Mechanical Response And Its Application Of The Spatial Variability Of Surrounding Rock For G-series High-speed Railway Tunnels

Due to the differences in mineral composition,sedimentary conditions,stress history and other geological processes,the spatial variability of the mechanical properties of rock and soil in stratum always exists objectively and will directly affect the mechanics response of surrounding rock after excavation,.This will also have obvious influence on the prediction of stratum deformation and calculation of supporting load and safety control during the tunnel designing process.At the current stage,the project analogy method based on experience and the deterministic checking design method are widely adopted in tunnel structure design,and this will make the ignorance of spatial variability of surrounding rock during the analysis process.The design section is generally larger for high-speed railway tunnel due to the aerodynamic effect of high-speed train.In the excavation process of large section tunnel,the spatial variability of the surrounding rock is particularly prominent,and its influence on the mechanical properties of the surrounding rock will also become more obvious.It will be obtained unreasonable or even contradictory results during the tunnel construction process if this characteristic are neglected,thus reducing the security reserve and endangering the safety of the project.Therefore,in order to address this issue,it is necessary to study the mechanical response of the spatial variability of surrounding rock and its engineering effect.In this paper,a systematic research was carried out on the spatial variability of the mechanical properties of the surrounding rock for high speed railway tunnel.First of all,the spatial variability of mechanical properties of surrounding rock is modeled.On this basis,an optimization model based on geological condition was established.Secondly,the mechanical response of surrounding rock under the spatial variability was studied after excavation.The mechanical characteristics of the supporting structure under the spatial variability of surrounding rock load and its own resistance randomness were analyzed according to the stage of tunnel construction and operation.Finally,a robust design method with mathematical model and related engineering application was proposed to solve the engineering response of the uncertainty of the support and surrounding rock system.The main work and conclusions are as follows:(1)Simulation Method for Uncertainty of Tunnel Surrounding RockA classification for the uncertainty of surrounding rock was proposed from the aspect of engineering scale and a modeling method was proposed aimed at the classification results.Based on the Karhunen-Loeve series expansion,an efficient method was developed to simulate the spatial variability of the surrounding rock under the basic framework of the theory of random field.A constrained random field was established based on the geological prospecting data based on the combination of the Kriging method in geostatistics and the simulation of the random field.A non-intrusive stochastic finite difference model was thus proposed through the design of the interface program with FLAC3D.(2)Stochastic Analysis of Tunnel Surrounding Rock Behavior Considering Spatial Variation of Rock ParametersThe non-intrusive stochastic finite difference model was applied to analysis the two basic elements of the spatial variability in the surrounding rock,the influence of parameter variability and spatial correlation on the arch settlement,horizontal shrinkage and surface subsidence was studied.On this basis,the four typical effects of the mechanical response of the surrounding rock under the parameter variability were analyzed,including the dominant effect of the low strength load,the anisotropic effect of the spatial correlation,functional sensitivity difference,the nonlinear effect and the transformation of energy distribution function.(3)Stochastic Analysis of Supporting Structure under the Spatial Variability conditionIn order to study the support design requirements under the condition of surrounding rock spatial variability,the mechanical response characteristics and fracture failure characteristics of the supporting structure under the spatial variability of surrounding rock load and its own passive resistance randomness were analyzed according to the stage of tunnel construction and operation.Based on the supporting structure force problems according to the stage of tunnel construction,a nonlinear ground beam element model considering multi-parameters spatial variability was established.Take the IIIa and Va supporting structure of the speed 350km high speed railway double line tunnel as an example,the influence of spatial variability of load and reaction effect of surrounding rock and randomness of lining thickness on the mechanical response of supporting structure was studied with this model,the results were compared with the deterministic model.Based on the supporting structure lining cracks problems according to the stage of tunnel operation,a three stage fracture stochastic analysis model was established.A systematic analysis of the spatial variability of load of surrounding rock and randomness of fracture toughness to the fracture failure characteristics of high speed railway single/double line tunnel supporting structure in different speed and different grade of surrounding rock.(4)Research on Robust Design Method in Tunnel EngineeringAiming at the engineering response of the uncertainty of the support and surrounding rock system,three robust design mathematical models were established.On this basis,the four engineering application fields of robust design were put forward combined with the engineering characteristics of high-speed railway tunnel.Based on the robust design engineering application field of precise analysis based on basic data,a precise analysis model of surrounding rock for tunnel construction based on the geological condition was established.This model was applied to the simulation of the Hejie Tunnel construction of Guiyang-Guangzhou.Based on the robust design engineering application field of high confidence of time series parameter prediction,a nonlinear autoregressive time series prediction model was established.This model was applied to the short term prediction of crown settlement in the new Badaling tunnel of Beijing-Zhangjiakou G-Series High-Speed railway.Based on the robust design engineering application field of alleviating the influence of the uncertainty of support and surrounding rock system,the pre-reinforcement robustness and its sensitivity were pertinency analyzed.Through the comprehensive analysis of the above key issues,it is strongly recommended to promote the development of high-speed railway tunnels from facile experience-based design to robust,scientific and normalized design.At the same time,this article provides theoretical support and technical basis to the rapid development of high-speed railway in China.