Abstract:

In normal cases, 6～8 m cover depth is taken for mined Metro stations in Quaternary strata in accordance with experience. If the arch of the Metro station tunnel is located in the influence scope of the interfacial water, the safety of the construction of the Metro station cannot be guaranteed by the conventional support means. In the design of the Military Museum station on Line 9 of Beijing Metro, field water pump tests are conducted, and calculations and analysis are made, so as to minimize the risks in the construction of the mined Metro station close to waterrich interface. Conclusions drawn are as follows: 1) In the design stage, emphasis shall be paid to the study on the hydrogeological conditions and appropriate cover depth shall be selected for the Metro station so that the crown of the Metro station will not be located within the influence scope of the interfacial water and the construction safety can be improved; 2) The thickness of the waterproof protection strata reserved on the top of the arch of the Metro station is determined as 4.5 m in accordance with the water head and the tunnel excavation width; 3) During construction, advance probing shall be emphasized and advance reinforcement measures such as curtain grouting and selfboring bolts shall be taken on basis of the advance probing results; 4) Due to the increase of the cover depth, the structural steel pipe columns shall be strengthened according to the forceundertaking conditions. 

Key words: Metro station, excavation under shallow cover, interfacial water, cover depth