Cemented Tailings Backfill Samples Research Articles

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.

Equivalent numerical method and sensitivity analysis of microparameters for micropore compression stage of cemented tailings backfill

The discrete element method has been widely used to study the mechanical properties of rock and cemented tailings backfill (CTB). The high matching degree of mechanical properties between numerical simulation and experiment is the precondition of accurate numerical simulation research. However, as the discrete element method’s particle system cannot characterize pore structure of rock and CTB, it cannot simulate the micropore compression stage (MPCS) of laboratory test. Therefore, the traditional discrete element method cannot accurately simulate the whole process of stress − strain curve of rock and CTB. To solve this problem, in this study, the variation law of the porosity and pore radius of CTB samples’ MPCS were first explored using nuclear magnetic resonance and computed tomography scanning tests. Based on the findings, the equivalent cell model of CTB is proposed. The relative deformation of cells can equivalently characterize the compressive deformation of pores in CTBs. Thus, the initial effective modulus, E0, the progressive coefficient of the effective modulus, k, and cycle steps, b, were introduced to improve the soft-bond model (SBM) in a particle flow code (PFC). This improvement changes the contact structure between particles and makes the contact deformation between particles more consistent with the deformation behavior of micropores in laboratory test. A numerical method for the nonlinear deformation of MPCS is established in PFC. Finally, the parameter sensitivity of the softening factor, softening tensile strength factor, friction coefficient, E0, k, and b in the improved SBM was analyzed. The variation law of samples’ macromechanical parameters with different microparameters is obtained. The results provide a basis for a more accurate study of the mechanical behavior of rock and CTB based on the discrete element method.

Study on mechanical properties and damage characteristics of rice straw fiber-reinforced cemented tailings backfill based on energy evolution.

Low-cost and underutilized plant fibers can affect the mechanical behavior of cementitious materials such as cemented tailings backfill (CTB). This paper attempts to explore the mechanical properties and damage evolution characteristics of rice straw fiber (RFS)-reinforced CTB (RSFCTB) from the perspective of energy. A series of mechanical and microscopic tests were carried out on CTB and RSFCTB samples. On this basis, the energy evolution law and of the filling body under different stress paths were analyzed. Meanwhile, a damage variable based on dissipation energy was established, and the damage evolution process of the filling body was discussed. The results show that uniaxial compressive strength (UCS) of filling body first grew and then dropped with the enhancement of RSF content, and indirect tensile strength (ITS) was positively correlated with RSF content. Scanning electron microscope showed that RSF was encapsulated by hydration products, which promoted the bridging effect of RSF. The bridging effect of RSF improved the integrity of RSFCTB after compression failure and resulted in bending and asymmetric tensile cracks after tensile failure. The energy storage limit and dissipation energy of the filling body under different stress paths were enhanced due to the incorporation of RSF. The damage curve based on dissipation energy showed three stages of slow, steady, and fast damage under compressive loading. The damage curve of RSFCTB was located below CTB depending on the crack arresting effect of RSF. Moreover, the damage curve under tensile load shows three stages: slow, stable damage, and sudden increase in damage. The damage value of RSFCTB at the mutation point was increased, and the ability of RSFCTB to resist tensile damage was enhanced. The energy evolution and acoustic emission parameters were combined, and their development trends were similar, which proved that it was reasonable to characterize the damage of filling body based on the dissipated energy.

