Formation Mechanism and Treatment Measures of Special Mud Cake for Shield Tunnelling in Sandy Cobble Strata

A kind of special mud cake might be formed in earth chamber during shield construction in water-rich sandy cobble stratum, which causes many difficulties for smooth construction. Based on the running tunnel section of Xiyuan station-Wanquanheqiao station of Beijing metro line 16, the special mud cake formed during shield tunnelling in sandy cobble strata was studied, the formation mechanism and basis of pre-judgement of special mud cake were analyzed; a kind of new mixed solution which can better dissolve the mud cake was developed through dissolution test; the treatment and control technologies for the special mud cake were proposed in light of the test results. Case application shows that the problem of special mud cake has been well solved and the solution can be used to dissolve mud cake when it′s not convenient to open the chamber.