Study on Gas Permeability Test in Water Sand and Gravel Stratum

摘要

Water sand and gravel stratum is characterized by high gravel content, big grain size and high strength, easy permeation for water and air, brittleness and hysteresis quality in stratum failure, causing great difficulties in EPBM hyperbaric intervention and changing cutter tools working under air pressure. Due to the special geological conditions and no useful reference or criterion about gas permeability in such stratum all over the world, gas permeability test is done to fetch air loss data in natural state and bentonite-added state. Based on the practical situation of ChengDu Metro Line 1-Lot 3 project, by using methods of site test and theoretical analysis, the air loss before/after bentonite is added are given: At the air pressure of 1.0 bar, the air loss with bentonite added is 27% of that without bentonite. The acreage of pressure air loss around excavation face is from 35.2 m~2 (In case of half chamber muck and bentonite slurry is 100% in effect around shield machine) to 129.6m~2 (In case of empty chamber and bentonite slurry is 50% in effect around shield machine), providing reference in choosing air compressor, also for other project in this stratum and similar project.