High Ground Temperature Research Articles

FLAC3D simulation of combined support effect under different prestress parameters of deep soft rock roadway

In coal mining, as the mining depth increases, a complex mechanical environment of “high ground stress”, “high ground temperature”, “high karst water pressure”, and “mining disturbance”, namely “three highs and one disturbance” appears. Many roadways have the characteristics of soft rock roadways with large deformation, large ground pressure, difficult support, and high support cost, which brings severe challenges to the safe and efficient production of coal mines. Therefore, it is very important to explore the support technology and support parameters of deep soft rock roadways. In this paper, numerical simulation is used to study the influence of different prestress on the displacement, axial force and vertical stress of the surrounding rock of the roadway in the joint support of deep soft rock roadway. The results show that in the simulation of prestressing 20KN, 40KN, 60KN, and supporting method of bolt and anchor cable combined support, the comprehensive support effect of 60KN prestressed bolt + anchor cable is the best.

A numerical investigation into the use of directionally drilled wells for the extraction of geothermal energy from abandoned oil and gas wells

Geothermal energy is an ideal renewable resource for power production since it is not limited by the intermittency issues associated with other renewables like wind and solar. Despite its ability to provide a steady supply of electricity on demand, the adoption of geothermal is not widespread, largely due to the high cost of drilling. One way to mitigate this cost is to use abandoned oil and gas wells, which are abundant (with an estimated 2.3 million in the United States) but pose a potential hazard to the environment. Studies in the literature have proposed installing heat exchangers in vertical wells to solve this problem. Vertical designs, however, would undergo high friction and temperature losses due to the use of internal piping. Such designs also do not enable the use of the L-shaped directionally drilled wells which have greater contact with the ground at high temperatures. This paper proposes an approach for extracting geothermal energy from abandoned oil and gas wells by using directionally drilled wells, thereby improving upon the existing designs by eliminating internal piping and maximizing contact with high ground temperatures. Through additional drilling, two adjacent wells can be connected to create a continuous loop from which thermal energy can be collected for use in a power cycle. The proposed geometry was studied numerically to determine the outlet temperatures and heat extraction rates from the system for the prediction of thermal energy extraction and electrical power production. The results show that a system with 4000 m deep vertical wells and a 4800 m horizontal section could produce approximately 2 MW of thermal energy and 200 kW of power using an organic Rankine cycle. Moreover, these wells are capable of providing a heat source for electricity generation for several decades.

The genesis of high ground temperature in the Long mountain road tunnel

Highway traffic increasingly extends to the mountainous area, requiring highway tunnels to be longer. Highway tunnel construction is risky and challenging, especially in the high ground temperature area of Western China. In this study, the Nige Tunnel of Yunnan Honghe Jian(ge) Yuan highway is the research object. By conducting numerous field temperature tests, geological surveys, water quality experiments, and other processes, the causes of high temperatures in the ground have been analyzed. The results show that the hot liquid or vapor from the earth’s crust deep area carries various chemical materials, passing through various channels (faults and fissures) to the superficial area and forms the geothermal of the tunnel. The thermal anomaly bodies in the deep crust move upward through faults Fn1 and Fn2. Some heat sources are exposed to the surface and form hot springs, and others are distributed through secondary channels after being transmitted to the shallow part of the crust. Among them, the entrance section of the Nige Tunnel is limestone, and the groundwater infiltrating the fracture channel is mixed in the conduction process, resulting in the overall low water temperature, and the rock wall temperature is lower than the water body temperature. The exit section of the Nige Tunnel is granite, the heat source is mainly conducted through structural fractures or rock mass, resulting in high rock temperature at the exit. By analyzing the causes of high ground temperature, this study provides a theoretical basis for developing the tunnel scheme.

