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Question

Difficulty: HardIdentifying Implied Meanings

Passage:
During mechanized subterranean tunneling through water-saturated silt, operators of slurry shield tunnel boring machines continuously adjust the hydrostatic pressure of the bentonite slurry pumped into the excavation chamber. If the slurry pressure falls below the surrounding groundwater and earth pressure, the tunnel face risks sudden structural collapse. However, when operators maintain excessive slurry pressure over prolonged intervals, slurry penetrates deep into the permeable sediment fissures ahead of the cutterhead, fracturing the overlying strata and creating slurry blowouts at the ground surface.

Based on the passage, what is implied about managing slurry pressure during tunnel excavation?

  1. A
    Increasing slurry pressure well above surrounding earth levels eliminates the danger of fracturing overlying soil layers.
  2. B
    Tunnel boring machines require complete dewatering of water-saturated silt before excavation can proceed safely.
  3. Maintaining chamber stability requires operating within a narrow pressure threshold, as deviations in either direction cause structural failure.Answer
  4. D
    Prolonged excessive pressure causes sudden tunnel face collapse by washing away the bentonite slurry.

Answer

Maintaining chamber stability requires operating within a narrow pressure threshold, as deviations in either direction cause structural failure.
The passage describes two failure modes: pressure falling below earth and groundwater pressure causes tunnel face collapse, while excessive pressure over prolonged intervals causes strata fracturing and surface blowouts. Deducing the relationship between these two facts implies that safe excavation requires maintaining slurry pressure within a calibrated operational window where neither under-pressurization nor over-pressurization occurs.

Step-by-Step Solution

1
Identify the cause-and-effect relationships presented in the text regarding slurry pressure.
Identified that pressure lower than surrounding ground pressure leads to tunnel face collapse, while excessive pressure fractures strata and causes surface blowouts.
Mapping the consequences of both pressure extremes is necessary to determine what is logically implied about proper pressure control.
2
Synthesize the two failure conditions to deduce the required operational boundary.
Because falling too low causes an internal collapse and climbing too high causes external fracturing and blowouts, operators must keep pressure strictly between these two critical bounds.
An unstated inference must be drawn directly from the interplay of stated facts without introducing outside conjecture.
3
Evaluate the options against this synthesized deduction.
The option stating that operators must work within a narrow pressure threshold accurately captures this dual-sided constraint.
Eliminates choices that contradict the passage, misattribute causes, or introduce unsupported external concepts.

Key Concept

Identifying implied constraints from dual-sided cause-and-effect evidence in technical passages
Estimated Time:1m 15s
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Topics

Identifying Implied Meanings

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