This paper aims to enhance the effective utilization of construction solid waste renewable brick powder (RBP) and circulating fluidized bed fly ash (CFBFA), addressing the issues of resource consumption and environmental pollution associated with these two types of solid waste. It employs CFBFA to synergistically activate RBP for the preparation of solid waste-based earthwork subgrade backfill. This research examines the impact of RBP and CFBFA content on the performance of earthwork subgrade backfill (ESB), while the microstructure of the paste test block was investigated using XRD, SEM, FTIR, and TG-dTG techniques. The synergistic mechanism of multisolid waste was examined at the micro level, and the appropriate ratio of solid waste-derived lowcarbon ESB was thoroughly assessed. The findings indicate that an increase in the CFBFA content generally enhances the mechanical strength of the paste. At the experimental ratio of RBP: CFBFA: coarse-grained soil = 8: 32: 60, the 28-day unconfined compressive strength (UCS), California Bearing Ratio (CBR) value, rebound modulus value, shear strength value, and compression modulus value of the sample attain their maximums, measuring 5.3 MPa, 41.9 %, 71.9 MPa, 10.5 KPa, and 15.76 MPa, respectively, all exceeding the standard values. The hydration products of cementitious materials based on RBP and CFBFA mostly consist of C-S-H gel, ettringite (AFt), and calcite. The robust honeycomb gel structure, created by the staggered interconnection of C-S-H gel and ettringite, is the primary contributor to mechanical strength. The modified cementitious material, composed of RBP-CFBFA, exhibits effective cementation and solidification properties for heavy metals, achieving leaching concentrations that comply with Class III water standards as outlined in the Chinese standard GB/T 14848-2017.

When uranium heap leaching tailings (UHLT) are used as filling aggregates, their discontinuous and non-uniform grading characteristics can easily cause segregation, settlement of the filling slurry, and deterioration of cemented body mechanical properties, seriously affecting the safety of the filling system and filling quality. To address the bimodal distribution defects of UHLT, characterized by excessively high proportions of coarse and fine particles with a lack of intermediate particle sizes, this study simulated its particle size characteristics using inert materials such as loess, fine sand, sand, and gravel. The study systematically verified the impact of grading defects on flow stability and mechanical properties. The filling slurry exhibited a spread of 222.5 mm with obvious segregation, and the uniaxial compressive strength at 28 days was 9.09 MPa. To overcome this bottleneck, this research innovatively proposed optimization strategies of qualitative reconstruction (QLR) and quantitative reconstruction (QTR). QLR involves adding medium-sized particles in stages and replacing equal amounts of coarse and fine particles, reducing the spread to 202.7 mm under an optimized quantity of 50 g, with a uniaxial compressive strength of 6.84 MPa at 3 days. However, slurry segregation still occurred. QTR established a multi-particle-size independent calculation model based on the extended Talbot gradation theory, and through the staged quantitative reconstruction of UHLT with aggregate having a grading index of 0.4, the spread decreased to 168.4 mm without segregation, achieving a uniaxial compressive strength of 5.58 MPa at 3 days and 9.11 MPa at 28 days. The study shows that both QLR and QTR can effectively improve the grading of UHLT, with QLR being simple and QTR offering precise control. The research provides new approaches for regulating filling slurries with similar discontinuous and non-uniform graded aggregates, and its innovative methodology can be extended to multiple fields such as concrete aggregate optimization.

Ground vibrations from operating railway in tunnels is a significant obstacle to sustainable development of subway. The backfill grouting layer, formed during shield tunneling, serves as a critical medium in propagation of tunnel vibrations, highlighting its potential in vibration mitigation. A semi-analytical model for the tunnelgrouting layer-soil system is proposed in this study, in order to clarify the influence of backfill grouting layer on the dynamic responses in a half-space, subjected to tunnel vibrations. In establishment of the closed-form solution, the tunnel and grouting layer are considered as two nested hollow cylinders embedded in a halfspace, with applying the Fourier transform and wave transformation. As a validation, the numerical results from the proposed semi-analytical model are compared with those reported in literature. Parametric studies, with respect to the geometric configuration (i.e., the thickness) and material parameters (i.e., the Young's modulus, material damping, and density) of the backfill grouting layer in the mitigation of tunnel vibrations, are carried out. It is found that incorporation of the backfill grouting layer significantly changes the dynamic responses of the soil and, by appropriately designing its material parameters, especially the Young's modulus, effective mitigation of tunnel vibrations can be achieved.

In this experimental study, comprehensive laboratory tests were conducted to investigate the mechanical properties of tire-derived aggregate (TDA) Type A and TDA-soil mixtures applicable in the construction of drainage layer, embankment fill, and backfill materials for retaining walls, pipes, and bridge abutments. This study was an investigation of the mechanical properties of TDA, as a lightweight material, and TDA-fine-grained soil mixtures for different mix ratios of 15%, 20%, 35%, 40%, 50%, and 60% of TDA-A relative to the dry weight of the soil. Various composite samples were tested using triaxial and direct shear apparatus. Measured properties include specific gravity, Proctor maximum dry density and optimal water content, unconfined compressive strength, peak compressive strength, shear strength, and hydraulic conductivity. Test results revealed that the addition of TDA to the soil significantly improved the compressive strength under confinement and permeability of the composite specimens. Based on the test results and supporting data from intensive literature reviews, the TDA-soil mixture showed very encouraging results for use in civil engineering applications as a lightweight backfill material.

