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?
- AIncreasing slurry pressure well above surrounding earth levels eliminates the danger of fracturing overlying soil layers.
- BTunnel boring machines require complete dewatering of water-saturated silt before excavation can proceed safely.
- Maintaining chamber stability requires operating within a narrow pressure threshold, as deviations in either direction cause structural failure.Cevap
- DProlonged excessive pressure causes sudden tunnel face collapse by washing away the bentonite slurry.
Cevap
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.
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Anahtar Kavram
Identifying implied constraints from dual-sided cause-and-effect evidence in technical passages
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