Karst collapse columns (KCCs) are naturally formed geological structures that are widely observed in North China. Given their influence on normal mining operations and the progress of mining work, collapse columns pose a hidden danger in coal mining under the influence of manual mining. By communicating often with the aquifer, the water inrush from KCCs poses a serious threat to construction projects. This paper adopts three flow field models, namely, Darcy aquifer laminar flow, Forchheimer flow, and Navier–Stokes turbulent flow, based on the changes in the water inrush flow pattern in the aquifer and laneway, and uses COMSOL Multiphysics software to produce the numerical solutions of these models. As the water inrush flow velocity increases, the Forchheimer flow shows the effect of additional force (inertial resistance) on flow in KCCs, in addition to the effect of viscous resistance. After the joint action of viscous resistance and inertial resistance, the inertial resistance ultimately dominates and gradually changes the water inrush from the KCCs to fluid seepage. Forchheimer flow can comprehensively reflect the nonlinear flow process in the broken rock mass of KCCs, demonstrate the dynamic process from the Darcy aquifer to the final tunnel turbulence layer, and quantitatively show the changes in the flow patterns of the water inrush from KCCs.

Underground fault water inrush is a hydrogeological disaster that frequently occurs in underground mining and tunnel construction projects. Groundwater may pour from an aquifer when disasters occur, and aquifers are typically associated with fractured rock formations. Water inrush accidents are likely to occur when fractured rock masses are encountered during excavation. In this study, Comsol Multiphysics, cross-platform multiphysics field coupling software, was used to simulate the evolution characteristics of water flow in different flow fields of faults and aquifers when water inrush from underground faults occurs. First, the Darcy and Brinkman flow field nonlinear seepage models were used to model the seepage law of water flow in aquifers and faults. Second, the Forchheimer flow field was used to modify the seepage of fluid in fault-broken rocks in the Brinkman flow field. In general, this phenomenon does not meet the applicable conditions of Darcy’s formula. Therefore, the Darcy and Forchheimer flow models were coupled in this study. Simulation results show that flow behavior in an aquifer varies depending on fault permeability. An aquifer near a fault is likely to be affected by non-Darcy flow. That is, the non-Darcy effect zone will either increase or decrease as fault permeability increases or decreases. The fault rupture zone that connects the aquifer and upper roadway of the fault leads to fault water inrush due to the considerably improved permeability of the fractured rock mass.

An optimal mix proportion design program was developed firstly in this research by analyzing most relevant factors affecting the mix ratio, such as water‐cement ratio, workability, drying mass, adding and mixing method of MPCM, etc. Then, the influences of MPCM on density, porosity, compressive strength, thermal conductivity, specific heat capacity, and thermal diffusivity of LWAC were investigated by changing curing time, MPCM content, and MPCM state. Results shown that the porosity of MPCM‐LWAC linearly increases and corresponding density linearly decreases with the increase of MPCM content. SEM images of MPCM‐LWAC reveal weaker connection and higher porosity between aggregate and mortar caused by more MPCM. The addition of MPCM to LWAC causes a compressive strength loss proportional to the MPCM content. The compressive strength of MPCM‐LWAC increases with the increasing curing time; however, growth rate of compressive strength decreases with the increasing MPCM content. When the MPCM content reaches a maximum of 10%, the compressive strength of MPCM‐LWAC at 50°C is 4.7% less than that of MPCM‐LWAC at 20°C. For the 10% MPCM addition, the specific heat capacity increased by 32.09%, and the thermal conductivity and thermal diffusion reduced by 19.0% and 23.9%, respectively.

