Abstract:

Compared to cohesive soil strata, waterrich sand strata have higher porosity, higher permeability and higher water content. When hyperbaric operation is needed during shield boring in waterrich sand strata, it is of great importance to keep the air tightness of the strata around the shield. An EPB shield for Line 3 of Xi’an Metro bores through fullface waterrich sand strata, and hyperbaric operation has to be conducted. The strata around the shield is sealed by bentonite slurry, which is injected through the holes on the shield; the tunnel face is sealed by filter membrane formed by highefficient slurry, the simultaneous grouting and grease injection at the tail shield is enhanced, so as to ensure the air tightness of the sand strata around the shield and in turn to facilitate the hyperbaric operation. Furthermore, a series of air tightness testing and evaluation means are used to verify the sealing effect. In the end, successful air tightness has been achieved and successful hyperbaric operation has been conducted.

Key words: Xi’an Metro, EPB shield, waterrich sand strata, hyperbaric operation, air tightness, filter membrane, air tightness verification