Study of Temperature Field Distribution in Topographic Bias Tunnel Based on Monitoring Data

In recent decades, numerous tunnels have been built in the cold region of China. However, the temperature field of topographically biased tunnels in the monsoon freeze zone has not been sufficiently studied. In this study, we monitored the temperature of the surrounding rock in two topographic bias sections of the Huitougou Tunnel and analyzed the results by fitting them to the monitoring results. The results showed that the temperature of the surrounding rock on both sides after tunnel excavation varied periodically in an approximate triangular function. As the distance from the cave wall increased, the annual average temperature of the surrounding rock did not change significantly, the amplitude decreased, and the delay time increased, while the annual maximum temperature decreased, and the annual minimum temperature increased. The heat generated by blasting, the heat of hydration of the primary and secondary lining, and the decorated concrete all caused a significant increase in the temperature of the surrounding rock within 4 m for a short period of time. Both construction and topographic factors led to asymmetry in the distribution of the surrounding rock temperature in different ways. The results of this paper are intended as a reference for other studies on temperature in deviated tunnels.

Investigation of the Centers of Endogenous Fires at the Rock Dumps of the Coal Enterprises

The formed rock dumps of sections, mines and washing plants are composed of carbonaceous rocks and are capable of spontaneous combustion when the required amount of air is supplied. The conducted studies evaluated the efficiency of detecting a center of spontaneous combustion at the rock dumps of sections by measuring the temperature of rocks in the wells with a depth of 2.5 m, drilled at the distance of 20 m from each other, according to the current normative documents. For the landfill, a dump site with a long-existing center of spontaneous combustion was selected. The experiment showed the impossibility of drilling wells on the slopes of the dumps, as well as the need for casing the wells with pipes along the entire length. The temperature of rocks in the wells at a depth of 2.5 m varied from 69 to 773 °C. It was found that in the heated zone there are sharp temperature drops in the rocks, which cannot be detected with an interval between the measurement points equal to 20 m. With such a distance between the control wells, the places with a diameter of 1–10 m may remain undetected at the initial stage of spontaneous combustion. Measurements showed that in all the wells the rock temperature increases with depth. At the same time, the recommended well depth of 2.5 m does not allow determining the size of the heated zone deep into the rock dump. The upper layer of rocks above the center of spontaneous combustion exceeds the ambient temperature, so remote temperature measuring devices can be used to detect endogenous fires in the rock dumps. The use of thermal imagers installed on the unmanned aerial vehicles will significantly reduce the cost of detecting spontaneous combustion centers on the rock dumps and increase the efficiency of detecting fire centers not only on the dump sites, but on the slopes of the dump side and in other hard-to-reach places. Moreover, with a decrease in the atmospheric air temperature, the efficiency of remote thermal photography does not decrease. To clarify the parameters of the center of endogenous fires, it is advisable to use the temperature measurement of rocks with a contact thermometer at a depth of 0.5 m.

Numerical Study on Thermal Damage Behavior and Heat Insulation Protection in a High-Temperature Tunnel

Deepening our understanding of temperature and stress evolution in high-temperature tunnels is indispensable for tunnel support and associated disaster prevention as the rock temperature is remarkably high in hot dry rock (HDR) utilization and similar tunnel engineering. In this paper, we established a two-dimensional thermal–mechanical coupling model through RFPA2D-thermal, by which the temperature and stress field of the surrounding rock in a high-temperature tunnel with and without thermal insulation layer (TIL) were studied, followed by the evolution of thermal cracks. The associated sensitivity analysis of the TIL and airflow factors were then carried out. We found that (1) the tunnel rock is unevenly cooled down by the cold airflow, which induces thermal stress and damages the rock element when it exceeds the tensile strength of the rock mass. Those damaged rock elements accumulate and coalesce into visible cracks in the tunnel rock as the ventilation time goes, reducing the tunnel stability. (2) TIL effectively reduces the heat exchange between the airflow and tunnel rock and weakens the cold shock by the airflow, delaying the crack initiation which provides efficient time to adopt engineering measures for tunnel supporting. (3) TIL parameters are of pivotal importance to the long-term cold shock by the airflow. Increasing the TIL thickness and reducing the TIL thermal conductivity both significantly enhance the thermal insulation effect. The results cover the gap in the study of cold shock in high-temperature tunnels, which is helpful in designs to prevent thermal damage in high-temperature tunnels.

