| In recent years,China’s infrastructure development has mainly focused on the southwestern region,which has complex geological conditions.Especially in early urbanization projects,the "cut-and-fill" method is commonly used to level the construction sites,resulting in a large number of soil-rock backfill layers.When tunnels pass through such soil-rock backfill areas,serious engineering accidents such as excessive deformation of surrounding rock,uneven load on the lining,and even rock collapse can occur.Therefore,accurately analyzing the stability of tunnel surrounding rock in soilrock backfill layers becomes crucial for solving these engineering problems.Based on this,this study relies on the special funding from the Chongqing Postdoctoral Research Project "Numerical Simulation Methods and Applications for Fine Modeling of Loose Rock Backfill Tunnels." Firstly,a tunnel model is established and validated using the discretecontinuum coupling method,and the optimal range of the discrete domain is determined.Secondly,based on a specific soil-rock backfill tunnel project in Chongqing,a soil-rock backfill tunnel model is developed considering the real shape of rock blocks and the structural characteristics of surrounding rock.The typical failure modes of soil-rock backfill tunnel surrounding rock are studied,and the influences of various factors on the stability of the surrounding rock in soil-rock backfill tunnels are systematically investigated.Lastly,the impact of grouting ring thickness on the stability of surrounding rock in soil-rock backfill tunnels is analyzed,and the excavation process of soil-rock backfill tunnels is simulated.The main content and achievements are as follows:(1)The influence of size effect on the mechanical parameters of sandstone was studied.A tunnel model was established based on the discrete-continuum coupling method,and the reliability and accuracy of the model were verified from three aspects.The influence of the discrete domain range on the tunnel model,including boundary effects,was considered comprehensively by taking into account the deformation range,stress range,and computational efficiency of the surrounding rock.The optimal range of the discrete domain was determined.(2)A soil-rock backfill tunnel model was established based on the discretecontinuum coupling method,considering the real shape of rock blocks and the structural characteristics of the surrounding rock.The typical failure modes of the surrounding rock in soil-rock backfill tunnels were studied,revealing the failure modes of the surrounding rock in soil-rock backfill tunnels from macroscopic and microscopic perspectives.(3)The influence of four factors,namely,the thickness of the soil-rock cover layer,surface slope,angle of the soil-rock interface,and position of the tunnel crossing,on the stability of the surrounding rock in soil-rock backfill tunnels under composite soil-rock conditions was systematically studied using the discrete-continuum coupling method.The displacement,stress,block rotation angle,contact force chain,cracks,coordination number,and other macroscopic and microscopic mechanical characteristics of the surrounding rock in soil-rock backfill tunnels were obtained.The impact of different composite soil-rock conditions on the stability of the surrounding rock in soil-rock backfill tunnels was summarized.(4)The influence of two factors,namely,the rock content and maximum particle size,on the stability of the surrounding rock in soil-rock backfill tunnels was systematically studied using the discrete-continuum coupling method.The displacement,stress,block rotation angle,contact force chain,cracks,and other macroscopic and microscopic mechanical characteristics of the surrounding rock in soil-rock backfill tunnels were obtained.The impact of the rock content and maximum particle size on the stability of the surrounding rock in soil-rock backfill tunnels was summarized.(5)The influence of grouting ring thickness on the stability of the surrounding rock in soil-rock backfill tunnels was studied based on the discrete-continuum coupling method.The overall safety factor of the surrounding rock in the tunnel under different grouting ring thicknesses was obtained,and the failure characteristics of the surrounding rock in soil-rock backfill tunnels after grouting were analyzed.By simulating the excavation process of soil-rock backfill tunnels,the stability of the surrounding rock in different excavation stages was analyzed. |
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