Cement-tailings Ratio Research Articles

Research on the strength influence and crack evolution law of layered backfill based on macro and meso mechanical response

This article analyzes the effects of inclined angle (IA), filling times (FTs) and cement tailings ratio (CTR) on the uniaxial compressive strength (UCS) and crack development law of layered cemented backfill (LCB) using various research methods, including indoor experiments, numerical simulation, and computed tomography (CT) scanning. The research shows: (1) In the indoor experiments, it was observed that increasing the IA, increasing the number of FTs, and decreasing the CTR had a significant weakening effect on the UCS of the specimens. The greater the IA, the more pronounced the separation and dislocation of the layered contact surface, resulting in a significant increase in macroscopic cracks at the bottom. As the FTs increases, the center of gravity of the failure of the LCB gradually moves downwards. This causes the damage and failure time to advance, and the peak stress to change from one main crack to multiple main cracks. (2) During the numerical simulation, compressive stress accumulates and increases around the pores in the layered contact surface. Microcrack aggregation occurs on the contact surface, and downward expansion and extension. The peak strain energy decreases as the IA increases with the FTs. The number of shear cracks increased more at 20° to 30° than at 0° to 20°. The strain energy of the 0° specimen is the highest, while that of the 30° specimen is the lowest. (3) The CT scan shows that the LCB is affected by stress conduction hysteresis. When the bottom backfill is in the stage of crack evolution, the top backfill is in the stage of compaction.When the LCB reaches the peak stress, both the bottom and middle layers of the backfill lose load-bearing capacity, and the top layer of the backfill has no cracks. This paper provides reference value and research ideas for the destruction of backfill that contain layered defective structures.

Multi-angle research on the performance of self-foaming filling materials and analysis of engineering applications

Utilizing self-foaming filling material to fill the hollow area is an effective way to settle the issues of low rate and poor effect of filling and roofing in the large stope. There are fewer studies related to the expansion rate, hydration exotherm and strength properties of self-foaming fillers in mines. Based on this, this paper investigates the expansion characteristics, hydration exothermic characteristics and compressive strength characteristics of the self-foaming filler under different cement-tailings ratios (1:4, 1:6, 1:8), reveals the hydration reaction mechanism of the material and its microscopic characteristics through XRD, TG and SEM tests, and evaluates the application effect and economy of the self-foaming filler in practical engineering with the background of Mashong Iron Ore Mine. The main findings are as follows: (1) The volumetric expansion of self-foaming filling material can be divided into the initial stage Ⅰ (0–1.5 h), the rapid reaction stage Ⅱ (1.5–8 h) and the stabilization stage, and as the cement-tailings ratio grows, the expansion rate of the filling body increases, and the expansion rate of the filling material with 1:4 ratio is as high as 20.4 %. (2) The hydration process of a self-foaming filled body does not contain induction and acceleration stages; under the same conditions, the self-foaming filled body has more exothermic heat of hydration than that of a self-foaming filled body by about 50 J/g, and the bigger the cement-tailings ratio, the bigger the hydration exothermic rate and exothermic quantity. (3) The compressive strength of self-foaming filler is inferior to the strength of conventional filler, the higher the cement-tailings ratio, the greater the degree of hydration, the more hydration products are produced, and the greater the compressive strength. (4) The bigger the ratio of gray sand, the greater the proportion of macropores and the actual engineering of self-foaming filling materials to catch the top rate of up to 98 %, directly saving the total cost of 11.6 %. The above research results can offer theoretical support and scientific guidance for the utilization of spontaneous foam materials to fill the goaf and control the roof rate, temperature, and strength of the stope.

