Theoretical frontiers of in-situ rock mechanics under multi-physics-phase coupling in deep exploration of fluidized coal mining

As shallow energy resources on Earth are progressively depleted, enhancing the capability to extract deep coal resources has become an inevitable trend in global scientific frontiers and technological development, as well as a strategic choice to ensure China’s long-term energy security. The solid fossil resource nature and inherent energy attribute of coal endowment. Coal-fluidized mining is a disruptive technology that aims to break through the depth limits of solid mineral resource extraction. Its key lies in establishing a new theoretical and technical foundation for deep engineering science that can account for the influence of the in-situ occurrence environment in solid-mineral-resource-fluidized mining. Existing rock mechanics theories and methods struggle to incorporate the effects of the deep in-situ environment (current strength criteria, constitutive equations, etc., are depth-independent and unrelated to the deep in-situ environment), making them inadequate for effectively guiding the development of fluidized mining technologies and disaster prevention and control. There is an urgent need to develop new theories and methods for in-situ rock mass mechanics that consider the multi-physics and multi-phase environmental influences in fluidized mining of deep coal resources. Establishing a theory of in-situ multi-physics and multi-phase rock mass mechanics is fundamental to achieving solid-mineral-resource-fluidized mining. Regarding the new theoretical system of rock mechanics that accounts for the influence of the in-situ occurrence environment in fluidized mining of deep coal resources, four key scientific issues have been identified: ① The differential laws of the intrinsic parameters of the occurrence environment at different depths in solid-mineral-resource-fluidized mining and the physical-mechanical behavior of rock masses; ② In-situ rock mass mechanics theory that considers the multi-physics and multi-phase environmental influences in solid-mineral-resource-fluidized mining; ③ Mechanisms of surrounding rock stability and strata control, as well as the genesis of dynamic disasters in solid-mineral-resource-fluidized mining; ④ Topological structure and construction of negative-carbon backfill materials in solid-mineral-resource-fluidized mining. Complementarily, five key technological issues are proposed: ① Technology for acquiring intrinsic information on the in-situ multi-physics and multi-phase occurrence environment at different depths in solid-mineral-resource-fluidized mining; ② Synchronous multi-parameter testing technology for rock mass deformation under reconstructed fluidized mining environments of solid mineral resources; ③ Intelligent numerical simulation technology for the multi-physics coupled failure of surrounding rock in fluidized mining of solid mineral resource; ④ Modification and performance regulation technology of negative-carbon backfill materials for solid-mineral-resource-fluidized mining; ⑤ Negative-carbon efficient backfilling technology for solid-mineral-resource-fluidized mining. Finally, based on the scientific and technological issues, seven main research topics are delineated: ① Principles and technology for in-situ testing of rock mass mechanical behavior at different depths in solid-mineral-resource-fluidized mining; ② Methods and technology for synchronously testing multi-field and multi-phase rock mass deformation under reconstructed fluidized mining environments of solid mineral resource; ③ In-situ rock mass mechanics theory and disaster prediction methods for solid-mineral-resource-fluidized mining; ④ Technologies for surrounding rock stability and safety evaluation methods in solid-mineral-resource-fluidized mining; ⑤ Fine acoustic wave detection technology for disaster sources ahead of roadways during excavation in solid-mineral-resource-fluidized mining; ⑥ Negative-carbon backfilling and strata control technology in solid-mineral-resource-fluidized mining; ⑦ Methods for preventing and controlling dynamic disasters in deep mining and engineering demonstrations. Based on the above, a theoretical framework of in-situ multi-physics and multi-phase rock mass mechanics for solid-mineral-resource-fluidized mining will be constructed, providing a theoretical foundation and technological support for solid-mineral-resource-fluidized mining in the future.