Mechanical properties, damage evolution and energy dissipation of cemented tailings backfill under impact loading

In order to explore the influence of average strain rate(ASR) on mechanical properties, damage evolution and energy dissipation of cemented tailings backfill(CTB), the dynamic test of CTB was carried out in the laboratory. This study shows that dynamic peak stress and initial crack stress of CTB increase exponentially with the increase of ASR, indicating that the characteristic stress of CTB has a significant strain rate effect. The dynamic peak strain and initial crack strain of CTB also increase exponentially with the increase of ASR, and the CTB with lower cement content is more likely to produce deformation and failure. The increase of ASR can improve the energy indexes of CTB at the peak stress point, and the increase of cement content can also improve the energy parameters of CTB. The energy storage limit of CTB increases exponentially with the increase of ASR. In addition, a dynamic statistical damage constitutive model of CTB was established considering ASR, and the accuracy and reliability were verified. There are three stages for the damage failure of CTB: rapid growth stage of damage, slow growth stage of damage and stable growth stage of damage. In addition, the high strain rate has a certain retarding effect on the development of cracks inside the CTB, thus inhibiting the rapid growth of damage value. Under impact loading, the CTB samples are mainly axial macroscopic main crack tensile failure and crushing failure. When the average strain rate is higher than the critical strain rate, the failure pattern of CTB is mainly crushing failure. When the average strain rate is basically the same, the damage degree of CTB with higher cement content is smaller.

Influence of different fibers on compressive toughness and damage of early age cemented tailings backfill.

For improving the utilization rate of tailings and the safety of cemented tailings backfill (CTB) as earthwork materials, the influence of three types of fibers (e.g., glass, polyacrylonitrile and mixture fibers of both) on compressive toughness and damage of early age CTB was studied. An equation for quantitative analysis of compressive toughness of fiber-reinforced CTB was established. An uniaxial compression test was carried out to monitor the damage acoustic emission (AE) activities of CTB during the loading process. Then, the microstructure of CTB after uniaxial compression test was observed by scanning electron microscope (SEM). The results indicated that mixed fiber has the most comprehensive reinforcement effect on compressive toughness and peak load of CTB. Three fibers inhibited the crack development rate of CTB, glass fiber mainly absorbed axial strain energy of CTB before peak load, while polyacrylonitrile fiber mainly absorbed fracture energy generated during the crack development of CTB after peak load, mixed fiber combined their advantages. The AE activities of three fiber-reinforced CTB samples are much stronger than those of non-reinforced CTB samples in the loading process, and these are no "quiet period" of AE activities. Three fibers all improved the durability of CTB in the damage process, and the damage process of mixed fiber-reinforced CTB is the most stable and showed an approximate linear growth trend. Polyacrylonitrile fiber has a strong resistance to crack after the peak load of CTB because of its ellipsoid part on the surface. As a result, this study can provide a theoretical reference for construction units to use fiber-reinforced CTB for engineering applications and filling work.

Mechanical properties of cemented tailings backfill with chloride-free antifreeze.

In cold regions with sub-zero surface temperatures, the addition of chloride-free antifreeze (Ca(NO2)2, Ca(NO3)2, and CO(NH2)2) is an inexpensive method to prevent pipeline freezing during cemented tailings backfill (CTB) transport. However, the curing temperature of CTB after reaching the mine cavity tends to be above-zero. The mechanical properties of CTB with a chloride-free antifreeze in above-zero environments have not been investigated. Therefore, this study aimed at thoroughly exploring the effect of chloride-free antifreeze on the mechanical properties of CTB in above-zero environments. CTB samples with chloride-free antifreeze (Ca(NO2)2, Ca(NO3)2, and CO(NH2)2) and different concentrations (0, 5, 15, and 35g/L) were prepared and cured in different above-zero environments (2, 20, and 35°C). The unconfined compressive strength tests were performed after 1, 3, 7, and 28days. In addition, a series of microstructural analyses and monitoring experiments were conducted. The results indicated that the addition of a 15-g/L chloride-free antifreeze decreased the strength of CTB curing at 20°C after 1, 3, and 7days and increased the strength after 28days. Moreover, the CTB strength evolution with the curing time depends on the chloride-free antifreeze concentration and above-zero curing temperature. According to the TG/DTG analyses results, calcium ions had a promoting effect on the carbonation of calcium hydroxide. The findings of this study can provide a guideline for the application of chloride-free antifreeze on the mine backfill in cold regions.