Impact of weak interlayer characteristics on the mechanical behavior and failure modes of cemented tailings backfill: A study on thickness, strength, and dip angle

The mechanical properties of cemented tailings backfill (CTB) are crucial for managing ground pressure and sustaining mine productivity. However, multiple fillings often result in weak interlayers (WI) within the backfill, compromising its stability. This study investigates the mechanical behavior and failure modes of composite cemented tailings backfill (CCTB) with different WI characteristics—thickness (ranging from 0 mm to 30 mm), strength (cement-tailings ratio from 1:4 to 1:20), and dip angle (from 0° to 9°)—after 28 days of curing through uniaxial compression tests. Regression and error analysis methods were employed to establish the relationships between WI physical characteristics and CCTB mechanical properties. Additionally, the inherent mechanisms of mechanical strength deterioration in CCTB containing WI were discussed based on experimental and simulation results of CCTB failure modes. The results found that the uniaxial compressive strength (UCS) and elastic modulus (E) of CTB decrease with lower cement content, while the peak strength strain (PSS) increases. Incorporating WIs weakens CCTB, reducing UCS and E, and increasing PSS. Regression analysis combined with error analysis revealed that WI thickness has an exponential relationship with UCS, E, and PSS. As WI thickness increases, reduction coefficients for UCS and E rise significantly, exacerbated by the WI’s diminished strength. The WI’s dip angle significantly affects CCTB’s mechanical behavior, disrupting stress distribution and load transfer, resulting in heightened stress concentrations and structural weakening. COMSOL simulations corroborated these experimental findings, providing deeper insights into stress distribution and failure mechanisms within the CCTB structure. These findings aim to provide a theoretical basis for mitigating the impact of WI characteristics on the stability and load-bearing capacity of CCTB in future mining operations.

Strength, deformation and crack evolution behaviour of cemented tailings backfill composite structures with different strength ratios

ABSTRACT This work comprehensively investigated cemented tailings backfill composite structures (BCS) mechanics and crack evolution mechanisms. A new crack classification method combining Gaussian Mixture Modeling (GMM) and Moving Average Filtering is proposed for the BCS acoustic emission RA-AF dataset. The findings indicate that the upper CTB did not incur significant damage following BCS destruction, enabling BCS to maintain a certain bearing capacity post-failure. The compressive strength of BCS often approximates that of CTB monomers with a lower cement-tailings ratio (this trend diminishes as the upper CTB’s strength increases), and the loss of bearing capacity in BCS is attributed to the failure of CTB monomers with lower strength. The deformation damage in the upper and lower CTB displays a cooperative characteristic throughout the loading-induced damage process, with the axial and transverse strains in the lower CTB surpassing those in the upper CTB. Analysis results from GMM reveal that the compression failure process of BCS is predominantly characterized by tensile failure, with minimal shear failure. The propagation of cracks in the lower CTB exerts a certain influence on the crack evolution of the upper CTB. The findings offer a novel perspective on discerning the fracture evolution behavior of materials.

Energy Mechanism and Acoustic Emission Characteristics in Rock-Backfill Composite Structure Specimens under Multi-Level Cyclic Loads: Cement-Tailings Ratio Effect

Energy Mechanism and Acoustic Emission Characteristics in Rock-Backfill Composite Structure Specimens under Multi-Level Cyclic Loads: Cement-Tailings Ratio Effect

Study on the influence of contact surface characteristics on strength and fracture evolution of layered cemented backfill (LCB)

The stability of backfill plays a crucial role in the process of mine operation. In this study, author combined indoor experiments, surface fitting, numerical simulation, and theoretical derivation to investigate how the filling times (FTs), cement tailings ratio (CTR), and minimum CTR filling position (MCFP) affect the uniaxial compressive strength (UCS) and fracture evolution behavior of LCB. The findings demonstrate that an augmentation in FTs reduces the UCS of LCB. Moreover, the highest strength ratio resulting from diverse MCFP amounts to 2.25 times. When once filling, backfill sustain damage as a result of cracks penetrating, whereas LCB that are filled multiple times first encounter damage at the layered contact surface, followed by the gradual spread of cracks until penetrate the LCB. Through an interactive regression model, it is evident that FTs, CTR, and MCFP significantly affect the UCS. Additionally, the interaction between CTR and MCFP has a considerable impact on the UCS. Based on numerical simulation, an increase in FTs results in a wider large displacement area generated by the backfill, leading to greater horizontal and vertical displacement. The MCFP has a significant impact on the lateral displacement and maximum stress of the backfill. Theoretical derivation verifies that MCFP at the top or middle layer results in an increase in the UCS, which is consistent with the experimental findings and numerical simulation. This paper elaborates on the mechanical mechanism behind the interaction between CTR and MCFP. These findings can provide a foundation for assessing the durability and stability of LCB in subsequent stages.

