Hong Li

The 2019–2020 Black Summer fires affected approximately 33.5% of Kosciuszko National Park, Australia's largest alpine reserve; post-fire recovery models in Australia have rarely used spatial validation. We quantified recovery across severity classes and elevation zones (2021–2025), tested whether driver importance shifts over time, and whether predictors generalise to unseen locations. A Sentinel-2 Normalized Difference Vegetation Index (NDVI)-derived recovery index was modelled with Random Forest at one, three and five years post-fire using twelve predictors and random/spatial cross-validation; SHapley Additive exPlanations (SHAP) importance used bootstrap confidence intervals, and recovery was cross-validated against the Normalized Burn Ratio (NBR). Severity's importance declined sharply (mean |SHAP| 0.116 to 0.019); elevation remained important throughout. Fast-recovery clusters occurred at lower elevation (877 versus 1284 m; P < 0.001), and montane and subalpine trajectories were statistically distinguishable. NDVI overstated recovery relative to NBR every year (P < 0.001). Spatial cross-validation R² stayed near zero regardless of block resolution, versus 0.10–0.16 under random splitting. Fire severity's influence is transient; elevation-mediated differences persist over at least five years, and static covariates cannot predict recovery at unseen sites. Post-fire monitoring should be reassessed periodically rather than prioritised on severity alone; spatial cross-validation should become standard for spatially autocorrelated recovery data.

To investigate the mechanical properties, energy evolution, and failure behavior of coal–rock composite structures under mining disturbances, a mining-induced stress path was designed based on the actual stress evolution ahead of a mining face. Triaxial tests were carried out under these stress conditions on coal–rock composite samples at various confining pressures, supplemented by conventional triaxial compression tests for comparison. The results show that the coal–rock composite samples exhibited marked brittle failure under mining-induced stress, with no sign of the brittle–ductile transition observed in conventional triaxial tests as the confining pressure increased. Using dual circumferential extensometers, it was found that the circumferential deformation of the coal and rock was initially governed by their intrinsic mechanical properties and later controlled by crack propagation. At higher confining pressures, the growth rate of circumferential strain at failure increased significantly, indicating that deeper excavations result in more severe unloading-induced failure. Comparative analysis revealed that the coal component had a higher elastic energy density and faster energy accumulation and release rates than the rock, identifying coal as the dominant medium for elastic energy storage and release within the composite samples. Furthermore, at peak stress in mining-induced stress tests, the coal showed less circumferential deformation than in conventional tests, while the rock exhibited the opposite trend, confirming the presence of a bonding constraint effect at the coal–rock interface. These findings enhance our understanding of the mechanical behaviors and failure mechanisms of coal–rock composites under mining disturbances, thus providing practical guidance for ensuring safety and efficiency in deep coal mining.

Coalbed methane (CBM) reservoirs have emerged as a crucial source of natural gas, but their efficient recovery remains challenging due to complex interactions between mechanical deformation, fluid migration, and permeability evolution. CO₂-enhanced coalbed methane (CO₂-ECBM) recovery has gained attention as a promising technique for improving gas extraction while simultaneously sequestering CO₂. However, a comprehensive understanding of the reservoir's mechanical behaviour and permeability evolution during CO₂ injection is still lacking. To address this gap, we develop a 3D thermo-hydro-mechanical (THM) coupled numerical model to simulate the CO₂-ECBM process. This model captures reservoir deformation, geological formation shifts, and surface responses while integrating field monitoring data to enhance accuracy and reliability. A key innovation of this study is the coupled analysis of simulated surface deformations with measured data, enabling a more precise assessment of permeability evolution and mechanical responses. A representative 2D cross-section of the coal seam is analysed to examine how injection pressure and production temperature influence gas pressure, permeability, and reservoir deformation. The results indicate that surface micro-deformation induced by CO₂ injection arises from the interplay of geo-stress, injection pressure, gas adsorption/desorption, and temperature effects. Notably, CO₂ adsorption-driven expansion outweighs CH₄ desorption-induced contraction, leading to net volumetric expansion. In the vicinity of the injection well, higher injection pressures cause significant permeability reductions, whereas near the production well, permeability initially increases due to extraction-induced pressure drops before later declining due to rising effective stress. However, increased CH₄ migration toward the production well under higher injection pressures partially mitigates this permeability loss. Elevated temperatures further expand the adsorption/desorption zone, induce coal matrix thermal expansion, and compress pores, collectively reducing permeability and volumetric strain. This study offers critical insights into the dynamic coupling between stress redistribution and fluid flow in CO₂-ECBM operations. The findings provide a theoretical foundation for optimizing CO₂ injection strategies, enhancing methane recovery efficiency, and ensuring the mechanical stability of the reservoir-caprock system.

