Study On Construction Deformation Control And Stability Of Large Section High Speed Railway Tunnel In Soft Rock

China has engaged in large-scale construction of high-speed railway tunnels since 2016,so as to meet traffic demands of the "eight vertical and eight horizontal" high-speed rail network.High-speed railway tunnels have higher construction requirements and acceptance standards than ordinary railway tunnels,since deformation and damage caused by excavation crossing soft rock formation and fault fracture zones are found occasionally.In this case,it is difficult to ensure the safety and quality of tunnel construction apart from resulting in severe economic loss.To this end,researches on deformation control measures and stabilities of surrounding rocks for high-speed railway tunnels under the working conditions of high-speed railway tunnel crossing soft rock formations and fault zones should be strengthened together with the modern machine learning theory based on measured data.Focusing on high-speed railway tunnels in Yangshan County,various excavation methods methods and support measures were studied against deformation behaviors of the tunnel crossing the steeply inclined soft rock formation and surrounding rocks in the fault zone.The main research contents and conclusions are stated as follows:(1)The study established a deformation control criterion for Yangshan tunnels and summarized influencing factors as well as mechanisms of tunnel deformation in the soft rock large section through analyzing deformation characteristics of the weak surrounding rock with field monitoring data.Also,stabilities of the surrounding rocks in the soft rock formation of the tunnel were analyzed using the seismic reflection method,the geological radar method,and the advanced horizontal drilling method.On this basis,the grade and property of the surrounding rock in the soft rock formation as well as the intersected mileage between the F26 fault and the tunnel body were determined to provide a geological basis for subsequent construction simulations.(2)Optimal kernel parameters and penalty parameters of support vector machines(SVM)were searched respectively using the particle swarm algorithm,the genetic algorithm,and the cross-validation method.By comparing the fitness values and model prediction values of the above three algorithms,it can be found that the precision of the genetic algorithm is evidently superior to that of the particle swarm algorithm and the cross-validation method.Based on this,optimal kernel parameters and penalty parameters were determined to ensure the precision of the inversion result.(3)Sensitivities of the genetic algorithm and the SVM algorithm to sample level were studied.Concretely,four inversion samples at different levels were designed through orthogonal experiments,Then,the sensitive studies were accomplished by means of inputting numerical values that were calculated using the finite difference software,FLAC3 D.The results show that the optimizing efficiency and the result precision of the genetic algorithm in the test horizontal zone are positively correlated with the sample level,in terms of parameter inversion of surrounding rocks in the Yangshan tunnel.Moreover,the SVM prediction precision is positively associated with the sample level at the 4-6 level interval.Thus,the number of inversion sample levels can be defined.(4)The SVM algorithm based on the optimized genetic algorithm was studied to model parameter inversions of surrounding rocks in Yangshan high-speed railway tunnels.model is highly precise,which can provide reliable parameters for optimized analysis of construction.(5)Numerical models of the tunnel soft rock formation and F26 fault section were built using the finite difference software,FLAC3 D,so as to numerically simulate a multitude of excavation methods.Furthermore,deformation behaviors of tunnel surrounding rock,the vertical stress distribution of the surrounding rock in the tunneling process,initial distribution of support stress and characteristics of plastic zone were studied to disclose the deformation mechanism and the stress distribution law of surrounding rock under various excavation methods.By comparing results,it is determined that the annular reserved core soil method is the optimal excavation method for tunnel crossing steeply inclined soft rock strata and fault zone.What’s more,suggestions for deformation control were also proposed in combination with engineering experience.Simultaneously,calculation models were established with system rock bolt,the long anchor bolt support,the arch bottom bolt support,high-rigidity support systems and combined support systems system were also built to verify the reinforcing effect of varied support measures.As can be seen from the result,the system bolts have limited reinforcement effect on weak surrounding rocks;long bolts can be effectively applied for confining the deformation of surrounding rock,while the arch bottom anchor support can contribute to improving the deformation of surrounding rocks at the arch bottom.The high-rigidity support system can effectively enhance the stability of tunnel structure,whereas the combined support system has an optimum effect on controlling the vertical deformation of surrounding rocks.The research achievement will provide a reference for the follow-up evacuation of F24&F33 faults and other lithological formations of Yangshan high-speed railway tunnels.