Transient Temperature Field Of Surrounding Rock Of The High Geothermal Roadway And Its Heat Control Mechanism By Heat Insulation

Heat hazard has become the sixth largest natural hazard in underground mine,following after roof accident, gas disaster, water accident, fire disaster and coal dust.The geothermal temperature factor plays the decisive role in the formation of hightemperature damage in deep coal mines. Because of long ventilation lines, largeexposure area, and complex ventilation system, the high geothermal temperatureroadway most possibly influences the meteorological environment with largest regionin underground mines. It not only directly heats wind flow, but also indirectly reducesthe air-conditioning cooling effect by polluting cool air flow. Therefore, it is necessaryto research the heat transfer problems in surrounding rock of the high geothermaltemperature roadway, whose fundamental problem is the temperature field.This paper adopted the combined method of theoretical anlysis, physicalsimulation and numerical test to research the temperature field of surrouding rock ofroadway and its evolution law, and obtained some corresponding results. Similarsimulation test method for the research on the temperature of surrounding rock in highgeothermal roadway was proposed. With the similar simulation test system of thermaland humid environment in high geothermal roadway, designed and developedindependently, the paper carried on the research on temperature field, and revealed thetemperature distribution characteristics and their evolution laws in high geothermalroadway’s surrounding rock. A numerical solution method suitable for transienttemperature field was established to carry on the numerical test research ontemperature field of surrounding rock in high geothermal roadway, and the evolutionlaws of temperature field were further discussed. A mathematical model of transientconduction in surrounding rock with heat insulation zone in high geothermal roadwaywas established to carry on the research on insulation mechanism of the heatinsulation zone, and the scientific connotation of the heat insulation zone concept wasfurther perfected. The specific results are listed as follows:1) A physical similar simulation method suitable for the research on thetemperature field of surrounding rock in high geothermal roadway was proposed inthis paper. Based on the law of conservation of energy and the Fourier’s law, the heattransfer problem in surrounding rock of roadway was simplied to the heat conductionproblem in a semi infinite hollow circle slice with one dimension, and a mathematicalmodel for transient conduction in roadway’s surrounding rock was built. At the same time, this article derived the similarity criterion of temperature field in roadway’ssurrounding rock according to the theory of similarity, and got the relationalexpression of similarity constant in the process of physical simulation experiments oftemperature field of roadway’s surrounding rock. Finally, the paper anlyzed andsummarized the physical simulation method suitable for the research of thetemperature field of surrounding rock in high geothermal roadway.2) We designed and developed the Similarity Simulation Test System forThermal and Humid Environment in High Geothermal Roadway independently, withwhich the ventilation cooling, the air conditioning cooling and the insulation coolingcould be simulated. So far, the testing system is a specialized testing platform with thelargest size and the most perfect function at home and abroad, applied to simulate thethermal and humid environment in high geothermal roadway.3) Temperature distribution of surrounding rock in high geothermal roadway andits evolution law were investigated using the physical similarity experiment method.The main achievements are as follows:(1) After ventilation in roadway, the roadwaysurface temperature decreases rapidly, which would be soon close to the windtemperature; the temperature disturbance range of the surrounding rock expandsgradually from the shallow to deep.(2) The temperature of the surrounding rock inroadway grows exponentially from the surface to depth.(3) With the extension ofventilation time, the temperature of surrounding rock decreases as Hill function, andthe decreasing amplitude is also gradually decreasing.(4) The variation process oftemperature gradient, heat flux density and heat flux in roadway’s surrounding rockcould be divided into three stages. They keep a relatively lower level before thetemperature of surrounding rock is disturbed. When the surrounding rock enters theregion of temperature disturbance, the temperature gradient, heat flux density and heatflux will gradually increase until they reach the peaks. The third stage is when thetemperature of surrounding rock is fully disturbed. At that time, the temperaturegradient, heat flux density and heat flux gradually decrease, and finally return to avery low level.4) Transient conduction characteristics of surrounding rock in high geothermalroadway were studied with the numerical simulation method. The experimental resultsand the mathematical model of transient conduction of surrounding rock were provedreasonable, and the evolution laws of temperature field were further discussed. Themain achivements are as follows:(1) It is proved that the relationship between dimensionless temperature and dimensionless radio fits exponential function, and therelationship between dimensionless temperature and dimensionless time fits hillfunction by the numerical method. Meanwhile, it is proved that there are three stagesin the distribution characteristics of temperature grandient, heat flux density and heatflux.(2) The temperature disturbance range in surrounding rock is expanding toaround in a power function law as the transient conduction goes on. After ventilationfor4years, the temperature of the surrounding rock reaches quasi-steady state, andthe largest temperature disturbance range is about25meters.(3) The relationshipbetween dimensionless temperature and Bi fits exponential function, and the more theBi is, the lower the dimensionless temperature is, which demonstrates that increasingwind speed promotes thermal discharge. When the Bi reaches to the peak, thetemperature of the surrounding rock doesn’t decrease obviously with the Bi increasing,which demonstrates the cooling effect will not be obvious when the wind speedreaches to a certain high level.5) The temperature distribution characteristics and insulation mechanism of theheat insulation zone wer studied in the paper. Mathematical model for heat conductionin surrounding rock of high geothermal roadway with heat insulation zone was built inthis article. Based on the heat conduction characteristics of composite material, thenumerical solution method was also built by the energy balance method. Meanwhile,the special computer programme for temperature field simulation of heat insulationzone was written, with which the insulation mechanism of heat insulation zone wassimulated. The main achivements are as follows:(1) There exists obvious regionaltemperature distribution characteristic in the heat insulation zone, and the boundarylines are the interface between the spouting layer and the grouting layer, and theinterface between grounting layer and the rock mass.(2) The temperature of theroadway surface with heat insulation zone decreases more quickly during initialperiod of ventilation, and the lower the conductivity coefficient of the spouting layer,the temperature of the surface is lower.(3) The lower the heat conductivity coefficientof the spouting layer and the grouting layer, the higher the temperature of the rockmass in deep is.(4) The temperature distribution in the grouting layer can be dividedinto two parts. In the first part, whih is a small region close to the spouting layer, thebetter the heat conductivity of grouting layer is, the higher the temperature. In otherregion, the better the heat conductivity is, the lower the temperature is.(5) The lowerthe heat conductivity coefficient of the spouting layer and the grouting layer is, the larger the temperature grandient is, and the lower the heat flux density is, whichdemonstrates that the insulation effect is more obvious. During the preliminary stageof ventilation, the insulation effect of spouting layer is better than that of groutinglayer with the same decreasing amplitude of heat conductivity. However, theinsulation effect of grouting layer is better than spouting layer after3month’sventilation.(6) Researches show that the heat insulation zone is significantly effectiveto reduce heat dissipation of the roadway’s surrounding rock. There would be an about29~40%cut in heat emission, and the cooling effect is more obvious during thepreliminary stage.