Study On Diffusion And Reinforcement Law Of Split Grouting In Heterogeneous Soft Stratum

With the rapid economic growth and the rapid development of urbanization construction,a large number of population is concentrated in the cities,which brings great challenges to the urban transportation.Rail transit has become an important means to relieve urban traffic pressure and promote economic development by virtue of its speed,efficiency and safety.In the process of subway tunnel construction,various kinds of soft strata,such as sandy soil layer and clay layer,are often encountered,which are characterized by loose structure,poor stability and low strength.Under the influence of overlying load and construction disturbance,it is easy to induce surrounding rock instability and collapse,lining deformation and cracking,and even surface collapse and other geological disasters,which seriously threaten people’s lives and property and urban environmental safety.Split grouting is an effective measure to strengthen weak strata and is widely used in construction.However,most of the previous studies on split grouting focused on a single homogeneous layer.However,in the actual engineering construction process,heterogeneous soft strata are often encountered.Multiple soft strata are distributed in layers,with great property difference and uneven hardness and hardness,which lead to great changes in the grout diffusion mode in the grouting process,and the reinforcement effect is also discrete.The existing theories and methods of split grouting are difficult to provide effective guidance for the heterogeneous soft stratum.Therefore,the research on grouting diffusion and reinforcement in the heterogeneous soft stratum has important theoretical guiding significance for the safety construction and risk control of subway tunnel.In this paper,a series of studies were carried out on the diffusion and reinforcement law of split grouting in heterogeneous weak stratum by laboratory test and numerical simulation.The influence law of formation structure,grouting pressure and grouting position on the diffusion mode and reinforcement effect of split grouting in heterogeneous stratum was analyzed,and the lining structure and surface deformation characteristics caused by tunnel advanced split grouting were studied.The control method of advanced split grouting for tunnel in heterogeneous soft stratum is studied.The main research contents are as follows:(1)Based on the heterogeneous soft strata in the tunnel construction of Fuchunjiang Road Station of Qingdao Metro Line 6,the physical and mechanical parameters and deformation and failure laws of different soils were obtained through field sampling and laboratory soil tests,which provided the basis for subsequent laboratory simulation tests and numerical simulation studies.(2)Based on the self-designed split grouting simulation test system,the indoor simulation test of split grouting in heterogeneous weak stratum was carried out to study the influence law of formation structure and grouting pressure on the grout diffusion mode and reinforcement effect,and analyze the grout diffusion mode,the shape characteristics of the slurry vein,the change of soil stress and displacement and the change of mechanical parameters before and after grouting.The diffusion mode and reinforcement characteristics of split grouting in heterogeneous soft stratum are expounded.(3)The particle flow discrete element software PFC2D was used to carry out the numerical simulation study of splitting grouting in heterogeneous weak stratum.The grout diffusion morphology during the grouting process was analyzed and compared with the results of laboratory simulation test.Furthermore,the variation law of soil stress and porosity under different stratum structure,grouting pressure and grouting position was further analyzed.(4)Based on the actual project of Qingdao Metro and combined with the geological conditions and structural characteristics of the tunnel,the numerical model of advanced split grouting in heterogeneous weak strata was established to study the influence of grouting pressure,pipe distribution mode and porous grouting on the lining structure and surface deformation.The splitting grouting control method of heterogeneous weak stratum is explored,which takes lining structure and surface deformation as control index,backward grouting in stratum interaction area and multi-step grouting pressure.