Numerical Study on Ground Subsidence Due to Crushing Single Isolated Boulder by Tunnelling

Abstract

Distinct from shield tunnelling in clayey and sandy strata, crushing undetected single isolated boulder by tunnelling machine frequently resulted in severe ground subsidence hazards (e.g., cave-in of ground). These ground subsidence usually happened suddenly with little warning, occurred few hours to few years post-tunnelling, and did not feature a continuous settlement trough curve like those of tunnelling in fine grained soils. In light of these, it is extremely difficult to predict potential ground subsidence hazards and then to adopt appropriate countermeasures or post-tunnelling remedial measures to prevent associated damages. By applying a systematic methodology that can randomly yield close approximation of morphology of rock blocks into commercial particle flow code PFC2D, the influence of boulder location on ground settlements, overburden pressures, and bending moments in the tunnel lining was investigated. The numerical simulations disclosed that the shape of ground settlements trough reflected the location of crushed boulder. In the meantime, crushing and removing the boulder would change earth pressure around the tunnel and thus caused the bending moments in the lining to redistribute.