| The long-term effect of groundwater makes the underlying bedrock have deterioration in strength and stability,which can easily cause the uneven settlement or even collapse of the foundation,it seriously threats the operation safety of the high-speed railway passes through the karst developing areas such as southwest China.Grouting technology has been widely used in disaster management of water-rich underground engineering,which can not only plugging groundwater but also filling reinforced broken rock mass.However,limited by the concealment of grouting engineering,the research on grouting theory and reinforcement technology of complex karst foundation lagged far from useful,which lead to the strong empirical in grouting design and construction,systematic and scientific theoretical guidance is urgently needed.Meanwhile,higher requirements and standard are also satisfied for the engineering stability of subgrade structures in karst area.In this paper,the key technology of karst foundation grouting on the new qianjiang-zhangjiajie-changde high-speed railway was used as the application background,the experimental study on properties controlling of the polymer-cementitious composite materials(MPC)were investigated to meet the high performance damand for complex karst formation grouting.The technological measures including theoretical analysis and numerical simulation were performed to exploring the diffusion law and water plugging mechanism of grouts with time-dependent viscosity which under effect of the groundwater.Then the key technology of composite grouting reinforcement for karst foundation was proposed,which combined with the field test research.Finally,the numerical analysis of the deformation characteristics and stability of karst subgrade under embankment load and train dynamic load were carried out respectively to establish a comprehensive evaluation system for karst subgrade of high-speed railway,which included settlement controlling and engineering stability ensuring.The main research contents and achievements are as follows:(1)The properties controlling experiments of cement-based grouting materials were carried out with accelerator,superplasticizer and super-absorbent polymer,obtained the optimum components and their dosage for the foundation reinforcement in Karst.The performances of modified slurry are superior to traditional grouting materials on pumpability,dimension stability and late strength.Then the mechanism of polymers on cementitious materials was deeply explored on the rheological-hydration process and pore structure.Meanwhile,the association between microstructure and macroscopic mechanical properties and of MPC was investigated revealed.The difference of pore size distribution of hardened MPC is consistent with the results of compressive strength test at 28d age,which reveals that there is an essential correlation between the macroscopic mechanical properties and microscopic structure of cement-based composite grouting materials(2)The diffusion model of karst fissure grouting was established which based on generalized Bingham fluid with time-dependent viscosity,then the numerical analysis of effect law by the underground water,slurry properties,fracture characteristics and grouting parameters were investigated.The research results found the plugging mechanism of water-flowing fracture with cement-based composite materials.(3)The key theory of composite grouting strengthening techology was put forward on the grouting treatment field test of qianjiang-zhangjiajie-changde railway,its main technical procedure includes the design of multi-sequence curtain grouting hole,the application of various grouting materials,bottom-penetration grouting method and composite monitoring of grouting consequences.(4)Based on the engineering geological conditions and strength reduction method,the numerical model of the covered karst subgrade of high-speed railway under the embankment load was established to investigate the deformation characteristics and stability under the effect by the height of earth bank,engineering properties of overburden and the morphology of karst cave.Taking the foundation deformation coefficient and stability safety factor as the critical value of instability failure,the double-index control system of overburden karst roadbed reinforcement design which consideration to deformation and stability was constructed,and the combined reinforcement measures of "reinforced supporting+grouting filling" were proposed.(5)The spatial coupling dynamic model which integrated the high-speed railway train,ballastless track and karst subgrade was established,which for exploring the influence laws of train run speed,Karst degree,cave features and grouting treatment measures on the dynamic characteristics and long-term stability of the karst subgrade under train load. |
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