热作用下煤层顶板岩石力学性质动态演化特征OA

[Objective]Underground coal gasification(UCG)represents a key technology for the clean utilization of coal resources.However,during the UCG process,thermal damage to surrounding rocks under thermal effects directly af-fects the stability and engineering safety of gasification channels.[Methods]To address the thermal damage to sur-rounding rocks during UCG,this study investigated the silty mudstones and coarse-grained sandstones in the coal seam roof of the Xishanyao Formation,Baikouquan area,Xinjiang.Through high-temperature uniaxial compression experi-ments,combined with characterization methods like X-ray diffraction(XRD)and scanning electron microscopy(SEM),this study delved into the dynamic evolutionary patterns of rock mechanical properties and the macro-micro damage dif-ferentiation of both rock types under thermal effects.Moreover,this study quantified the critical threshold of thermal damage and analyzed the synergistic damage-inducing mechanisms.[Results and Conclusions]In terms of rock mech-anical properties,the silty mudstones experienced thermal strengthening(25 ℃ to＜400 ℃),thermal damage(400-600 ℃),and thermal sintering(＞600 ℃ to ≤ 800 ℃)stages,with peak stresses showing an increase of 36.24％,a de-crease of 45.99％,and a surge of 75.20％,respectively.In contrast,the coarse-grained sandstones experienced the dehyd-ration weakening(25 ℃ to＜200 ℃),thermal expansion-induced compaction(200 ℃ to＜400 ℃),and thermal damage(400-800 ℃)stages,with peak stresses decreasing by 50.74％,45.16％,and 52.78％,respectively.At 400-600 ℃,the elastic moduli of the silty mudstones and coarse-grained sandstones significantly decreased to 58.87％and 69.42％,re-spectively,and their damage variables surged to 0.59 and 0.69,respectively.Concerning the controlling mechanisms in the three evolutionary stages,the silty mudstones were subjected to the synergistic effects of thermal evaporation and ex-pansion,the synergistic destruction of thermal cracking and mineral phase transitions,and the sintering reaction process,sequentially.In contrast,for the coarse-grained sandstones,the controlling mechanisms in the three stages were domin-ated by thermal evaporation,thermal expansion,and thermal cracking-mineral phase transition in sequence.A temper-ature of 400 ℃ was identified as the initial threshold for the synergistic destruction by thermal cracking and mineral phase transitions(e.g.,α-β phase transition of quartz,and kaolinite dehydroxylation)of both rock types.Beyond this threshold,damage to the transition zone of surrounding rocks accelerated.Therefore,in engineering practice,the temper-atures of key roofs with sealing capacities in oxidation zones must be controlled below 400 ℃ to mitigate the rock in-stability risk.Overall,this study determines the thermal damage threshold and rock mechanical differentiation mechan-isms of surrounding rocks under UCG-induced thermal effects in the Baikouquan area,providing key temperature-sensit-ive parameters and stability control criteria for the safe design of gasification channels.