Determining the physical and mechanical behavior of sedimentary rocks is one of the most common challenges in deep rock mass engineering. Experiments were con-ducted to study the physical and mechanical properties of coal measure mudstone with SEM, XRD, and uniaxial compression testing. The results show that temperature has a significant effect on the physical and mechanical properties of coal measure mudstone. The presence of clay minerals in the evaluated mudstone contributes to the unique characteristics seen at high temperature. The mudstone experiences obvious color changes on the surface as temperature rises. This is mostly attributed to the iron-bearing clay minerals. Internal color change is caused by thermal de-composition of kerogen associated with the clay minerals. As the major clay mineral in mudstone, kaolinite undergoes significant phase changes at high temperatures, which leads to changes in mechanical properties. From 25?C to 200?C, due to the evaporation of absorbed water from the clay minerals, the strength of the mudstone increases significantly. As the temperature continues to rise beyond this, water evaporation continues and the rock strength increases gradually from 200?C to 400?C. When the temperature reaches 400?C, this mudstone was strengthened as a result of decomposition of the kaolinite and thermal expansion of crystalline minerals. Above 600?C, dehydration of the clay minerals ends while thermal cracking initiates gradually, which results in decreasing strength

The rock mechanical properties under the effect of high temperature present a great significance on underground rock engineering. In this paper, the mechanical properties of sandstones, marbles, and granites under real-time heating were investigated with a servo-controlled compression apparatus. The results show that mechanical behaviours of all the three types of rocks are influenced by real-time heating to different degrees. Due to thermal cracking, the uniaxial compressive strengths decrease as the heating temperature rises from room temperature to 400°C. Above 400°C, the sandstone exhibits a significant increase in UCS because of the sintering reaction. The sintering enlarges the contact area and friction between crystal grains in the sandstone, which strengthens the bearing capacity. For marbles, the UCS continues to decrease from 400°C to 600°C due to thermal cracking. However, the carbonate in the marble begins to decompose after 600°C. The generated particles would fill the cracks in the marble and increase the strength. For granites, their UCS presents a sharp decline after 400°C because of thermal cracking. For all rock elastic modulus, they present a decreasing trend, and this indicates that the rock’s ability to resist deformation gradually weakens under the effect of temperature. In general, rock mechanical behaviours under real-time heating differ from those in normal situations, and use of the parameters presented here is important for underground rock engineering related to high temperature and can improve the precision in theoretical and numerical analysis.

Thar Coalfield in Pakistan is the largest reserve of lignite coal in the country, which is outlined by thick coal seams. The preferred mining method for these thick coal seams is the Longwall Top Coal Caving (LTCC). The connection of both the top coal caving and its compactness are still rare; therefore, the capability of top coal caving mechanism is the most significant factor in LTCC that must be adequately explained and examined. Moreover, in order to achieve the ideal coal production, a comprehensive modeling of deformation and induced stress is mandatory. In this study, a 12 m thick coal seam with cutting to caving height ratios like 1:2 and 1:3 has been modelled, and the mechanism of longwall top coal caving demonstrated and front abutment vertical stress distribution in front of face line values were computed with the help of UDEC at Block-IX, Thar Coalfield. The results reveal that a thick layer of top coal can be progressively caved behind the face at the ratio 1:3 instead of 1:2 (which explained the incompetent caving progress of top coal). Similarly, the maximum vertical abutment stress of 20 MPa was observed at 6m in front of the face when cutting to caving height ratio was 1:2 and at 3m in front of face with 1:3 (which is comparatively capable for the face advancement), respectively. Therefore, this numerical modeling study proposes the reasonable height of top coal caving at cutting to caving height ratio 1:3 for the efficient production of thick coal seams at Thar Coalfield.

