Question 1

In the full-face method of tunnel excavation, into how many working sections is the face generally divided for efficient drilling, blasting, and mucking?

Accepted Answer

Introduction / Context: The full-face method advances the entire perimeter of the tunnel, but for practical drilling and blasting the face is commonly organized into zones. Subdivision helps with sequencing (cut, stoping, lifters), improves fragmentation control, and facilitates mucking while maintaining face stability and access for support installation. Given Data / Assumptions: Method: full-face excavation of the entire outline. Objective: determine the typical number of working sections used in practice. Assume conventional drill-and-blast in rock with standard patterns. Concept / Approach: In many method statements, the face is divided into three practical zones that align with blasting patterns: a central cut (to create relief), the surrounding stoping holes, and the bottom (lifter) holes near the invert. This three-part organization synchronizes drilling, charging, and mucking cycles and yields a stable advance profile. Step-by-Step Solution: Recognize that 'full-face' means perimeter advance, not necessarily a single undivided working area.Identify common zoning: cut, stoping, lifters → three sections.Select the option 'three sections' to reflect standard practice. Verification / Alternative check: While variations exist (e.g., additional wedges or pre-splitting), the tripartite division remains a textbook convention for organizing the blast round and mucking sequence. Why Other Options Are Wrong: Two sections: Over-simplifies and can hinder controlled breakout. Four or five: Possible in special cases but not the general baseline. One undivided section: Impractical for controlled blasting and mucking logistics. Common Pitfalls: Assuming 'full-face' means no internal sequencing. Neglecting to provide proper cut relief, causing poor fragmentation and overbreak. Final Answer: three sections

Question 2

In underground tunnelling near the working face, what is the maximum permissible concentration of respirable dust particles in the size range 0.5–5 microns (measured as number of particles per cubic centimetre) to protect workers and equipment?

Accepted Answer

Introduction / Context: Dust control at the tunnel face is central to occupational health and visibility. The most harmful fraction comprises fine respirable particles, typically in the 0.5–5 micron range, which can penetrate deep into the lungs. This question checks recall of a benchmark ceiling for particle counts close to the working face to guide ventilation, water-spray, and housekeeping measures. Given Data / Assumptions: Location: immediately adjacent to the active tunnel face. Particle size band: 0.5–5 microns. Metric: number of particles per cubic centimetre (particles/cm3). Objective: identify the maximum recommended concentration for safe operations. Concept / Approach: Engineering controls (face ventilation, scrubbers, misting) target keeping airborne fines below a practical, easy-to-monitor threshold. Particle-count ceilings complement mass-concentration limits (mg/m3) used in hygiene standards. As a memory aid for site practice, many syllabi adopt 300 particles/cm3 as the not-to-exceed guideline for the critical 0.5–5 micron band at the face. Step-by-Step Solution: Identify the hazardous fraction: 0.5–5 μm particles are respirable and remain airborne.Relate to tunnel-face controls: apply ventilation rate, sprays, and sequencing to reduce counts.Select the standard ceiling used in exam practice: 300 particles/cm3. Verification / Alternative check: If portable counters show counts trending near 300 particles/cm3, increase air quantity at the face, improve wet drilling, or delay re-entry after blasting until counts drop. Why Other Options Are Wrong: 200 or 250 particles/cm3: stricter than the commonly taught threshold; conservative but not the standard reference value.400 or 450 particles/cm3: too lenient; may allow visibility loss and higher health risk. Common Pitfalls: Confusing particle-count thresholds with mass-based limits (mg/m3); the two metrics are related but not interchangeable.Measuring too far from the face where dilution lowers counts, giving a false sense of safety. Final Answer: 300 particles/cm3

Question 3

Why are highway or railway tunnels often more advantageous than surface alternatives? Identify the comprehensive set of benefits that commonly justify tunnelling over a detour or open cut.

