Research On Numerical Simulation Of Transient Temperature Field And Temperature Effect Of High Temperature Water Diversion Tunnel

In hydraulic engineering,high ground temperature has attracted more and more attention.High ground temperature has an important influence on the stability of surrounding rock and lining structure of underground caverns.The study of temperature distribution characteristics,mechanical properties and plastic zone distribution of high ground temperature tunnel has theoretical significance for engineering practice.Combining with the high geothermal water diversion tunnel of a hydropower station in Xinjiang,this paper obtained the temperature variation characteristics of surrounding rock through the actual borehole layout of the field test tunnel,used the finite element numerical simulation method to simulate the transient temperature field of surrounding rock and lining structure of the geothermal water diversion tunnel,and then analysed its characteristics.Based on Mohr-Coulomb criterion,the surrounding rock of the high geothermal water diversion tunnel was analyzed.The transient coupled stress field of rock and lining and the spatio-temporal evolution of its plastic zone were simulated and calculated.Accodingly,some conclusions as follows:(1)In-situ monitorin.The temperature value of surrounding rock increases with the increase of drilling depth.The temperature value of surrounding rock at the same depth increases gradually from the opening to the depth(face).The correlation between them is non-linear.Temperature at different distances from the tunnel wall has the same trend with time,showing the same rise and fall.From the monitoring data,the temperature field of surrounding rock is affected by construction progress,ventilation conditions and working conditions.The change of boundary conditions,construction schedule and working conditions has great influence on the variation and distribution characteristics of the transient temperature field of the tunnel.(2)Temperature field numerical simulation.The lining structure and surrounding rock of the test tunnel are characterized by higher temperature at the face of the palm,the lowest temperature near the opening,and the temperature change from the opening to the depth is non-linear.Because of the influence of the main tunnel,the temperature value of the waist arch in the same section and depth of the surrounding rock of the test tunnel is slightly lower than that of the top arch and the bottom arch,and the influence decreases gradually with the increase of the distance between the section of the test tunnel and the opening.Therefore,when excavating a test tunnel in the main tunnel to predict the temperature field of the main tunnel,the influence of the main tunnel on the test tunnel should be taken into account and appropriate correction methods should be sought.The temperature field is greatly affected by the excavation process,and the temperature field of surrounding rock rises after lining process.The trend is the same as that obtained from field monitoring.The temperature field of high geothermal water diversion tunnel varies periodically in terms of basic period.Its basic life cycle is the epitome of the temperature field of the whole life cycle of the tunnel.The temperature field of the surrounding rock of high geothermal tunnel varies dramatically during the whole life cycle of lining and overhaul period,with daily variation rates of 17.79% and 17.33% respectively,and its additional temperature stress may be large.(3)Numerical simulation of temperature-stress coupling.The plastic zone of surrounding rock is different in different excavation methods.The whole section excavation method of high geothermal water diversion tunnel is twice as large as that of the plastic zone of the layered excavation method.Therefore the layered excavation method is superior to the full section excavation method.With the increase of excavation time,the compressive stress at the waist arch of surrounding rock decreases gradually,and the high stress zone moves from the tunnel wall to the depth gradually.Therefore,the redistribution of stress in surrounding rock after excavation is beneficial to the stability of surrounding rock.Seeking appropriate supporting structure for a short time after unloading of surrounding rock after excavation can prevent excessive deformation of surrounding rock.The plastic deformation of the surrounding rock makes the energy release in the surrounding rock,which shows that the stress decreases,the maximum compressive stress area moves to the surrounding rock,and the maximum stress is located at the depth of 0.4m of the waist arch of the surrounding rock.Therefore,the surrounding rock at the waist arch should be strengthened earlier.Temporal and spatial distribution characteristics of stress at arch waist and vault of surrounding rock under temperature-stress coupling during the whole life cycle of high geothermal tunnel are as follows: in time,every point of surrounding rock changes with the life cycle conditions,and the stress increases and decreases are consistent.Spatially,the stress of surrounding rock decreases with the increase of depth,and the greater the depth,the less the stress is affected by working conditions.The plastic zone of surrounding rock of high geothermal tunnel develops rapidly and then slowly under the coupling of temperature and stress during the whole life cycle.Therefore,the mechanical characteristics of surrounding rock and lining during the construction period and the first basic period should be taken into account.