Model test research on excavation face stability of slurry balanced shield in permeable sand layers

In slurry balanced shield tunneling, how to ensure the safety of construction and to reduce the influence on the environment has arisen wide attention of scholars both at home and abroad. But now it is still in the stage of experience as to the instability mechanism of the slurry shield tunneling excavation and its stability analysis, especially to research on instability mechanism, judgment methods and calculation methods for the complex stratum cases. Regarding the excavation face in slurry balanced shield of the high permeable sand layers as research object, large-diameter modeling test are adopted to do systematical research on the excavation face instability features when properties of sand body and water head heights are different. The results show that: the ground settlement exits hysteresis effect, because it exists soil-arching effect at the same time of the excavation face active failure in the slurry balanced shield tunneling; the development mode of the excavation face active failure in the sandy stratum can be divided into three parts: anhydrous mode, lower water head mode and higher water head mode; it will induce excess pore water pressure during the slurry cake forming and the supporting force imposing; so that excess pore water pressure should be considered in process of the selection of supporting force. This research work has an important guiding sense to the stability of excavation face in the slurry balanced shield tunneling.