| The development and utilization of hot dry rock(HDR)geothermal energy is attracting widespread attention.Because it stores in dense,high-temperature deep rock masses lacking fractures,mining deep thermal ore energy by the well construction method is one of the ways people have explored to break through the bottleneck of the commercialization of enhanced geothermal systems in recent years.Aiming at the innovative Enhanced Geothermal System based on Excavation Technology(EGS-E),this thesis has conducted a preliminary quantitative study of the tunnel as a basic element of EGS-E,including the distribution characteristics of the surrounding rock fracture zone during excavation,ventilation and cooling,also the simulation analysis of the mechanics and heat transfer behavior of the tunnel fracture zone through literature research,numerical simulation(FLAC3D)and theoretical analysis methods.The main research contents and conclusions are as follows:(1)Through literature review,the micro-mechanism and evolution law of the changes in the physical and mechanical properties of high-temperature rocks are discussed,and a set of high-temperature characteristic parameters derived from the experimental foundation are provided for the numerical simulation of high temperature rock mass less than 300?.Through literature research,it is found that the deep-ground high-temperature rocks within this temperature range are still typical brittle and hard rocks,and the behavior of deep-ground granites needs to be simulated by mechanical parameters modified by temperature.(2)Based on CWFS model,the distribution and change of plastic yield strain representing the surrounding rock excavation disturbance zone(EDZs)under unloading are revealed,the failure patterns of surrounding rock under the condition that the initial deep ground stress is close to hydrostatic pressure are discussed.A basic attempt was made to quantify the scale of the fracture damage zone caused by excavation disturbance under high temperature conditions.The study on the mechanics,permeability and heat transfer behavior of tunnel excavation provides the foundation for the subsequent artificial construction of heat storage in hightemperature rock masses and is the basis for the safety discussion of deep engineering construction.Through thermal-mechanical coupling simulation,analyzed the surrounding rock stress and the evolution law of excavation disturbance damage rupture zone as the process of tunnel ventilation and cooling is analyzed.The results show that the ventilation cooling of high temperature and high in-situ stress tunnel have a significant effect on the EDZS scale.Additional tensile stress is generated in the shallow of tunnel surrounding rock,and the compressive stress concentration transfers to the far field.EDZs experiences three stages of slow,rapid and deceleration with cooling time,and the installation of a thermal insulation liner will significantly extend the time of the slow growth phase.(3)Considering the use of boiling heat transfer and natural convection of the working fluid,two heat transfer mechanisms are of great significance to the regulation of heat recovery in rock mass fractures caused by excavation,drilling and blasting.Though the use of plastic volume strain correlation formula,combined with the results of numerical simulation analysis,this paper preliminarily characterizes the non-linear distribution of permeability in the damage and fracture zone of surrounding rock caused by excavation.Based on the ideas of natural convection and boiling evaporation,the heat transfer process is simplified,and a simple calculation method for the heat transfer behavior in the fracture zone caused by the excavation disturbance of the primitive tunnel is discussed.The results show that compared with the natural convection of the fluid filled in the cracks of the rock mass,the use of boiling heat transfer to develop the dry hot rock can obtain higher heat recovery efficiency. |
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