assumed to transfer a uniform line load to equally spaced struts. The tributary length for an interior strut is the 3.0 m spacing. The compression demand is therefore line load multiplied by tributary length. Calculation gives 70(3.0) = 210 kN. Actual strut design must also address buckling, connection loads, construction tolerances and the appropriate load combinations.
వివరణ:
Question 23
ప్రశ్న 23
During staged excavation beside a buried water main, an already installed brace shows rapidly increasing strain and the excavation wall moves further toward the cut. Which construction response is most appropriate?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Increasing wall movement and brace force can indicate that the temporary support system is approaching an undesirable condition. Nearby buried utilities may be damaged by lateral soil displacement. The excavation sequence should not be advanced blindly while such observations remain unexplained. A qualified engineer should review the monitored response against the design assumptions and action levels. Suitable correction may involve additional support, revised dewatering or changes to excavation staging.
వివరణ:
Question 24
ప్రశ్న 24
Which pairing of Indian Standards and their principal subjects is correct for foundation excavation works?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
IS 9759 provides Indian guidance for dewatering during construction. IS 3764 addresses safety-related requirements for excavation work. Groundwater control and excavation stability are related but different parts of a safe construction plan. The applicable documents should be used with current project specifications and the actual ground conditions. Neither standard eliminates the need for site-specific engineering judgement and temporary-works design.
వివరణ:
Question 25
ప్రశ్న 25
A deep pumping-station excavation is planned beside settlement-sensitive buildings in layered ground with a shallow water table and a confined aquifer below. Which preliminary design strategy is most defensible?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A deep urban excavation must satisfy structural and hydraulic stability requirements at the same time. The retaining system manages lateral earth and water pressures and limits wall movement. A suitably designed cutoff and pumping or pressure-relief arrangement can control seepage and artesian head. Excessive drawdown outside the excavation may cause settlement in neighbouring compressible deposits. Monitoring and a staged response plan are therefore essential parts of a defensible excavation scheme.
వివరణ:
Answer Key సమాధానాల పట్టిక
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Question 1 ప్రశ్న 1Answer: B. Dewatering controls groundwater levels or pressures, while shoring and bracing resist soil and water loads and control excavation-wall deformation. సమాధానం: B.
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Question 2 ప్రశ్న 2Answer: C. Collection ditches leading to a filtered sump and a suitably sized pump. సమాధానం: C.
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Question 3 ప్రశ్న 3Answer: D. Treat the observations as possible internal erosion or boiling and review pumping, filters, cutoff or well systems and base stability before continuing. సమాధానం: D.
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Question 4 ప్రశ్న 4Answer: A. Screened wellpoints collect groundwater, riser pipes connect them to a common header, and the pumping or vacuum system removes water from the header. సమాధానం: A.
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Question 5 ప్రశ్న 5Answer: B. The claim is incorrect because atmospheric-pressure and practical suction losses limit lift, so multiple stages or another method may be needed for deeper lowering. సమాధానం: B.
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Question 6 ప్రశ్న 6Answer: C. Consider multistage wellpoints installed at successively lower levels, with excavation stability and stage sequencing assessed. సమాధానం: C.
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Question 7 ప్రశ్న 7Answer: D. 4.8 m. సమాధానం: D.
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Question 8 ప్రశ్న 8Answer: A. Four pumps. సమాధానం: A.
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Question 9 ప్రశ్న 9Answer: B. A series of properly screened deep wells with submersible pumps, designed for the required inflow and drawdown. సమాధానం: B.
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Question 10 ప్రశ్న 10Answer: A. Jet-eductor wellpoints or wells using a pressurized circulating-fluid system to induce suction at depth. సమాధానం: A.
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Question 11 ప్రశ్న 11Answer: C. Applying vacuum may improve groundwater extraction in suitable fine-grained soils, but performance must be checked against permeability, air leakage and attainable lift. సమాధానం: C.
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Question 12 ప్రశ్న 12Answer: D. 1.20 L/s. సమాధానం: D.
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Question 13 ప్రశ్న 13Answer: B. 2.00. సమాధానం: B.
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Question 14 ప్రశ్న 14Answer: C. Upward seepage forces may be reducing effective stress and causing boiling or piping, requiring immediate assessment of hydraulic gradients and seepage control. సమాధానం: C.
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Question 15 ప్రశ్న 15Answer: A. Changes in pore pressure and effective stress outside the excavation may cause ground settlement and building movement. సమాధానం: A.
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Question 16 ప్రశ్న 16Answer: D. FS = 1.08; does not meet the required value. సమాధానం: D.
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Question 17 ప్రశ్న 17Answer: C. Evaluate pressure-relief wells or other aquifer depressurization measures, while verifying uplift stability and monitoring piezometric heads. సమాధానం: C.
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Question 18 ప్రశ్న 18Answer: A. A sheet-pile cutoff can reduce groundwater inflow, while adequate embedment, struts, walers or anchors may still be required to resist lateral loads and wall deformation. సమాధానం: A.
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Question 19 ప్రశ్న 19Answer: B. Walers distribute forces along retaining walls, struts commonly span across the excavation in compression, and rakers provide inclined compression support to a wall through a suitable reaction point. సమాధానం: B.
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Question 20 ప్రశ్న 20Answer: D. Inclined raker braces with appropriately designed base reaction or thrust blocks. సమాధానం: D.
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Question 21 ప్రశ్న 21Answer: C. 120 kN/m and 1.33 m. సమాధానం: C.
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Question 22 ప్రశ్న 22Answer: A. 210 kN. సమాధానం: A.
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Question 23 ప్రశ్న 23Answer: D. Pause the affected excavation activity, evaluate the support and groundwater conditions, and implement engineered corrective measures before proceeding. సమాధానం: D.
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Question 24 ప్రశ్న 24Answer: B. IS 9759 addresses dewatering during construction, while IS 3764 addresses excavation-work safety provisions. సమాధానం: B.
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Question 25 ప్రశ్న 25Answer: C. Integrate an appropriate retaining and cutoff system, staged bracing, controlled groundwater drawdown or pressure relief, and monitoring of pore pressures and adjacent movements. సమాధానం: C.