Strength Of Backfill Research Articles

Experimental investigation of mechanical, hydration, microstructure and electrical properties of cemented paste backfill

Filling mine goafs with cemented paste backfill (CPB) is an effective approach to protect the ecological environment and alleviate major safety hazards in practice. In this study, using full tailings of the Xianglushan Tungsten Mine as experimental materials, the relationship between compressive strength, hydration products, microstructure, and electrical resistance (ER) of CPB was investigated through macro and micro characterization at different curing times. The results show that under standard curing conditions, the uniaxial compressive strength (UCS) of CPB was the highest at 28d with the tailing to cement ratio (T/C) of 4 and the concentration of 72%. The Weibull average compressive strength was (1.058 ± 0.064) MPa. The mineral composition and chemical types of CPB hydration products at different backfill curing times were quantitatively analyzed using X-ray diffraction (XRD) and standard powder diffraction (PDF) data. Further, the quantitative relationship between hydration product content and strength of backfill was established. The evolution of microstructure, pore characteristics, and electrical characteristics of CPB was investigated by scanning electron microscopy-energy dispersive spectroscopy, nuclear magnetic resonance, and inductance-capacitanceresistance testing (LCR). The results of this work would be helpful for the analysis of strength characteristics and hydration product properties of CPB.

Strength and deformation behavior of cemented foam backfill in sub-zero environment

Mining operations in permafrost or cold region have an urgent need to understand the behavior of frozen cemented foam backfill for its practical application. The aim of this paper is to experimentally investigate the strength and deformation behavior of frozen cemented foam backfill (FCFB) that contains cementitious material, foaming agent and aggregates with different particle size distributions in sub-zero environment (−10 °C). Several techniques have been used to examine the mechanical properties and the microstructure. The experimental results show that the strength and elastic modulus of FCFB increases as the ultra-fine particles content of building stone waste in FCFB increases. With the extended freezing time, FCFB exhibits more ductility due to strain-hardening. The mechanical strength of FCFB has a slighter increment with increased freezing interval time. Freeze-thaw cycles lower mechanical strength by deteriorating the structure. Additionally, FCFB with a higher content of ultra-fine portion presents a higher degree of cement hydration because of more contained unfrozen water, and the significant reduction of hydration rate occurs at an early age due to large amount of water freezing into ice. These findings will provide technical information for the optimal design of cemented foam backfill in cold-region.

Developing a hybrid model of salp swarm algorithm-based support vector machine to predict the strength of fiber-reinforced cemented paste backfill

Developing a hybrid model of salp swarm algorithm-based support vector machine to predict the strength of fiber-reinforced cemented paste backfill

Characterization of early age behavior of cemented paste backfill through the magnitude and frequency spectrum of ultrasonic P-wave

Cemented paste backfill (CPB) is broadly used for underground backfilling, improving the mechanical performance through the modification of its composition and, therefore, its microstructure and characteristics. In order to assess the applicability of ultrasonic waves to better comprehend relations among composition-microstructure-characteristics; an experimental program was realized using the magnitude and frequency spectrum of ultrasonic P-wave which is considered as an effective system for characterizing the hardening processes of cementitious materials. In this study, different binder contents (3, 5 and 7 wt%) and curing temperatures (20 and 35 °C) were tested for investigating CPB’s hardening processes. Silica fume (0, 5 and 20 wt% of binder) was used as an additive in replace of binder to determine its effect on behavior of ultrasonic waves. Component (TG and DTG) and microanalysis (SEM) were adopted to improve the understanding of ultrasonic behavior. Results show that there is a positive relationship between the strength and magnitude of ultrasonic P-wave in CPB, except for the sample with 3 wt% binder. The magnitude and frequency spectrum of ultrasonic P-wave is more sensitive than P-wave velocity to reflect the variation in the backfill strength. Higher binder content can densify the microstructure of CPB with longer curing time and reduce the energy attenuation of ultrasonic P-wave, resulting higher magnitude obtained. The addition of silica fume makes CPB having a finer pore structure enhanced, thereby improving in the strength, P-wave velocity and magnitude. The energy attenuation of ultrasonic P-wave can be notably weakened at a curing temperature of 35 °C due to a dense network formed by both hydration products and tailings. The magnitude and frequency spectrum of ultrasonic P-wave can be capable of reflecting and characterizing the pore structure, hydration processes and water content in CPB comprehensively. Consequently, the proposed technique can be well used to illustrate the hardening processes of CPB and hence improve the understanding of its early-age behavior.

