Backfill Material Research Articles

Deposition morphology and mechanical properties of lean cemented gangue backfill material: Laboratory test and field application

Backfilling mining technology provides an efficient and environmentally-friendly solution for treating additional products (such as tailings, coal gangue and other solid waste) in coal mining process, which are filled into the underground goaf area, thus reducing surface subsidence, roof strata damage, and associated geological disasters. In this study, a novel backfill material called lean cemented gangue backfill material (LCGBM) is introduced, and various experiments, including uniaxial compression tests, creep tests, CT-SEM scanning and reconstruction are carried out to evaluate its mechanical properties and engineering practicability. The test results indicate that the strength and volume fraction of self-compacting cement (SCC) slurry and solid waste aggregate jointly control the uniaxial compressive strength and failure mode of LCGBM, reflecting the bucket effect under the influence of two components. Although the volume fraction of aggregate and SCC slurry is intentionally reduced to control the cost, this cemented granular material shows excellent compressive strength, overall stiffness and long-term bearing capacity in laboratory and field tests. In the process of engineering application, the uniaxial compressive strength of the LCGBM reaches 14 MPa, and the initial setting time is 120 s, which reduces the consumption of gangue aggregate by 35 % and greatly reduces the construction time. In addition, a calculation method of the optimal mixing ratio of raw materials is proposed, which can adjust the strength and volume fraction of SCC slurry according to the optimal mixing range, so as to maximize the utilization of the strength of LCGBM, and reduce the construction time and aggregate of backfilling. The research findings emphasize the potential of the LCGBM in promoting clean and sustainable coal mining practice.

Examination of the use of binderless zeolite blend as backfill materials to enhance CO2 adsorption in coal mine working face

The release and accumulation of CO2 in the working face of the coal mine is a major safety concern and requires an effective means to avoid the incidence of the mine. This present study therefore sought to develop a self-CO2 adsorbing backfill (SCAB) material to remove CO2 from the working environment, and simultaneously mitigate the movements of the surrounding rock layers. SCAB was formulated using coal mine solid waste activated with an alkali activator, and binderless 4 A zeolite was embedded in the backfill body. The total CO2 adsorption capacity was investigated using a CO2 flow-through method under ambient pressure and temperature conditions. The adsorption plateau was found in stages II and III respecting the predetermined curing time and zeolite contents. The maximum adsorption capacity was 143.8 mg-CO2/g-SCAB, resulting in an increase of up to 82 % in UCS compared to reference samples. The underlying mechanism was discovered in morphological analyses.1) The well distribution of zeolite in the SCAB body provided as diffusive pathways and adsorption sites for CO2 after standard curing. 2) The adsorbed CO2 underwent a desorption stage when the CO2 concentration decreased and reacted to the cementitious matrix of the SCAB body. 3) More CaCO3 crystals were generated and filled in the micro spaces of the SCAB body, which contributed to an increase in compressive strength. This study developed an effective approach to remove CO2 gas from the working face of the coal mine during backfilling. Adsorbed CO2 improved the strength of the material, provided as a novel multi-function backfill mining for sustainable green coal mining technology.

Reducing Load Transfer to Buried Pipes Through Coupled Use of Geogrid Reinforcement and Sand Rubber Zone in the Backfill Material

A laboratory study, consisting of 21 tests, was conducted to examine precisely the impact of using a sand-rubber mixture with three different ratios of rubber (3, 5, and 7%) in a particular zone within the backfill and a geogrid reinforcement on the pressure transferred to buried pipes from surface loads. The pipe was buried at two different burial depths of 1.5 and 2 times the pipe diameter. Tests were conducted with a geogrid-reinforcement layer placed above and below the sand-rubber zone to determine the optimal performance of the proposed system. The findings from these tests are expected to contribute valuable insights into the development of effective strategies for reducing the impact on buried pipes and enhancing their overall resilience, particularly in the face of increasing surface loading. The results revealed that using a rubber ratio of 5% would present the optimum rubber ratio and using a geogrid layer above the sand-rubber zone would provide additional stability, where the bearing capacity of the system was increased by 33.7%, independent of the pipe burial depth and rubber ratio. Furthermore, the use of a sand-rubber mixture and a geogrid layer contributed to decreasing the pressure transferred to the pipe crown and the deformation of the soil surface, respectively.

