Secondary Grouting Pressure Limit of Shield Tunnels in Loess Strata Based on Bolt Shear Behavior

A loess stratum was selected as the research object, assuming that slurry diffuses in a hemispherical shape during secondary grouting. Based on unified strength theory describing failure characteristics of and critical condition bolt shear failure, pressure value grouting strata determined theoretically. The reliability theoretical analysis verified by numerical modeling realizing large deformation formation dynamic injection slurry. 821.80 kPa calculation obtained. Comparing results simulation analysis, it found calculated using equation had safety index 1.14. Bounded βu (the ratio expansion radius RP soil plastic zone to Ru slurry) equal 2.65, water at port is main factor affecting upper limit when less than effective internal friction angle layer greater 2.65. influence matric suction can be ignored.