Backfill Material Research Articles

Swelling characteristics of montmorillonite mineral particles in Gaomiaozi bentonite

Highly compacted bentonite is an ideal back-filling (buffer) material for the deep geological disposal of high-level radioactive waste. Montmorillonite is the main constituent mineral of it. The nanoscopic swelling characteristic of montmorillonite mineral particles greatly influences the macroscopic buffering performance of highly compacted bentonite blocks. Firstly, the montmorillonite suspension liquid was exfoliated by freeze-thaw cycles, the appropriate mineral particles were selected by atomic force microscope (AFM) for making colloidal probes. Then, the swelling pressure between mineral particles was measured by AFM, investigating the effects of interlayer distance, layer number, temperature, and interlayer cation type on the nanoscale swelling pressure. The experimental results showed that the swelling pressure of montmorillonite mineral particles peaks at about 0.7–0.8 nm interlayer distance. The swelling pressure of mineral particles with more layers is smaller. The higher the ambient temperature, the greater the swelling pressure. The swelling pressure of Ca-montmorillonite is significantly larger than that of Na-montmorillonite. The Laird model has a relatively good applicability with the interlayer distance of 0.6–1.2 nm; the DLVO theory has a good applicability with the interlayer distance greater than 1.5 nm. Finally, a predictive model was developed for the swelling pressure of nanoscopic mineral particles considering the effect of layer number. The research results provide data support and theoretical support for swelling pressure generation and cross-scale transmission mechanism of highly compacted bentonite hydration.

Experimental study on mechanical and microstructure properties of cemented tailings-waste rock backfill with continuous gradation

To reduce the risk of engineering disasters and improve the comprehensive utilization rate of solid waste from mines, cementitious tailings-wasted rock filling as a green and safe technology has been widely used in mines. Mechanical properties and microstructural characterization of cementitious tailings-wasted rock backfill (CTWRB) prepared with gradation coefficients (n) of 0.3–0.7 and waste rock contents (e.g., 10 %, 20 %, 30 %, 40 %, and 50 %) were investigated by using UCS (unconfined compressive strength) tests (e.g., peak strength, stress-strain curves, and damage modes), surface strain field analysis and SEM micro-graphs. The results indicate that the UCS value shows an overall “increasing and then decreasing trend” with increasing gradation factor n and waste rock dosage. The UCS value of CTWRB is maximum at 3.94 MPa when n = 0.5 and waste rock admixture is 30 %. The UCS has increased by 17.96 %. The compacting stage of CTWRB is more pronounced under loading. In the post-peak stage, CTWRB has superior resistance to deformation damage. The destruction form of backfill is dominated by the tension destruction parallel to the loading direction. The waste rock constrains the expansion path of cracks inside the specimen, which can effectively improve the UCS of backfill. The grayscale of the strain field in CTWRB shifts towards higher gray levels. The proportion of peaks in the strain field gray histogram changes slowly at first and then rapidly, with the peak stress serving as the boundary. Ettringite/CSH gel are the main hydration products in the backfill material. An overvalue of n leads to worse densification of the specimen and increased voids, which causes the UCS of CTWRB to decrease. The study's results could be a significant guide for ensuring safe mining production.

Research on the bearing creep characteristics and constitutive model of gangue filling body

The creep characteristics and potential deformation patterns of gangue backfill material are crucial in backfill mining operations. This study utilizes crushed gangue from the Gangue Yard in Fuxin City as the research material. An in-house designed, large-scale, triaxial gangue compaction test system was used. Triaxial compaction creep tests were conducted on gangue materials with varying particle size distributions. Analysis was performed based on different particle sizes, stresses, and confinement pressures. The study investigates the creep characteristics of the gangue under different conditions and explores the underlying causes. It reveals the relationship between the creep deformation of gangue materials and the passage of time. Mathematical methods are applied to develop a triaxial compaction creep power law model for gangue backfill materials. Finally, the creep results are fitted using an empirical formula approach.

