Abstract: In view of the serious cross grouting and overflows grouting in the construction of conventional grouting technology, and the unsatisfactory effect of stratum reinforcement, the grouting technology of mold bag sleeve valve tube is often used in advance grouting construction of tunnels. But at present, the selection of mold bag grouting pressure is mostly based on experience. In this paper, it is considered that the mold bag keeps cylindrical expansion during grouting and forms a stress-affected zone consisting of elastic and plastic zones in the surrounding compacted soil. Based on the elastic-plastic theory and considering the non-correlative flow rule in the plastic influence zone of surrounding soil, the expressions of the relationship between the initial radius R0 of grouting, the radius Ru of grouting reflection and the radius Rp of plastic zone of soil during the mold bag grouting process are derived, and the theoretical formula for calculating the mold bag grouting pressure P can be derived. The results of parameter analysis show that the grouting pressure is significantly affected by the elastic modulus, internal friction angle, cohesion and initial stress of the soil. The theoretical formula of mold bag grouting pressure was applied to the grouting project of the sleeve valve tube of the People's Hall Station. From the variation rule of grouting expansion radius Ru with grouting pressure P, it can be concluded that when the grouting effect on the surrounding soil is the best, the grouting pressure of the mold bag is 2.0 MPa and the final expansion radius of the grouting body is 20 cm. The test results of grouting effect show that the sealing batholite of mold bag grouting expansion has successfully controlled the grouting diffusion, and achieves the expected effect of controlling grouting area.

Key words: expansion mold bag, sealing batholite, curtain grouting, grouting pressure, expansion of cylindrical cavity