A new acoustic emission characteristic parameter can be utilized to evaluate the failure of cemented paste backfill and rock combination

In backfill mining, there is a phenomenon of the joint bearing of cemented paste backfill and rock, so it is essential to study the destabilization damage mechanism of cemented paste backfill and rock combination (BRC). This study aimed to improve the evaluation system for the instability failure of BRC. A new evaluation index, Dr, based on acoustic emission (AE) characteristic parameters was proposed for predicting BRC instability failure caused by the load. This index comprehensively considers the time dependence and interaction of the AE rise time, amplitude, and average frequency during BRC failure. The study conducted uniaxial compression and simultaneous AE experiments for various ratio combinations of BRC to obtain the AE rise time/amplitude (RA) and average frequency (AF) values of BRC. Then, the RA/AF values were numerically calculated with fractal theory to obtain the Dr index, and the intrinsic relationship between Dr and BRC instability failure was further discussed. Finally, the index was validated through comparison with the statistical index b-value based on AE amplitude, and a discrimination criterion for BRC instability failure was proposed. The results show that: After reaching the yield stress, the number of AE events of the rock gradually decreases. In contrast, the number of AE events of the CPB fluctuates in the high-level range. The cement-tailings ratio significantly affects the BRC AE frequency and amplitude distribution. The decrease of the cement-tailings ratio enhanced the high-frequency amplitude signal of CPB, while weakening the medium and high-frequency amplitude signal of rock. The sudden drop of Dr in the near-failure stage can be used as a criterion for BRC failure determination. Compared with the b-value, using Dr as an evaluation index to predict BRC failure can obtain a slightly conservative result. The research provides a new and effective method for evaluating BRC instability failure, which can be used for real-time prediction of BRC instability failure in mining engineering practice.

Pore fractal characteristics of fiber-reinforced backfill based on nuclear magnetic resonance

To investigate the pore fractal characteristics of fiber-reinforced backfill, uniaxial compression tests and nuclear magnetic resonance (NMR) tests were conducted on reinforced backfills with different cement-tailing ratios (1:6, 1:8, and 1:10) and different fiber types (polyacrylonitrile fiber and glass fiber). The relationship between the pore size distribution, elastic modulus, uniaxial compressive strength, and cement-tailings ratio of the backfill was investigated, and the pore fractal dimensions of three types were quantified. The results showed that the peak signal amplitude and total spectral peak area of the fiber-reinforced backfill were highest reduced by 21.2% and 25.3%, respectively, compared with that of the fiber-free backfill. The uniaxial compressive strength and elastic modulus of the backfill specimens decreased with decreasing cement-tailings ratio. The micropore fractal dimension values of the backfill specimens ranged from 0.30 to 1.00, while the mesopore and macropore fractal dimension values were in the range of 2.96 to 3.00. The correlation coefficients of the mesopore and macropore fractal dimensions of the backfill are >0.94, and the fractal dimension of mesopores and macropores was not significantly correlated with the cement-tailings ratio and fiber type. The results can provide a reference for discussing the relationship between the microscopic pore structure and macroscopic physical parameters of fiber-reinforced backfill.

Application of deep neural network in the strength prediction of cemented paste backfill based on a global dataset