Seroja Tropical Cyclon Destruction Case Study: Permanent Slope Protection Evaluation at Downstream of Rotiklot Dam Nomenclature Building, East Nusa Tenggara, Indonesia

Abstract Rotiklot Dam was one of some infrastructures which was affected by the Seroja Tropical Cyclone in East Nusa Tenggara Indonesia in April 2021. There are several landslides at the downstream of the dam that can threaten the safety of the dam, especially at the downstream of the nomenclature building. The right design of permanent slope protection must be determined in a limited time. Geotechnical investigations such as boring, resistivity survey, standard penetration test, and water pressure test were conducted in a short time. Back analysis method was carried out to find extreme soil parameters conditions. The slope protection must meet the national standard minimum safety factor or greater than 1.5. Safety factors of slope protections are evaluated by a finite element method to get the safety factor and maximum total displacements. Every stage of slope protection can give the optimal safety factor values which are required or greater than 1.5, however backfill material will give more load and decrease the safety factor value.

Mechanical Behavior of Waste Tire Steel Fiber–Modified Mine-Cemented Backfilling Materials: Early Strength, Toughness, and Failure Mode

Mechanical Behavior of Waste Tire Steel Fiber–Modified Mine-Cemented Backfilling Materials: Early Strength, Toughness, and Failure Mode

Dualistic effect of the deformation of protective structures made of broken rock in mine workings under static load

Purpose is to reveal physical essence of the dualistic (double) nature of deformation effects and their influence on the mechanical properties of protective structures made of broken rock while unloading coal-bearing mass to ensure stability of side rocks and operational conditions of the development mine working within the working areas of coal mines. Methods. The deformation properties of protective structures made of broken rock was modeled on experimental samples during their static load in terms of uniaxial compression with the possibility of lateral expansion of the original material or its compressive stress. Findings. A dualistic effect of deformations for the conditions of uniaxial compression of protective structures was revealed. Under the effect, a complex transformation of volume and shape occurs in the structures caused by the process of relative changes in the backfill material volume. The observed phenomenon occurs within the range of 0.12 ≤δV ≤ 0.32 and the values of the compaction coefficient of broken rock being 1.13≤k con. ≤ 1.47, depending on the granulometric composition of the source material and its bulk density. It was established that under conditions when broken rock is compressed, there is an effect of forming the bearing capacity of protective structures, which is observed when a relative change in the volume of backfill material is 0.14 ≤ δV ≤ 0.38, and its compaction factor reaches 1.16 ≤ kcon. ≤ 1.59. Depending on the homogeneity degree of the backfill material of protective structures, when comparing the values of kcon., a dualistic (double) effect is manifested in the difference of deformation characteristics of broken rock under uniaxial and compressive stress, reaching two or more times. Originality. A regularity was established that determines the relationship between compaction factor kcon. of broken rock and a relative change in the volume (δV) of backfill material, which makes it possible to evaluate bearing capacity of protective structures, being under static load in a stress-strain state. Practical implications. The research results can be used to substantiate the selection of a method to protect development mine working with flexible supports made of broken rock. To clarify the assessment of bearing capacity of such structures, it is advisable to carry out specific field studies in mine conditions.

Lightweight rPPU Eco-block Using Recycled Plastic (rP) and Polyurethane (PU) for Soft Subgrade Soil Stabilisation

The stability of the soil plays a crucial role in the safety and longevity of various civil engineering structures. However, problematic soil conditions, such as clay soil and peat soil, often pose challenges due to their high-water content, poor strength, low bearing capacity, and high compressibility. This research focuses on addressing these challenges by utilizing lightweight fill materials as an effective solution for backfilling applications. The study aims to investigate the characteristics and performance of a novel lightweight fill material using recycled plastic (rP) and polyurethane (PU) known as rPPU ecoblock. The eco-block is mainly fabricated using recycled plastic bottles, recycled plastic packaging, and polyurethane, offering a sustainable approach to waste management and construction materials. To achieve the research objectives, a series of experiments will be conducted. The strength and density of plastic bottles filled with recycled plastic packaging will be analyzed, providing insight into their mechanical properties. Furthermore, the water absorption and buoyancy of the lightweight rPPU eco-block are evaluated, considering its suitability for various construction scenarios. The research findings contribute to the understanding of the physical and mechanical characteristics of the rPPU eco-block, providing valuable information for its potential application as a backfill material. The compressive strength, water absorption, and buoyancy tests conducted per ASTM standards provide quantitative data on the eco-block's performance. The use of lightweight fill materials, particularly the rPPU eco-block, offers benefits such as reduced embankment self-weight, improved stability, and minimized environmental impact. Moreover, the recycling of plasticwaste contributes to the circular economy and aligns with sustainable development goals (SDG): SDG9 and SDG11. The results of this research provide valuable insights for engineers, construction professionals, and stakeholders involved in geotechnical and civil engineering projects.

