Physical Model Test Study On Deformation And Failure Mechanism Of Layered Soft Rock Tunnel Under The Thermal-mechanical Action

In recent years,with the rapid development of China’s economy and society,and the development of the western region,the rapid development of China’s highways,railways and urban subways,and more and more tunnel projects.Nowadays,the construction of tunnel engineering is gradually developing into "long,big and deep".In nature,layered structure of sedimentary rocks accounts for two-thirds of land area,at the same time,in the face of bad environment,such as high temperature,high ground stress is also more and more,geological disasters become more and more complicated,put forward a severe test to the design and construction of tunnel engineering,seriously affect the engineering safety.In order to study the deformation and failure mechanisms of layered soft rock tunnels under high ground temperature,a physical model test was used to study the deformation and failure mechanisms of layered soft rock tunnels under thermal-force interaction.Based on the physical model test at home and abroad,this paper makes a layered physical model with similar materials.Heating the model before test,conducted physical model test under the temperature condition of room temperature(20 ℃),40 ℃,60 ℃ and 80 ℃,the nearly horizontal layers soft rock tunnels and surrounding rock deformation and failure physical model tests is did under horizontal stress and high temperature.Graded loading during the test,strain monitoring system,acoustic emission monitoring system,temperature monitoring system and camera system are used to monitor the heating process,loading process and tunnel failure process of model test.The following main achievements were obtained through research:1.In order to reduce the influence on the internal structure of the model,the layer model and the heating element are combined,using nickel-chromium wire,tin foil paper,silica gel tube and conductive silicone grease to make layered heating device.The heating system of the physical model is designed and produced,and establish a set of model test heating scheme,the heating effect is effective.2.The loading process is affected by the pressure,main strain is the compressive strain in every place,pressure increases strain also increases.When tested at 60°C,the warming causes inhomogeneous tangential strain and radial strain of surrounding rock,which makes the strain and stress during loading larger,and the strain at 20°C is minimum.The vault,spandrel,arch foot and the bottom of arch have great strain,and the sidewall has the least strain.Tangential strain is greater than radial strain.3.The stress concentration of the cave walls.Destruction of stress rapidly decreases at 20°C,but under the condition of 40 ℃,60 ℃ and 80 ℃ surrounding rock has experienced significant stress redistribution process,the regulation of stress in complex process,according to the different stress development trend,the stress tendency of each measuring line is divided into stress transfer,stress release and stress accumulation.4.The deformation and failure of layered soft rock tunnels have obvious temperature effect.The temperature affects the mechanical properties and stress distribution of the surrounding rock,and the main control factors that cause the destruction of the surrounding rock change,and the failure modes of the surrounding rock under different temperature conditions also change,the increase of temperature increases the damage degree of tunnel surrounding rock.5.Model load,the ultimate stress is maximum under the condition of 40 ℃,minimum under the condition of 80 ℃.Model through short time heating,model`s intensity would rise,as the growth of the heating time,model inside and surrounding rock began to appear thermal damage and material cohesive force is reduced,model strength will reduce.6.In the process of this experiment,with the different surrounding rocks temperature,the main controlling factors of the destruction of surrounding rock have changed,resulting in different mechanical mechanisms of deformation and failure of surrounding rock,when under the conditions of 20℃ is tension damage,40℃ is rock shape shear failure.60℃ is plastic shear failure of rock mass and bending failure of arch bottom,80℃ is bedding slip damage and rock shape shear failure.There are different failure modes of the surrounding rock,and cumulative acoustic emission data are different in each phase.