With the development of the mining industry, the increasing global content of tailings is causing environmental pollution and the use of tailings as a cemented paste backfill (CPB) for underground filling is an effective method of disposal. The application of the backfilling mining method is heavily dependent on the stability of the CPB. However, experimentally evaluating the unconfined compressive strength (UCS) of CPB is time-consuming and expensive. This study discussed the feasibility of using a deep neural network (DNN) model to predict the UCS of CPB. This study established the first global dataset of UCS values of CPB through a literature search and laboratory studies, for the first time. The dataset comprised 986 CPB samples, where each sample included 14 feature values and a target value. The dataset was divided into three parts, i.e., a training set, a validation set, and a testing set, which were used to build, validate, and test the model. The correlation coefficient (R), coefficient of determination, mean absolute error, and mean square error metrics were used for model evaluation. After the hyper-parameter tuning, the number of layers in the DNN model was 4, the learning rate was 0.001, and the dropout rate was 0.25. The optimal DNN model achieved excellent predictive performance on this dataset, with R values on the training, validation, and testing sets of 0.989, 0.964, and 0.967, respectively. The feature importance was analyzed using permutation importance and the Shapley Additive Explanation value, with the cement–tailings ratio found to be the most important feature value with the greatest impact on the model output. This study provides, for the first time, a UCS prediction based on the global CPB dataset, a method that can quickly and accurately obtain the UCS of CPB. The method can save a lot of experimental time and provide a theoretical reference for subsequent environmental management as well as tailings utilization, and promotion of paste filling.

Remediation of grassland subsidence and reduction of land occupation with tailings backfill technology: a case study of lead-zinc mine in Inner Mongolia, China

The mining industry provides essential mineral resources for human society’s development. However, this industry generates a large quantity of waste material while rapidly extracting valuable elements from ore, such as processed tailings. The existence of mined voids will cause surface subsidence, and the surface stockpiling of tailings and waste rocks occupy a large amount of land and the risk of Tailings Storage Facility (TSF) failure. This paper proposes tailings backfill technology to mitigate surface subsidence and provides an alternative disposal method for tailings generated during ore extraction. Tailings backfill technology prepares the slurry by adding a certain amount of cementitious material into the tailings and transporting it to the underground goaf through a pipeline. The backfill slurry could then gradually build up its strength during the hydration of. Cementitious material. A case study of a lead-zinc mine in the Inner Mongolia Autonomous Region of China using tailings backfill technology was introduced in detail to solve the problems of grassland collapse caused by mine excavation and environmental damage due to tailings disposal. Spread test and rheological test were carried out to study the flow characteristics of filling slurry and the uniaxial compressive strength (UCS) of backfill was tested as well. The result illustrates that the spread of the filling slurry with a solid content between 72% and 76% and cement-tailings ratio between 1:4 and 1:8 is greater than 14 cm, and the UCS of backfill is above 1 MPa. The research shows that the tailings backfill technology recycles tailings waste while mitigating surface grassland subsidence and land occupation of waste disposal. Tailings backfill technology can significantly reduce tailings discharge or even achieve no discharge. A leaching test for heavy metal element classification of the backfill sample was carried out. The results show that the heavy metal detection indicators meet the environmental protection standard requirements and will not cause secondary environmental pollution. Therefore, tailings backfill technology can realize green and efficient management of mine waste and has great application and promotion prospects.

Acoustic emission characteristics and fracture mechanism of cemented tailings backfill under uniaxial compression: experimental and numerical study

Cemented tailings backfill (CTB) is the most cost-effective and environmentally friendly method to recycle tailings for filling mining. It is of great significance to study the fracture mechanism of CTB for safe mining. In this study, three cylindrical CTB samples with a cement-tailings ratio of 1:4 and a mass fraction of 72% were prepared. An acoustic emission (AE) test under uniaxial compression (UC) with WAW-300 microcomputer electro-hydraulic servo universal testing machine and DS2 series full information AE signal analyzer was carried out to discuss the AE characteristics of CTB, such as hits, energy, peak frequency, and AF-RA. Combined with particle flow and moment tensor theory, a meso AE model of CTB was constructed to reveal the fracture mechanism of CTB. The results show that (1) the AE law of CTB under UC has periodic characteristics, which can be divided into the rising stage, stable stage, booming stage, and active stage. (2) The peak frequency of the AE signal is mainly focused on three frequency bands. The ultra-high frequency AE signal may be the precursor information for CTB failure. (3) The low frequency band AE signals represent shear crack, while the medium and high frequency band AE signals represent tension crack. The shear crack initially decreases and then increases, and the tension crack is the opposite. (4) The fracture types of the AE source are divided into tension crack, mixed crack, and shear crack. The tension crack is dominant, while a larger magnitude AE source is frequently shear crack. The results can provide a basis for the stability monitoring and fracture prediction of CTB.