Experiments were conducted to study the mechanical characteristics of arkosic sandstones sampled from Pingyi, China. Rock samples were all thermally treated under the temperature ranging from room temperature to 800°C. Results show that as the treatment temperature rises, the arkosic mineral composition does not change obviously, but the mechanical behaviors change regularly. Variation trend changes dramatically at 200°C, 400°C, and 500°C. With thermal expan¬sion of mineral particles being the dominant factor, mechanical behaviors barely change below 200°C. When temperature ranges from 200-400°C, it has an important effect on the mechanical properties because of the thermal fracture. From 400-500°C, mechanical properties change dramatically as a result of the mutual influence of thermal fracture, fusion and re-crystallization, but the thermal fracture is the leading factor. Because of the fusion and re-crystallization, fractures are partly filled, which results in partial recovering of the mechanical strength. With the combined action of thermal fracture, fusion and re-crystallization after 600°C, mechanical performance of arkosic sandstones degrades rapidly. Generally, the porosity and peak strain of arkosic sandstones increase with the temperature rising. However, the peak stress, elastic modulus and deformation modulus decrease simultaneously. Influenced by mineral particles’ thermal expansion, thermal fracture, fusion, and re-crystallization and so on, the variation trend and amplitude are not the same at different temperature ranges, and the damage mechanism of sandstones also makes a difference.

A mathematical model of heat conduction in surrounding rocks of the high geothermal roadway with thermal insulation layer was established in this paper, and its finite difference scheme was also proposed. On this basis, thermal insulation mechanism of thermal insulation layer was investigated. Results show that distinct regional temperature distribution exists in the thermal insulation layer. The temperature is continuous while the temperature gradient has a sudden fluctuation at the interface of different media. The wall temperature is lower and the inner surrounding rock temperature is higher in surrounding rocks with thermal insulation layer compared to that in surrounding rocks without thermal insulation layer. Moreover, the smaller the thermal conductivity of the medium in the thermal insulation layer, the larger the temperature gradient and the smaller the heat flux density. At the beginning of ventilation, thermal insulation of the gunite layer is better than that of the grouting layer. After three months, thermal insulation of the grouting layer is better than that of the gunite layer. Thermal insulation layer can reduce 29-40% of heat dissipation and the thermal insulation would be more significant if the thermal insulation layer was constructed earlier.

To explore the spatial-temporal evolution law of rock mass temperature in high geothermal roadway during mechanical ventilation, a series of experiments were conducted based on the physical simulation test system of thermal and humid environment in high geothermal roadway, which is a method independently developed by China University of Mining and Technology. The results indicate that during ventilation, the disturbed region of the temperature extends gradually from shallow area to deep area in the surrounding rock mass of the roadway. Meanwhile, the temperature increases as the exponential function from shallow area to deep, with steady decrease of the temperature gradient and heat flux. As the ventilation proceeds, the relationship between dimensionless temperature and dimensionless time approximately meets Hill function.

As one of the key technologies for hot dry rock (HDR) geothermal exploitation, artificial reservoir is giant hydraulic fracturing at its core and takes the theory of hydraulic fracturing of rocks under thermo-mechanical coupling as its key scientific problem. With large samples of Shandong grey granite being the experimental subject, this paper conducted hydraulic fracturing experiment under triaxial stress at 20°C, 100°C, 200°C, 300°C and 400°C, analyzed the characteristic of water pressure loading curves in the experiment, and found that crack initiation pressure decreased remarkably after 300°C. In order to verify the factors controlling the influence of temperature on crack initiation, this paper established a strong transient thermal stress model, carried out numerical computation on this model and compared it with the experimental results. The results showed that the cooling effect of fracturing fluid for high temperature borehole can lead to thermal shock phenomenon and cause tensile stress near the borehole surface; the area near the borehole experienced two impact shocks, namely, elastic wave and thermal wave; the mechanism for the effect of temperature on the hydraulic fracturing of granite is not changes of rock mechanical parameters, but the thermal shock generated by the action of fracturing fluid of rock at high temperature.

Man-made geothermal reservoir is one of the key technologies in heat extraction in HDR.The fundamental issue is the massive hydraulic fracturing and the key scientific problem is hydraulic fracturing theory when considering the thermo-mechanical coupling effects on the rock.The self-developed "600℃ 20 MN servo-controlled rock tri-axial testing machine with high temperature and high pressure" was adopted to carry out the hydraulic fracturing experiments for large sized specimen under high temperature and tri-axial stress.The size of Luhui granite specimen is Φ200 mm×400 mm.Characteristics of the hydraulic loading curve and fracture morphology were analyzed after the experiment.The results show that fracture cracking model of granite specimens transformed from brittle cracking into continuous cracking with the increase of temperature.When the temperature is larger than 300 ℃,the main control criteria of fracture cracking becomes the temperature.When the temperature varies from the room temperature to 200℃,the control mechanism of the impact of temperature on the initiation pressure is the decrease of tensile strength of rock masses,while from 200℃ to 400℃,the control mechanism is the thermal stress caused by the decrease of temperature.The fracture propagation orientation changed from axial direction into radial direction with the increase of temperature.