Prediction of the Mechanical Performance of Cemented Tailings Backfill Using Ultrasonic Pulse Velocity Measurement

Cemented tailings backfill (CTB), prepared by a mixture of tailings, binder, and water in a certain proportion, is widely applied to mines worldwide for ground support and tailings disposal. The prediction of the mechanical properties of CTB during the whole consolidation process is of great practical importance. The objective of this paper focuses on the investigation of the prediction of the mechanical performance of CTB based on the ultrasonic pulse velocity (UPV) method. The CTB samples prepared with different binder-to-water (b/w) ratios, as well as solid content were monitored by the UPV method during the curing age of 28 days. The evolution of dynamic shear modulus and dynamic elasticity modulus properties of CTB samples were studied by UPV monitoring. Meanwhile, uniaxial compressive strength (UCS) and microstructure tests were performed on CTB samples at curing times of 3, 7, and 28 days. The results showed that the UPV development follows a trend that increases fast at early curing ages and then becomes stable at the 10 d curing age. UPV and UCS increased with the increase in b/w, solid content, and curing age. From the results of microstructure tests, the increase in UPV is attributed to the low porosity and compact structure due to the increase in the b/w ratio and solid content. For the purpose of predicting the UCS of CTB utilizing UPV monitoring, the empirical equations for the relationship between UCS and UPV of CTB with variation b/w ratios and solid content were regression analyses. F-tests, as well as t-tests, were used to check the validity of the equations, which indicate that higher calculated values for CTB to predicted UCS by means of the UPV method. The main finding of this paper shows that the UPV monitoring method can be an effective way to predict the mechanical property of CTB in the field and is non-destructive and effective.

Influence of types and contents of nano cellulose materials as reinforcement on stability performance of cementitious tailings backfill

This study explores the quality of cemented tailings backfill (CTB) reinforced with diverse nano cellulose materials (NCMs) such as micro-fibrillated cellulose (MFC), hydroxylated cellulose nanofiber (CNF), and cellulose crystal (CNC) at macroscopic/microscopic levels. Uniaxial compressive strength (UCS), cracking/failure patterns, deformation analysis, and microstructure of NCM-reinforced CTB samples were thoroughly explored. The results are as follows: the addition of CNF, CNC and MFC to samples augmented its UCS values by 0.95 MPa to 1.39 MPa, 1.43 MPa and 1.29 MPa, respectively. A two-aspect effect on UCS of CNF-, CNC–, and MFC-based samples was observed, namely an escalation followed by a reduction. The optimal concentration of NCM-reinforced CTB samples is 0.9 kg/m3, and the strengthening effect of CNC on CTB is better than CNF and MFC. The cracks witnessed in CTB were created in the stress clouds after loading. NCM-reinforced CTB’s failure pattern was portrayed by tensile/shear failure. Addition of NCMs to CTB well-inhibited crack propagations. Three types of nano cellulose showed diverse morphologies at 2000X, but CNF, CNC and MFC on cracks capably upgraded CTB’s strength characteristics. It was lastly proven that unlike synthetic fibers, incorporating NCMs as a reinforcing material in fill could be a wise solution for boosting CTB recipes in terms of cost-efficiency, operational ease, and sustainability.

Influence of 3D-printed polymer structures on dynamic splitting and crack propagation behavior of cementitious tailings backfill