Characteristic Law of Borehole Deformation Induced by the Temperature Change in the Surrounding Rock of Deep Coalbed Methane Well

The borehole stability of the coalbed methane (CBM) well has always been vital in deep CBM exploration and development. The borehole instability of the deep CBM well is due to many complicated reasons. The change in the surrounding rock temperature is an important and easily overlooked factor among many reasons. In this research, we used methods that include experiment and numerical simulation to study the characteristic law of the borehole deformation induced by the changes in the surrounding rock temperature of deep CBM well. The experimental results of the stress–strain curves of five sets of experiments show that when the experimental temperature rises from 40 °C to 100 °C, the average stress when coal samples are broken gradually decreases from 81.09 MPa to 72.71 MPa. The proportion of plastic deformation in the entire deformation stage gradually increases from 7.8% to 25.7%. Moreover, the characteristics that some key mechanical parameters of coal samples change with the experimental temperature are fitted, and results show that as the experimental temperature rises from 40 °C to 100 °C, the compressive strength, elastic modulus, and main crack length of coal samples show a gradually decreasing trend. By contrast, the Pois-son's ratio and primary fracture angle show a gradually increasing trend. Moreover, the relativity of the linear equations obtained by fitting is all close to 1, which can accurately reflect the corresponding change trend. Numerical simulation results show that a high temperature of the surrounding rock of the deep CBM well results in a high range of stress concentration on the coal seam borehole and high deformation.

Rocks of different mineralogy show different temperature characteristics: implications for biodiversity on rocky seashores

As some intertidal biota presently live near their upper tolerable thermal limits when emersed, predicted hotter temperatures and an increased frequency of extreme-heat events associated with global climate change may challenge the survival and persistence of such species. To predict the biological ramifications of climate change on rocky seashores, ecologists have collected baseline rock temperature data, which has shown substrate temperature is heterogenous in the rocky intertidal zone. A multitude of factors may affect rock temperature, although the potential roles of boulder surface (upper versus lower), lithology (rock type) and minerology have been largely neglected to date. Consequently, a common-garden experiment using intertidal boulders of six rock types tested whether temperature characteristics differed among rock types, boulder surfaces, and whether temperature characteristics were associated with rock mineralogy. The temperature of the upper and lower surfaces of all six rock types was heterogeneous at the millimetre to centimetre scale. Three qualitative patterns of temperature difference were identified on boulder surfaces: gradients; mosaics; and limited heterogeneity. The frequency of occurrence of these temperature patterns was heavily influenced by cloud cover. Upper surfaces were generally hotter than lower surfaces, plus purple siltstone and grey siltstone consistently had the hottest temperatures and white limestone and quartzite the coolest. Each rock type had unique mineralogy, with maximum temperatures correlated with the highest metallic oxide and trace metal content of rocks. These baseline data show that rock type, boulder surface and mineralogy all contribute to patterns of heterogenous substrate temperature, with the geological history of rocky seashores potentially influencing the future fate of species and populations under various climate change scenarios.

Evolution regularity of temperature field of active heat insulation roadway considering thermal insulation spraying and grouting: A case study of Zhujidong Coal Mine, China

To study the active heat insulation roadways of high-temperature mines considering thermal insulation and injection, a high-temperature −965 m return air roadway of Zhujidong Coal Mine (Anhui Province, China) is selected as a prototype. The ANSYS numerical simulation method is used for the sensitivity analysis of heat insulation grouting layers with different thermal conductivities and zone ranges and heat insulation spray layers with different thermal conductivities and thicknesses; thus, their effects on the heat-adjusting zone radius, surrounding rock temperature field, and wall temperature are studied. The results show that the tunneling head temperature of the Zhujidong Mine is >27°C all year round, consequently causing serious heat damage. The heat insulation circle formed by thermal insulation spraying and grouting can effectively alleviate the disturbance of roadway airflow to the surrounding rock temperature field, thereby significantly reducing the heat-adjusting zone radius and wall temperature. The decrease in the thermal conductivities of the grouting and spray layers, expansion of the grouting layer zone, and increase in the spray layer thickness help effectively reduce the heat-adjusting zone radius and wall temperature. This trend decreases significantly with the ventilation time. A sensitivity analysis shows that the use of spraying and grouting materials of low thermal conductivity for thermal insulation is a primary factor in determining the temperature field distribution, while the range of the grouting layer zone and the spray layer thickness are secondary factors. The influence of the increased surrounding rock radial depth and ventilation time is negligible. Thus, the application of thermal insulation spraying and grouting is essential for the thermal environment control of mine roadways. Furthermore, the research and development of new spraying and grouting materials with good thermal insulation capabilities should be considered.

Study of the parameters of spontaneous fire seats in coal pit rock dumps

The presence of coal and coal-bearing rocks in waste rock dumps of open-pit coal mines contributes to the occurrence of spontaneous combustions that negatively affect the environment and people. Measurements of the temperature and the content of hazardous gases in the temperature anomaly that arose in the waste rock dump of the open-pit coal mine were made to assess the parameters of spontaneous fire seats. In the course of the study, the efficiency of detecting spontaneous fire seats in waste rock dumps was assessed by measuring the rock temperature in the wells with a depth of 2.5 m, drilled at a distance of 20 m from each other. The experiment showed the difficulty of drilling control wells in waste rock dumps and the impossibility of drilling them on the slopes of dumps, especially in spontaneous fire seats with a high rock temperature. The necessity of casing control wells with pipes makes it difficult to measure the rock temperature at different depths. It was found that there are sharp drops in the rock temperature in the heated area of the dump, which cannot be detected when the wells are located at the recommended distance. The measurements showed that in all wells the temperature increases with depth, therefore the depth of wells recommended by the regulatory documents does not allow determining the size of the heated area.