Based on finite difference method, a mathematical model and a numerical model written by Fortran language were established in the paper. Then a series of experiments were conducted to figure out the evolution law of temperature field in high geothermal roadway. Research results indicate that temperature disturbance range increases gradually as the unsteady heat conduction goes on and it presents power function relationship with dimensionless time. Based on the case analysis, there is no distinct expansion of temperature disturbance range after four years of ventilation, when the temperature disturbance range R = 13.6.

A self-designed experimental installation for transient heat transfer in the modelling surrounding rock mass of high geothermal roadways was elaborated in this paper. By utilizing the new installation, the temperature variation rules in surrounding rock mass of the high geothermal roadway during mechanical ventilation were studied. The results show that the roadway wall temperature decreases dramatically at the early stage of ventilation, and the temperature at every position of the surrounding rock mass is decreasing constantly with time passing by. From roadway wall to deep area, the temperature gradually increases until reaching original rock temperature. The relationship between dimensionless temperature and dimensionless radius demonstrates approximately exponential function. Meanwhile, the temperature disturbance range in the simulated surrounding rock mass extends gradually from the roadway wall to deep area in the surrounding rock mass. Besides, as the air velocity increases, heat loss in the surrounding rock mass rises and the ratio of temperature reduction becomes larger, the speed of disturbance range expansion also gets faster.

Mine Geothermal and Heat Hazard Prevention and Control (MG-HHPC), a new concept, is proposed in this paper, based on the research status and development trend in China. The scientific connotation of MG-HHPC is as well expounded. MG-HHPC includes three aspects, i.e., mine geothermal, mine heat transfer, and mine heat hazard prevention and control technology. The key issues need to be researched and solved about the three aspects above are analyzed, and the fundamental theory and technology system for MG-HHPC are also built. Then the paper points out that the train of thought for heat hazard prevention and control technology is to stress both prevention and control while with emphasis on control. And the hypothesis of laneway's surrounding rock heat resistance zone and heat control method with gob full filling are also proposed.

Geothermal energy from the surrounding rock of roadway is one of the significant factors of the mine heat hazard. Hence, the research on temperature field of surrounding rock is the basis of heat hazard prevention and control. This paper established the mathematical model for heat conduction in the semi infinite hollow circle slice with one dimension, and studied the transient temperature field of the surrounding rock of high geothermal roadway by using finite difference method. The results indicate that the dimensionless temperature of surrounding rock is the exponential function of the dimensionless radius, and the temperature will gradually approach and finally reach the original rock temperature. However, along with the distance from roadway wall increasing, the temperature gradient and heat flow density in the surrounding rock are decreasing gradually. At the beginning of the transient conduction, the wall temperature will be rapidly close to the wind temperature when the dimensionless time is about 0.8. What's more, the relationship between dimensionless temperature of the surrounding rock and the dimensionless time approximatively fits the Hill equation. Results also show that the temperature disturbance range in surrounding rock is expanding to around in a power function law as the transient conduction goes on.

In order to study the suitability of the probability integral method applied to the mining subsidence estimation of a steep inclined seam,a simulation study method of the similar material model was applied.With the nonlinear least square fitting method of Matlab,the results showed that partial surface ground moving parameters obtained from the fitting could not meet the original physical meaning.Thus a surface ground subsidence estimation correction model was provided based on the probability integral method.The correction effect of the model was analyzed and the correction parameters were obtained.The study results showed that when the seam angle was 50~70°,the subsidence fitting accuracy of the model would be less than 2% and the expression between the correction parameter and the seam inclination could be obtained.When the seam angle was over 70°,the model would not be suitable.

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地理信息系统(GIS,Geographic Information System)一门学科,用以描述一切与地理相关的内容;也是一个技术系统,以空间数据组织和处理为基础,采用地学模型分析方法,及时提供多种空间地理信息和动态地理信息,为政府部门提供决策,在生活各个领域具有广泛的应用。