Adaptability Analysis of Compressed Air and Stratum in Non-full Chamber Excavation of Earth Pressure Shield

Abstract:

Aiming at increasing engineering practice of compressed-air-assisted method， based on the numerical calculation model of air-water-solid coupling established by Geostudio Air/w， the influence of different shield tunnel top buried depth， thickness of overlying airtightness layer， stratum property and pressure chamber height on the seepage volume of excavation face was discussed. The results show that： The application case of compressed-air-assisted method in a section of Guangzhou Metro Line 21 is analyzed. The seepage gas volume is controlled within 1.2 m³·min^-1. A stable support pressure is established on the excavation surface to ensure that the shield tunneling reaches the micro-disturbance control level. When the earth pressure shield tunneling in silty clay and clay stratum with high airtightness ability， appropriate compressed air can be injected into the pressure chamber to better maintain the stability of the support pressure of the excavation face； To ensure the seepage volume is less than the gas production. When it is difficult to carry out full-cabin excavation in sandy cobble ， upper soft and lower hard stratum with large permeability coefficient and unequal geological distribution， the appropriate empty chamber height can be selected according to the buried depth and the thickness of the overlying airtightness layer. When the earth pressure shield crossing permeable stratum and the thickness of the overlying airtightness layer exceeding 10.0m， or the buried depth exceeding 28.0m， compressed air escape amount is less， and it is not easy to occer roof fall under compressed air.