Strength development and microstructural investigation of lead-zinc mill tailings based paste backfill with fly ash as alternative binder

The increasing popularity of paste backfilling demands alternative binder optimisation and bulk waste disposal. This study investigates the efficacy of fly ash (FA) as partial replacement of ordinary portland cement (OPC) for paste backfill application in underground mines. The effect of FA addition on uniaxial compressive strength (UCS) and cohesion of paste backfill are demonstrated. The strength development was correlated with microstructural evolution using scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS). The study revealed that the rate of strength development in paste backfill slowed down when OPC was substituted by FA. However, the targeted 28 days' UCS of 1.1 MPa for the backfilling stope of lead-zinc mine was achieved with binder dosages of 8 wt% OPC, 7 wt% OPC, 6 wt% OPC, 7 wt% OPC +1 wt% FA and 6 wt% OPC +2 wt% FA. Thus, FA is a suitable binder substitute and up to 25% of OPC (8 wt%) can be replaced with FA. Analysis of microstructural evolution in paste backfill revealed that calcium silicate hydrate (C–S–H) did not develop in OPC-FA binder based paste backfill at its early days’ of curing and gypsum was found only in samples with OPC as sole binder. The multiple linear regression analysis on interaction effects of OPC, curing time, FA replacement percentage for 8 wt% and 5 wt% binder groups indicated that the UCS development is more sensitive towards FA replacement. The obtained results would help in better understanding and design of paste backfill for lead-zinc underground mines.

Strength and ultrasonic properties of cemented waste rock backfill considering confining pressure, dosage and particle size effects

It is of great significance to study the material properties of cemented waste rock backfill (CWRB) for preventing mining damages, solving environmental problems and ensuring engineering security. Consequently, this paper carried out the comprehensively factorial tests to investigate the effects of the confining pressure, dosage of cementitious material and particle size distribution (PSD) of aggregate particles on the strength and ultrasonic properties of CWRB, for which the PSD of aggregate particles obeyed Talbot gradation theory. The results show that the relations between the confining pressure and dosage of cementitious material and the compressive strength and ultrasonic pulse velocity (UPV) of CWRB present the positively linear functions. However, the relations between the PSD of aggregate particles and the UPV, compressive strength, cohesive force and internal friction angle of CWRB perform the quadratic functions. It is considered that there is an optimal PSD of aggregate particles in the CWRB for characterizing its optimum material properties, and using the gradation Talbot index for describing that optimal PSD is between 0.4 and 0.6. The microstructure characteristics show that the CWRB with finer PSD of aggregate particles produces more distributions of microvoids and microcracks, while the CWRB with coarser PSD of aggregate particles contains coarser microvoids and microcracks that cannot be completely filled by hydration products and secondary hydration products. However, the dense hydration products can be formed among the particles in the CWRB with a suitable PSD of aggregate particles to reduce these defects. Its mechanism is considered that the superior PSD of aggregate particles can improve the microstructure of CWRB including the scale and distribution of defects, thereby resulting in the improvements of its strength and ultrasonic properties.