Accepted Answer

Introduction / Context: Selecting between tunnelling and a surface alignment is a fundamental planning decision. Tunnels can provide straighter, shorter routes through mountains or dense urban areas, mitigate severe weather exposure, and minimize disruption to existing communities or land rights. This question evaluates understanding of the multifaceted advantages that make tunnelling attractive in feasibility studies. Given Data / Assumptions: Alternatives considered: detour around terrain obstacles, open cut through hills, or tunnel. Performance factors: climate resilience, alignment length, costs, maintenance, and surface rights. Goal: choose the option that aggregates the primary benefits. Concept / Approach: Tunnels reduce grades and curvature, resulting in shorter route length and operating savings. They are protected from surface snow/ice, improving reliability and reducing closures. Maintenance for stabilized underground works is often less than for long exposed cuts or high embankments. Additionally, tunnelling preserves surface land use and avoids complex right-of-way acquisition—crucial in urban or environmentally sensitive areas. Step-by-Step Solution: Compare alternatives: detour increases distance and travel time.Open cut: large excavation volumes, landslide/erosion risk, snow accumulation on approaches.Tunnel: shorter alignment, stable microclimate, limited surface impacts. Verification / Alternative check: Life-cycle costing that includes operations and maintenance typically shows tunnels becoming competitive or cheaper when surface works are extensive or weather exposure is severe. Why Other Options Are Wrong: Each single benefit is true, but only “All the above” captures the full set of common advantages. Common Pitfalls: Focusing solely on initial construction cost without factoring maintenance, closures, and right-of-way complications. Final Answer: All the above.

Question 4

For railway alignment in rugged terrain, which options may be considered depending on economics and terrain—detour around the hill, open cut through the hill, or tunnelling—and which overall statement best reflects practice?

Accepted Answer

Introduction / Context: Railway route selection weighs cost, grade constraints, curvature, land acquisition, and environmental impacts. Depending on site conditions, engineers may choose to detour, cut, or tunnel. This question checks recognition that all three are legitimate alternatives evaluated during feasibility and detailed design, with the final choice being context-dependent. Given Data / Assumptions: Terrain: hill or ridge obstructing the desired rail alignment. Feasible solutions: detour, open cut, or tunnel. Decision basis: economics, operations, safety, and environmental factors. Concept / Approach: A detour can avoid heavy works but increases distance and operational energy. An open cut shortens the route but demands large excavation and slope stabilization. A tunnel provides the straightest line but requires specialized construction and ventilation. Since any of these can be “preferred” in the right circumstances, the comprehensive answer acknowledges all three options as valid choices considered by railway planners. Step-by-Step Solution: Quantify costs for each alternative including earthworks, structures, and track geometry.Check operational impacts: grades, curvature, travel time, and energy consumption.Assess environmental and land impacts, then choose the least-cost, most reliable solution. Verification / Alternative check: Case histories show all three approaches used successfully; the “best” option varies project to project. Why Other Options Are Wrong: Each single alternative may be optimal sometimes, but none is universally superior. Hence only “All the above” captures the real design choice set. Common Pitfalls: Assuming tunnels are always costlier; deep open cuts can exceed tunnel costs when stabilization is extensive. Final Answer: All the above.

Question 5

Rock tunnelling workflow: choose the correct chronological sequence of operations—removing foul gases, marking the tunnel profile, setting up and drilling, checking misfires, and mucking (spoils removal).

Accepted Answer

Introduction / Context: Efficient and safe drill-and-blast tunnelling follows a repeatable cycle at the face. The order of profiling, drilling, blasting, ventilation, safety checks, and mucking is critical to minimize delays and incidents. This question tests the correct sequencing around blasting events in rocky terrain. Given Data / Assumptions: (1) Removing foul gases after a blast. (2) Marking the tunnel profile (setting out the cut and trimmers). (3) Setting up equipment and drilling the blast holes. (4) Checking misfires after blasting and ventilation. (5) Mucking—removing broken rock. Concept / Approach: The cycle begins with layout (marking profile) followed by drilling. After blasting, ventilation clears fumes; then a careful misfire check ensures no live explosives remain before mucking. Skipping or reordering these steps risks overbreak, rework, or accidents. Step-by-Step Solution: First, mark the face to the designed profile (Step 2).Second, set up and drill per the marked pattern (Step 3).After blast, remove gases with forced ventilation (Step 1).Then, perform misfire checks per safety protocols (Step 4).Finally, muck out the blasted rock (Step 5). Verification / Alternative check: Standard tunnelling cycles list “profile → drill → blast & ventilate → check → muck → support,” matching the selected order up to the mucking stage. Why Other Options Are Wrong: Any sequence that places mucking before misfire checks or ventilation is unsafe.Starting with gas removal or misfire checks before blasting is illogical. Common Pitfalls: Rushing to muck without adequate gas clearance or misfire inspection. Final Answer: 2 3 1 4 5