Originally developed for polymer materials, 3D printing is an encouraging technique to create versatile geometric shapes and high-precision construction elements from various materials. 3D-printed polymer structures are now employed effectively in various industries, including construction and mining since they significantly improve the ductility properties of cementitious materials like cemented tailings backfill (CTB). Considering the lower tensile strength of CTB (compared to its compressive strength), the study of fill's tensile properties is significant for improving the safety and ensuring the stability of the underground CTB structures. Indeed, this aspect is fairly crucial for the development of green mining which allows sustainable and affordable mining operations. To supremely enhance the tensile strength of CTB, three kinds (OR: ordinary resin) and forms (cross, quarter, and 8 equal parts) of 3D printing polymers (3D-PPL) were employed for this study. A number of experiments including Brazilian splitting tests, digital image correlation (DIC) measurements, and SEM failure/micro-structure analyses were fulfilled for exploring both dynamic splitting and crack propagation behavior of 3D-PPL reinforced CTBs. Results designated that dynamic splitting characteristics of 3D-PPL reinforced CTB samples unveiled a robust strain rate dependence. Besides, the tensile strengths of 3D-PPL reinforced CTB samples are increased under the same conditions and the best results are obtained for cross-shaped reinforced CTB increased by 31.6%. 3D-PPL reinforced CTB samples are characterized with higher strains, and the addition of 3D-PPL effectively inhibits the overall damage process of ordinary CTB and improves the backfill’s strength property. As a result, the results of this study are vital and prominent for realizing the tensile/crack behavior of the backfills placed in underground mined-out openings.

Coupled effects of fly ash and calcium formate on strength development of cemented tailings backfill

Cemented tailings backfill (CTB) is widely adopted to ensure the safety of underground goafs and mitigate environmental risks. Fly ash (FA) and calcium formate (CF) are common industrial by-products that improve the mechanical performance of CTB. How the coupling of the two components affects the strength development is not yet well-understood. Neural network modelling was conducted to predict the strength development, including the static indicator of uniaxial compressive strength (UCS) and the dynamic indicator of ultrasonic pulse velocity (UPV). Sobol' sensitivity analysis was carried out to reveal the contributions of FA, CF and curing time to CTB strength. SEM microstructure investigation on CTB samples was implemented to reveal the mechanism of strength development and justify the predictions by neural network modelling and sensitivity analysis. Results show that the combination of FA content, CF content and curing time can be used to predict both UCS and UPV while providing adequate accuracy. The maximum of UCS of 6.1215MPa is achieved at (FA content, CF content, curing time) = (13.78 w%, 3.76 w%, 28days), and the maximum of UPV of 2.9887km/s is arrived at (FA content, CF content, curing time) = (11.67 w%, 3.08 w%, 10days). It is also implicated that prediction of UCS using UPV alone, although common in field application is not recommended. However, UPV measurement, in combination with the information of FA dosage, CF dosage and curing time, could be used to improve UCS prediction. The rank of variable significance for UCS is curing time > FA content > CF content, and for UPV is FA content > curing time > CF content; variable interaction is strongest for FA with CF for UCS development, and for FA with curing time for UPV evolution. Influence of FA on CTB strength development is due to improved polymerisation and consumption of Ca(OH)2. Influence of CF on strength development is a result of accelerated hydration and increased combined-water content in calcium silicate hydrate (CSH). Effect of curing time is attributed to the evolution of CSH product and pore-water content during cement hydration.

Effect of fiber on early strength and interface stiffness of cemented tailings backfill

This paper studies the early mechanical properties of fiber-reinforced cemented tailings backfill (CTB) and discuss its modification mechanism. The effects of fiber types and addition (polypropylene fiber, basalt fiber and glass fiber) on unconfined compressive strength of CTB were studied by unconfined compressive strength test (UCS). Scanning electron microscopy (SEM) was used to investigate the microstructure of fiber-reinforced CTB. Based on the theory of interface mechanics and the contact mechanism of fiber interface, the evolution mechanism of fiber-reinforced CTB interface characteristic stiffness was further explored. The results show that the fiber type and content have a significant effect on the strength of CTB, and the optimum addition of fibers is 0.4%. The strength of fiber-reinforced CTB samples increased first and then decreased with the increase of fiber content. The stress of CTB sample without fibers reaches the maximum value when the strain is 1.01%, while introduction of basalt fiber increases that value to 3.74%. In addition, the microstructure characteristics show that the hydration products around the fiber make the CTB sample have better compactness, and fibers can effectively inhibit the crack development of the CTB samples. Finally, using the theory of interface mechanics, it is found that the interface stiffness of CTB sample with basalt fibers is the largest, but the interface contact stiffness increases first and then decreases with the increase of fiber content, which is consistent with the law of macroscopic strength change.