Plastic materials are extensively utilized in various aspects of daily life. However, the substantial amount of plastic waste generated can cause significant global environmental issues without efficient waste management practices. To address this problem, the utilization of waste plastics in high-value applications such as highway construction through hot mix asphalt (HMA) has been deemed ideal. Polyethylene terephthalate (PET), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) are the three most prevalent types of plastic waste found in municipal solid waste. The impact of plastic-type and content on the mechanical, volumetric, and durability properties of hot mixed asphalt (HMA) was investigated by utilizing varying plastic contents of PET, LDPE, and HDPE. Tests were conducted in accordance with ASTM standards on twelve HMA mixtures made with an optimal binder content (OBC) of 4.3%, and plastic contents of 3%, 6%, 9%, and 12% by weight of OBC. Marshall stability and flow tests were conducted to ascertain the optimal plastic content for each tested mixture. The findings indicated that the stability and flow values improved as the plastic content was raised. 9% LDPE mix gave a maximum Marshal stability value of 12 kN. Additionally, as the plastic content increased, the values for air voids and voids filled with asphalt decreased in all 12 mixes tested. This research aligns with the United Nations 2030 sustainable development goals (SDGs), including SDGs 9, 11, 12, 13, 14, and 15, and presents a viable method for implementing the 3Rs approach towards sustainable plastic waste management.

An inverse solution strategy using linear element of Boundary Element Method(BEM)was developed, which will become a novel application base to potentially reflect the equivalent mechanical effect around reservoir corresponding to CO₂ spreading during its injection process. Firstly, a linear-element BEM code was studied to improve the accuracy in analyzing the connection between induced ground minute deformations and underground inner loading. Secondly, the space regularization was adopted to deal with the ill-posed problem during the optimization to inverse problem solution. The boundary conditions of a near-field structure as active source were reversely figured out in an efficient numerical way based on its passive deformation that was sampled at a few specific positions at far field. Meanwhile, the effectiveness of linear-element BEM in solving inverse problems was demonstrated. Finally, based on the implementation of hydraulic fracturing in a coal seam in Alberta, Canada, the monitored data of its induced surface displacements was input to invert the equivalent internal pressure onto are-opened fracture within reservoir. The results show that the proposed inverse solution workflow and programmed algorithm are applicable to effectively guiding hydraulic fracturing interpretation so as to further facilitating coal bed methane recovery.

On the basis of a conceptual model for an Excavation based Enhanced Geothermal System (EGS-E), which proposed to extract heat from Hot Dry Rock at depth through dominantly adopting shaft, roadways, and caved rock failure techniques but not depending on either wellbore drilling or fracturing stimulation, a novel extensive version of heat extraction is proposed in this paper. Considering its mechanical stability issues, the new scheme contains two fields apart away: the ones are near-field by piping flow to touch the tunnel wall; the others are far-field through filling and driving fluid within the voids of collapsed rock. The former is represented as a tunnel unit being installed hollow linear, which can extract and produce heat precisely according to structural design and accurate operative prediction. The latter is represented as interconnective fissures being induced by stope excavation due to gravitational weight and unloading of a deep-buried squeeze. The EGS-E uses a two-stage heat exchange system of “fluid-rock” and “fluid-fluid.” Then, a 3D transient thermal-hydraulic model is established to demonstrate the heat extraction performance. The temperature field and accumulated heat energy are investigated. The modeling work provides a tentative workflow to simulate an EGS-E system and, most probably for the first time, demonstrated that the deep underground Hot Dry Rock heat mining turns out to be preliminarily studied in a quantitative way.