Question 6

Survey and control for tunnelling: identify the correct composite statement covering the use of Survey of India topo maps in mountains, reciprocal ranging for ridge height points, planimetric control accuracy, and the angular precision target with a…

Accepted Answer

Introduction / Context: Tunnel alignment demands robust surface control and careful transfer underground. Understanding how topographic resources, ranging methods, linear-control accuracy, and angular precision targets fit together helps avoid breakthrough errors and costly corrections. This item checks several foundational survey concepts used in tunnel projects. Given Data / Assumptions: Mountainous terrain requires careful reconnaissance; national topo maps guide feasibility and preliminary alignment. Reciprocal ranging helps intervisibility and height checks across ridges/valleys. Planimetric control accuracy on the order of 1 in 10,000 is a reasonable target for tunnel works. Using a 1-second theodolite, an often-quoted practical closure target is about 15 seconds times square root of the number of angles (15″√N). Concept / Approach: Topo maps enable route reconnaissance and initial control planning. Reciprocal ranging is a classic technique to mitigate line-of-sight curvature/refraction errors across obstacles. Planimetric accuracy of 1:10,000 aligns with the precision typically required for long drives. Angular precision guidelines translate instrument capability into expected closure error, giving surveyors a yardstick for quality control in triangulation/traverses. Step-by-Step Solution: Affirm topo-map utility for reconnaissance in mountains.Recognize reciprocal ranging as valid for ridge height/line checks.Note 1:10,000 planimetric control as an appropriate accuracy.Select the precise statement: a 1″ theodolite aiming for ≈ 15″√N angular error. Verification / Alternative check: In practice, traverse closures and breakthrough tolerances confirm that these values are fit-for-purpose for many tunnel projects. Why Other Options Are Wrong: Dismissing topo maps or reciprocal ranging contradicts standard practice.Calling 1:10,000 “excessive” ignores typical engineering requirements for control networks. Common Pitfalls: Confusing instrument reading resolution (1″) with guaranteed closure; environmental and procedural factors still matter. Final Answer: A 1-second theodolite is used to achieve angular error of 15″√N

Question 7

Permanent drainage of tunnels: which measures are typically adopted to ensure long-term dry and durable operation of the tunnel and its lining?

Accepted Answer

Introduction / Context: Water management is a defining feature of tunnel durability. Even small inflows can degrade trackbeds, pavements, or utilities and promote lining damage. Designers therefore combine multiple permanent drainage tactics to intercept, convey, and reduce inflow throughout the life of the tunnel. Given Data / Assumptions: Tunnel through rock/soil with potential inflow. Goal: long-term drainage and watertightness. Available measures: longitudinal drains, open channel drains, linings, and pre/post grouting. Concept / Approach: Longitudinal drains collect seepage along the sidewalls or invert and take it to sumps. Continuous open drains provide redundancy and access. Concrete or segmental linings reduce seepage and protect the structure. Grouting seals discontinuities in the surrounding ground. Used together, these measures minimize pore-pressure buildup and protect the tunnel envelope and track/roadbed. Step-by-Step Solution: Provide longitudinal/invert drains with adequate gradient to sump/pump rooms.Detail open channels or perforated pipes with clean-out points.Use linings with waterstops; add drainage layers/geotextiles as needed.Apply pre- or post-excavation grouting to cut off significant inflows. Verification / Alternative check: Reduced inflows at inspection points and dry operating conditions validate the combined drainage scheme. Why Other Options Are Wrong: Each single option is effective, but best practice employs them in combination; hence “All the above.” Common Pitfalls: Relying solely on lining without drainage; hydrostatic pressure can still damage the structure. Final Answer: All the above.

Question 8

For Broad Gauge (B.G.) single-track railway tunnels, what is the typical recommended clear width of the tunnel section?