Dynamical mechanical properties and microstructure characteristics of cemented tailings backfill considering coupled strain rates and confining pressures effects

This paper discusses the relationship between the average strain rate (ASR), confining pressure, dynamic peak compressive strength (DPCS), and cemented tailings backfill (CTB) crack volume through the SHPB test and microscopic computed tomography (CT). The CTB samples with a water-cement ratio of 1:4 and a slurry concentration of 75% were prepared to carry out SHPB tests with different ASR (25.6 ∼ 104.73 s−1), different ASR (12.16 ∼ 152.05 s−1) at different confining pressures (0.5 ∼ 2 MPa). The results show that with the increase of ASR when there is no confining pressure, the DPCS shows a trend of first increasing and then decreasing. However, when the confining pressure is 0.5 and 1 MPa, the DPCS increases linearly. When the confining pressure is 1.5 and 2 MPa, the DPCS increases exponentially and logarithmically, respectively. The micro-CT analysis shows that the total crack volume generated after the SHPB rises first and then falls with the increase of the ASR under confining pressure of 1 MPa. When the impact amplitude is 150 mV, the crack volume also decreases with the improvement of the confining pressure (0.5–2 MPa). The internal cracks of the CTB change from shear cracks to tensile cracks, and the initial pores of the samples first decrease and then increase. The failure pattern of all CTB samples by SHPB was mainly shear, tensile, and hybrid failure (shear and tensile). The research results can provide a valuable reference for the dynamic performance of CTB under confining pressure and the design of mining backfill.

Study on Backfill Acoustic Emission Characteristics and Source Location under Uniaxial Compressive

This study investigates the acoustic emission (AE) characteristic of cemented tailings backfill (CTB) under uniaxial compressive loading. A classified tailings material source from Wushan Copper Mine was used to prepare cylindrical CTB samples. This study used an SLB10 loading machine for the uniaxial compressive test. A PCI‐2 acoustic wave system was attached to the CTB specimen to measure the acoustic emission during loading. Overall, the backfill specimen’s uniaxial compressive strength (UCS) is 3.58 MPa. The failure modes of the CTB sample could be divided into five stages, including the pore microfracture compacting stage (stage‐a), linear elastic deformation stage (stage‐b), yield deformation stage (stage‐c), failure stage (stage‐d), and residual stage (stage‐e). At each stage, the AE characteristic parameters such as the hits per second (HPS), the cumulative number of impacts, energy rate, and total energy vary a lot, which indicates the AE parameter reflects the internal failure evolution of the CTB sample. In stage‐a, no apparent AE behavior was measured. In Stage‐b, there is no evident macroscopic change in the specimen, while the AE parameters steadily and continuously increase. During stage‐c, the number of AE impacts grows sharply, the energy rate increases significantly, and changes suddenly. The cumulative number of AE impacts is 31.3% in stage‐d, and the cumulative energy rate is 49.4%, which is the most active stage of acoustic emission activities. The specimen has prominent crack propagation and bifurcation phenomena. In stage‐d, the CTB sample was destroyed entirely, and the characteristic parameters of acoustic emission were significantly reduced. Finally, multiple regression analysis methods are introduced into the time difference positioning method to locate the AE source. The positioning results show that the technique can better invert the close relationship between the damage and destruction of the CTB and the generation and penetration of the internal cracks and describe it to a certain extent. The failure surface of the filler specimen has an excellent guiding value for the analysis of the interior failure characteristics of the sample.

