The Study On Calculation Method Selection And Parameter Influence Of Pu Caogou Tunnel

As our country accelerates the construction of transportation facilities in the central and western regions,the scale of the road network in the southwest region continues to expand.Due to its complicated geological and topographic conditions,biased tunnels are a common and typical problem.Bias effect brings greater difficulty to tunnel construction and operation safety.It is the key to reduce bias effect through design calculation.However,due to the numerous and variable factors involved in tunnel design calculation,the existing code cannot cover all types.For tunnels that are not clearly specified,engineering designers often determine the calculation method through personal subjectivity,which will inevitably cause large deviations.Based on the research results of a highway tunnel,this paper determined the indexes that affect the calculation method of the tunnel through the study of the relationship and failure mechanism between surrounding rock and tunnel support,and weighted the index combination with the ANP method and the entropy weight method.The evaluation model of the tunnel design calculation method was established by introducing the unascertained measurement theory,compared and verified with the existing results.Finally,it was applied to the Pu Caogou tunnel.Combined with the on-site geological survey and monitoring measurement of the Pu Caogou tunnel,a numerical model was established with the aid of Midas/GTS,and the construction methods suitable for the tunnel were compared and selected.Afterwards,the influence of parameters such as the formation dip angle,the excavation surface of the middle and lower steps of the tunnel,the length and spacing of the anchor rod,etc.was studied.?1?6 qualitative indexes and 10 quantitative indexes are determined according to the relationship and mechanism of deformation and failure between tunnel and surrounding rock.Each index is divided into???grades under the quality and effect of supporting and surrounding rock by referring to national standards and research data;Aiming at the selected highway tunnel group which is taken as the research object,the combination of ANP and entropy weight method is used to analyze and calculate the index weights.The unascertained measurement theory method is used to construct the tunnel design calculation method evaluation model.Taking the D₁ section tunnel as an example for verification,and comparing with the existing research results,it shows that the model evaluation results are basically consistent with the actual situation,which has practical value for reference.?2?Based on the ?-level shallow-buried bias tunnel at Pu Caogou Village of Qianjiang Distric,Chongqing,it is determined to use the stratum method to model the tunnel through Midas/GTS finite element software through the design calculation method evaluation system established in Chapter 2.The procedures of the three-step temporary arch method,CRD method and double-wall guide pit method commonly used in?-level biased tunnels is introduced.The appropriate tunnel construction method is selected by comprehensive analysis of the surrounding rock vertical deformation,lateral deformation,surrounding rock stress,construction disturbance to the surrounding rock and economic construction period and other indicators.?3?Combined with the geological structure and construction operation level,compared with on-site monitoring and measurement data,a realistic three-dimensional shallow buried bias tunnel numerical model is established for construction simulation.It can provide prediction guidance for subsequent construction by analyzing the initial support deformation.The guidance also provides a model basis for subsequent research.?4?In view of the phenomenon that the ground slope angle is overemphasized and the formation dip angle is ignored in the biased tunnel,in order to explore the influence of the formation dip angle on the tunnel structure,the dip angle of the conglomerate and sandstone layer is studied.The dip angle of conglomerate-sandstone layer is set to 0°,8°,16°,25°to simulate the calculation for analyzing the change law of tunnel with the dip angle of conglomerate-sandstone layer.?5?For biased tunnels,asymmetrical excavation and support are suitable and economical.The numerical simulation method is used to optimize and adjust the three parameters which are the excavation surface on the left and right sides of the tunnel,the length and spacing of the anchor rod.A total of 13 working conditions are studied for the most suitable parameter configuration to reduce the bias effect.