| Shield tunnels play an increasingly important role in China’s infrastructure network,and are often difficult to repair once they have suffered seismic damage.As a key supporting technology in shield tunnelling,backfill grouting is characterized by high mechanization and flexible operation,which mainly plays the role of filling gaps and reinforcing formations,protecting segment lining and improving the impermeability of shield tunnels.At the same time,using appropriate grouting materials,the tunnel seismic mitigation can be carried out efficiently through backfill grouting.Therefore,it is of great theoretical value and practical significance to study the related mechanism and application.In this paper,shield tunnels constructed in multi-porous formations with relatively uniform isotropic such as medium or high weathered rock layers,sandy soil layers and sand pebble layers are studied as the research objects,where the backfill grouting is prone to filling and penetration diffusion.Then,various analytical methods were used to carry out the research on the filling-permeation diffusion model of backfill grouting in unsaturated strata,the effect of backfill grouting diffusion pattern on seismic performance of shield tunnels,the evaluation of seismic effect of backfill grouting in shield tunnel based on vulnerability analysis,and the research on aseismic materials for backfill grouting of shield tunnels.The main work and the results obtained are as follows.(1)According to the unsaturated soil theory,the microscopic flow behavior of slurry in the capillary pores of soil was analyzed,and the permeation diffusion of shield tunnel backfill grouting in unsaturated strata was divided into three patterns;based on the Maag spherical permeation diffusion theory,Van Genuchten model and Green Ampt model are introduced to derive the calculation equations for the permeation diffusion of slurry in different patterns.Then,a calculation model for the permeation diffusion of backfill grouting in unsaturated strata related to the water content was established.It was found that with the increase of grouting pressure and grouting time,the permeation diffusion radius of backfill grouting slurry basically increases linearly;with the decrease of volumetric water content of the stratum,the permeation diffusion radius of slurry decreases non-linearly;by default,when the stratum is saturated,the calculation result of grout diffusion radius is large,which leads to the overestimation of the grouting reinforcement effect on the formation.(2)Based on the formation characteristics of shield tail gap during tunnelling process and the stratum conditions,the backfill grouting were divided into two types: Type 1,in the stratum with good stability,when the shield tail gap is a continuous and uniform ring-shaped pore,the slurry mainly fills and osmotically diffuses.The slurry forms a tunnel liner-slurry filling layer-grouting reinforcement layer-surrounding rock system,and the use of slurry material lower than the elastic modulus of the surrounding rock for backfill grouting can play a better role in seismic isolation which can absorb the displacement from stratum,and the effect of the change in diffusion range is not obvious.Type 2,in the stratum with poor stability,when the shield tail gap is closed and wrapped by soil,the slurry mainly osmotically diffuses.The system of tunnel liner-grouting reinforcement layer-surrounding rock is formed after the slurry solidifies.The backfill grouting with slurry material higher than the elastic modulus of surrounding rock can play a better seismic effect,and increasing the elastic modulus of grouting material and expanding the grouting reinforcement range are beneficial to tunnel seismic reduction.(3)An integrated analysis flow reflecting the influence of grouting parameters and stratigraphic factors on the seismic performance of tunnels was established.It was found that when the default formation is in saturated for grouting seismic mitigation analysis under the same grouting time and grouting pressure,it will make the seismic reduction efficiency large and lead to overestimation of the seismic mitigation effect.(4)Take the shield tunnel backfill grouting in a stable formation as an example,the seismic vulnerability analysis shows that the seismic response of the tunnel lining under lower intensity(lower than 0.5g in this paper)input motion can be effectively reduced after performing backfill grouting,but its seismic damping effect is not obvious under high input intensity(1.0g).For the shield tunnel project in this study,after grouting with three different strength materials at a seismic intensity of 9 degrees,the probability of tunnel lining beyond minor damage under earthquake action decreased from 23% to 15%,17% and 19%,respectively.(5)A-C grouting & ant-seismic material that meets the construction requirements of backfill grouting in shield tunnels was studied.The test results show that the variation of cement content has a significant effect on both the fluidity and consistency of A-C material,with the decrease of cement content,the lower the compressive strength,the better its deformation ability;while the higher the cement content,the higher the final compressive strength of A-C material,but its brittleness is also more obvious.For the background project in this study,good seismic effects can be achieved by using A-C grouting material at the soft and hard intersection of the strata,with a reasonable setting range of 3.5 times the tunnel diameter. |
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