A Novel Damage-Based Permeability Model for Coal in the Compaction and Fracturing Process Under Different Temperature Conditions

Before a coal mining operation, it is necessary to carry out coal-bed methane (CBM) pre-extraction to prevent coal and gas explosions, causing accidents. However, gas extraction and coal mining will lead to coal damage, which results in a change in the gas migration law. Especially, under deep mining conditions, the gas migration mechanism is more complicated owing to a high ground temperature. Coal permeability is the most important constituent that determines gas flow properties. Therefore, the coal permeability evolutionary law related to damage-induced conditions under different temperatures should be further researched. In this paper, a series of triaxial seepage experiments during the whole stress-induced process, and in the changing of the effective stress process were carried out. The results have shown that during the whole stress–strain process, with an increase in axial strain, coal permeability gradually decreases to a minimum value at first, then increases sharply, and finally keeps nearly constant. A higher temperature resulted in a lower elastic modulus, peak strain, and peak strength, but it caused higher thermal damage. When the coal fractures, coal permeability increases with the increase in temperature. During a change in the effective stress process, higher temperatures resulted in higher permeability. Under higher effective stress, the impact of temperature on permeability was not significant. Based on the above results, a novel damage-based permeability model was developed to describe the permeability evolutionary law caused by damage-induced conditions under compaction, and in a fracturing situation. In the proposed model, an exponential function has been used for the combination between permeability and damage variable. The damage variable is composed of thermal damage and mechanical damage. In addition, the damage variable has been modified by introducing a modified function of the initial damage. Finally, the proposed model has been applied to fit two sets of experimental data available. The fitting results showed that the proposed permeability model could well reflect the permeability behaviors of damage-induced coal at different temperatures.

Experimental Research on Viscosity Characteristics of Grouting Slurry in a High Ground Temperature Environment.

The grouting method is a technical means to prevent and control the thermal damage of the tunnel with high ground temperature in the underground hot water area, and the viscosity characteristic of the slurry is the key factor of grouting treatment. When grouting in high ground temperature geological conditions, the slurry inevitably has both time-varying and temperature-varying characteristics of viscosity in the process of filling high-temperature fissures and plugging geothermal water. At present, the research on the viscosity characteristics of slurry at high temperature is rarely reported in the literature. In this paper, laboratory tests were carried out to measure the time-varying viscosity of ordinary cement slurry; cement-sodium silicate slurry, widely used in engineering; and high ground temperature grouting slurry (HGTGS), independently developed by our research group, at different preheating temperatures (20, 40, 60, 80 °C). The viscosity function curves of the three kinds of slurry were obtained by function fitting method, and the viscosity variation law of slurry was analyzed. The study found that the time-varying process of viscosity of the cement-sodium silicate slurry and the HGTGS in specific temperature conditions can be divided into two stages: The slow rising period of viscosity and the rapid rising period of viscosity. Whereas, the time-varying process of viscosity of ordinary cement slurry in specific temperature conditions includes only one stage of the slow rising period of viscosity. The viscosity of ordinary cement slurry and cement-sodium silicate slurry increases with the increase of temperature, while the viscosity of the HGTGS decreases with the increase of temperature. There are corresponding viscosity time-varying equations for the three kinds of slurry in different temperature conditions. The viscosity time-varying equation of the ordinary cement slurry accords with the linear function form, and the viscosity time-varying equation of the cement-sodium silicate slurry accords with the power-law function form. The viscosity time-varying equation of the HGTGS conforms to the exponential function form. On this basis, the unified description equation of the viscosity characteristics of grouting slurry in high ground temperature and the applicability of different types of grouting materials are obtained. This study has a certain reference value and guidance for theoretical analysis, numerical simulation and engineering application of grouting in high ground temperature environment.

Application of Thermal Pressure Ventilation Technology in Extra Long Construction Tunnel with High Ground Temperature

The feasibility of thermal pressure ventilation technology for ventilation and cooling of extra long construction tunnel with high altitude and high ground temperature was discussed. A physical model was built with a proportional factor of 1:1 based on the design documents of Zilashan tunnel in China. The CFD model considering buoyancy effects was used to evaluated the influence of the initial rock temperature, the insulation performance of the left tunnel and the outdoor air temperature on the effect of thermal pressure ventilation. Results show that the effect of thermal pressure ventilation increases by 12.2%, and the effect of cooling enhances by 3.7% when the left tunnel has no insulation. Compared with the initial rock temperature, the outdoor air temperature has a greater influence on thermal pressure ventilation. When the initial rock temperature is below 54 °C, outdoor air temperature is below 17.5 °C and the left tunnel has no insulation, thermal pressure ventilation technology is feasible for ventilation and cooling of Zilashan tunnel with a shaft of 450 m height. The thermal pressure ventilation technology provides a reference for other construction tunnel projects as a design of ventilation and cooling.

