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Under the action of the Earth’s inner dynamics, the lithosphere shapes different types of the Earth’s surface, and the crustal stress state and its dynamic change law are captured by the comprehensive observation technology of drilling crustal activity. It is an important way for human beings to understand the internal dynamic process of the Earth and study the mechanism of inner dynamic geological hazards. The contribution of developed countries such as Japan, the USA, and the IODP International Cooperative Research Program to the development of integrated borehole crustal observation technology is summarized in this paper. The paper also systematically reviews the development history and present situation of borehole strain observation technology and borehole strain observation instrument in China. Especially since the 13th Five-Year, under the background of the national strategy of deep-sea exploration, the China Geological Survey Bureau (CGS), the China Earthquake Administration, and other systems have successively carried out research and development of the integrated geophysics observation system in wells, and have been put into use in integrated land and sea observation stations. The Institute of Geomechanics has successfully developed an integrated geophysics observation system for crustal activity using the key techniques of system integration. The system has a variety of strain, tilt, seismic, geomagnetic, geothermal, pore pressure, other sensors, and 16 components capable of observing crustal deformation, stress, strain, tilt, earthquake, and their induced geodynamic changes in the lithosphere, such as geotemperature, hydrology, geoelectricity, geomagnetism, etc. It has been put into use in Shandan (installed depth 253 m) and Pingwu (WFSD-4, 1600 m) observatories in Gansu and Sichuan provinces and has achieved initial results. It is a milestone for our comprehensive crustal activity observation technology to break through the 3000-meter-deep well in the future. It can provide vital information for geodynamics research, safe exploitation of deep mineral and geothermal resources, and prediction of internal dynamic geological hazards. At the same time, based on the national strategy of deep-sea exploration in the 14th Five-year, the future development direction of integrated observation system of deep-well crustal activity is pointed out.

Underground space and resources are crucial for solving energy, resource, and living space problems faced by mankind. Shafts are throats that extend from the ground into the strata and thus require safe, efficient, green, and intelligent construction. In this paper, we analyze the need and necessity for developing large-diameter drilling technology and equipment, examine the development status in China and abroad, and analyze the challenges faced by China from the perspectives of basic research, applied technology development, high-end equipment manufacturing, and project demonstration. Moreover, we pinpoint the development directions of shaft construction technology and equipment and propose that China should establish the development concept of intelligent drilling, clarify the development path and tasks of intelligent drilling, establish relevant standards and specifications of large-diameter drilling, and promote the construction of intelligent drilling platforms and demonstration projects, thereby providing support for shaft construction in fields such as mining, hydropower, transportation, and urban construction.

Crack stress thresholds in rocks have long been a popular subject in rock mechanics and engineering research. In this study, the applicability of existing methods for determining the crack stress thresholds of granite and weakly cemented porous siltstone is investigated using step loading and unloading tests. In addition, a novel method for decomposing the volumetric strain into solid-phase linear elastic strain, gas-phase nonlinear elastic strain, and plastic volumetric strain is presented. A quantitative calculation method for determining these thresholds is proposed based on the evolution law of the gas-phase volumetric strain and the physical significance of crack stress thresholds. The initiation and termination points of the stationary stage of the gas-phase volumetric strain are determined as σ cc and σ ci ; the point at which the gas-phase strain changes from positive to negative is determined as σ cd . To validate the proposed method, statistical results of the existing methods after screening are compared with the results of the proposed method. The results show that the proposed method provides reasonable crack stress thresholds for siltstone and granite and is applicable to rocks with similar stress–strain behaviors. The proposed method offers the advantages of independence from other methods, suitability across high and low confining pressures, and the capability for the quantitative calculation and processing of numerous samples. [ABSTRACT FROM AUTHOR]

Co-mining of the deep mineral and geothermal resources is crucial for the sustainable development of deep mining and provides a brand-new technical means for geothermal mining in deep high-temperature strata. In this article, we analyze the important values of the co-mining, introduce the current status of development and utilization of geothermal resources worldwide, and summarize the basic research progress of the co-mining in China. Subsequently, we analyze the technical and management challenges faced by the co-mining and establish a technical system that is urgently required for comprehensive development and utilization, which involves (1) the investigation and prospect judgment of the joint development and utilization of deep mineral and geothermal resources, (2) the excavation and construction of underground tunnels and chambers in high-temperature and hard rock strata, (3) the key theory and technical system of co-construction, coexistence, and sharing of a deep mineral resource exploitation system and a geothermal development system, and (4) the theories and technologies of geothermal energy exchange and transmission in the deep high temperature strata. Furthermore, development suggestions are proposed in terms of geological exploration, scientific and technological innovation, supporting policies, top-level planning, and scientific research demonstration bases; these aim to provide a reference for the sustainable and high-quality development of the mining and geothermal industries in China.