Research On The Evolution Law Of Rock Instability And Collapse In Deep And Shallow Buried Tunnels

Tunnel collapse has always been a key issue of concern in the field of tunnel engineering,often occurring in soft rock tunnels.Due to different burial depths,the forms of stable tunnel collapse may vary.Generally speaking,deep buried tunnels exhibit local or arch collapse,while shallow buried tunnels often exhibit through collapse.Under special conditions,local or arch collapse may also occur.When analyzing landslide problems,it is customary to distinguish them based on the depth of the tunnel,and the focus of research also tends to be on the factors and treatment of tunnel collapse.There is relatively little research on the process analysis of landslide evolution.Therefore,conducting research on the evolution law of surrounding rock instability and collapse in deep and shallow buried tunnels has important theoretical significance for ensuring the safety and reliability of underground engineering.This article starts with the instability and collapse of tunnels,and adopts a research method that combines theory,statistical analysis,and numerical simulation.By summarizing and analyzing the information of a large number of on-site tunnel and model test collapse case studies,and on this basis,with the help of FLAC3 D finite element software,in-depth research is conducted on the evolution law of collapse in two lane soft rock highway tunnels.The main research results and work are as follows:Firstly,the prerequisites,basic assumptions,and applicability of the traditional theory of dividing deep and shallow buried tunnels are summarized and evaluated,and the failure modes under each method are compared.The traditional theoretical research results are based on the theory of rock and soil strength and the geometric shape of the tunnel instability failure surface.By analyzing the stress of the isolation body in the failure area,the calculation formula for the surrounding rock pressure at the top of the tunnel under different burial conditions is obtained,And provide specific methods for determining whether the tunnel is deeply or shallowly buried.Then,through statistical analysis of 100 engineering site collapse cases and 80 model test collapse cases,the influencing factors of collapse,the relationship between burial depth and collapse,the initial state of collapse,the evolution process of collapse,and the final state of collapse were studied.It is believed that there is a quantitative or qualitative relationship among the three types of tunnel collapse(local collapse,arch collapse,and through collapse).There is a quantitative process from local collapse to arch collapse,which is generally under the condition of larger tunnel burial depth;However,there is a qualitative transformation process from arch collapse to collapse through collapse,and generally,there is a high incidence of tunnel burial depth.On this basis,the same viewpoint was proposed regarding the initial evolution law of collapse in deep buried and shallow buried tunnels,which generally undergoes a stage of local failure followed by arch failure;Shallow buried tunnels may sometimes experience collapse type failure due to surface deformation or cracking.Finally,by numerical simulation of tunnel excavation failure under different burial depths,the effects of stress field,displacement field,plastic zone,and strength parameters on tunnel collapse failure were analyzed.The results show that the tension at the arch of shallow buried tunnels is significant,and cracks caused by uneven settlement are prone to occur within a certain range of the surface,revealing the reason why shallow buried tunnels are prone to penetrating landslides;At the same time,it also confirms the reason why the surrounding rock of deep buried tunnels is prone to arch collapse due to instability.At the same time,based on the development law of the plastic zone,it is confirmed that regardless of the burial depth of the tunnel,the initial evolution process of surrounding rock collapse has consistent characteristics;In addition,compared to cohesion,the internal friction angle has a more significant impact on tunnel collapse.