Physical Simulation Of Deformation And Failure Characteristics Of Surrounding Rock After Temperature Drop In High Temperature Hard Rock Tunnel

With the development of West China,the underground and tunnel construction gradually developed to the development of Tibet plateau.large depth and high stress,high temperature and other complex geological conditions has become a major problem facing researchers and builders.The geological conditions of high temperature not only makes the constructor difficult to work in a high temperature environment,but also makes the rock failure mechanism under thermo mechanical coupling complex,after the actual excavation in high temperature tunnel,the opportunity to quickly cold air into the tunnel face near,rapidly reduce surrounding temperature,which makes the surrounding rock deformation and failure more complex.Therefore,it is necessary to study the characteristics of deformation and failure of rock tunnel after high temperature hard rock tunnel excavation.Based on the summarization of physical model test,the rock temperature drop of basic research in mechanical properties after the change,from the point of view of the similarity theory,made a physical model with hard brittle characteristics,the temperature of hard rock tunnel excavation model after cooling surrounding rock deformation test.By using the similar materials with hard and brittle properties of the large-size model produced 4 models with 60 cm length,width 60 cm and 20 cm thick(circular tunnel,tunnel diameter 9cm),the physical model test of cooling conditions 3 side pressure coefficient for?=2 and temperature from 40?-20?,60?-20?,80?-20?,cooling condition 1 side pressure coefficient for?=1 and temperature from 40?-20?.The process of the test strain monitoring system,acoustic emission monitoring system,temperature monitoring system,monitoring camera system model in the initial loading,heating,cooling tunnel,tunnel damage process of stress and strain,acoustic emission,temperature change characteristics and deformation characteristics.The main achievements are as follows:1?Based on geological mechanics 2D simulation loading system Chengdu University of Technology,with similar material and similarity theory as the basis,using stress,acoustic emission,video monitoring system,the high temperature hard rock tunnel model test were designed,established and perfected the technique of high temperature model of hard rock tunnel with a set of image data,and to obtain the failure process of tunnel.2?The side pressure coefficient for ?=2 under the condition of 3 gradient cooling process,the surface strain model value presents a slow change to compressive strain trend,has been in the area of compressive strain areas,the value increases slowly,in the tension strain area value is decreased slowly,the cooling process that makes the surface of surrounding rock is mainly affected by compression effect and reduce the influence of stretching effect.The cooling effect inside the tunnel by far than the surface of the model is more violent,so that inside the tunnel surrounding rock pressure analysis function is more intense,and cool at the same time also caused changes in the temperature field of the surrounding rock,the temperature in the cooling process,the model of internal and excavating the temperature difference gradually reduced,the temperature stress is reduced gradually thus,the surrounding rock stress is relatively reduced,is conducive to the stability of surrounding rock in general.The side pressure coefficient?=1 under the condition of loading,excavation and cooling process,the strain had no significant change in the side pressure coefficient ? =1,loading and cooling process influence on surrounding rock deformation characteristics of small.3?In the heating process of acoustic emission counts reached the peak at 35?,the acoustic emission activity is relatively severe about 40?,and acoustic emission activity is relatively calm about 80?,so a conclusion can be drew that the 40? source rupture model of internal micro cracks most developed,so the cooling process presents 40?-20?,60?-20?,80?-20? condition,acoustic emission peak energy decreased,so that the internal cooling process of surrounding rock with micro-fracture,micro-cracks more development,the cooling process of acoustic emission intensity.4?Comparing the acoustic emission energy peak when the physical model destroyed,the side pressure coefficient for?=2 and temperature 40?-20? and 60?-20? tunnel conditions damage energy peak intensity is close,and the 80?-20? under the condition of tunnel damage energy peak strength is far less than the above two conditions,it is thought that because the temperature gradient is larger.The cooling time is longer,the internal energy dissipation caused by the surrounding rock,so the 80?-20? under the condition of minimum peak energy damage.5?When the side pressure coefficient ?=2 and under the high geo-stress conditions,the stress concentration appears at the vault and the bottom of the arch after the excavation,and the stress concentration appears in the location of the side wall.In the cooling effect,the rock surface strain toward the compressive strain trend,completed after cooling,again after the loading process,the 3 conditions of the tunnel are sudden destruction,first from the arch shoulder or vault appear small pieces falling,and the rapid development of large fragments fall and side wall extrusion the arch bottom cut,peeling,dumping,bending-drum fold failure mode is consistent with the previous summary of hard rock tunnel deformation,cooling process,similar to the damage for each condition,the temperature of tunnel if cooling to the same temperature,deformation and failure characteristics of breaks when is similar.6?Model of side pressure coefficient?=1 in the early loading and cooling process of stress and strain of small changes,analysts believe that this is due to the side pressure coefficient under the condition of the tunnel is generally not affected by in situ stress,excavation and cooling effect on the tunnel.During the process of failure,the peak energy of side pressure coefficient for ?=1 tunnel is far less than the side pressure coefficient for ?=2 tunnel,but the damage intensity was much higher than that of deep buried tunnel,starting directly from the big pieces fall,and quickly complete destruction.The analysis shows that the side pressure coefficient for ?=1 tunnel is affected by temperature variation is small,if the hard rock tunnel under the side pressure coefficient is greater than the compressive strength of surrounding rock stress and rock mechanics parameters,damage degree is far greater than the lateral pressure coefficient of the tunnel.