The Effects of Thermal-mechanical Coupling on the Thermal Stability of Coal

ABSTRACT As the depth of coal mining continues to increase, the weight of the overlying strata and the ground stress on the residual coal in goaves also increase. At the same time, the temperature of the coal rocks continues to rise, and the high ground temperature environment of the mining and heading faces becomes more severe. As a result, coal oxidation and spontaneous combustion disasters become more prominent. In this work, an anaerobic heating experiment of coal under the thermal-mechanical coupling effect was performed. The effects of thermal-mechanical coupling on the thermal stability of coal were studied by analyzing parameters such as the heat flow peak temperature, endothermic peak value, heat absorption, and activation energy. The results showed that the heat flow peak temperature exhibited hysteresis as the initial temperature and the initial stress increased. At the same time, the endothermic heat flow peak value and the heat absorption decreased. Under the same initial stress, the activation energy gradually decreased as the initial temperature of the coal sample increased; the higher the initial stress, the lower the decrease in the activation energy. At the same initial temperature, the activation energy first increased and then decreased as the initial stress increased; the higher the initial temperature, the more sensitive this change in the activation energy was to stress. In this study, the influence of thermal-mechanical coupling on the thermal stability of coal was obtained. This work provides on-site guidance for the prevention and control of spontaneous coal combustion in deep mining.

Physical simulation experiment of factors affecting temperature field of heat adjustment circle in rock surrounding mine roadway

ABSTRACT With the development of deep mining, the problem of heat damage is becoming more and more serious. The deep mine has a longer ventilation route, which will cause the tunnel exposed area is very large, and the surrounding rock with a high ground temperature could heat the ventilation air. Therefore, in this study, a facility to conduct a series of physical similarity simulation experiments for studying the heat conduction and transfer in mine roadway’s surrounding rock is designed. The facility is applied to analyze, systematically and quantitatively, the effect of physical parameters on temperature field of the surrounding rock as well as its dynamic changes. The experimental results show that: the airflow velocity is strongly related to the temperature distribution of the surrounding rock when the temperature field is becoming stable. The maximum of the influence thickness can be up to 7 meters; the rock thermal diffusion coefficient of the rock also has a great effect on the curve of the rock’s temperature when the curve is becoming stable but has a slight effect on the curve’s shape; the rock’s moisture content has a great effect on the range of the temperature field. But the effect does not last long; The roadway with the structure of thermal resistance circle that is a sign of the increasing of the medium’s total thermal resistance has a large effect on heat transfer, which prolongs the period for the rock to reach a new thermal equilibrium state.

A Numerical Simulation Model and a Software of Using Ground Temperature to Predict Water Inrush from Heterogeneous Porous Rocks

Water inrush in deep mines is a major problem due to the complicated geological conditions of high water pressure, high stress, and high ground temperature. Because the high ground water and high ground stress have great influence on ground temperature distribution, the temperature change can be used to predict water inrush. In order to use ground temperature to predict water inrush from porous rock under thermal–hydraulic–mechanical (THM) coupling geological environments and simplify the process of establishing THM coupling model, a numerical simulation model specialized for using ground temperature to predict water inrush was established and a software specialized for establishing this model was developed by the secondary development of COMSOL Multiphysics. The temperature change law were studied under the impacts of the interaction of the water pressure, working face length, the geothermal gradient, and fault dip angle. Results indicate that the temperature in porous rock increases with increasing geothermal gradient, water pressure and fault dip angle, and decreases with increasing working face length. The ground temperature is higher in the heterogeneous porous media than in the homogeneous. At high water pressure, the temperature change is very large especially at the first few advancing steps of working face, which can provide an obvious temperature change to predict water inrush from porous rock. The software can provide a more convenient method to establish this model and use ground temperature to predict water inrush from porous rock.

