Study on the Influence of Earth Pressure Balance Shield Construction on Cutterhead Mud Cake in Composite Stratum

Due to the high mud content in the mudstone strata, the mud cake is easy to occur in earth pressure balance shield excavation. Through the improved direct shear apparatus, the interface tangential adhesion strength test was carried out on the mudstone slag sample considering the influence of temperature, and the growth law of adhesion strength was discussed. The influence of cutterhead on soil extrusion and interface adhesion strength of excavation face under different shield tunneling parameters is analyzed. Combined with the shear strength of mudstone, the analysis model of the occurrence conditions of the cutterhead mud cake and the influence of shield tunneling parameters on the cutterhead mud cake are proposed. According to the analysis model, the critical penetration of mud cake during EPB shield tunneling is obtained. The results show that: The shear strength and adhesion strength of clay are used as indicators to establish a judgment model for the risk of mud cake formation on the cutterhead, which has certain rationality; The adhesion strength of clay increases linearly with the increase of penetration, the decrease of opening rate and the increase of buried depth; For Nanjing Metro Line 6, the critical penetration of shield tunneling should be controlled below 1.9 cm/r. The research results can provide construction guidance for the prevention of mud cake in EPB shield.