This study numerically evaluates the stability of RS walls with select, marginal, and fly ash backfills under rainfall infiltration. A transient seepage, global stability, and lateral deformation were analyzed considering different rainfall intensities. As infiltration flux increases from 10 mm/h (low rainfall) to 80 mm/h (very heavy rainfall), wall stability decreases significantly due to the excessive buildup and inadequate dissipation of pore water pressure. Pore water pressure increases considerably due to infiltration. Fly ash fill exhibits approximately 125% higher pore water pressure than select fill. To allow for the dissipation of pore water pressure, the effect of chimney drains of various thicknesses was analyzed on the stability of the RS wall. It was observed that the stability of the wall increased with increasing thickness of the chimney drain.

Red mud (RM) is a strongly alkaline waste residue produced during alumina production, and its high alkali and fine particle characteristics are prone to cause soil, water, and air pollution. Phosphogypsum (PG), as a by-product of the wet process phosphoric acid industry, poses a significant risk of fluorine leaching and threatens the ecological environment and human health due to its high fluorine content and strong acidic properties. In this study, RM-based cemented paste backfill (RCPB) based on the synergistic curing of PG and ordinary Portland cement (OPC) was proposed, aiming to achieve a synergistic enhancement of the material's mechanical properties and fluorine fixation efficacy by optimizing the slurry concentration (63-69%). Experimental results demonstrated that increasing slurry concentration significantly improved unconfined compressive strength (UCS). The 67% concentration group achieved a UCS of 3.60 MPa after 28 days, while the 63%, 65%, and 69% groups reached 2.50 MPa, 3.20 MPa, and 3.40 MPa, respectively. Fluoride leaching concentrations for all groups were below the Class I groundwater standard (<= 1.0 mg/L), with the 67% concentration exhibiting the lowest leaching value (0.6076 mg/L). The dual immobilization mechanism of fluoride ions was revealed by XRD, TGA, and SEM-EDS characterization: (1) Ca2(+) and F- to generate CaF2 precipitation; (2) hydration products (C-S-H gel and calixarenes) immobilized F- by physical adsorption and chemical bonding, where the alkaline component of the RM (Na2O) further promotes the formation of sodium hexafluoroaluminate (Na3AlF6) precipitation. The system pH stabilized at 9.0 +/- 0.3 after 28 days, mitigating alkalinity risks. High slurry concentrations (67-69%) reduced material porosity by 40-60%, enhancing mechanical performance. It was confirmed that the synergistic effect of RM and PG in the RCPB system could effectively neutralize the alkaline environment and optimize the hydration environment, and, at the same time, form CaF2 as well as complexes encapsulating and adsorbing fluoride ions, thus significantly reducing the risk of fluorine migration. The aim is to improve the mechanical properties of materials and the fluorine-fixing efficiency by optimizing the slurry concentration (63-69%). The results provide a theoretical basis for the efficient resource utilization of PG and RM and open up a new way for the development of environmentally friendly building materials.

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/).

Microbial induced carbonate precipitation (MICP) is gaining recognition for enhancing the mechanical properties of construction materials. This study aims to explore the potential of using phosphogypsum (PG), a solid waste mainly composed of CaSO42H(2)O, as both a sufficient calcium source for MICP based bio-cement and an aggregate for mine backfill applications. First, the interaction between MICP bacteria and the PG was assessed by monitoring pH, electrical conductivity, and Ca2 + and SO42- levels. Results indicated that bacteria maintained robust urease activity in the PG environment, leading to CO32- production. These ions, combined with the Ca2+ naturally present in PG to form CaCO3 precipitation, which acted as a binding agent for PG backfill. Further testing of the bio-cemented PG backfill showed excellent fluidity which is suitable for efficient pipeline transportation in underground mining. After a 7-day curing period, the backfill exhibited an unconfined compressive strength (UCS) of 947 kPa, meeting the standards for mining backfill applications. Additionally, the environmental impact of the bio-cemented PG backfill was notable. Unlike traditional cement-based backfills with high pH levels (>11), the leachate from the bio-cemented PG backfill maintained a neutral pH (7.16), highlighting its eco-friendly nature. This positions the bio-cemented PG backfill as a sustainable solution for the construction and mining industries.

Bridge abutments are often damaged by girder impacts during major earthquakes. Very limited studies have been conducted. None of the past studies have incorporated abutment damage as an integrated system, i.e. the interaction between the deck and the back wall as well as between abutment and backfill. First, the reliability of the numerical model for damage assessment is validated with the result obtained from the shaking table test. Second, numerical simulations of the impact effect were carried out on four abutments with different shapes and dimensions of wing wall. The developed numerical models can simulate the nonlinear backfill soil, the backfill-back wall interface, and damage to reinforced concrete with the strain rate effect of the concrete and steel reinforcement. Parametric studies were conducted on the influence of the nonlinearity of the backfill soil, back wall-to-backfill friction, constitutive law of concrete, hourglass ratio, and impact energy. The results show that the nonlinear behaviour of the backfill soil and wing wall plays a significant role in the impact force on the back wall behaviour. Since poundings can be repetitive, this study confirms that the velocity of the initial impact of a bridge deck can precisely predict the severity of abutment damage.