Crushed Waste Rock Research Articles

Experimental Study and Mathematical Description of Gradation Effect on the Mechanical Characteristics of Crushed Waste Rocks

Crushed waste rocks, generated from mining operations, have been widely used for mining infrastructure constructions such as haul roads because of their low cost, high strength, and availability. Crushed waste rock gradation can, however, vary greatly, depending on blasting, mineralogy, and crushing process, but it is a key factor influencing the mechanical properties of crushed waste rocks (including resilient modulus, permanent deformation, and shear strength). Gradation should therefore be optimized to enhance their performance in the field. A series of repeated load and monotonic triaxial tests were carried out on crushed waste rocks with different gravel-to-sand (GS) ratios and fines contents (FC). Results showed that the optimum GS ratio was between 1 and 1.5 and contributed to provide higher resilient modulus and shear strength, and lower permanent strain. An increase in FC could, to the contrary, result in the decrease of resilient modulus and permanent strain and also a significant increase in shear strength. The structure state of crushed waste rocks was quantified using the cm model, and the mechanical properties of crushed waste rocks were dominated by sand and fines when the content of sand and fines was higher than 80%, while it was dominated by gravel particles as the content of sand and fines was lower than 60%. Here, the MR − θ model and the Rahman and Erlingsson model (extended using time-hardening approach) were well adapted to describe resilient modulus and accumulated permanent strain, respectively. Prediction models were also developed based on correlation analyses to predict the resilient modulus and permanent strain of crushed waste rocks based on gradation parameters.

Influence of particle size distribution on fractal characteristics of waste rock backfill materials under compression

Broken waste rock as backfill materials is filled into the underground goaf and will encounter particle breakage under the overburden pressure. The damage degree of the crushed waste rock materials directly affects the compression properties of the backfill body and the control effect of strata movement and surface subsidence. Fractal theory can be used to quantify the breakage degree of waste rock particles. In this study, compression tests are carried out on the broken waste rock materials with different particle size distributions to investigate the influence of the particle size distribution on the fractal characteristics of waste rock backfill materials under compression. The results show that the waste rock specimens with discontinuous size grading and containing more coarse particles have higher stress when entering the stable deformation stage, larger strain if at the same stress level and larger breakage ratio after compression. The particle size distribution of the crushed waste rock specimens after compressive loading has superior fractal characteristics and the fractal dimension increases with the content of fine particles and decreases significantly under discontinuous size grading. The fractal dimension has significant negative exponential function regression relationship with the strain and the breakage ratio. The strain and the breakage ratio decline with the growing fractal dimension. If the waste rock specimens have continuous particle size gradation and higher content of fine particles, the fractal dimension, the strain and the breakage ratio of the waste rock backfill materials tend to be optimal and stable, proving a desirable initial particle size distribution of the waste rock backfill materials.

Estimation of permanent deformation behaviour of crushed waste rocks using multistage repeated load triaxial and CBR tests

ABSTRACT Crushed waste rocks (CWR) are widely used to build mine haul roads. However, the permanent deformation in waste rocks layers can result in surface rutting. Realistic prediction of pavement rutting requires models that can accurately capture the permanent deformation behaviour under repeated loading. However, such models are usually based on advanced laboratory apparatus such as multistage (MS) repeated load triaxial (RLT) tests. In this study, a new approach, using MS repeated load California Bearing Ratio (RLCBR) tests, was proposed to estimate the permanent deformation behaviour of CWR. MS RLCBR tests are faster, easier and more often available than MS RLT tests. A series of MS RLCBR and MS RLT tests for different stress levels were therefore carried out on the same material to characterise CWR permanent deformation behaviour. Results showed that Rahman and Erlingsson model that modified by time hardening approach could satisfactorily capture CWR permanent deformation behaviour for MS RLT tests. A new model was proposed and fitted on MS RLCBR test results to predict CWR permanent deformation behaviour. This model performed well in describing MS RLCBR test results and predicting the CWR permanent deformation behaviour. Results indicate that MS RLCBR tests could be an effective alternative to MS RLT tests for estimating the permanent deformation behaviour of CWR.

Experimental Investigation and Prediction of the Permanent Deformation of Crushed Waste Rock Using an Artificial Neural Network Model

Experimental Investigation and Prediction of the Permanent Deformation of Crushed Waste Rock Using an Artificial Neural Network Model

Effect of freeze–thaw and wetting–drying cycles on the CBR, shear strength, stiffness and permanent deformation of crushed waste rocks

Waste rocks produced from mining operations are widely reused for the construction of mine haul roads. However, seasonal changes expose mining facilities to repeated freeze–thaw and wetting–drying cycles which can significantly affect the geotechnical characteristics of the materials in situ. In this study, cyclic and monotonic triaxial and California bearing ratio (CBR) tests were conducted to measure the geotechnical properties of crushed waste rocks subjected to freeze–thaw and wetting–drying cycles. Results showed that freeze–thaw cycles caused a reduction of the resilient modulus and shear strength, and an increase of the permanent deformation. A greater water content during freeze–thaw cycles resulted in a significant increase of the permanent deformation. Wetting–drying cycles could contribute to increase the stiffness, CBR and permanent deformation of crushed waste rocks. Predictive models were also developed to estimate the effect of freeze–thaw cycles on resilient modulus and permanent deformation.