Assessment of thermal conductivity prediction models for compacted bentonite-based backfill material

Assessment of thermal conductivity prediction models for compacted bentonite-based backfill material

Development of insulating backfill materials produced from the ternary mixtures of red mud, fly ash and preformed foam

Many public utility lines to transport power, water, natural gas, water, sewer, and communication are placed beneath trafficable areas. However, insufficient or inadequate backfill induces sudden subsidence, damage, or pothole on the road. This study aims to develop lightweight controlled low-strength materials (CLSM) with low thermal conductivity using the ternary mixtures of red mud to replace aggregate sand, high carbon fly ash, and preformed foam. Changes in flow consistency, air void characteristics, bulk unit weight, unconfined compressive strength (UCS), and thermal conductivity (k) of the tested materials with varying red mud contents were investigated as a function of the foam volume ratio (FVR). The results demonstrate that the UCS and k of tested materials decreased with increasing FVR due the decrease in unit weight, and a greater UCS but smaller k was observed at a given FVR with increasing red mud content because the inclusion of red mud in the lightweight CLSM mix design helps improve the stability of air bubbles and achieve uniform distribution of air voids. In addition, the red mud can act as a NaOH supplier, leading to the developed material had additional strength gain from the alkali activation. Thus, the developed insulating backfill material showed 43 % decrease in k while maintaining UCS similar to non-foam CLSM without red mud.

Experimental Study on Influence of Lime on Cross-Scale Characteristics of Cemented Backfill with Multiple Solid Wastes.

The utilization of industrial solid waste in mines is an important approach to resource utilization. The backfill material in mines is mainly composed of solid waste, which plays a supporting role. The excitation effect of lime on phosphogypsum and fly ash in backfill was studied in this paper. The macroscopic and microscopic characteristics of the backfill material were tested using uniaxial compression, nuclear magnetic resonance, scanning electron microscopy, and electrochemical techniques, and a relationship model was established between them. Furthermore, the influence of industrial solid waste on the properties of the backfill material under the action of lime and the hydration mechanism between different industrial solid wastes were studied. The results show that (1) under the action of lime, fly ash reacts with lime to produce C-S-H and C-A-H, and then C-A-H reacts with phosphogypsum to produce AFt. (2) The excess phosphogypsum also fills the pores. Therefore, 1.8% lime reduces the porosity of the backfill by 17.88% and increases the strength by 21.57%. (3) The cross-scale relationship shows that strength is inversely proportional to each type of pore content and fractal dimension, and it logarithmically increases with impedance at different frequencies. The lower the frequency, the stronger the relationship is. (4) This study indicates that industrial solid waste is a suitable cement replacement.

Mechanical response of coal pillar-backfill composite confined by CFRP jackets: parametrical study

The composite structure consisting of the coal pillar and backfill material is the critical component for the room-and-pillar mining system, the stability of which is mainly relevant to the interface in between. To eliminate the premature instability and potential disasters attributed to the breakage of the weak interface, the innovative strengthening technique incorporating the carbon fiber-reinforced polymer (CFRP) jacket was recently developed and the comprehensive studies including the uni-axial compression tests and the numerical investigation were carried out. In the present study, the digital interface of the coal-backfill composite was initially reconstructed with the 3D laser scanning and then imported into the mesoscopic continuum-discontinuity coupling model via the PFC-FLAC coupling method. Based on the analysis of the deformation characteristics and damage patterns of the coal -backfill composite, the strengthening mechanism of the exterior CFRP jacket was discussed. The results showed that both the load-bearing performance and the stability of the coal-backfill composite interface have been well enhanced mainly attributed to the effective lateral confinement provided by the exterior CFRP jacket. Moreover, the application of the CFRP jacket enhances the energy dissipation capacity of the coal-backfill composite as suggested by laboratory tests. It is also suggested that both the peak strength and elastic modulus of the coal-backfill composite exhibited the initial decrease and then rising as the interface angle increases. As demonstrated by the systematic research, the CFRP strengthening technique is effective in maintaining the stability of the coal-backfill composites for underground mines.