Analysis of tensile mechanical characteristics of fibre reinforced backfill through splitting tensile and three-point bending tests

ABSTRACT The cut-and-fill mining method is used in metalliferous mines thanks to backfilling instead of ore pillars. However, the stability of the artificial cemented tailings backfill (CTB) roof is one of the key influencing factors for this method. CTB has the characteristics of poor bending resistance and strong brittleness, which is unfavourable for the preparation of artificial CTB roof. In this study, gold tailings and polypropylene fibres were used to make fibre reinforced backfill (FRB). Some splitting tensile strength and three-point bending tests were executed on laboratory-made FRB samples. The feasibility of FBR’s industrial application was also assessed. The results verify that FRB’s splitting tensile and bending strengths increase significantly when added fibres to the mix. This is mostly as a result of the fibre effect of inhibiting crack propagation in FRB samples. Artificial backfill roof was manufactured by using CTB and FRB samples. Besides, the thickness of fibre reinforced backfilling is 0.8 m. The unique findings from this study attest that it is reliable to use FRB material for preparing artificial CTB roof in mines. Besides, this study will hopefully contribute to the secure filling design for underground metalliferous mines and enhance the stability of backfilling structures.

Investigation on Dynamical Mechanics, Energy Dissipation, and Microstructural Characteristics of Cemented Tailings Backfill under SHPB Tests

As mining depth increases, the backfill mining method is more and more widely used in underground mines. The dynamic load generated by the blasting can affect the stability of the cemented tailings backfill (CTB). The CTB samples were prepared to conduct a test of the split Hopkinson pressure bar (SHPB) to investigate the dynamic disturbance of CTB. The present paper discusses dynamical mechanics, energy dissipation, and microstructure analysis of CTB. Micro-computer tomography (micro-CT) scanning of CTB samples after the SHPB test was performed to analyze the evolution of internal cracks. The experimental results showed that when the average strain rate (ASR) increased from 30 to 98 s−1, the dynamic uniaxial compression strength (DUCS) of the CTB showed a trend of first increasing and decreasing with the increase in ASR. The dynamic stress–strain pre-peak curve of CTB directly enters the linear elastic stage. As ASR increases, the absorbed energy of the CTB shows a trend of first increasing and then decreasing. Moreover, according to the micro-CT scanning results, the crack area of CTB accounts for about 16% of the sample near the incident bar and about 1% near the transmitted bar. The crack area ratio is exponentially related to the specimen height. These findings can provide reasonable dynamical CTB strength data selection for underground pillar mining.

Experimental study on stress-strain-strength behavior of cemented tailings backfill with different curing age

In order to understand the changes in the properties of the cemented tailings backfill (CTB) during the curing process. In this paper, the CTB samples with a cement-sand ratio of 1:6 were prepared and cured for 3, 5, 7, 14, 21, 28, 60, 140 and 200 days respectively, and then a series of uniaxial compression tests were carried out. Then the stress-strain relationship, compressive properties, elastic modulus, etc. of the CTB with different curing age were analyzed. Results indicate that when the samples are cured at a short curing age that is shorter than 7 days, CTB mainly shows plasticity, while as the age increases, the samples’ deformation mainly experienced four stages. And as the age increases, the unconfined compressive strength (UCS) and the modulus of elasticity keep increasing, but the growth rate gradually slows down.

