The coal mining under the goaf of close-up room mining coal pillars is prone to chain instability and damage of the overlying coal pillars, aquifer damage, surface subsidence, soil erosion, vegetation withering, and other problems. In this paper, theoretical analysis was conducted on the stability of the remaining coal pillars in room mining, and numerical simulations were used to study the influence characteristics of the plastic zone, strain energy, and stress field of the overlying coal pillars during the mining of the lower close coal seam. The stability of the coal pillars under the influence of mining was analyzed with the safety factor. The proposed technologies of cemented paste backfilling on the ground and backfilling the goaf of the lower coal seam are applied, the influence of different water-cement ratios, aeolian sand, and cement content on the mechanical properties of backfilling materials was studied through experiments, and the stability of overlying coal pillars with different dimensions of the backfilling pier columns under certain ratio conditions was studied using numerical simulation method. The research results indicate that when the dimensions of the backfilling pier columns are 40 m x 40 m and the compressive strength is 3.12 MPa, the stability of the overlying coal pillar can be effectively controlled, achieving safe mining under the remaining coal pillar. The research results can provide new ideas for the mining of coal resources and environmental protection under the remaining coal pillar of room mining.

The application of a new liquid soil material and the treatment effect of backfilling an underpass tunnel in an airport are studied. The deformation and mechanical properties of liquid soil and conventional soil under load are comprehensively compared and analyzed via a numerical simulation with finite element software. The effects of the buried depth of overlying fill, tunnel height, and traffic load on the backfilling of liquid soil abutment are analyzed. The research results show that under the action of load, the overall deformation and stress distribution of the liquid soil and conventional soil show similar laws. However, liquid soil backfilling has great advantages over conventional soil backfilling in all aspects. Liquid soil backfilling can reduce the deformation and the compressive stress at the corner of the backfilling area by approximately 13% and 15%, respectively. The overburden buried depth has a great impact on the subgrade deformation. In the actual construction, the overburden buried depth should be 1.5 m. The overburden depth has a greater impact on the vertical deformation of the road, and the self-weight of the overburden will act as an additional load on the overall roadbed, compared with conventional soil backfill. The overburden depth of 2.0 m conventional soil backfill is about equal to the overburden depth of 1.5 m liquid soil backfill. The use of liquid soil backfill is equivalent to the use of the overburden fill in reducing the additional load of 0.5 m. The height of the box culvert has a greater impact on the stress, but this change is not linear. The actual construction in the case of meeting the specific requirements of use should try to control in the vicinity of 8.4 m, and at the same time the use of liquid soil backfill can reduce the compressive stress of about 14%. The compressive stress increases first and then decreases with the increase in the liquid soil modulus. The liquid soil modulus should be controlled to 180 MPa. Moreover, liquid soil backfilling can reduce the compressive stress in the backfilling area by approximately 25%. The trapezoidal slope of the backfill area is proportional to the deformation amount. Although an obvious correlation with compressive stress exists, the regularity is not strong. Thus, the trapezoidal slope should be set to 1:1 during construction. Traffic load slightly affects the overall deformation and compressive stress of the road. However, the distribution trends of deformation and stress change obviously under the action of aircraft load. In the actual design, only one load form of aircraft load should be considered. (c) 2025 Tongji University and Tongji University Press. Publishing Services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Food security is an important guarantee for national security and public health. Underground reinforced concrete (RC) grain silos can provide a quasi-low temperature environment for grain storage, effectively ensuring the quality of the stored grain. The stress status of the underground silo during soil backfilling construction is complex, which puts the structure at risk of failure. The present study developed a numerical simulation method to investigate the mechanical properties of underground silos during backfilling construction processes. A finite element (FE) analysis of the backfilling construction process of an underground RC grain silo was conducted, and the nonlinear contact between the underground silo and the surrounding soil, as well as the material nonlinear behavior of the soil, was considered. The deformation characteristics and stress distribution of the underground silo during the backfilling construction process were revealed. The results indicate that the underground RC grain silo exhibits good mechanical performance. The underground silo underwent overall settlement during the backfilling construction process, with a total settlement of 21 mm. The maximum radial displacement of the silo wall and the maximum deflection of the radial primary beam were 0.84 mm and 5.67 mm, respectively, both of which were smaller than the limit values. After the completion of backfilling construction, there was a high risk of concrete cracking of the silo wall. The maximum radial and circumferential tensile stresses of the concrete at the silo top were both high, which led to cracking in the top of the silo. Our research results provide important support for the design and evaluation of underground RC grain silos.

