Pre-grouting time-varying model and engineering application in shallow buried sand mudstone interbed under rivers

Grouting is an effective foundation reinforcement and anti-seepage treatment technology. The prediction of slurry diffusion range is one of the key points and difficulties of grouting technology. Due to the anisotropy of the physical and mechanical properties of the layered rock mass,the diffusion of the slurry is more complicated. Three inclined shafts of Xinwei Mine pass through the bottom of Zhenzhou River. The nearest distance from the inclined shaft to the strong weathered layer of the riverbed is only about 10 m. In order to eliminate the threat of water inrush during construction,an advanced pre-grouting anti-seepage technology was adopted. The excavation working face adopted a cyclic operation,excavation by drilling and blasting method,advanced support,cast-in-place reinforced concrete arch,and then waterproof treatment. Considering the near-horizontal distribution of sand-shale interbeds and the time-varying viscosity of the slurry,a denatured grouting model for sand-shale interbeds was established,and the grouting diffusion range under different working conditions was simulated. Referring to the simulation results and on-site conditions,the cement single-liquid slurry was mainly used,and the cement-water glass double-liquid slurry was used as the supplementary material. 16 grouting holes were arranged on the excavation face,and the grouting pressure was 6 MPa,and the segmented grouting was adopted. The length of a pre-grouting cycle was 30 m,the drilling and grouting were from the back to the front,then to the final depth,the length of a single grouting section was 5 m with repeated grouting,and repeated drilling. When grouting,the P-q-t curve was used to test the single-hole grouting effect,and the grouting pressure reached the preset value and the grouting flow rate continued to decrease as the stopping condition. In addition,the borehole coring test found that the slurry formed a stone with the fractured rock mass,which has a low permeability and high strength. Moreover,the diffusion of the slurry in the horizontal direction was obviously superior,far greater than the penetration distance in the vertical direction,and the slurry diffusion range was approximately ellipsoidal. In addition,by comparing the permeability of the surrounding rock before and after grouting,it was found that the permeability coefficient obtained by the Babkin formula after grouting was about 3 mm / d,compared with the rock mass permeability coefficient obtained by the water pressure test before grouting (0. 239 m / d and 0. 204 m / d). The permeability coefficient reduced by nearly two orders of magnitude. The practice shows that the advanced pre-grouting technology and the time-varying grouting diffusion model have been successfully applied in the anti-seepage of sand-shale interbed,which ensures the safe and efficient construction of the mines under the river.