Study on the Operation Optimization of Medium-Depth U-Type Ground Source Heat Pump Systems

Deep geothermal energy is a sustainable and renewable spacing heating source. Although many studies have discussed the design optimization of deep borehole systems, few have accomplished optimization and in-depth analysis of system operation control. In this study, an analytical model of the U-type deep borehole heat exchanger is proposed, and the average relative error between the simulated outlet temperatures and experimental data is −3.2%. Then, this paper presents an integrated model for the operation optimization study of the U-type deep-borehole ground source heat pump system. The optimal control of flow rate is adopted to match the variation in heating load. Compared with the constant-flow rate (110 m3/h) operation mode, the variable flow rate method reduces the power consumption of the heat pump and circulating pump by 22.1%, from 288,423 kW·h to 224,592 kW·h, during 2112 h of operation. In addition, the system has a larger RHS and COP when the thermal conductivity of the backfill material increases. When the borehole depth increases by 200 m from 2300 m, the energy consumption of the circulating pump will drop from 85,844 kW·h to 56,548 kW·h. The COP of the heat pump unit will decrease approximately linearly as the heating load increases, and the total power consumption will increase accordingly. This work can provide guidance for the design and optimization of U-shaped GSHP systems.

Experimental Study on Macro and Meso Characteristics of Steel-Slag-Based Cemented Backfill Due to Microbial Mineralization Action.

Steel slag is an industrial solid waste, which can provide a new calcium source for microbial mineralization as it contains abundant calcium elements. This study treated cemented backfill material with microorganisms and steel slag to enhance its performance. The influence of microbial treatment on the strength, microstructure, and pore characteristics of the backfill was assessed using a strength test, nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction. The results indicate that (1) the microbial mineralization and the hydration reaction take place at the same time; (2) when the proportion of bacterial solution exceeded 50%, microorganisms excessively consumed Ca2+, which hindered the following hydration reaction; (3) the additional amount of bacterial solution added into the steel-slag-based cemented backfill material should be less than 50%, which increases the strength by up to 22.10%; (4) the excessive bacterial solution sharply reduces the strength of the backfill even by 21.41%; and (5) the addition of bacterial solution affects the pore characteristics. A 50% bacterial solution can make backfill reach its lowest porosity. The strength has an inversely proportional relationship with porosity, diameter, and roundness (σ = ax + b, a < 0).

Enhancing geothermal heat pump efficiency with fin creation and microencapsulated PCM: A numerical study

The main cause of global warming is the emission of carbon dioxide from fossil fuels. Several methods to reduce CO2 emissions have been explored to ensure energy conservation. Many researchers have focused on renewable energy sources for this reason. Ground-source heat pumps (GSHPs) have emerged as a popular alternative in various sectors that utilize shallow geothermal energy sources for heating and cooling. This study presents a novel approach to enhancing the efficiency of geothermal heat exchangers, a critical component of GSHPs, through numerical simulation using computational fluid dynamics (CFD) with Ansys Fluent software. The research investigates the impact of adding four models of spiral fins to the exterior body of the heat exchanger: single spiral and double spiral configurations with pitches of 60 mm and 40 mm, respectively. Additionally, the study explores the effect of incorporating microencapsulated phase change materials (PCMs) with volume fractions of 0 %, 10 %, 30 %, and 50 % into the backfill material surrounding the heat exchanger. The results demonstrate that the double spiral fins with a 40 mm pitch significantly enhance thermal efficiency by reducing the output temperature by up to 1 °C compared to the model without fins. Furthermore, the addition of 50 % microencapsulated PCM by volume to the backfill material can further decrease the output temperature by up to 4 °K. The combined use of double spiral fins and microencapsulated PCMs results in a 7.5 % improvement in the efficiency of the heat exchanger and the coefficient of performance of the heat pump. This study highlights the potential of innovative design modifications and material enhancements to significantly improve GSHP performance for more efficient and sustainable heating and cooling solutions.

