Analysis Of Stress Characteristics And Fracture Origin Of Shotcrete Layer Structure Of High Ground Temperature Hydraulic Tunnel

In order to study the bearing capacity and the cause of cracks of the shotcrete layer structure of hydraulic tunnel under complicated high ground temperature environmen.In this paper,based on a high geothermal water diversion tunnel of hydropower stations in xinjiang,using the field monitoring,theoretical analysis and numerical simulation method,high geothermal water diversion tunnel was studied under different working conditions of the stress field,displacement field,strain field,temperature field distribution,shotcrete layer structure load-bearing characteristics analysis of influencing factor,and the equivalent under the age of concrete shotcrete layer structure of temperature stress.The main work and conclusions are as follows:(1)Monitor the construction site of the shotcrete layer.Monitor the temperature field of the surrounding rock,the stress field and strain field of the shotcrete layer.After the shotcrete layer is applied to the surrounding rock,the temperature will rise by about 10? compared with the previous one,because the surrounding rock blocks the direct heat dissipation process between the surrounding rock and the air.The radial stress of steel fiber spray layer is between 0.2-0.4MPa.The annular compressive stress is between 0.4 and 1.8MPa.This is due to the absence of constraints on the radial side and the observed greater influence of temperature on the cyclic stress.The radial strain and circumferential strain gradually change from tensile strain to compressive strain in the process of construction.(2)According to theoretical calculation and numerical simulation analysis,the radial compressive stress of the outer layer is greater than the radial tensile stress of the inner layer,and the annular stress of the arch waist is greater than the annular stress of the arch top and the arch bottom.The maximum value of cyclic stress is located inside the arch waist of the spray layer,and its value is 35.37 MPa,where the compressive stress exceeds the compressive strength of C30 concrete.Therefore,measures to prevent cracking should be strengthened here.(3)As for the radial displacement of the spray layer structure,it tends to be deformed into the hole.The radial displacement ranges from 0.24 mm to 2.1mm and gradually decreases from the top to the bottom of the arch.For annular displacement,the spray layer deforms counterclockwise in the left half cycle and clockwise in the right half cycle.The annular displacement ranges from 0mm to 0.95 mm,and the radial and annular displacements do not exceed the limit.From the Angle of displacement,the structure of spray layer will not produce cracks.(4)In the analysis of influencing factors,four factors related to the bearing characteristics of the spray layer structure are analyzed.The simulation results show that the stress value of the spray layer is proportional to the linear expansion coefficient.With the increase of temperature difference,the compressive stress of arch waist decreases gradually and that of arch roof increases gradually.The annular stress is directly proportional to the horizontal lateral pressure coefficient of in-situ stress.The stress of the spray layer is inversely proportional to the thickness of the structure of the spray layer.The temperature difference and the thickness of the spray layer have great influence on the bearing capacity of the spraylayer.Linear expansion coefficient has little influence.These four factors can be taken into account in the design of the spray layer structure,under the premise of economic and reasonable,the design of the best bearing capacity of the spray layer.(5)The radial and circumferential stress of steel fiber shotcrete structure increases first and then decreases with the age as the heat of cement hydration changes.Among them,the final value of the radial stress in twenty-one days is 0.7mpa,and the annular stress is 5.1mpa,neither of which exceeds the compressive strength of C30 concrete.There is no need to consider pressure measures.(6)The cracks of the shotcrete structure can be divided into compression cracks and tensile cracks according to the mechanical properties.The radial and annular compressive stresses of the shotcrete during the construction period are relatively large,and it is more likely to generate compression cracks.Adjust the appropriate ratio;Select concrete material with large linear expansion coefficient;The compressive strength of spraying layer structure can be improved by increasing the thickness of spraying layer appropriately.The tensile strength of spraying layer structure can be improved by adding steel fiber or steel mesh.High ground temperature is a geological hazard,and the study of the spray layer structure of the high ground temperature diversion tunnel has certain theoretical significance for practical engineering.