Research On The Stability Mechanism And Support Measures Of Super Large Span Flat Caverns

Due to its unique structural characteristics,the stability of the surrounding rock around the super large span flat cavern in layered rock mass will be significantly reduced.A very small flattening rate is not conducive to the self stability of the surrounding rock.Excessive span will expose defects in the surrounding rock,reduce the integrity of the surrounding rock,and cause great difficulty in construction.In addition,there is currently relatively little research on super large span flat caverns,but in recent years,there has been a trend towards large span flattened caverns.Multiple flat caverns with spans of over50 m have also been built in China.Therefore,in response to the current research status,there is an urgent need for relevant theoretical knowledge reserves.This article adopts numerical simulation,theoretical analysis,and literature research methods to conduct research on the stability mechanism and support strategies of super large span flat caverns.The basic research content can be summarized into four parts: the characteristics of cave failure and factors affecting cave stability in layered rock masses,the analysis of cave instability mechanism,the study of arch support countermeasures,and the analysis of rock column stability and support countermeasures.The main research results are as follows:(1)Through numerical simulation,the failure characteristics of the cavern in the layered rock mass with different bedding angles are studied,and the distribution characteristics of the relaxation range of the vault of the cavern are analyzed.Furthermore,the influences of bedding angle,burial depth of the cavern,lateral pressure coefficient,surrounding rock grade and excavation span on the stability of the cavern are analyzed.(2)By establishing numerical models for different excavation steps,the stress and displacement fields of the cavern under different bedding angles and lateral pressures are analyzed,and the stability mechanism of the cavern is studied.(3)By analyzing the support mechanism of the support structure,suitable support forms for super large span flat caverns were obtained,and numerical models for cavern support under different working conditions were established.Based on the numerical calculation results,the support effects of different support methods and the distribution characteristics of the loose area on the arch roof after support were analyzed.Furthermore,the support form of the tunnel roof was optimized,and a more reasonable support form was provided,especially the asymmetric support form of anchor cables.(4)By using the discrete element program UDEC,a numerical model of the rock column was established,and the effects of bedding inclination angle and burial depth on the width of the plastic zone of the rock column,as well as the stress distribution characteristics within the rock column,were obtained.The stability analysis of the rock column was then carried out,and the support forms of the rock column were compared and selected,providing a reasonable support form for the rock column.At the same time,force analysis was conducted on the rock column and the tension anchor rod,and the ultimate load that the rock column can withstand was obtained.Combined with some numerical calculation results,the calculation formula for the actual load that the rock column can withstand and the calculation formula for the ultimate load of the rock column after support were provided.Finally,the support design method for the rock column was provided.