Study on Temperature Control of Ventilation System in Construction Period of High Ground Temperature Tunnel

As China’s infrastructure continues to advance, tunnels will encounter increasingly complex geological conditions during construction. High geothermal heat seriously affects not only the normal construction of tunnels but also the physical and mental health of construction workers. Due to the existing cooling measures have poor effect and high energy consumption, so the cooling effect of the ventilation system is neglected. This paper studies the influence of ventilation system on the temperature inside the tunnel under different air supply volumes, and the distribution of temperature inside the tunnel. The numerical results show that the ambient temperature in the tunnel decreases gradually with the increase of air supply volumes at the same air temperature, but it will not change with the increase of air supply at a certain temperature. This study provides the theoretical basis for optimizing the ventilation and cooling system, it will provide a better construction environment for tunnel workers.

A novel high-toughness, organic/inorganic double-network fire-retardant gel for coal-seam with high ground temperature

In order to address the issue of spontaneous combustion of coal, this paper proposes a high-toughness hydrogel (P(AA-co-AM)/WG gel) for fire prevention and extinction, which is suitable for the conditions of coal-seam with high ground temperatures. In the initial stage, the silicic acid molecules in the material system react under the action of the coagulant to form the first network structure. Simultaneously, the superabsorbent monomers in the material system use the geothermal energy in the mines to polymerize and form the second network structure. The first and second network cross each other, forming P(AA-co-AM)/WG gel with interpenetrating network structure and high toughness. The differences in WG gel, P(AA-co-AM), and P(AA-co-AM)/WG gels were analyzed via testing of their in-situ infrared, and viscoelasticity. The results indicate that P(AA-co-AM)/WG gel had the best water retention, elasticity, inhibitory performance, compression resistance and lowest cost among the studied gels. In addition, the fire extinction experiments of comparison with other fire extinction materials indicated that P(AA-co-AM)/WG gel could uniformly cover the surface of the burning coal body forming a dense enwrapping on the coal and densely filling the cracks. Moreover, the fire extinction effect of the proposed gel is stable as there was no re-ignition phenomenon.

The effects of high temperature on the compaction behaviour of waste rock backfill materials in deep coal mines

To study the mechanical properties of backfill materials during compaction at high ground temperature in deep backfill mining, the WAW-1000D electro-hydraulic servo universal machine was used to conduct compaction testing of crushed sandstones heated to different temperatures. The stress–strain curves of crushed sandstones with four particle sizes heated to different temperatures were obtained. In this way, this study analysed the influence of temperature on the stress–strain relationship, porosity changes, and deformation mechanisms during the compaction of crushed sandstones. The experimental results demonstrate the following: (1) At the same particle size, with increased heating temperature, the strain in crushed waste rock decreased at a given applied stress. (2) After heating to the same temperature, the final strains in crushed waste rock samples of different particle size distributions decreased with particle size. (3) As heating temperature increased, the porosities of crushed waste rock samples heated to 100 °C, 200 °C, 300 °C, and 25 °C are ranked thus (in descending order) at the same stress. (4) After compaction of the samples at 25 °C, the number of large blocks decreased, while that of smaller blocks increased slightly. After compaction of heated samples of crushed waste rock, the amount of large blocks gradually reduced, while that of medium- and small-sized blocks gradually increased with increasing temperature. The temperature affects the deformation mechanisms during compaction of the samples of crushed waste rock, thus affecting their stress–strain relationships and porosity.

Research on The Exploration Technology and Method of Natural Gas Hydrate in China

new clean energy is essential for the rapid development of society. The appearance of natural gas, water and materials can timely alleviate the energy shortage in China. Natural gas water and substance is a kind of clean energy formed by hydrocarbon gas molecules such as water and methane under high pressure and ground temperature. At present, the main methods of land gas hydrate exploration are: high-precision seismic exploration technology, geophysical logging technology, geochemical exploration technology, remote sensing detection technology, audio magnetotelemental technology, and ultrasonic ground penetrating radar technology. In this paper, the basic exploration characteristics of different exploration technologies are introduced, which provides technical support for the rapid detection of terrestrial gas hydrate.