Experimental study of strength, pore structure and phase evolution characteristics of iron tailings cemented paste backfill under high-temperature

With the deepening of mining depth, the geothermal temperature faced by the pit backfill is getting higher and higher, so the spontaneous combustion probability of sulfur-bearing minerals increases. In addition, sudden fires can expose the backfill to high temperatures, which will endanger the structural safety of the backfill. Therefore, in order to fully understand the mechanical response and pore structure evolution characteristics of backfills under high-temperature loading, the compressive strength and splitting tensile strength of backfills with different ages: 7 days, 28 days and 60 days and cement-tailings ratios: 1:6, 1:8 and 1:10 were tested using high-temperature furnace to simulate different temperature loads: 100, 200, 400, 600 and 800°C. The pore structure characteristics of the backfill after high temperature are analyzed by mercury intrusion porosimetry. To further understand the mechanism of backfill transformation at high temperature, the phase evolution characteristics of iron tailings and cementitious materials are analyzed by X-ray diffractometer and differential ther-mal/thermogravimetric analyzer. The results show that the strength and pore structure of iron tailings backfi ll at high temperature are related to the curing age. The strength and most probable pore size of backfill cured at 7 days increased fi rst and then decreased with the increase of temperature. Among them, the compressive strength and splitting tensile strength reached their peak values at 200°C and 100°C, respectively. While after 28 days, the pore size increased with the increase of high temperature, and the strength of backfill decreased continuously with increasing temperature. No matter what age of backfill is, it almost loses its tensile strength after being subjected to a high temperature above 400°C. These characteristics are closely related to the expansion of mica in iron tailings and the dehydration and decomposition of cementing material hydration products, such as ettringite and C-S-H phase at high temperature.

A Strength Design Method of Cemented Backfill with a High Aspect Ratio

To calculate the required strength of a cemented backfill with high aspect ratio, the confirmation of lateral pressure is fundamental and needs to be determined first. As for the backfill with a high aspect ratio of height to length, the shape of the slip surface is not straight when in the active state due to the limited space, which is different from the general backfill. For this reason, a formulation of the slip surface with a curved shape and a lateral pressure calculation method based on this curved slip surface were proposed. The proposed equation of the slip surface is affected by the geometry parameters of the backfill, internal friction angle of the backfill, and the friction angle of the backfill‐rock interface. Then, by the combination of the minor principal stress trajectory method and the horizontal slice method, an ordinary differential equation of stresses was established and then solved numerically. Finally, the method based on Mitchell’s three‐dimensional limit equilibrium model was used to calculate the required strength of the cemented backfill. The calculated results were compared with previous studies and validated with numerical models. The results showed good consistency for the backfills with high aspect ratios.

A Hybrid Artificial Intelligence Model for Predicting the Strength of Foam-Cemented Paste Backfill

Foam-cemented paste backfill (FCPB) has become a trend to solve the problem of roof-contacted filling. In order to solve the time-consuming and labor-intensive disadvantages of laboratory uniaxial compressive strength (UCS) tests, a hybrid artificial intelligence model which combines random forest (RF) algorithm and grid search optimizer (GSO) was proposed for FCPB strength prediction. Moreover, the effects of foaming agent on cement hydration and pore structure characteristics were studied. The results showed that GSO can effectively tune the hyper-parameters of the proposed GSO-RF model and the developed model is an efficient and accurate tool to predict the UCS for FCPB. Though the foaming agent will not change the influence trend of cement-tailings ratio, solid content and curing time, the influence degree will be weakened by the foaming agent. The ranking of the relative importance of influencing variables is: cement-tailings ratio > curing time > foaming agent dosage > solid content. In addition, the foaming agent has no significant effect on the hydration of cement. The foaming agent mainly changes the strength by changing the pore structure characteristics (especially the large pore volume). This research can provided some guidance for developing UCS prediction model for FCPB.

Stabilization of backfill using TDA material under a footing close to retaining wall

Reutilization of solid waste such as Tire Derived Aggregate (TDA) and mixing it with soft soil for backfill material not only reduces the required volume of backfill soil (i.e., sand-mining procedures; reinforcement), but also preserves the environment from pollution by recycling. TDA is a widely-used material that has a good track record for improving sustainable construction. This paper attempted to investigate the performance of Kaolin-TDA mixtures as a backfill material underneath a strip footing and close to a retaining wall. For this purpose, different types of TDA i.e., powdery, shredded, small-size granular (1-4 mm) and large-size granular (5-8 mm), were mixed with Kaolin at 0, 20, 40, and 60% by weight. Static surcharge load with the rate of 10 kPa per min was applied on the strip footing until the failure of footing happened. The behaviour of samples K80-G (1-4 mm) 20 and K80-G (5-8 mm) 20 were identical to that of pure Kaolin, except that the maximum footing stress had grown by roughly three times (300-310 kPa). Therefore, it can be concluded that the total flexibility of the backfill and shear strength of the strip footing have been increased by adding the TDA. The results indicate that, a significant increase in the failure vertical stress of the footing is observed at the optimum mixture content. In addition, the TDA increases the elasticity behaviour of the backfill.