Improving the thermal performance of vertical ground heat exchanger by modifying spiral tube geometry: A numerical study

Ground heat exchanger (GHE) is the most crucial element of a ground source heat pump (GSHP) system for building cooling and heating by the utilization of geothermal energy. Therefore, intending to enhance the performance of GHE, the present study conducts a computational investigation of the thermal performance of modified spiral tube vertical GHEs. Several modifications of uniform-pitched spiral GHE are made to increase its thermal performance. Some modifications are introduced as variable-pitched spiral tube GHE where spiral inlet pipes are densified in the lower part of GHEs by reducing pitch distance. Conversely, in some modifications, the position of the outlet straight pipe is changed. Water is considered as the working fluid and the inlet temperature of the water is maintained fixed at 300.15 K. After extensive analysis, it is evident that, when the outlet pipe is placed outside of the spiral coil, there is a 7.67 % enhancement in the thermal performance than a traditional uniform-pitched spiral tube GHE. However, modifications like variable-pitched spiral tube GHEs are not significant to improve the thermal performance due to the quick saturation of the ground soil temperature around the GHE pipes. To have a balance between heat transfer rate and pressure drop, thermal performance capability (TPC) and coefficient of performance improvement (COPimprvt) criterion were evaluated and it is found that the uniform-pitched spiral tube GHE along with the outlet pipe at the outside of the spiral provides maximum thermal performance with a maximum TPC value of 1.062 and provides the positive value of COPimprvt criterion. The positive values of COPimprvt indicate that the spiral tube GHEs are energy efficient based on heat transfer and pressure drop. Moreover, spiral GHE with high-density polyethylene (HDPE), concrete pile, and sandy clay outperform the other materials for pipe, backfill, and soil, respectively. Specifically, HDPE pipe, concrete backfill, and sandy clay as soil offer around 7 %, 5 %, and 7.8 % higher thermal performance compared to polyethylene, sand silica, and clay, respectively.

Experimental investigation on the anti-detonation performance of composite structure containing foam geopolymer backfill material

The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts, reducing the vibration effect on the structure. Explosion tests were conducted using several composite structure models, including a concrete lining structure (CLS) without foam geopolymer and six foam geopolymer composite structures (FGCS) with different backfill parameters, to study the dynamic response and wave dissipation mechanisms of FGCS under explosive loading. Pressure, strain, and vibration responses at different locations were synchronously tested. The damage modes and dynamic responses of different models were compared, and how wave elimination and energy absorption efficiencies were affected by foam geopolymer backfill parameters was analyzed. The results showed that the foam geopolymer absorbed and dissipated the impact energy through continuous compressive deformation under high strain rates and dynamic loading, reducing the strain in the liner structure by 52% and increasing the pressure attenuation rate by 28%. Additionally, the foam geopolymer backfill reduced structural vibration and liner deformation, with the FGCS structure showing 35% less displacement and 70% less acceleration compared to the CLS. The FGCS model with thicker, less dense foam geopolymer backfill, having more pores and higher porosity, demonstrated better compression and energy absorption under dynamic impact, increasing stress wave attenuation efficiency. By analyzing the stress wave propagation and the compression characteristics of the porous medium, it was concluded that the stress transfer ratio of FGCS-ρ-579 was 77% lower than that of CLS, and the transmitted wave energy was 90% lower. The results of this study provide a scientific basis for optimizing underground composite structure interlayer parameters.

