Due to the rapid growth of the electric power system, the silicone rubber composite insulator is so widely employed around the world. However, the aging damage and decommission of it inevitably generates plenty of waste silicone rubber. It takes up large amounts of land for non-degradation, which is becoming a serious environmental issue. In this paper, the effort has been made to reuse the silicone rubber of composite insulator by peeling, breaking and adding it into the cement mortar to partly replace river sand by 5%, 10%, 15%, 20% and 30% in volume. Moreover, the surface modification of silicone rubber particles with H₂O₂ and KOH is explored to improve hydrophilicity. The mechanical strength of silicone rubber mortar and modified silicone rubber mortar are measured in detail, and the effects of particle size, content and modification of silicone rubber on the properties of mortar are investigated. This study shows that at least a 5% addition of silicone rubber can reduce the strengths, while the 15% addition is obviously favorable for increasing the toughness. Furthermore, the mortar strength gets promoted due to the surface modification. Lastly, the superior thermal insulation and noise reduction of the mortar are obtained as the addition of silicone rubber particles, and an equation between dry apparent density and thermal conductivity of mortar has been developed.

To improve the durability of cement-based grout in high geothermal tunnel grouting projects, metakaolin was incorporated to replace 8% of the cement. The permeability, chloride penetration, and sulfate and carbonate erosion tests were carried out on the grout cured at varying temperatures (20, 30, 40, 50, and 60 °C). It was shown that with the increase in curing temperature, the impermeability and resistance to chloride penetration initially increased and then decreased, reaching the highest values at 40 °C. Furthermore, the incorporation of metakaolin into grout enhanced the impermeability by 11.11-38.91% and resistance to chloride penetration by 12.23-12.77%. As attacked by sulfate, the surface spalling of the specimen was more obvious with the increase in the curing temperature and immersion time. Conversely, the appearance remained almost unchanged under carbonate erosion. As immersion time increased, both the antisulfate and anticarbonate erosion coefficients declined. The effect of curing temperature on erosion resistance was assessed via the relative antierosion coefficient. When immersed in sulfate, the coefficient achieved the highest value of 1.08 as cured at 30 °C, and in carbonate, the coefficient reached a maximum of 0.99 as cured at 40 °C. Through scanning electron microscopy and binarized images, it was verified that gypsum and ettringite were formed during sulfate attack, leading to volume expansion and cracking, consequently reducing the strength. Meanwhile, in the case of carbonate erosion, calcium hydroxide (CH) and calcium silicate hydrate gel (C-S-H) were dissolved and degraded, resulting in a large number and size of pores in the grout. The research results have certain theoretical significances and reference values for the application of cement-based grouting materials in high geothermal environments.

Vacuum tube well dewatering technology has gradually become an effective means to deal with low-permeability soil groundwater. The vacuum degree transfer law is an important element in the study of the mechanism of deep foundation pit vacuum tube well dewatering. To further study the transfer law of vacuum degree in vacuum tube well dewatering, a laboratory test setup for vacuum tube well dewatering was developed, and vacuum tube well dewatering tests were conducted under various in-well vacuum values, tube diameter, depth of tube well, and other factors. The variation law of vacuum degree under various working condition coupling was thoroughly analyzed in this research. The results show that with the increase of vacuum value in the well, the radial vacuum degree and vertical vacuum degree have about 14.9~47.7% and 14.9~32.4% increase, respectively, and transmission attenuation of radial vacuum degree, transmission attenuation of vertical vacuum degree, and the range of the vacuum field all increase to some extent. With the outward transmission of the vacuum degree, the transmission attenuation of the radial vacuum degree decreases rapidly and then tends to be stable, and the transmission attenuation of the vertical vacuum degree decreases gradually. The radial vacuum degree, the transmission attenuation of the radial vacuum degree, and the range of the radial vacuum field are not affected by the buried depth of the tube well. The study’s conclusions can serve as a foundation and point of reference for projects involving the design and implementation of deep foundation pit vacuum tube well dewatering.

Goaf areas are a significant hazard in mining, posing serious safety risks, and their management is a complex challenge due to their irregular spatial distribution and unpredictable roof collapses. Research on goaf areas focuses on detection technologies, disaster analysis, risk assessment, and remediation techniques. The characteristics of goaf areas vary based on different minerals and mining methods. With the rise of high-speed rail, the stability of foundations beneath high-speed rail lines crossing goaf areas becomes a critical concern, given the dynamic stresses generated by high-speed train operations. The coupling between goaf areas and high-speed rail, and the deformation mechanisms and stability control of foundations in such regions, are emerging as an essential research frontier. The integration of excavation, anchoring, and support technologies, along with an in-depth study of the surrounding rock microstructure under deep mining conditions, is crucial for ensuring the stability of high-speed rail lines in goaf areas.

To elucidate the influence of the coupling effect of a water-rich temperature environment and time on the mechanical properties of the grouted rock mass, we enhanced a self-constructed three-dimensional rock mass grouting simulation test device. Employing a uniform design method, five working conditions were established for conducting high-pressure grouting tests. A total of 270 standard cylindrical samples were prepared, with multi-gradient curing times ranging from 7 to 90 days in water-rich temperature environments, enabling a systematic investigation of the time-dependent evolution of compressive strength and permeability characteristics of the grouted rock mass. The findings demonstrate that the improved three-dimensional test system can accurately simulate the grouting environment of 20 ℃ to 60 ℃surrounding rock. Furthermore, a multi-field coupling physical test platform was successfully constructed, integrating temperature, seepage, and stress fields. The mechanical properties of the grouted rock mass exhibited a pronounced temperature threshold response. Specifically, the compressive strength in a 50 ℃ water-rich environment displayed a three-stage evolution characterized by peak-attenuation-stability over curing time, aligning with the Gaussian distribution law. After 28 days of curing, the influence of the water temperature factor surpassed that of the water-cement ratio and grouting pressure. Additionally, a double-critical transition phenomenon was noted in the permeability characteristics. The permeability coefficient in the 50 ℃ water-rich environment adhered to a cubic polynomial trend, while in the 60 ℃ water-rich environment, the 28-day curing time served as a turning point, resulting in abnormal permeability changes in the later stages, transitioning from continuous reduction to linear growth. Under the 60 ℃ water-rich conditions, a significant negative correlation was observed between compressive strength and permeability, with the two trend curves exhibiting two cross-turns. This observation revealed the deterioration mechanism linked to thermal damage accumulation and micro-fracture network evolution in the grouted rock mass due to the synergistic effects of water-rich temperature, seepage, and time. By transcending the traditional limitation of a 28-day curing period, the derived evolution law regarding the performance of the grouted rock mass, based on the dynamic water-rich temperature-time threshold, provides a theoretical foundation for optimizing grouting times in deep-buried tunnels and ensuring the long-term stability of surrounding rock.