Study On Mechanical Properties Of Cemented Paste Backfill Using Fly-Ash-Based Cementitious Materials

In Mongolia, the Ulan lead-zinc mine is now struggling with high backfill operating costs and poor Cemented Paste Backfill (CPB) mechanical performance after curing. To solve this problem, BGRIMM Technology Group has investigated an activator that could mix with fly ash from Choibalsan Power Plant in Mongolia as a supplementary cementitious material for backfill. In this study, the mechanical performance of CPB samples prepared with various fly ash content and activator types were studied to provide a basis for the industrial application of fly ash-based supplementary cementitious materials. The research results indicate that partially replacing cement with fly ash reduces the uniaxial compressive strength (UCS) of CPB samples. Compared with the CPB sample prepared with pure cement, when the fly ash substitution rate is 10%, 20%, and 30%, the UCS reduced by 15.66%, 18.69%, and 32.83%, respectively. With the use of chemical activators, the UCS of CPB samples could be significantly improved. Among them, CPB samples prepared by the activator sodium sulfate+ sodium chloride+ TEA have achieved the highest UCS. Overall, this study shows that the synergistic effect of fly ash and chemical activators could effectively enhance the mechanical performance of CPB, which is beneficial for mine backfill cost reduction and could provide a basis for the further industrial application of fly ash-based cementitious materials in mine backfill.

Comprehensive Assessment on Utilization of Iron Ore Tailing as Backfill Material in Mechanically Stabilized Earth Wall

Comprehensive Assessment on Utilization of Iron Ore Tailing as Backfill Material in Mechanically Stabilized Earth Wall

Improving the thermal-mechanical performance of bio-treated backfill materials by addition of magnetic iron oxide nanoparticles (nano-Fe3O4)

The thermal conductivity of backfill materials directly affects the heat transfer efficiency between energy geo-structures and the surrounding stratum. Microbially induced carbonate precipitation (MICP) possesses great potential for improving the thermal conductivity of backfill materials. Magnetic iron oxide nanoparticles (i.e., nano-Fe3O4) have been proven to enhance bacterial biochemical activity by altering the permeability of bacterial biofilms, thus potentially improving the MICP process. It was supposed to enhance the thermal conductivity of backfill materials, allowing for applying energy geo-structures in arid environments. In this study, MICP in a solution environment was conducted to analyze bacterial urease activity and morphology of precipitation at varying nano-Fe3O4 contents. Additionally, sand columns treated with MICP and different nano-Fe3O4 contents were performed to obtain the thermal conductivity and unconfined compressive strength (UCS) through the transient plane source (TPS) method and uniaxial compression (UC) experiment. The mineral type, precipitation morphology, and microstructure were identified using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanism of the effect of nano-Fe3O4 on bacterial urease activity and thermal-mechanical behaviors was also discussed. The results indicated that the nano-Fe3O4 could enhance bacterial urease activity and promote vaterite precipitation in the solution environment. Conversely, when applied to MICP-treated sand, nano-Fe3O4 could facilitate calcite formation. Increasing the nano-Fe3O4 content showed a positive correlation with increased thermal conductivity and UCS. Specifically, the optimal values of thermal conductivity and UCS increased by 2.42 times and 2.39 times, respectively, compared to MICP-treated specimens without nano-Fe3O4. Microstructure analysis revealed that calcite precipitation at the particle contact served a dual function: cementing particles, thereby improving the mechanical strength and simultaneously acting as a "thermal bridge" to enhance the thermal conductivity. Furthermore, this study provides a new perspective on utilizing magnetized bacteria to reinforce specific locations within rocks and soils in the presence of an external magnetic field.

Dynamic leaching assessment of recycled polyurethane-coated tire rubber for sustainable engineering applications

Assessing the material ramifications of waste tire rubber stands as a pivotal endeavor for its practical utility. Dynamic leaching analysis emerges as indispensable in delineating its potentialities within sustainable engineering domains. Waste materials stemming from tire recycling industries, notably polyurethane-coated rubber (PUcR), may exhibit promising viability owing to attenuated leaching, thus fostering the circular economy paradigm. Towards this end, upflow column percolation leaching tests were conducted on recycled rubber-soil mixture (RSM) alongside PU-coated rubber-soil mixture (PUcRSM). Analysis through Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) unveiled the leaching dynamics of assorted metals in RSM and PUcRSM, notably showcasing markedly diminished cumulative zinc content (by 99.4%) in PUcRSM, coupled with mitigated electrical conductivity, redox potential, and eluate pH. Leveraging HYDRUS-1D for analytical modeling predicated on the advection-dispersion equation further underscored these insights. These findings suggest that waste PUcR presents itself as a viable option, distinguished by its diminished leachability, suitable for a wide array of applications. These applications include vibration damping in infrastructure, tunnel linings, asphalt roads, rubberized concrete, and lightweight backfill materials for bridges and retaining walls, among others. This initiative will contribute to recycling a substantial quantity of over 1 billion used tires produced annually, ultimately supporting the circular economy ethos through assured and adaptable repurposing of waste from tire rubber recycling industries.