Strength characteristics of lightweight soil with waste modified expanded polystyrene particles

With the increase in population and urbanization around the world, waste materials have a significant negative impact on the environment; therefore, it is essential to reduce the adverse effects of waste materials on nature through innovative and sustainable solutions. This study aims to reveal the threefold benefits of utilizing waste modified expanded polystyrene (WMEPS) as a soil improvement agent, including the reuse of a waste material by recycling it from nature, obtaining lightweight backfill material, and the enhancement of the compressive behavior of the soil. For this purpose, two different sizes of WMEPS were added to the soil to varying proportions by dry weight of the soil (i.e., 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, and 6%) and their unconfined compressive strength (UCS) behavior was experimentally investigated on both 1 and 28 day cured specimens. The results were evaluated in terms of stress-strain behavior, UCS value, UCS increase ratio, normalized energy absorption index, deformability index, and elastic modulus. In addition, the optimum WMEPS participation ratio was determined by linear weighted sum optimization method. As a result, by adding the optimum rate of 5% WMEPS to the soil, the dry density decreased by 15% and UCS increased by 45.22% for the specimen cured for 28 day.

Ensemble learning evaluation of mechanical property for mining waste cemented backfill

Processing the large amount of waste rock generated from mining into backfill materials enables the resource utilization of waste materials. Additionally, the mechanical properties of backfill materials influence the stability of overlying strata. Therefore, this study established a large-scale dataset of coal gangue-based and tailing-based backfill materials. Three novel ensemble learning models were developed to evaluate the nonlinear effects of 29 dimensional factors on the mechanical properties of backfill material. Additionally, factors like material type, preparation method, and measurement error can cause discrepancies in mechanical properties, affecting evaluation accuracy. Consequently, this paper constructed SVR fusion models using three ensemble learning methods to enhance robustness on differentiated data. It investigated the impacts of ensemble methods, ensemble levels, and perturbation levels on the model. The study found that the Bagging-ensembled SVR performed optimally, with R2, MAE, and RMSE of 0.951, 0.369, and 0.560, respectively, exhibiting better robustness on perturbed datasets. This study contributes to resource utilization in mining waste.

A Decoupled Buckling Failure Analysis of Buried Steel Pipeline Subjected to the Strike-Slip Fault

Over the past few years, there has been an increased focus on offshore pipeline safety due to the development of offshore oil and gas resources. Both onshore and offshore pipelines may face significant geological hazards resulting from active faults. Pre-excavated soil can be used as backfill for trenches to prevent major pipeline deformations. Since these backfill materials have been heavily remolded, they are softer than the native soil. Therefore, the difference in shear strength between the backfill and native ground may have an effect on the interaction between the pipeline and the backfill. In this paper, the pipeline–backfill–trench interaction is investigated using a hybrid beam–spring model. The P-Y curves obtained from CEL analysis are incorporated into a 3D beam–spring model to analyze the pipeline’s response to lateral strike-slip faults. Additionally, the nonlinearity of pipeline materials is considered to study pipeline failure modes under strike-slip fault movements. A series of parametric studies were conducted to explore the effects of fault intersection angle, pipe diameter, buried depth of the pipe, and soil conditions on the failure modes of buckling pipelines. The developed method can be used to analyze and assess pipeline–backfill–trench interaction when subjected to strike-slip fault displacements.