Observation Scheme for Temperature and Deformation of Permafrost Subgrade in Yichun-Bei’an Highway

The permafrost in the region of Yichun-Bei’an highway is characterized by thin thickness, high ground temperature and high local ice content, and is in the process of degradation, resulting in highway thaw subsidence and longitudinal cracking, which has a very serious impact on traffic. In order to design the observation scheme reasonably and master the variation law of temperature and deformation of permafrost subgrade, based on determining the observation scheme for temperature and deformation of permafrost subgrade, we established a monitoring system of temperature, humidity change and subsidence deformation of permafrost subgrade after construction by selecting typical permafrost observation sections along the highway, which can provide basic data for the design, construction and maintenance of highway subgrade in permafrost regions.

Development, Performance, and Microscopic Analysis of New Anchorage Agent with Heat Resistance, High Strength, and Full Length

To solve the difficult problems of failure of pretensioned bolt supports under high ground pressure and temperature, a new kind of anchorage agent with excellent performance is developed. First, the selection and compounding of raw materials were conducted. The new anchorage agent was obtained by modifying the PET resin by mixing with a phenolic epoxy vinyl ester resin (FX-470 resin) and adding a KH-570 silane coupling agent. Then, the viscosity, thermal stability, compressive strength under different temperatures, and anchorage capacity of the new anchorage agent were tested. Moreover, the best proportion ratio of anchorage agent by mixing resin : coarse stone powder : fine stone powder : accelerator : curing agent : KH-570 = 100 : 275 : 275 : 1 : 32.5 : 1 is obtained. The test results showed that, with the addition of a KH-570 silane coupling agent, the viscosity decreased significantly, thereby solving the difficult technical problems of pretensioned bolt supports in full-length anchorage support. Compared with the conventional anchorage agent, the compressive strength of the new anchorage agent increased by 20.4, 82.5, 118.2, and 237.5% at 10, 50, 80, and 110°C, respectively, and the anchorage capacity increased by 4.7, 8.7, 40.2, and 62.9% at 30, 50, 80, and 110°C, respectively. Finally, the enhancement in compressive strength and heat-resistant mechanism are revealed through microanalysis.

Imaging Thermal Anomalies in Hot Dry Rock Geothermal Systems from Near-Surface Geophysical Modelling

Convective hydrothermal systems have been extensively studied using electrical and electromagnetic methods given the strong correlation between low conductivity anomalies associated with hydrothermal brines and high temperature areas. However, studies addressing the application of similar geophysical methods to hot dry rock geothermal systems are very limited in the literature. The Timanfaya volcanic area, located on Lanzarote Island (Canary Islands), comprises one of these hot dry rock systems, where ground temperatures ranging from 250 to 605 °C have been recorded in pyroclastic deposits at shallow (<70 m) depths. With the aim of characterizing the geophysical signature of the high ground temperature areas, three different geophysical techniques (ground penetrating radar, electromagnetic induction and magnetic prospecting) were applied in a well-known geothermal area located inside Timanfaya National Park. The area with the highest ground temperatures was correlated with the location that exhibited strong ground penetrating radar reflections, high resistivity values and low magnetic anomalies. Moreover, the high ground temperature imaging results depicted a shallow, bowl-shaped body that narrowed and deepened vertically to a depth greater than 45 m. The ground penetrating radar survey was repeated three years later and exhibited subtle variations of the signal reflection patterns, or signatures, suggesting a certain temporal variation of the ground temperature. By identifying similar areas with the same geophysical signature, up to four additional geothermal areas were revealed. We conclude that the combined use of ground penetrating radar, electromagnetic induction and magnetic methods constitutes a valuable tool to locate and study both the geometry at depth and seasonal variability of geothermal areas associated with hot dry rock systems.

Raindrop Size Distribution Characteristics of Summer and Winter Season Rainfall Over North Taiwan