Optimising Pavement Performance in Douala City Using a Mixture of Clay and Sand Fractions

Pavements are complex structures composed of multiple layers, designed to withstand various types of stress, including mechanical, organic, and climatic. The pavement is constantly subjected to cyclic, dynamic-mechanical actions caused by road traffic and different axle loads. Classified as engineering structures, the standard theoretical durability of this type of construction is generally estimated to be around one hundred years. However, this objective may not be achieved if the designer does not take into account certain specific factors that are endogenous and exogenous to the structure. Therefore, the durability of a road can be achieved through an optimized design that meets the needs defined by the public authorities and the context of its socio-economic framework. This passage discusses the factors that affect the performance of pavements, including soil type, machinery used, users, and climatic conditions. Exceeding axle loads, which form the basis of pavement design calculations, is also a disruptive factor from a civic perspective. A pavement consists of multiple layers, each made up of materials that must meet strict quality criteria and respect the anthropological, economic, social, and natural environment. It is important to consider all of these factors when constructing a pavement to ensure its longevity and avoid any negative impacts on the surrounding area. Additionally, it is crucial to maintain the pavement to prevent any loss of economic or infrastructural development opportunities. Several road infrastructures in urban and inter-urban areas experience issues that result from a combination of causes, each with varying degrees of impact. Douala is one such city where civil engineering projects are subject to an environment that is not conducive to the longevity of infrastructure, especially road infrastructure. The city is situated on a surface layer covered by a predominantly sandy-clay soil. This study aims to propose a proportional mixture of clay and sand soil fractions to create an anvil effect during compaction. The objective is to create a hybrid backfill material that can achieve a high compaction rate. Good compaction is crucial for achieving optimal pavement layer performance. The thickness of the material to be laid is greatly affected by this characteristic, which in turn affects the volume of equipment depreciation and user comfort. This has a significant impact on a wide range of socio-economic benefits. Based on soil mechanics and geotechnical tests, a new material is proposed to combat the early onset of disorders such as potholes, ruts, erosion, or pavement collapse in bad weather or heavy traffic.

Investigation of macro-micro mechanical behaviors and failure mechanisms in cemented tailings backfill with varying proportions of fine

This study investigates the impact of tailings characteristics, particularly fine tailings, on the efficiency and effectiveness of mining engineering backfill operations. Contrary to the common underestimation, fine tailings significantly affect the mechanical properties and failure mechanisms of Cemented Tailings Backfill (CTB). Through a series of experiments examining various particle size distributions and employing advanced Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) techniques, this research clarifies the role of fine tailings in modifying the mechanical strength and failure patterns of CTB. Adding 20 % fine tailings optimally enhances both the early and long-term strength of backfill materials. With aging, adding 30 % fine tailings shows a rapid strength increase from 7d to 28d, with the 28d strength slightly lower than that of specimens with 20 % addition, but the specimens demonstrate better ductility after reaching peak strength. As the content of fine tailings increases, crack propagation in the specimens shifts from radial to axial, simplifying the fracture mode from complex to singular. Consequently, the fracture mechanism changes from ductile to brittle, and then reverts to ductile. Moreover, using particle flow simulation and moment tensor analysis to study the failure processes indicates that while increased fine particle content boosts the material's initial strength, it ultimately leads to a simpler crack network and volumetric expansion as the primary failure mode. In terms of energy conversion mechanisms, as the content of fine particles increases, the energy first increases and then decreases. During the elastic stage and the early stage of the plastic stage, the energy is mainly converted into strain energy and PB bonding energy, which affects the elasticity of the sample. In the later stage of the plastic phase, the energy is mainly converted into dissipated energy, leading to the failure of the sample.