Application of industrial by-product waste as soil stabilising backfill material using a multi-layering method

Peat soil presents significant challenges for construction due to its inherent weak properties, including high water content, limited permeability, low shear Strength, low specific gravity, and acidity. Despite the potential of Mg-rich synthetic gypsum (MRSG) to improve soil properties, research on its use for stabilising severely poor peat soils is limited. This study addresses this gap by investigating the efficacy of MRSG in peat soil stabilisation using a novel multi-layering backfill approach. The methodology includes soil classification of peat soil. And, to understand the mechanical and chemical changes of stabilized peat soil, the unconfined compressive Strength (UCS) testing and microstructural analysis using SEM, EDX, and XRD before and after stabilisation are studied. Peat samples were treated with MRSG through backfilling method in 5, 7, and 9 layers and evaluated the strength increment after curing periods of 7, 28, and 60 days. Results demonstrate that MRSG significantly enhanced the compressive strength, increasing it to 210.33 kPa as early as 7 days for 9 layers of backfill incomparable with the untreated soil strength of 51.87 kPa. The new cementitious product in the soil known as ettringite was observed from SEM analysis and confirmed by the EDX and XRD analysis. By recycling industrial byproducts, this environmentally friendly method encourages sustainability and lessens dependency on raw resources, which is important for infrastructure construction and other projects in areas rich in peat.

Properties of Cemented Filling Materials Prepared from Phosphogypsum-Steel Slag-Blast-Furnace Slag and Its Environmental Effect.

Phosphogypsum (PG) occupies a large amount of land due to its large annual production and low utilization rate, and at the same time causes serious environmental problems due to toxic impurities. PG is used for mine backfill, and industrial solid waste is a curing agent for PG, which can save the filling cost and reduce environmental pollution. In this paper, PG was used as a raw material, combined with steel slag (SS) and ground granulated blast-furnace slag (GGBS) under the action of an alkali-activated agent (NaOH) to prepare all-solid waste phosphogypsum-based backfill material (PBM). The effect of the GGBS to SS ratio on the compressive strength and toxic leaching of PBM was investigated. The chemical composition of the raw materials was obtained by XRF analysis, and the mineral composition and morphology of PBM and its stabilization/curing mechanism against heavy metals were analyzed using XRD and SEM-EDS. The results showed that the best performance of PBM was achieved when the contents of PG, GGBS, and SS were 80%, 13%, and 7%, the liquid-to-solid ratio was 0.4, and the mass concentration of NaOH was 4%, with a strength of 2.8 MPa at 28 days. The leaching concentration of fluorine at 7 days met the standard of groundwater class IV (2 mg/L), and the leaching concentration of phosphorus was detected to be less than 0.001 mg/L, and the leaching concentration of heavy metals met the environmental standard at 14 d. The hydration concentration in PBM met the environmental standard. The hydration products in PBM are mainly ettringite and C-(A)-S-H gel, which can effectively stabilize the heavy metals in PG through chemical precipitation, physical adsorption, and encapsulation.

Experimental study on the heat treatment reaction process of bentonite

This study focuses on enhancing the pozzolanic activity of bentonite through heat treatment to improve its compressive strength, while also considering its expansion properties for applications. Sodium bentonite was subjected to various temperatures and analyzed using thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM–EDS). The results indicated that at 100 °C, adsorbed and interlayer water in montmorillonite was lost, and constitution water was eliminated at 700 °C. With further temperature increases, montmorillonite decomposes into an amorphous phase at 900 °C. At 1100 °C, the amorphous phase recrystallized into magnesium–aluminum silicate, which further decomposed into cristobalite. The study concludes that bentonite heat-treated at 800–900 °C can be effectively used as an additive in mining backfill materials to enhance compressive strength while maintaining its expansion properties.

Experimental study on CO2 sequestration capacity and mechanical characteristics evolution of solid wastes based carbon-negative backfill materials