AbstractRaindrop size distribution (RSD) characteristics of summer and winter seasons over north Taiwan are analyzed by using long‐term (~12 years) raindrop spectra from Joss‐Waldvogel disdrometer located at National Central University (24°58′N, 121°10′E), Taiwan. Along with the disdrometer data, radar reflectivity mosaic from six ground‐based radars, Tropical Rainfall Measuring Mission, Moderate Resolution Imaging Spectroradiometer, and ERA‐Interim data sets are used to establish the dynamical and microphysical characteristics of summer and winter rainfall. Significant differences in raindrop spectra of summer and winter rainfall are noticed. Winter rainfall has a higher concentration of small drops and a lower concentration of midsize and large drops when compared to summer rainfall. RSD stratified on the basis of rain rate showed a higher mass‐weighted mean diameter (Dm) and a lower normalized intercept parameter (log10Nw) in summer than winter. Similarly, diurnal variation of RSD showed higher Dm and lower log10Nw values in summer as compared to winter rainfall. In addition, for both seasons, the mean value of Dm is higher in convective precipitation than stratiform. Radar reflectivity (Z) and rain rate (R) relations (Z = A*Rb) showed a clear demarcation between summer and winter rainfall. Higher ground temperatures, deeply extended clouds with intense convective activity in summer modified the RSD through evaporation, drop sorting, and collision‐coalescence processes resulting with higher Dm and lower log10Nw values in summer as compared to winter rainfall.

Needle ice formation, induced frost heave, and frost creep: A case study through photogrammetry at Stelvio Pass (Italian Central Alps)

Needle ice growth is one of the more widespread and easily visible, but less studied, climate related processes shaping soil evolution, surface dynamics and ecosystem changes in the alpine environments. Here, we show the results of the monitoring of needle ice development at four plots located at 2670 m a.s.l. close to the Stelvio Pass in the Italian Central Alps during 2016. Needle Ice formation and evolution with time was monitored through the photogrammetric technique of the Structure from Motion (SfM). Our monitoring data included also quantitative measurements of some selected physical and climatic parameters like air temperature, ground temperature and ground water content at depths of 2 and 5 cm. Our data demonstrate that needle ice can develop with a relatively low ground water content (13.2%), at a relatively high minimum ground temperature (−0.3 °C) and with a low cooling rate (<1.8 °C h−1). Moreover, for the first time, we observed that needle ice can form below a thin snow cover (<25 mm) that can enhance the sensible heat flow from the ground to the atmosphere and, therefore, promote the cooling of the near surface ground. Statistically, the minimum air temperature results in the leading factor for the needle ice growth.The total frost heave seems to be related to the abundance of fine material (although we couldn't demonstrate it statistically). The absence of statistically significant relationships between frost heave and frost creep could be probably due to the importance of the observed needle ice toppling and the possible sliding of the clasts during the melting phases.

Unique spatial methane distribution caused by spontaneous coal combustion in coal mine goafs: An experimental study

Abstract A new type of incident in the form of a methane explosion caused by spontaneous combustion of coal is receiving more and more attention due to the high ground temperature and high methane content in coal mines. To investigate the formation process of this type of incidents and advance the research on methane explosion risk caused by spontaneous coal combustion, a self-designed experimental platform was used to determine the influence of spontaneous coal combustion on methane migration in the goaf. Additionally, the effect of different ventilation velocities at the mining face on methane migration in the goaf was studied. The results reveal that air leakage plays a key role in methane migration in the goaf. The bigger the ventilation velocity, the larger the area affected by air leakage. In addition, the superposition of the air leakage and the horizontal and vertical movement of hot gases creates the entrainment effect in the spontaneous combustion area. Eventually, the methane concentration at the location of spontaneous combustion is the lowest and it gradually increases outside the spontaneous combustion area because of the superposition of air leakage, ‘fire pressure’ and the entrainment effect.

Influence of temperature on the brittle failure of granite in deep tunnels determined from triaxial unloading tests

High ground temperatures lead to the risk of rockburst in hard rock tunnels located in high-stress environments. However, existing rockburst studies have not considered the influence of temperature. Therefore, the laboratory experiments were conducted to measure the brittleness of granite samples under different temperature scenarios, and the tendency of rockbursts were evaluated at different temperatures in this paper. The brittle failure mechanism of granite was explored by using uniaxial and triaxial rock tests under the influence of thermo-mechanical coupling. The results indicated that the post-peak deformation of the rock samples changes from ductile to brittle with an increase in temperature to 100 °C. The frequency of shear failure occurred in this test increases with increasing temperature, and the brittle failure of the surrounding rock is enhanced with an increase in temperature. The results indicated that rockbursts occurring in deep granite tunnels at high ground temperatures will be more intense than those occurring at room temperature. The results of this study can be applied to predict the intensity of rockbursts before the tunnels are excavated.