Energy geo-structures: A review of their integration with other sources and its limitations

Ground Source Heat Pumps, in the framework of Shallow Geothermal Energy Systems, outperform conventional Heating Ventilation and Air Conditioning systems, even the high efficiency Air Source Heat Pumps. At the same time, though, they require considerably higher installation costs. The utilization of dwellings' foundations as ground heat exchanger components has recently demonstrated the potential to generate significant cost reductions primarily attributed to the reduction in expenses associated with drilling and backfill material (grout). These elements are referred to in the literature as Thermo-Active Structures or Energy Geo-structures (EGs). The current study employs a ‘mixed studies’ review (i.e., literature review, critical review and state-of-the-art review) methodology to comprehensively examine and assess the compatibility and integration of different renewable energy sources and environmentally friendly technologies with foundation elements deployed as EGs. These mainly include heat pumps, district heating and cooling networks, solar-thermal systems, waste heat, biomass and other types such as urban structures. Emphasis has been given on the advancement on this area, with the current study identifying and addressing two primary categories. The first category involves the integration of EG elements with sources that are able to supply green electricity, referring to renewable energy electricity obtained from on-grid or off-grid integration. The second category, involves a direct or indirect integration with sources that provide heat, or vice versa. The technical and non-technical barriers of such integrations have been discussed in detail, with the technical challenges generally involving engineering design, and system optimization, whereas non-technical challenges encompassing the economic, social, and policy domains.

The Effects of Hydroxypropyl Methyl Cellulose and Metakaolin on the Properties of Self-Compacting Solidified Soil Based on Abandoned Slurry.

As a new type of backfill material, Self-compacting solidified soil (SCSS) takes the abandoned slurry of cast-in-place piles after dewatering and reduction as the main raw material, which brings a problem of coordinating the working performance with the mechanical property under the condition of high mobility. In this paper, hydroxypropyl methyl cellulose (HPMC) and metakaolin were introduced as additives to solve this problem. First, the workability and mechanical properties of SCSS were regulated and optimized by means of the water seepage rate test, the flowability test, and the unconfined compressive strength test. Second, this study also used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the effects of HPMC and metakaolin on the physical phase and microstructure of SCSS. In this way, the results showed that there was a significant impact on the flowability of SCSS, that is, when the dosage reached 0.3%, the water seepage rate of SCSS was reduced to less than 1%, and the compressive strength at 7 days reached its peak. At the same time, HPMC weakened the strength growth of SCSS in the age period of 7 days to 14 days. However, the addition of metakaolin promoted its compressive strength. XRD analysis showed that the additives had no significant effects on the physical phases. And, from the SEM results, it can be seen that although the water-retaining effect of HPMC makes hydration of cement more exhaustive, more ettringite (AFt) can be observed in the microstructure. In addition, it can be observed that the addition of metakaolin can generate more hydrated calcium silicate (C-S-H) due to the strong surface energy possessed by metakaolin. As a result of the above factors, SCSS filled the voids between particles and improved the interface structure between particles, thus enhanced the compressive strength.

A study on the evaluation of structural stability of masonry cultural heritage based on the characteristics of the back-fill material and the stiffness of the ground

A study on the evaluation of structural stability of masonry cultural heritage based on the characteristics of the back-fill material and the stiffness of the ground

Immobilization of phosphorus and fluorine from whole phosphogypsum-based cemented backfill material with self-cementing properties

The environmental effects of whole phosphogypsum-based cemented backfill material (WPG-CBM) with self-cementing properties have always been a concern. This study aimed to evaluate the immobilization effect of harmful elements in the WPG-CBM. It showed that the setting rate and strength of WPG-CBM were relatively stable when the quicklime content exceeded 1 %. The self-cementing properties deteriorated significantly as the dissolved phosphorus content exceeded a certain threshold. WPG-CBM leaching tests during the bleeding, hydration and hardening periods indicated that the leaching amounts of phosphate and fluoride fluctuated noticeably in early self-cementing period and then changed regularly due to the coupling effect of chemical reactions, eutectic phosphorus dissolution, decreasing pH value, and common ion effect. Moreover, three designed leaching tests for in-situ underground conditions showed that the influence of WPG-CBM backfill on groundwater could be ignored in the open dynamic leaching. In the closed dynamic or static leaching conditions, phosphate and fluoride were continuously enriched within the values permitted by national standard. According to microstructural analysis, the good self-cementing properties of WPG-CBM were attributed to the immobilization of phosphorus and fluorine in phosphogypsum by quicklime. The self-cementing properties and environmental effects of WPG-CBM with a pH of 7.5–8.5 were the most satisfactory.