Towards the Understanding of Damage Mechanism of Cemented Tailings Backfill

Recent studies have shown that the damage characteristics of cemented tailings backfill (CTB) are influenced significantly by the variation of cement-tailings ratio, while the effects of other influencing factors remain unanswered. The CTB damage constitutive model, which takes the corrected coefficient of damage variable into consideration, and peak toughness are introduced to investigate the effects of fine tailings contents, curing ages, curing temperatures, and water-to-cement ratios ( w / c ) on the damage evolution laws, damage ( D P ), and specific energy ( G P ) at peak stress point of CTB. The results show that appropriate content of fine tailings could improve the compressive strength of CTB and reduce its damage evolution speed and D P . The damage growth rate of CTB decreases with curing age in early curing period and increases with higher curing temperature and w / c . D P of CTB takes on a descending trend with higher w / c and fine tailings content but shows an increase with curing age. There exists no significant relationship between D P and curing temperature. G P of CTB increases with curing age and higher curing temperature with a quadratic function but is on a decline with increases of fine tailings content and w / c with logarithmic and exponential function, respectively. The results obtained from our study have important application to the successful design of backfill structures in underground mines.

Strength and Ultrasonic Characteristics of Cemented Paste Backfill Incorporating Foaming Agent

This work is a systematic study of the strength and ultrasonic properties of cemented paste backfill incorporating a foaming agent, known as foam-cemented paste backfill (FCPB). Based on determining the optimal admixture contents (foaming stabilizer, thickening agent, and foaming agent), a series of uniaxial compressive strength (UCS) tests were conducted to determine the relationship between the UCS of FCPB and four influencing factors, i.e., cement–tailings ratio (CTR), solid content (SC), curing time (T), and foaming agent content (FC). To analyze the sensitivity of UCS to these four factors, grey relational analysis (GRA) was introduced. Moreover, UCS results were correlated with the corresponding ultrasonic pulse velocity (UPV) parameters. The results indicate that the optimal contents of foaming stabilizer, thickening agent and foaming agent are 0.5%, 0.6%, and 1–3%, respectively. The UCS of FCPB exponentially increases with CTR and SC, while it logarithmically and linearly increases with T and FC, respectively. CTR has the most significant influence, followed by T, SC, and FC. There exists an evidently linear relationship between UPV and UCS of FCPB regardless of CTR, SC, T and FC. These results contribute to understanding the properties of hardened FCPB and to sound designs in practice.

Research on the Mechanical Properties and Energy Consumption Transfer Law of Cement Tailings Backfill Under Impact Load

The cemented tailings backfill (CTB), which plays a significant role in the stability of mine structure, is made of cement, tailings, and water in a certain proportion. When blasting and excavating an underground mine, the CTB will be disturbed by blasting. The impact load of blasting has an impact on the stability of the CTB, which is directly related to the safety of mine construction. The mechanical behaviour of CTB is generally affected by the cement-tailings ratio (C/T) and average strain rate (ASR). Therefore, a series of impact experiments were carried out on three CTB specimens with different C/T using a SHPB. Combined with the experimental results, this account reports studies on the effects of C/T and ASR on the mechanical properties of CTB, and on the energy transfer laws of CTB during impact compression. The research results show that when the ASR is less than 70 s−1, the peak stress and the peak strain have the same trend, and both of them continue to increase with the increase of ASR.When the ASR exceeds 70 s−1, as the ASR increases, the peak stress continues to increase, but the peak strain decreases gradually. Afterwards, the law of energy transfer of the CTB specimen was analyzed. It was found that as the incident energy increased, the energy reflection ratio of the CTB increased. Both the energy transmitted ratio and the energy dissipation ratio decreased. The volumetric energy showed a sharp increase first and then a trend Because of the slowly increasing trend. Finally, according to the failure morphology of the CTB, it is found that the ASR and the C/T together affect the failure of the CTB. The failure model of the CTB is mainly split failure and crush failure.