Accepted Answer

Introduction / Context: Tunnel cross-sections for railways must provide safe clearances for dynamic envelope, electrification equipment (if any), maintenance walkways, and aerodynamic effects. For Broad Gauge single track, standard practice converges to a moderate width band that balances construction economy with operational safety. Given Data / Assumptions: Gauge: Broad Gauge (single track). Quantity: clear width of tunnel section. Assume conventional clearance without extraordinary equipment allowances. Concept / Approach: Clear width reflects track centerline allowances, sway, and lateral clearances. Typical guidance for B.G. single track sits in the 4.9–5.5 m range, accommodating dynamic sway and minor maintenance space while keeping excavation volumes reasonable. Larger widths are reserved for special provisions (walkways both sides, heavy electrification fixtures) or future-proofing decisions. Step-by-Step Solution: Define the dynamic envelope and lateral clearances for B.G. stock.Include tolerances for track alignment, construction, and side drainage.Select the established width band: 4.9 m to 5.5 m. Verification / Alternative check: Cross-section checks for typical B.G. rolling stock show this band sufficient for non-electrified and many electrified corridors with compact fittings. Why Other Options Are Wrong: 4.2–4.8 m: may under-provide lateral clearance.5.5–5.8 m or larger: wider than typical baseline; increases excavation without necessity in many cases. Common Pitfalls: Ignoring special allowances (walkways, cable trays) that may push designers toward the top of the band. Final Answer: 4.9 m to 5.5 m

Question 9

In tunnelling logistics, an overhead track mounted on a large truss frame is specifically required with which car-changer/material-handling method for muck-car movements?

Accepted Answer

Introduction / Context: Efficient muck handling inside tunnels often uses rail-bound cars and specialized car-changing systems at transfer points. Some systems require elevated rails or overhead tracks to quickly swap loaded and empty cars without blocking the main track. This item probes identification of the method associated with a truss-mounted overhead track arrangement. Given Data / Assumptions: Setting: car-changing station at or near the portal/transfer point. Alternative methods: grasshopper, passing track, California crossing, Dixon conveyor. Feature in question: overhead track on a large truss frame. Concept / Approach: The Dixon conveyor method integrates conveyors with railcars and often uses elevated/overhead track arrangements supported by trusses to allow gravity-assisted or conveyor-assisted transfers while maintaining clearance for equipment underneath. Other methods rely on on-grade sidings, portable turnouts, or crossings and typically do not require a substantial truss-supported overhead rail system. Step-by-Step Solution: Match each method with its characteristic layout.Identify which one specifically uses overhead track on a truss frame: Dixon conveyor method.Select the corresponding option. Verification / Alternative check: Descriptions of Dixon conveyor systems emphasize combined conveyor/overhead arrangements to streamline car changes and discharge. Why Other Options Are Wrong: Grasshopper: portable turnouts/short panels moved near the face, not overhead car changers.Passing track: simple loop/siding on grade.California crossing: at-grade crossing arrangement, not an overhead truss system. Common Pitfalls: Confusing conveyor-integrated systems with ordinary rail passing layouts. Final Answer: Dixon conveyor method

Question 10

For a Broad Gauge (B.G.) single-track railway tunnel, what should be the typical clear height above top of rails (TOR) to accommodate rolling stock and services?

Accepted Answer

Introduction / Context: Tunnel vertical clearance must safely envelope the dynamic outline of trains, overhead equipment (if electrified), ventilation ducts, and maintenance space. For B.G. single track, a clear-height band has emerged from practice to balance safety, equipment needs, and excavation economy. Given Data / Assumptions: Gauge: Broad Gauge (single track). Reference: height above top of rails (TOR). Assume standard rolling stock and typical service provisions. Concept / Approach: The 6.7–7.3 m band accommodates train sway, overhead fixtures, and cable/duct allowances without excessive over-excavation. Lower bands may suffice in specific non-electrified contexts, but the stated range is a robust general guideline in planning and exam contexts, particularly where room for ventilation ducts or emergency systems is needed. Step-by-Step Solution: Identify TOR as the vertical datum for clearances.Include dynamic envelope, OHE (if applicable), and safety margins.Select the recognized safe band: 6.7 m to 7.3 m above TOR. Verification / Alternative check: Cross-sections of typical B.G. tunnels with OHE and walkways fit within this envelope while preserving aerodynamic and smoke clearance considerations. Why Other Options Are Wrong: Bands below 6.7 m risk inadequate space for equipment and safe clearances.Values beyond 7.3 m are conservative and raise excavation costs without generic justification. Common Pitfalls: Forgetting to check special rolling stock or emergency ventilation requirements that might push toward the upper end of the band. Final Answer: 6.7 m to 7.3 m