Damage constitutive model of stratified cemented backfill based on coupling macroscopic and mesoscopic deformations

The mechanical properties and stress-strain relationship of cemented backfills with different stratified structure have a direct effect on the mining-filling cycle and the mining of adjacent pillars. To obtain the stress-strain evolution curves, the uniaxial compressive strength tests were performed on backfills with stratified numbers of 0, 1, 2 and 3. The deformation of stratified backfill under the compressive load is regarded as a compound of closed deformation of the macroscopic stratified structure and elastic deformation of material. The damage constitutive model of cemented backfills with different stratified structure are established by considering the influence of compacted section. Comparative analysis reveals that the calculated curve based on the established sectional damage constitutive model conforms well to the trial curve. The maximum closed strain of the structural plane has a more significant effect on the mechanical properties of backfill. In the Weibull distribution, with the increase of the parameter m, the peak strength of backfill gradually increases and then reaches to a certain value, and the stress-strain curve gradually becomes steeper, which shows that m is a reflection of the concentration level of micro-unit strength distribution in the backfill..

Effects of chloride on the early mechanical properties and microstructure of gangue-cemented paste backfill

The addition of an early strength agent as an additive in cement-based materials provides several security-related, technical, and economic advantages, such as improving the early strength of the paste and accelerating the cycle frequency of mining and filling. In this paper, we present the results of an experimental investigation of the effects of chloride on the early age (3, 7, and 28 days) strength of gangue-cemented paste backfill (GCPB). The GCPB specimens had an initial chloride concentrations of 0‰, 5‰, 10‰, 20‰, 30‰, and 40‰, and the obtained samples were analyzed by performing uniaxial compressive strength tests, X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results show that chloride significantly affects the early-age strength of GCPB. At early ages, chloride can have positive and negative effects, i.e., the GCPB strength increased with an initial chlorine content of 10‰, while it decreased for GCPB with an initial chlorine content of 40‰. These positive or negative effects depend primarily on the initial concentration of chloride in the GCPB. The key reason for this characteristic is the promotion or suppression of cement hydration by chloride ions. The essential factor that affects the GCPB strength is the relationship between the volume of voids and the amounts of calcium silicate hydrate gel, ettringite, and Friedel's salt formed. These results indicate that it is important to consider the influence of chloride on the early strength of GCPB to improve the self-stabilizing strength of GCPB and the economic benefits of coal mines.

A Novel Prediction Model of Strength of Paste Backfill Prepared from Waste-Unclassified Tailings

Paste backfilling is an important support for the development of green mines and deep mining. It can effectively reduce a series of risks of underground goaf and surface tailings ponds. Reasonable strength of backfill is an effective guarantee for controlling ground stress and realizing safe mining function. Under the combination of complex materials and local conditions, ensuring the optimal design and effective proportion for paste backfill strength is the bottleneck problem that restricts the safety, economy, and efficiency of filling mining. The strength developing trend of paste backfilling prepared from waste rock and unclassified tailings has been studied. Different levels of cement contents, tailings-waste ratios, and slurry concentrations were investigated through orthogonal design to obtain the relationship between the UCS and the multi-influential factors. Combined with the experimental results and the previous strength prediction models, the waste rock-unclassified tailings paste strength prediction model was proposed. Introducing the water-cement ratio, the cement-tailings ratio, the amount of cement, and the packing density that characterizing the overall gradation of unclassified tailings and waste rock, as well as the curing time, a strength prediction model of multifactors was developed. Moreover, the microscopic structure of the paste prepared from waste-unclassified tailings was analyzed with an Environment Scanning Electron Microscope (ESEM), and the influence mechanism was ascertained. The weight coefficient of strength development is carded in this paper, and the strength model of unclassified tailings-waste paste considering five factors is obtained, which is of great significance to guide the mining engineering.

