Analysis On The Secondary Lining Cracking Mechanism And Remediation Effect Of South Lvliangshan Tunnel

Because of the geological conditions of underground engineering is a complex and unpredictable,railway tunnel is excavated,whose surrounding rock stress often takes a long time to the redistribution process.But Existence of geological disease is geological disease,for example,fault,cavity,lava and so on,is existed in rock mass,which will lead to tunnel lining two cracking phenomenon in different degree after completion of construction.In order to improve the bearing capacity of the tunnel structure and ensure the safety of the train operation,it is necessary to carry out the renovation of the lining cracking tunnel.The results is indicated by the practice of many tunnel remediation that remediation measures and schemes based solely on the experience of engineers to draft tunnel reinforcement that is not analyzing the crack propagation mechanism and lack of the speculative knowledge,which inevitably lead to unscientific remediation measures,procedures and methods and even draft the false crack remediation measures with the unnecessary waste of effort,material and financial resources.Based on the tunnel engineering in the southern Liangshan tunnel and the analysis of the causes of lining diseases,the mechanism of lining crack propagation is studied from the viewpoint of fracture mechanics in this paper and the effect of tunnel renovation is evaluated.(1)Based on the brief introduction of the Liangshan tunnel project and the two lining cracking,the causes of tunnel diseases are analyzed from the aspects of temperature stress,seepage,geological structure,construction and design.According to the four monitoring measures to analyze the degree of tunnel disease,partial regulation measures is put forward.On this basis,combined with the knowledge of fracture mechanics,the propagation mechanism of the tunnel lining crack is analyzed and numerical model of the selected four typical section lining with cracks by stratum structure method is established,therefore the stress intensity factor of the crack is obtained,which is used by safety coefficient formula of the two tunnel crack lining we proposed to calculate the safety factor to determine situation of the tunnel lining crack propagation.(2)The regulation measures of the tunnel is introduced,at the same time,regarding the selection of left line DK319+170 and DK319+122.9 of right line section as a typical section of monitoring data analysis,the result is that in addition to the individual measuring point stress and displacement present a instable trend,most of the remaining points are stable and the preliminary determination of tunnel structure and surrounding rock is stable.(3)The measured data that between the primary support and the two backing pressure is regarded as the initial load,which is loaded into the numerical simulation using the load structure method to conclude that the bending moment and axial force,and the safety was evaluated according to the size of the eccentric compression member in the specification checking method.The evaluation result indicates that the safety factor is greater than the one of the requirements of the standard,which means that the selected sectional bearing capacity can meet the requirements and the regulation measure of tunnel is effective.