Research on geological safety monitoring of urban underground space resource utilization in Beijing

Geological conditions in Beijing plain area are extremely complicated, involving interlaced alluvial-pluvial fan and plain as well as widespread weak soil layers (e.g., made ground, soft soils), which leads to changeable shallow groundwater flow field and various geological hazards such as active faults and land subsidence, thus increasing the difficulty of underground space construction and accident probability. The weak soil layers normally have poor stability, which may cause large degrees of stratigraphic affect the anti-floating stability and impermeability of underground space, and may result in serious damages such as gushes during constructions; the active faults, which can cause three-dimensional spatial deformation with properties of tension, shear and torsion, are likely to deform underground tunnels or even lining fractures; meanwhile, the increasing ground subsidence area and subsidence rate would affect the underground tunnels constructed across the non-uniform subsidence area, and cause abnormal displacement or foundation failure. In addition, a series of geologically related environmental issues may occur during underground development, e. g., groundwater contamination, changes of groundwater flow field, or the liquefaction of sandy powder soils. In this paper, the authors investigated the influence of geological conditions on underground utilization and relevant environmental issues that arise with constructions, and elucidated the monitoring objects, index and methods for underground space development, with the purpose of contributing to geological security insurance for underground space utilization.