Question 11

Transferring tunnel alignment down a shaft: choose the correct sequence of steps—(1) hang two or more plumb lines, (2) determine the bearing of the plumb plane, (3) suspend a 35 kg weight to each plumb line, and (4) immerse the weights in water buck…

Accepted Answer

Introduction / Context: Accurate transfer of alignment from surface to underground is achieved by plumbing down reference lines in a shaft and establishing a stable “plumb plane.” The order of operations must ensure that lines are hung, weighted, and sufficiently stabilized before precise angular observations are taken to set out headings below. Given Data / Assumptions: Two or more plumb lines are used to define a vertical reference plane. Weights (≈ 35 kg) are attached to minimize sway. Immersion in water acts as a damper to further steady the plumb bobs. Final goal: determine the plumb plane bearing accurately for transferring the alignment. Concept / Approach: Stability precedes measurement. Lines must first be hung (geometry established), then weighted (reduce oscillations), and only then should bearing observations be made. Water damping is often used after preliminary stabilization to maintain steadiness during prolonged observations or in drafty shafts. Step-by-Step Solution: Hang the plumb lines at the shaft top (Step 1).Suspend 35 kg weights to each line for stability (Step 3).Determine bearing of the plumb plane with a theodolite (Step 2).Immerse weights in water buckets to maintain damping during observation/transfer (Step 4). Verification / Alternative check: Field practice corroborates that unweighted or undamped lines yield erratic readings; stable lines give repeatable bearings for precise breakthrough control. Why Other Options Are Wrong: 1 2 3 4: attempts observation before stabilizing with weights.4 3 2 1 / 2 1 4 3: illogical ordering; stabilization must precede measurement. Common Pitfalls: Skipping water damping in drafty shafts; leads to wandering plumb lines and angular errors. Final Answer: 1 3 2 4

Question 12

In initial tunnel route surveys for civil engineering projects, arrange the activities in the correct order: (1) mark the portal point with concrete pillars on ground, (2) mark tunnel obligatory points on topographical maps, (3) perform preliminary …

Accepted Answer

Introduction / Context: Tunnel planning begins long before excavation. An orderly initial survey sequence ensures that the alignment is first conceptualized on authoritative maps, refined by fixing obligatory control points (e.g., portals, shafts, curve points), physically connected by lines on the map and ground, and finally materialized at the site with permanent markers. This question checks understanding of that logical progression from desk study to field control. Given Data / Assumptions: Four activities are listed and must be sequenced. Survey of India maps are the standard base for preliminary alignment. Obligatory points are critical control points governing line and grade. Portal points are materialized on ground with concrete pillars for durability. Concept / Approach: Good practice is to start with map-based preliminary setting to decide a viable corridor. Then, obligatory points are marked on the topo sheets. Next, the surveyor establishes control/connection between these fixed points by driving lines (joining them). Finally, the alignment is pegged on ground at the portal with permanent concrete pillars to serve as lasting benchmarks for subsequent detailed survey and construction layout. Step-by-Step Solution: Step 1: Preliminary setting on Survey of India maps → activity 3.Step 2: Mark obligatory points on topographical maps → activity 2.Step 3: Drive lines between fixed obligatory points → activity 4.Step 4: Mark the portal on ground with concrete pillars → activity 1. Verification / Alternative check: Reversing the order would either attempt to pillar a portal before the alignment is fixed, or join points that are not yet defined—both illogical. The selected sequence mirrors standard feasibility-to-field-transfer workflow. Why Other Options Are Wrong: 1 2 3 4: Starts construction marking before map-based decisions. 4 3 1 2 or 2 4 3 1: Join or mark elements before preliminary map setting—procedure is inverted. Any other order breaks the conceptual-to-physical progression. Common Pitfalls: Confusing “driving lines” on map versus staking on ground; here it refers to joining fixed points for control. Fixing portals prematurely without confirmed alignment. Final Answer: 3 2 4 1

Question 13

In tunnel construction safety and operations, which mechanical ventilation strategy is used to maintain breathable air at the face and along the heading?