Ultrasonic evaluation of strength properties of cemented paste backfill: Effects of mineral admixture and curing temperature

This paper presents the findings of a research study designed and conducted to investigate the effects of mineral admixture and curing temperature on uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) behavior of laboratory-prepared cemented paste backfill (CPB) samples. A total of 290 CPB samples were prepared at different replacement rates (10–80%), cured at various temperatures (10–50 °C), and respectively subjected to both UPV and UCS testing after curing times of 3, 7, 14, 28, 56 and 90 days. The obtained experimental results show that the addition of fly ash (FA) can lead to an increase or decrease trend in UCS and UPV behavior of CPB samples, depending on the replacement level of admixtures. There is a competition between the strength-increasing factor (micro-filler effect of FA) and strength-decreasing factor (lower amount of cement hydration products induced by replacement ratio). Both UPV and UCS are found to decrease with increasing blast furnace slag (Slag) replacement level mainly attributable to its low pozzolanic reactivity. Besides, the curing temperature has a significant influence on UCS and UPV behavior, depending on the curing time. Results also suggest that UPV is less sensitive to the variation in the admixture dosage and curing temperature than UCS. As a result, there exists a clear linear relationship between UPV and UCS behavior of both CPB samples prepared with FA and/or Slag admixtures, and CPB samples tested at each curing temperature. The main findings of this research study suggest that the UPV test can be reliably used for predicting CPB’s strength properties, saving money and time to mine operators.

Influence of temperature on compressive strength, microstructure properties and failure pattern of fiber-reinforced cemented tailings backfill

With the increase of mining depth, the geothermal temperature in deep stopes has becomes one of the significant factors affecting the mechanical strength and stability of cemented tailings backfill (CTB). This experimental study investigates the influence of curing temperature (20, 35 and 50 °C) on compressive strength, microstructure properties and failure pattern of fiber-reinforced cemented tailings backfill (FCTB). A series of unconfined compressive strength (UCS) and microstructural tests were conducted on FCTB specimens that are cured for 3, 7 and 28 days and prepared with different polypropylene (PP) fiber content (0.00%, 0.05%, 0.15%, 0.25% by the total mass of tailings and cement), respectively. The obtained results show that PP fibers and curing temperature effectively improve the unconfined compressive strength (UCS) of FCTB. The UCS values increase with the increase of fiber content, but decreases when there is 0.15% fibers by weight regardless of curing temperature. For a given fiber content, a higher temperature results in decreased porosity, thus the strength of FCTB specimens is increased. Moreover, fibers result in the transformation of the FCTB specimens from a relatively brittle to ductile failure state, which contributes to the mechanical stability of CTB structure. And, with higher fiber content, the brittleness of the FCTB specimens is reduced and ductility enhanced obviously. Mixing fibers can retard the propagation of cracks, constrain the deformation and improve the integrity of CTB structure, and thereby prevent ore dilution induced by the destabilization failure backfill in field stope, which provides a potentially economic method to reduce ore dilution for deep mines.

Experimental study on strength of cemented rock-tailings backfill

Waste rock tailings cementation filling is a filling technique that effectively disposes waste rock and tailings in mines, saves energy, and reduces costs. This paper systematically studies the cementation and filling strength of waste rock tailings. The relationship between compressive strength, shear strength and content ratio of waste rock and tailing sand, cement-sand ratio, concentration parameters and the variation of strength were analyzed by orthogonal test. Sensitivity analysis of factors affecting strength of backfill is conducted using extreme range in data process. Then the order of sensitivity is obtained as content ratio of waste rock and tailing sand > cement-sand ratio > concentration, the relationship between factor and strength is established and the optimal mixing proportion of materials is found. It provides the basis for the filling process design.