Mechanical response and acoustic emission characteristics of cement paste backfill and rock combination

Backfill mining method plays an important role in the treatment of tailings, and the failure law of a cement paste backfill (CPB) and rock combination under pressure has essential guiding significance for the safe production of mines using the backfill mining method. In this work, uniaxial compression acoustic emission (AE) experiments were conducted on single CPB and CPB–rock combinations with different cement tailings ratios, based on referring to fractal theory to investigate the crack evolution of the specimens at different stages. The results show that the content of the tailings has a significant influence on the crack evolution and AE characteristics at the different stages of the CPB. When the cement tailings ratio of the CPB is reduced from 1:4 to 1:10, the crack evolution in the compaction stage gradually changes from initial crack closure to tailing–cement cracking. The crack evolution in the instability stage changes from the production of a large number of microcracks to that of several macrocracks. After entering the instability stage, the elastic energy release of the upper rock in the combinational specimens aggravates the post–peak damage of the CPB, and the change in the fractal dimension changes from “rising with severe fluctuations” to “declining with small fluctuations”. There are significant similarities in the ring–down count fluctuation laws of the rock and CPB in the combinational specimens. Before approaching the stress peak, the ring–down counts and fractal dimensions of the specimens show a significant downward trend. Among them, the fractal dimensions of the CPB–rock combinations with ratios of 1:4, 1:8, and 1:10 decrease by 21.1%, 16.7%, and 16.8%, respectively. The research results of this work can provide guidance for predicting the instability and failure of a CPB–rock combination in a mine using the backfill mining method.

Mechanical properties, damage evolution, and constitutive model of rock-encased backfill under uniaxial compression

The backfill does not exist independently in the stope, but is in contact with the surrounding rocks to form a combination body to jointly bear pressure. In order to study the joint pressure-bearing mechanism of rock and backfill in the stope, the rock-encased backfill (RB) samples are produced, and the uniaxial compression tests and acoustic emission (AE) monitoring are carried out. The results show that: (1) The encased rock can strengthen the uniaxial compressive strength (UCS) and elastic modulus (EM) of the backfill. The UCS and EM of the RB samples are greatly affected by the cement-tailings (c/t) ratio and radius (r/R) ratio. When the c/t ratio decreases from 1:4 to 1:10, the UCS and EM decrease by about 14% and 29%, respectively; when the r/R ratio increases from 0.2 to 0.8, the UCS and EM decrease by about 63% and 72%, respectively. There is a positive linear function relation between UCS and EM. (2) AE energy release and AE event location characterize the crack growth rate and the crack spatial position of the RB samples respectively. (3) A damage constitutive model of the RB sample is established based on the principle of conservation of energy. The total damage D consists of the damage at the centre of the backfill D1 and the damage in the encased rock D2. All the damage curves are S-shaped. The damage first evolves at the centre of the backfill, then in the encased rock, finally co-evolves, leading to the overall instability and failure, which is mutually verified with the locations of AE events.

Improved strength prediction of cemented paste backfill using a novel model based on adaptive neuro fuzzy inference system and artificial bee colony

The cemented paste backfill (CPB) technology has matured as a promising way for tailings recycling in the mining industry. Nevertheless, the current CPB design requires a large number of lab experiments to determine the unconfined compressive strength (UCS) of CPB. The utilisation of artificial intelligence (AI) prediction to reduce the lab experiments has been attempted without reaching its full potential. In this study, a hybrid model based on adaptive neuro fuzzy inference system (ANFIS) and artificial bee colony (ABC) was used for performance improvement. The ANFIS was used to learn the relationship between inputs and UCS while the ABC algorithm was used to tune the parameters of the initial ANFIS. The convergence of the prediction performance was tested using Monte Carlo simulations. A comparison between this study and previous studies was conducted and a sensitivity analysis was performed to investigate the importance of input variables. The results show that the ABC algorithm was efficient in tunning parameters of the ANFIS model. The representative ANFIS-ABC model yielded an R2 of 0.967 on the training part and an R2 of 0.976 on the testing part, indicating an excellent prediction. 310 Monte Carlo simulations were needed before a stable performance was achieved for all quality assessment criteria. The proposed hybrid model outperformed AI models in the literature (R2 was increased from 0.83/0.958/0.86 to 0.976 on the testing set). Solid content, cement-tailings ratio and curing time were found to be the most significant input parameters for the UCS of CPB.