Accepted Answer

Introduction / Context: Tunnel works generate fumes, dust, and heat from drilling, blasting, mucking, and equipment. Mechanical ventilation is essential to supply oxygen, dilute contaminants, and keep visibility acceptable. Depending on the project and heading length, systems may blow, exhaust, or combine both to achieve target air quality at the working face. Given Data / Assumptions: The choices list blowing, exhausting, and a combined (push–pull) approach. All are recognized mechanical ventilation strategies. Objective: identify which of these is used in tunnels. Concept / Approach: Blowing systems push fresh air to the face via ducts, improving oxygen and flushing dust forward. Exhaust systems extract foul air at the face to reduce backflow into the heading. Combined systems use both to maintain desired flow patterns and contaminant removal, especially after blasting when noxious gases peak. Step-by-Step Solution: Recognize that each listed method is a valid mechanical strategy.Note that selection depends on heading length, cross-section, and equipment emissions.Therefore, the inclusive correct response is “All the above.” Verification / Alternative check: Construction method statements typically prescribe blowers for active headings and switch to exhaust or combined modes post-blast to clear fumes quickly, confirming the variety in practice. Why Other Options Are Wrong: Any single method alone ignores the fact that all three are used across projects. “None of these” contradicts established tunnelling practice. Common Pitfalls: Using inadequate duct diameter/length, reducing effective airflow. Delaying re-entry without achieving gas thresholds after blasting. Final Answer: All the above.

Question 14

In steep-gradient tunnels, a wooden bulkhead (used to control muck movement) is provided with how many openings to manage passage and controlled discharge?

Accepted Answer

Introduction / Context: On steep grades, muck tends to rush downhill after blasting, creating safety hazards and operational difficulties. A wooden bulkhead is installed to regulate flow, protect workers and equipment, and allow controlled loading into cars or conveyors. Its configuration typically includes openings that balance containment with operational throughput. Given Data / Assumptions: Tunnel grade is steep enough to require a bulkhead for muck control. Openings are necessary for track/pass-through and controlled muck discharge. We seek the standard number of openings. Concept / Approach: A practical wooden bulkhead has two openings: one larger opening for passage of equipment/track or controlled chute loading, and a second for regulated discharge or ventilation/inspection. This dual-opening arrangement allows operations while maintaining a barrier that prevents uncontrolled run of muck. Step-by-Step Solution: Identify functions needed: access + controlled discharge.Provide two dedicated openings to serve these functions.Select “Two openings are provided.” Verification / Alternative check: Construction manuals depict bulkheads with separate pass doors/chutes; a single aperture is usually insufficient, and no openings would make operations impractical, corroborating the two-opening convention. Why Other Options Are Wrong: One opening: Limits control and access. Three or four openings: Atypical and may weaken the bulkhead. No opening: Operationally unfeasible. Common Pitfalls: Over-sizing openings, reducing containment effectiveness. Neglecting reinforcement of openings against impact loads. Final Answer: Two openings are provided

Question 15

During tunnel excavation, when should concrete lining be provided concurrently with the driving operation to ensure ground stability and safety?

Accepted Answer

Introduction / Context: The timing of lining installation is driven by ground behavior. In competent rock, a lag between excavation and permanent lining is often acceptable. In weak or unstable soils—especially running ground that flows into the heading—immediate or concurrent lining is vital to prevent collapses and excessive deformation. Given Data / Assumptions: “Running soil” denotes cohesionless, unstable material prone to ravel or flow. Objective: identify the condition requiring concurrent lining with driving. Concrete lining provides rapid, rigid support and containment. Concept / Approach: In running ground, the unsupported stand-up time is negligible. Therefore, excavation and lining must progress in close sequence—often with immediate shuttering and concreting or with preformed segments—to stabilize the face and prevent inflow or ground loss that could damage surface structures. Step-by-Step Solution: Assess ground: running soil → low stand-up time, high instability.Adopt concurrent lining to provide instant support.Select “Running soil.” Verification / Alternative check: Historical failures in loose, water-bearing soils underline the necessity of immediate support. Modern shield/TBM segmental linings play the same role in such formations. Why Other Options Are Wrong: Rock terrain/soft rock: May allow delayed lining with temporary support. None/dense granular soil (low water): Often stable enough for staged support. Common Pitfalls: Underestimating water pressure; ignore it and even soft soils can “run.” Delaying lining due to logistics, increasing collapse risk. Final Answer: Running soil

Question 16

During tunnel excavation safety monitoring, identify the acceptable on-site air quality thresholds at the heading: oxygen, carbon dioxide, hydrogen sulphide, and carbon monoxide should satisfy which combined limits?