Enhanced geothermal systems (EGS) are a key technology for developing deep geothermal resources, yet they face significant challenges in constructing efficient thermal reservoirs within high-stress, high-strength, and low-permeability crystalline rock formations. Traditional hydraulic fracturing (HF) techniques encounter deep challenges in these environments, including excessively high fracturing pressures, limited fracture network patterns, and the risk of induced seismicity. This paper reviews the multi-scale thermal-mechanical mechanisms, fracture evolution patterns, and control strategies associated with thermal stimulation and permeability enhancement in the modification of deep geothermal reservoirs. Research indicates that thermally induced fracturing triggers intergranular and transgranular cracks at the microscopic scale due to mineral thermal expansion mismatches, which macroscopically manifests as nonlinear degradation of rock strength and modulus. The redistribution of the thermal elastic stress field significantly lowers the breakdown pressure, while matrix thermal contraction increases fracture aperture, leading to an exponential enhancement of permeability following a cubic law. However, the high confining pressure constraints, true triaxial stress anisotropy, and thermal short-circuiting risks present substantial suppression and challenges to the effectiveness of thermal stimulation in deep in situ environments. Different fracturing media, such as water, liquid nitrogen (LN₂), and supercritical CO₂, exhibit varying advantages in thermal stimulation efficiency due to their unique thermal-flow characteristics. Future research should focus on the thermal-mechanical coupling mechanisms under true triaxial stress conditions, and develop intelligent control strategies for permeability enhancement and thermal short-circuiting risk mitigation. This study synthesizes existing analyses and proposes potential engineering strategies for stimulating deep EGS reservoirs, offering significant strategic value for the development of geothermal energy as a baseload renewable resource.

The rockburst hazard has always been an important issue affecting the safety production of coal mines in China. The unreasonable sequencing of roadway driving can lead to the dynamic instability of coal pillars, which subsequently causes rockburst accidents in roadway backfilling mining engineering and poses a serious threat to the safety of the mines. Roadway backfilling mining technology is an effective approach with which to mine corner residual coal resources under buildings, railways, and rivers. An energy density criterion is established and programmed with FISH language using numerical analysis software for the rockburst risk evaluation of coal pillars. On this basis, a numerical simulation model is established based on four scheme types, namely, the sequential mining, one-roadway interval mining, two-roadway interval mining, and three-roadway interval mining schemes. The influence of the backfilling roadway driving sequence on coal pillar stability is investigated, and the change law of vertical stress and energy density factor of coal pillars in different driving sequences in roadway backfilling mining technology are analyzed. According to the research results, the maximum energy density factor value of 21,172 J/m⁴ for coal pillars in one-roadway interval mining is the lowest among the different schemes. Therefore, the one-roadway interval mining scheme is the optimal choice in roadway backfilling mining technology. The results can be treated as an important basis for the prevention and treatment of coal pillar instability and rockburst in roadway backfilling mining technology.

The addition of microencapsulated phase‐change materials (MPCM) to concrete will inevitably cause changes in the mechanical and thermal properties of concrete, and this is vitally important for the safety and energy saving of concrete building components. In this research, shale ceramsite and shale ceramics sand were used as the main raw materials to produce lightweight aggregate concrete (LWAC) mixed with MPCM. In order to investigate the effect of MPCM content and phase‐change cycle numbers on the mechanical and thermal properties of MPCM‐LWAC, two groups of MPCM‐LWAC specimens were prepared. One group consists of specimens containing 2.5%, 5.0%, 7.5%, and 10% MPCM, respectively, and they are used to reveal the change law of tensile strength, compressive strength, enthalpy, and specific heat capacity of LWAC integrated into MPCM. The other group includes specimens with the same MPCM content, but the specimens are subjected to different phase‐change cycle numbers of 50, 100, 150, and 200 at the environment temperature of −10–60°C to study the thermal properties of MPCM‐LWAC. Findings from the experimental results include the following: (1)The tensile and compressive strengths of MPCM‐LWAC concrete are negatively correlated with the MPCM content, while the enthalpy and specific heat capacity are positively correlated with the MPCM content. When the MPCM content reaches 10%, the compressive and tensile strengths of MPCM‐LWAC decreased, respectively, by 45.49% and 52.63% than the LWAC without MPCM. (2) Under heating and curing condition, the corresponding maximum specific heat capacity of LWAC with 10% MPCM is 328.35% and 249.50% higher than the LWAC without MPCM, respectively, and the average specific heat capacities increase 71.21% and 44.94%, respectively. (3) The melting enthalpy of MPCM‐LWAC is slightly larger than the curing enthalpy, and the difference is more noticeable with the increase of MPCM content. In addition, when the number of phase‐change cycle is below 200, the compressive strength and splitting tensile strength of MPCM‐LWAC decrease by less than 5%, and the specific heat capacity decreases by less than 1.33%. Hence, it concludes that shale ceramsite concrete with MPCM has promising application prospects.