The employment of solid waste, notably coal gangue, in carbon-negative backfill mining technology for mineralization and filling in coal mine gobs, is recognized as a productive method for carbon sequestration and waste management, with research primarily dedicated to engineering advanced mineralized backfill materials. Under this background, four variables, including the ratio of gangue to solids (RG-S), water-cement ratio (RW-C), ratio of fly ash to solid wastes providing calcium (Ca) (RA-Ca), and ratio of flue gas desulfurization (FGD) gypsum to carbide slag (RF-CS) were defined to formulate gangue-based mineralized backfill materials, with orthogonal experiments assessing their effects on CO2 sequestration and mechanical characteristics. The results indicate that RW-C consistently emerges as the primary factor influencing both the amount of sequestered CO2 and the mechanical properties of gangue-based solid waste mineralized backfill materials. The amount of sequestered CO2 demonstrates a direct proportionality to RW-C and mechanical strength demonstrates an inverse relationship with RW-C. After 45 minutes of stirring and carbon sequestration, samples in various groups exhibited an maximum sequestered CO2 amount of 18.96 g·kg−1, with a maximum sequestration rate of 0.20 g·kg−1·min−1. The process of CO2 sequestration enhances the compressive properties of mineralized backfill materials derived from gangue based solid wastes.

Optimizing mechanical performance and flow characteristics of alkaline fly ash/rice husk ash composite backfill: Insights from multi-factor analysis and engineering optimization

In order to effectively dispose of agricultural waste rice husk ash and improve the mechanical properties of backfill, the properties of fly ash/rice husk ash composite backfill material were studied in the laboratory. The effects of fly ash, rice husk ash, straw fiber and NaOH content on the properties of composite backfilling materials were studied, and the ratio parameters of composite backfilling materials were optimized based on engineering examples. Our findings reveal that fly ash content significantly impacts slump, with its addition enhancing the flow performance of composite backfilling materials. Conversely, straw fiber, rice husk ash, and NaOH content were found to have non-significant effects on slump. We observed that with the increase of fly ash content from 5 % to 20 %, the compressive strength of the backfill firstly increases and then decreases, and the optimal content range is about 10 %. Moreover, increased rice husk ash and NaOH content effectively enhance the UCS. However, higher fly ash and straw fiber content were found to impede the strengthening effect of NaOH on UCS. Nevertheless, higher NaOH content was observed to augment the strengthening effect of rice husk ash content. Furthermore, when the content of fly ash and rice husk ash is 5∼10 % and 3–12 % respectively, rice husk ash and fly ash effectively reduce the size range of internal void structures, enhancing the microstructure density and mechanical properties of the composite backfilling material. Based on engineering example, we determined the optimal ratio parameters of the composite backfilling material to be: 20 % fly ash content, 9 % rice husk ash content, 0.4 % straw fiber content, and 2.5 % NaOH content. This study is helpful to promote the application of waste rice husk ash and straw fiber in mine filling, and provides theoretical guidance for the parameter design of backfilling materials.

Study of Slope Stability of the Mining Wall in an Open-Pit Coal Mine by the Paste Cut-and-Backfill Method

According to this study’s findings, slope stability problems in open-pit coal mines can be avoided, and mine wall collapse can be effectively mitigated by the use of cut-and-backfill mining techniques. The main research results are as follows: (1) The stope and waste rock’s geotechnical, physical, and mechanical characteristics were gathered and examined; the geotechnical and mechanical characteristics found in this study largely satisfy the criteria for slope stability analysis. (2) Cemented paste backfill (CPB) materials were made of mine waste rock and fly ash at a desired ratio, mixed with cement as a bond material, and were tested in the laboratory, using a combination of cement percentages of 6%, 8%, and 10% for the cement content and 25%, 30%, 35%, and 40% for the fly ash content, to determine the ideal mix for artificial ground support in underground mines, taking into account both economic and performance factors. (3) By using this model, the changes in CPB strength were investigated under various factors influencing the cement ratio, and limit equilibrium modeling was used with the FLAC-Slope 8.1 program with different cement paste backfill ratio to calculate the factor of safety for each cement percentage after 1 day, 3 days, 7 days, and 28 days of curing time (CT) to obtain the optimum compressive strength and shear straight of cemented paste backfill with high paste fill shear strength on the slope. (4) The research results are of great significance for the safety of important facilities in open-pit mines and provide a basis for the design and safety implementation of open-pit slope engineering.

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.