Accepted Answer

Introduction / Context: Ventilation in tunnels must maintain breathable air and prevent toxic exposure for workers. Regulatory and industry guidelines specify minimum oxygen and maximum contaminant limits to guide re-entry after blasting, continuous equipment operation, and routine work at the face. This question tests familiarity with commonly cited safe-threshold values for key gases. Given Data / Assumptions: Parameters: O2, CO2, H2S, CO at the heading. Thresholds represent practical minima/maxima widely used on sites. Instrumentation (multi-gas meters) is used to verify compliance before entry. Concept / Approach: Safe practice requires O2 ≥ 19.5% to avoid hypoxia; CO2 ≤ 0.5% to limit asphyxiation risk; H2S ≤ 0.001% (≈10 ppm) due to its toxicity; and CO ≤ 0.01% (≈100 ppm) to prevent carboxyhemoglobin formation. Meeting all criteria simultaneously is necessary for worker safety and legal compliance. Step-by-Step Solution: Check oxygen: must be ≥ 19.5%.Check CO2: must be ≤ 0.5%.Check H2S: must be ≤ 0.001%.Check CO: must be ≤ 0.01%.Since each limit is required, the correct choice is “All of the above.” Verification / Alternative check: Post-blast ventilation plans typically target sustained airflow to clear NOx, CO, and SOx and verify with detectors that the above thresholds are met before resuming work. Why Other Options Are Wrong: Any single parameter alone is insufficient; safe atmosphere requires all limits. Values higher in contaminants or lower in oxygen would be unsafe. Common Pitfalls: Rushing re-entry without instrument confirmation. Ignoring localized pockets where heavier-than-air gases accumulate. Final Answer: All of the above.

Question 17

Historical development of tunnelling: choose the correct chronological order for these “firsts”—(1) the first Roman tunnel by Emperor Claudius, (2) the first highway tunnel in Hungary, (3) the first underground railway tunnel in Great Britain, and (…

Accepted Answer

Introduction / Context: Milestones in tunnel history span from ancient Roman works to modern transport systems. Knowing the broad chronology helps students contextualize technology shifts—from manual excavation and masonry linings to mechanized construction and mass transit. Given Data / Assumptions: (1) Roman era work under Emperor Claudius predates early-modern European projects. (4) French navigational canals and tunnels (e.g., Malpas) emerged in the early modern period. (2) Dedicated highway tunnels appeared later with roadway expansion. (3) The first underground railway tunnel in Britain follows in the 19th century context. Concept / Approach: Arrange from earliest to latest based on eras: Roman antiquity → early modern canal navigation → early roadway tunnels → industrial-age urban rail. This yields 1 → 4 → 2 → 3 as a widely taught sequence in classic MCQs. Step-by-Step Solution: Ancient works (Emperor Claudius) occur first → 1.Canal/navigational tunnel era in France (early modern) → 4.Highway-tunnel development period → 2.Urban underground rail in Great Britain (19th century) → 3. Verification / Alternative check: Although specific dates vary by reference, the above ordering represents the commonly accepted educational sequence contrasting ancient, canal-era, roadway, and railway breakthroughs. Why Other Options Are Wrong: Options placing Roman works after modern tunnels invert history. Sequences that put underground rail before canal-age navigation are inconsistent with typical timelines. Common Pitfalls: Confusing the first underground “service” with earlier tunnel structures. Assuming all transport tunnels are contemporaneous with rail development. Final Answer: 1 4 2 3

Question 18

Forepoling (driving spiles ahead of the face) is generally adopted for tunnelling in which type of ground condition to maintain face stability?

