Earth Pressure Balance Shield Construction Strata Subsidence Control

EPB (earth pressure balanced) Shield tunneling method is an effective method in tunneling construction and has the obvious advantage in the aspect of controlling the distortion of stratum, because the close front shield that is pushed by the shield machine balances the earth and water pressure. However, because on one side, the surrounding rock mass is disturbed more or less during the course of shield construction, on another side, the shield construction is consisted of many processes and has many governing factor, the events of apophysis and settlement of ground surface and the stratum horizontal displacement are unavoidable. The undue stratum settlement is likely to cause the bad effect to the around environment such as incline of building, rupture of underground pipelines, destroy of ground and bridges and roads.Therefore, through the investigation and analysis of the stratum distortion caused by the shield construction, some rules about the stratum distortion are summarized,based on the measured datus, and can be used as references of construction through forecasting the potential instance of stratum distortion in advance in the later shield construction.Shield construction is a complicated systemic engineering that rely much on geological conditions. The settlement of ground surface caused by shield construction has many factors, but one of the important factors is stratum losses caused by the disturbing of surrounding rock mass in construction. Among those stratum losses, the loss resulted from the soil in front of shield machine is not effectively balanced by earth and water pressure and the gap between the lining andexcavated tunnel cavity is not backed-filled timely and sufficiently is abnormal and harmful, and is the primary reason to the ground surface undue settlement.According to the principles of the shield construction and the reasons of ground surface settlement, the measures of ground surface settlement control are comprehensive and should be properly carry out based on the practical conditions, which relate to the techniques of be properly carried out based on the practicalconditions,which relate to the techniques of excavating direction control, segment assembling, waterproof, inspecting and examining, the shield machine's manufacture precision and some accessorial methods such as compressed air and rotary spray compaction besides the well-balanced working face and sufficiently shield tail void backfill injection.