Reinforcement effect of polypropylene fiber on dynamic properties of cemented tailings backfill under SHPB impact loading

Dynamic loads such as blasting may lead to diverse levels of failure in cemented tailings backfill (CTB) under diverse strain rates and frequency spectral amplitudes. Hence, changes in dynamic properties of filling due to these loads should be studied as a function of strain rates for CTB mixtures. In this study, the dynamic characteristics of CTB samples containing polypropylene fiber contents were examined with the use of split Hopkinson pressure bar (SHPB) system and high speed photography technology. The experimental results illustrate that the backfill has a damping influence on the elastic wave. The original waveform noise of CTB with fiber is higher than the one without fiber, and the average strain rate changes the reflected waveform. The effect is greater than the impact velocity. Secondly, the dynamic strength of CTB with fiber is higher than the static strength, which obeys a great effect of the strain rate. Meanwhile, the backfill (with fiber) stress-strain characteristics show a ‘double peak’ phenomenon, and the difference between the first and the second peak stresses decreases with increasing fiber content. The failure mode analysis demonstrated that the fiber reinforcement stopped the development of big cracks during the tensile fiber pull-out failure regime. Lastly, the findings of the present study can offer an important reference to the overall design of backfilling regarding the understanding of the good dynamic characteristics and the reduction of operational costs.

Constitutive Modeling of Cemented Tailings Backfill With Different Saturation States Based on Particle Swarm Optimization and Support Vector Machine

Mine tailings disposal has been a serious environmental issue for decades. The wide application of cemented tailings backfill (CTB) technology could indirectly abate tailings pollution by recycling the tailings for backfilling. CTB constitutive modeling helps with design by improving the understanding of its compressive behavior. This study focused on CTB intelligent constitutive modeling considering the coupled effects of the cement content and saturation state. An artificial intelligence model was established and utilized based on particle swarm optimization (PSO) and the support vector machine (SVM). CTB samples with different cement contents and water saturation states were prepared, and unconfined compression tests were conducted to obtain the dataset. We verified the feasibility of using integrated PSO and SVM (P-S) in the CTB constitutive model using experimental data. We analyzed model errors. The results showed that the CTB stress strain curve was complex and nonlinear and could be significantly affected by the saturation states. PSO was feasible and efficient for tuning the SVM hyperparameters. The lowest minimum MSE value of 0.0108 was achieved in the eighth iteration. The PSO and SVM modeling was indicated to be accurate in the CTB constitutive model (a high R-square value of 0.9935 and a low mean squared error value of 0.001664 were achieved on the testing set). This model may accelerate the CTB structure design process.

Strength and deformation behaviors of cemented tailings backfill under triaxial compression

It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB). The influence of cement content, curing age and confining pressure on strength and deformation properties of CTB was examined and discussed. Results indicate that the triaxial compressive and deformation behavior of CTB is strongly affected by the cement content, curing age and confining pressure. The increase in cement content, curing age and confining pressure leads to a change in stress-strain behavior and an increase in the axial strain at failure and post-peak strength loss. The cohesion of CTB rises as the curing age and cement content increase. However, the enhancement in internal friction angle is trivial and negligible. It should be noted that the failure pattern of CTB samples in triaxial compression is mainly along a shear plane, the confining pressure restrains the lateral expansion and the bulging failure pattern is dominantly detected in CTB samples as curing age length and cement content increase. The results will help to better understand the triaxial mechanical and deformation behavior of CTB.

Effect of microwave heating on thermo-mechanical behavior of cemented tailings backfill

Cemented tailings backfill (CTB), which is a mixture of tailings, binder and water, is used to fill underground mined-out areas. Once placed, the CTB is required to provide enough ground support as soon as possible, in order to improve the mining efficiency. A relatively high temperature can accelerate the consolidation of CTB, and microwave radiation can afford a quick temperature rise. Therefore, this study proposed an experimental program incorporating the microwave heating into the conventional curing of the CTB samples. The thermal behavior and strength development of the CTB was investigated, and the CTB deformation under gravity and compression was also evaluated. The obtained results showed that the microwave radiation could significantly increase the CTB temperature. Besides, the microwave heating could either enhance or reduce the mechanical performance of the CTB samples with different curing ages, depending on when the microwave radiation was applied (delay time) and how long it lasted (heating time). This study demonstrates that the microwave technique can definitely be used in mine backfill, for improving the thermo-mechanical performance of the backfill.