| The probability of disaster during departure and reception of shield tunnel was not low, maybe causing severe event. Sum up the common disaster type of departure and reception, analysis the mechanism of hazards, three aspects were divided about disaster control research, feature and inadequacies were also pointed out, some new research ideas and issues in the field has been put forward to study.The causes of piping and sand boiling of shield launching is analyzed, the model that groundwater permeates from reinforced soil pervious underlying layer to wall is established. Using semi-confined aquifer seepage theory, a example is given to demonstrate that, suppose the reinforced soil is impervious, the accident that water and sand inflows from tunnel portal is influenced by range of soil reinforcement, groundwater level and the gap of wall; the cost and safety of engineering have the positive correlation with the length of reinforced soil; the depth of reinforcement isn't so deep but reasonable; the gap of wall also plays a key controlling role to shield launching's safety. The factors are mutual constraint, construction parameters are influenced by security, economy and time limit for a project.The relation model between water pressure and flow, hydraulic gradient is built to explain the spewing mechanism when portal excavating and shield advancing. Consequently, the critical conditions of the spewing are put forward.Using 2D FEM software to make numerical simulation and compare with analytic solution, then the treatment of wall gap as the key factor is acknowledged during influencing groundwater seepage, the aggressive influence of decreasing groundwater level and lengthened reinforcement soil to control accident is verified in the analytic solution.
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