Accepted Answer

Introduction / Context: Forepoling installs short, closely spaced spiles or boards ahead of the advancing face to create a protective canopy. This technique is part of the observational method in weak or unstable soils and prevents sudden inflow or collapse at the heading. Given Data / Assumptions: Question seeks the ground type where forepoling is “generally adopted.” Running ground denotes cohesionless, unstable, or water-bearing soils with negligible stand-up time. Objective: select the most critical condition warranting forepoling. Concept / Approach: Forepoling is most associated with running ground where advance without a canopy leads to face sloughing or runs. By pre-supporting the face and crown, forepoling creates a controlled arch, allowing incremental excavation beneath the spiles with immediate temporary support and subsequent lining. Step-by-Step Solution: Identify hazards: flowing sand/silt or heavily fractured zones.Apply forepoling to provide instant overhead support.Choose “Running ground.” Verification / Alternative check: Modern analogues include pipe-roof canopies and jet-grouted umbrellas used in similar ground, reinforcing that forepoling targets the most unstable soft ground conditions. Why Other Options Are Wrong: Soft ground (general) is broad; forepoling is specifically for the “running” subset. Firm ground or sound rock usually does not require such pre-support. “None” contradicts established practice. Common Pitfalls: Insufficient overlap of spiles reduces canopy effectiveness. Ignoring groundwater pressure that can still destabilize the face. Final Answer: Running ground

Question 19

For Indian railway tunnels, the difference in required tunnel clearance height above rail top between Broad Gauge (BG) and Metre Gauge (MG) tracks is maintained at what value?

Accepted Answer

Introduction / Context: Tunnel clearance envelopes depend on gauge, rolling stock dimensions, dynamic sway, and electrification provisions. In India, BG rolling stock is larger than MG, so tunnel vertical clearance above rail top differs. Designers must remember these standard differences to avoid costly over/under design when converting or constructing tunnels for various gauges. Given Data / Assumptions: Comparing vertical clearance above rail top (ART) for BG and MG. We need the standard difference to be maintained in tunnel profiles. Assume conventional nonelectrified baseline envelopes. Concept / Approach: BG has a larger loading gauge, leading to a greater minimum tunnel height. The commonly cited difference maintained between BG and MG tunnel headroom clearances is about 0.45 m, capturing the incremental height needed for the broader, taller BG stock. Step-by-Step Solution: Identify that BG requires higher tunnel clearance than MG.Use the standard difference figure → 0.45 m.Select 0.45 m from the options. Verification / Alternative check: Design tables for Indian Railways list distinct vertical envelopes for BG and MG; the differential headroom aligns with the 0.45 m order of magnitude for classic MCQs. Why Other Options Are Wrong: 0.30 m: Too small; risks infringement for BG stock. 0.60 m or 0.75 m: Overly conservative for the standard difference. 0.15 m: Much too low. Common Pitfalls: Ignoring additional clearances for OHE equipment in electrified routes. Using MG envelopes for BG conversion projects without re-profiling tunnels. Final Answer: 0.45 m

Question 20

For tunnelling in firm ground, which excavation approach is generally adopted to balance speed, stability, and control of overbreak?

Accepted Answer

Introduction / Context: The choice of tunnelling method depends largely on ground conditions. In firm ground with reasonable stand-up time, the heading can be advanced across the full section. This reduces cycle interfaces and can shorten construction time compared with multi-stage or pre-support-intensive methods. Given Data / Assumptions: Ground: firm (neither running nor very weak). Goal: select the generally adopted method. Consider drill-and-blast or mechanical excavation without heavy pre-support. Concept / Approach: The full face method advances the entire perimeter in one operation, relying on the ground’s ability to remain stable during drilling, blasting, and support installation. In firm ground, this is typically the most efficient approach, limiting construction joints and simplifying ventilation and mucking logistics. Step-by-Step Solution: Assess ground stand-up time: adequate → full face feasible.Compare with heading-and-benching or drift: these are used where stability is poorer or sections are large.Choose “Full face method” as generally adopted for firm ground. Verification / Alternative check: Textbook method-selection charts place full-face at the firm–competent end of the spectrum, with benching and drift reserved for reduced stability or large spans needing staged excavation. Why Other Options Are Wrong: Top heading and benching/drift: Useful but not the general first choice in firm ground. Forepoling: Intended for running ground, not firm formations. Common Pitfalls: Choosing staged methods without need, increasing time and cost. Failing to provide timely support even in firm ground after full-face blasts. Final Answer: Full face method

Tunnelling Questions