This paper critically evaluates and proposes innovative approaches to address the technical challenges associated with extracting existing piles and backfilling the associated boreholes, specifically in the context of Japan. Japan's rapid post-war economic growth has resulted in an infrastructure that is now aging, necessitating the demolition and subsequent reuse of structures. The prevalent use of pile foundations in soft soil conditions in Japan presents unique challenges following demolition, including differential settlement and complications for future construction on the same site. Current practices in Japan for pile removal are outdated and rely heavily on field experience without the support of standardized guidelines, leading to unresolved issues in improving the removal process. This paper provides an in-depth review of the status of technological advances in pile extraction and removal, as well as the development of backfill materials, with a focus on Japan's unique geological, demographic, and urban development factors. It highlights the risks associated with the traditional wire rope method and presents an innovative pile tip gripping and lifting method that aims to improve safety and efficiency by minimizing friction and preventing accidents. It also discusses the critical role of backfill treatment in preventing subsidence and outlines the performance requirements for fill materials, emphasizing the need for materials that provide uniform strength, prevent material segregation, and resist groundwater infiltration. Specifically, the paper discusses the development of cement-based fillers for borehole backfilling in Japan and demonstrates the effectiveness of sodium carbonate and thickeners in improving the physical and rheological properties of cement slurries. Finally, the paper emphasizes the urgent need for innovative technologies and methodologies for pile extraction, removal, and borehole backfilling in the Japanese context, highlighting their importance in ensuring safe, sustainable, and efficient land use in urban areas while addressing environmental concerns and stakeholder interests in land transactions and construction projects.

Utilizing natural expansive clays that are available on-site as sewer trench backfill can cause destructive deformations due to volume changes, which are caused by seasonal climatic changes. Such deformations result in manhole structures protruding from the surface, which cause damage to the surrounding infrastructure and generate potential trip hazards. In this study, mixtures of recycled materials with minor sensitivity to moisture variations and superior compactibility were investigated using geomechanics theories associated with granular materials as an alternative backfill material. Blends of recycled glass (RG), plastic (RP), and tire-derived aggregates (TDA) were mixed on-site, wetted to the required moisture content (MC), and used to backfill excavated trenches around two manhole structures and extended to approximately 11 m along the trench. A benchmark trial was constructed by backfilling with natural soils available on-site according to the normal procedure. The full-scale trial sites were instrumented using settlement plates and MC sensors at various locations and depths for performance monitoring. The results of approximately 17 months of field monitoring showed that settlements over both areas that were backfilled with recycled blends were <20% of those over areas backfilled with site-won soils. Approximately 82% of the settlements in the recycled blends occurred during construction. In contrast, trenches that were backfilled with site-won soils continued to exhibit deformation due to consolidation and swell-shrink cycles. The outcome of this study could contribute to the United Nations' Sustainable Development Goals, in particular, Goal 12, by improving the industry's confidence in the reuse of wastes in geotechnical applications.

In the northern Da Xing'anling Mountains in Northeast China on the southern margin of the Eastern Asia permafrost body, the ground thermal state and boreal ecological environment are sensitive to climate change and human activities. Since the 1980s, the Hola Basin here has been continuously and extensively developed. In particular, open pits and later backfilling in strip coal mining alters land-atmospheric hydrothermal exchanges in permafrost regions, leading to serious damages to the permafrost environment and boreal forest. After mining, pits need to be backfilled timely and properly for hydrothermal recovery of Xing'an permafrost and the boreal ecological environment. In this study, based on the comparative analysis of monitored ground temperatures in backfilled and undisturbed areas, influencing factors of thermal recovery after backfilling were analyzed through numerical simulations. Results show that the thermal recovery of permafrost in the backfilled area is closely related to temperature, depth, material, and soil moisture content of backfill. The warmer, finer, and thicker the backfill soils, the longer the permafrost recovery. Thermal recovery of permafrost also depends on the moisture content of backfill; the shortest recovery occurs at 15-25% in the backfilled soil moisture content. Based on numerical simulations and combined with enlightenments from features of the ecosystem-protected Xing'an permafrost in Northeast China, a composite configuration of organic soil, crush-rock layer, and proper re-vegetation measures is advised. Based on prudent regulation of heat transfer modes, this composite backfilling method can effectively cool the backfilled ground and can even possibly offset the climate warming.