Impact of Temperature on the Strength Development of the Tailing‐Waste Rock Backfill of a Gold Mine

This study investigated the influencing rules of curing temperature (5, 10, 16, and 20°C), cement ratio (8%, 10%, 12%, and 14%), and mass concentration (70%, 73%, 74%, and 75%) on the strength of backfill. In addition, a scanning electron microscope (SEM) is employed to analyze the microtopography of the backfill. Experimental results indicate that the uniaxial compressive strength (UCS) of the backfill decreases as the curing temperature diminishes; temperature substantially influences the earlier strength of backfill (it is much significant below 10°C). In addition, as the cement ratio rises, the critical point for the impact of temperature on strength gradually moves toward a low‐temperature zone; in pace with the slurry mass concentration increase, the compressive strength of the backfill also rises and its rate of increase enlarges after going beyond the critical concentration. In case the curing temperature is lower than 10°C, the extent of hydration is also low inside the backfill. Through experiments, the critical concentration of slurry in the Jinying gold mine is determined as 73%, and the critical interval of the cement ratio ranged between 10% and 12%. Corresponding measures can be taken to increase the strength of backfill in the Jinying Gold Mine by 129.9%. As a result, backfill collapse is effectively controlled.

Mechanical Response and Parametric Sensitivity Analyses of a Drainage Pipe under Multiphysical Coupling Conditions

Current research was not dedicated to investigate the mechanical behavior of a concrete drainage pipe under multiphysical coupling conditions of overburden pressure, traffic loads, groundwater, and pipe fluids. This study proposes a new numerical solution method for coupled stress, seepage, and flow fields based on a validated finite element model. The model was developed by ABAQUS and FLUENT and then solved simultaneously using the MpCCI (mesh‐based parallel‐code coupling interface) platform. Results show that the tensile stress at the springline and the radial displacement at the crown (or invert) of the bell under the effect of groundwater alone were reduced by 50.5% and 38.1%, respectively, compared to the effect of traffic load alone. Parametric analyses show that vehicle speed and fluid height have a slight impact on the pipes. The soil cover depth, wheel pressure, and gasket strength are directly proportional to the pipe stress and vertical displacement. Within the scope of their respective changes, the pipe stresses were increased by 34.4%, 36.7%, and 28.5%, and the vertical displacements were increased by 124%, 95.85%, and 87.7%. The bedding and backfill strengths are proportional to the pipe stress and inversely proportional to the vertical displacement. Within the scope of their respective changes, the pipe stresses were increased by 18.2% and 20.0%, and the vertical displacements were decreased by 11.4% and 10.4%. Sensitivity analyses show that soil cover depth has a greatest impact on the pipe, followed by traffic load.

Backfilling Mixture Preparation Using Milled Granulated Blast-Furnace Slag

Backfilling mixture preparation technology using a cement-slag binder is developed for the Artem’evsky mine. It is shown that backfill with granulated blast-furnace slag reaches project strength at its fineness 80% of content milled down to -80 urn size. The authors analyze influence of milling fineness of granulated blast-furnace slag from different manufacturers on strength and rheological properties of backfill. The economic analysis of cost of binder in formation of load-bearing layer of backfill prepared using fly ash and milled granulated blast-furnace slag is performed.

Prediction of Mechanical Strength Based on Deep Learning Using the Scanning Electron Image of Microscopic Cemented Paste Backfill

The mechanical strength of cemented backfill is an important indicator in mining filling. To study the nonlinear relationship between cemented paste backfill (CPB) and mechanical response, a deep learning technique is employed to establish the end-to-end mapping relationship between the scanning electron microscope (SEM) images and mechanical strength. A seven-layer convolution neural network is set up in the experiment, and the relationship between the SEM image and mechanical strength is established. In addition, the difference between the measured and predicted values is calculated and the mean and variance of the error are analyzed. The average accuracy of the mechanical strength prediction is found to be 8.28%. Thus, the proposed method provides a new technique for the quantitative analysis of mechanical strength of microscale CPB.