Damage Strengthening Constitutive Model of Cemented Paste Backfill

In order to consider the influence of mesoscopic characteristics of materials on the constitutive model of cemented paste backfill (CPB), the uniaxial compression variables and the damage constitutive model, considering the influence of porosity and pore size of filling materials, were derived based on the strain equivalence principle and Weibull probability distribution function. The nuclear magnetic resonance (NMR) tests and unconfined compression strength (UCS) tests were carried out on 8 groups of CPB specimens with different slurry concentrations and cement‐tailings ratios. Then, the expression of damage strengthening coefficient is determined, and the stress‐strain curves measured by the theoretical model were compared with the experimental ones. The results show that the uniaxial compression constitutive model proposed is in good agreement with UCS test results and can effectively describe the damage evolution law and the development process of stress‐strain curve of CPB under uniaxial compression. The 28‐day compressive strength of CPB can reach 8 MPa, the residual strength is about 1∼2 MPa, the elastic modulus is about 200∼2000 MPa, and the porosity is about 3∼5%. The CPB with slurry concentration of 74% and 76% and cement‐tailings ratio of 1 : 4 and 1 : 6 is more reasonable, and the relevant mechanical parameters are more stable.

Correlation between the Pore Structure and Water Retention of Cemented Paste Backfill Using Centrifugal and Nuclear Magnetic Resonance Methods

This research combines a centrifugal test and nuclear magnetic resonance (NMR) technology to study the water retention capacity of the cemented paste backfill. Backfill samples with cement–tailings ratios of 1:4, 1:8, and 1:12, and solid concentrations of 71%, 74%, 77%, 80%, and 83% respectively, were prepared for the test. The relative centrifugal force ( RCF ) required for accurate testing and the T2 cutoff value that characterizes the water retention capacity were obtained through an NMR test on the backfill samples after centrifugation in saturated conditions. Based on the soil–water characteristic curve (SWCC), the NMR pore water characteristic distribution model was established, and the pore size distribution and effective water retention characteristics were analyzed. This study shows that when the rotating speed is between 1500 and 4000 rpm, the R C F of the backfill ranges from 125.8 to 894.4 g/min , and the T2 cutoff value will vary from 3 to 10 ms. With an increase in solid concentration of the backfill, both the RCF and T2 cutoff value decline. The Scanning Electron Microscope (SEM) analysis confirms that an increase in the solid concentration and cement–tailings ratio will lead to obvious bimodal characteristics of the pore size distribution curve of the backfill. In addition, the porosity will decrease, the critical pore value, which represents a value to distinguish pores with different movable fluid retention capabilities and characterizes the pore size classification, will become smaller, and the pore size distribution will become more diverse. These changes indicate that a high-concentration backfill can effectively reduce the flow of a fine-grained matrix with large pores.

Mechanical behaviour and failure characteristics of cemented paste backfill under lateral unloading condition

A key issue associated with mine backfill design is the determination of mechanical behaviour and failure characteristics of the cemented paste backfill (CPB), especially for CBP under lateral unloading conditions caused by excavation of adjacent stopes. In this research, a series of lateral unloading tests with RFPA3D were conducted to investigate the relationships among the cement-tailings ratio (1:4 and 1:8), lateral unloading stress (0 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa and 1.0 MPa), mechanical behaviour, failure modes and acoustic emissions (AE) characteristics. Similar mechanical behaviour of all the CPB specimens was obtained. With different cement-tailings ratios and preloading stress values, the ultimate failure modes of CPB specimens show different forms. Additionally, increasing the preloading stress value caused a rising of AE counts. The results of this study can provide a significant reference for the backfill design and study of underground mining.