Prediction of CBR and resilient modulus of crushed waste rocks using machine learning models

Prediction of CBR and resilient modulus of crushed waste rocks using machine learning models

Effect of gradation, compaction and water content on crushed waste rocks strength

We reduced the size of the abstract to 170 words, but we cannot go lower without loosing meaning. We hope it will be ok like this --> Open-pit mining operations generate large volumes of waste rocks. It can be both economically and environmentally attractive to valorise waste rocks in mining infrastructures such as haul roads. However current practice usually consists of using waste rock directly, without any preparation or selection, thus frequently resulting in punctures, dust generation and low durability. The aim of this study was therefore to determine optimal geotechnical properties of crushed waste rocks for use in surface course layer. Crushed waste rocks were characterised in the laboratory. Their strength was evaluated using California Bearing Ratio (CBR) tests. Several compaction energies were used, and he effect of maximum particle size, fines content, and dry density on the strength were assessed. Results showed that these parameters had a significant impact on the performance of the material. The strength was maximum for an optimum FC of around 10%, a high density and in the presence of coarser particles. Two regression models were also proposed to predict the CBR value of crushed waste rocks based on their physical properties.

Study on the possibility of using artificial pillar to replace the protection coal pillar of the preparation roadways during the mining process at underground coal mines in Quang Ninh region, Vietnam

The coal reserves in protection pillar of roadways are expected to be left in the mining processin underground mines in Quangninh coal basin which is relatively large (about 16% of the total reserves).If it can be exploited, it will help to save non-renewable coal resources, reduce the cost of preparingroadway meters, extend the mine life and increase the efficiency of construction investment. In the world,in order to reduce coal loss in protection pillar of roadways, mining technology to exploit and use artificialprotection pillars are quite popular. Accordingly, in order to simultaneously exploit coal in the protectionpillar and maintain the transport roadway as a ventilation roadway for the longwall in below level, thepost-mining coal pillar will be replaced by artificial pillars formed from the stone backfill cribs, columns,metal cribs, chemical materials or low-grade concrete mortar mixes formed from fly ash, bottom ash ofthermal power plants, combined crushed waste rock and a cement additive,... This paper will evaluate thepossibility and propose a number of mining technological scheme as well as the type of constructionmaterials suitable for artificial columns.

Deformation Behaviour of Crushed Waste Rock Under Lateral Cyclic Loading

Deformation Behaviour of Crushed Waste Rock Under Lateral Cyclic Loading

A black‐box automated approach to calibrate numerical simulations and optimize cover design: Application to a flow control layer constructed on an experimental waste rock pile

AbstractMining operations often produce large volumes of waste rock to access economically valuable mineralized zones. Waste rock is usually stored in surface piles, the construction and reclamation of which represent a challenge for the industry. A flow control layer (FCL) made of crushed waste rock or sand and constructed on top of each waste rock bench could contribute to control water infiltration, thus improving waste rock pile stability and limiting contamination. An experimental waste rock pile was built and instrumented at the Tio mine (Rio Tinto Fer et Titane, Canada) to evaluate the performance of an FCL in field conditions. Large infiltration tests and rainfall monitoring were carried out, and measured outflow and water contents were used to calibrate numerical simulations. However, data were noisy and sometimes incomplete, and the models were difficult to calibrate. A new automated calibration approach was therefore proposed. An algorithm was developed to automate the numerical simulation calibration, using a black‐box method that involves solving an optimization problem on a function without an analytic form. The approach was applied on measurements obtained from large‐scale infiltration tests and validated using 2 yr of field monitoring data. Finally, the automated approach was adapted to optimize the design of the FCL, and an optimal design (material properties and layer thickness) was recommended based on local climate conditions. The proposed automated method could contribute to reduce the bias induced by manual calibration and allows for rapid multivariable calibration and optimization for a broad spectrum of mine waste cover system applications.

Estimation of resilient behavior of crushed waste rocks using repeated load CBR tests

Crushed waste rocks (CWR), generated from mining operations, have been widely used for the construction of mine haul roads because of their low-cost, high-strength, and availability. Resilient modulus is a necessary input to mechanistic design for mine haul roads, but its determination usually requires advanced and complex equipment such as repeated load triaxial (RLT) test. Repeated load CBR (RLCBR) tests are simpler and more often available, and were therefore investigated in this study to estimate CWR resilient behavior under low and high stress levels. RLCBR equivalent modulus calculated using various equations were validated using RLT resilient modulus. The MR-θ model showed good representation and prediction of CWR resilient behavior under both low and high stress levels. A new equation was also proposed to predict more precisely the equivalent modulus of CWR based on RLCBR tests. Results showed that the impact of loading frequency and waveform was limited, while the measured equivalent modulus increased significantly with contact stress (especially when contact stress < 10%). The effect of dry density and soaking on equivalent modulus was negligible, but specimen drying resulted in a marked increase of the equivalent modulus. The good agreement between RLCBR equivalent modulus and RLT resilient modulus indicates that RLCBR tests could be an effective alternative to RLT tests to estimate resilient behavior of CWR used in mine haul roads.

Fiber Optic Measurements of Soil Moisture in a Waste Rock Pile.

The design and construction of a waste rock pile influences water infiltration and may promote the production of contaminated mine drainage. The objective of this project is to evaluate the use of an active fiber optic distributed temperature sensing (aFO-DTS) protocol to measure infiltration and soil moisture within a flow control layer capping an experimental waste rock pile. Five hundred meters of fiber optic cable were installed in a waste rock pile that is 70 m long, 10m wide, and was covered with 0.60 m of fine compacted sand and 0.25 m of non-reactive crushed waste rock. Volumetric water content was assessed by heating the fiber optic cable with 15-min heat pulses at 15 W/m every 30 min. To test the aFO-DTS system 14 mm of recharge was applied to the top surface of the waste rock pile over 4h, simulating a major rain event. The average volumetric water content in the FCL increased from 0.10 to 0.24 over the duration of the test. The volumetric water content measured with aFO-DTS in the FCL and waste rock was within ±0.06 and ±0.03, respectively, compared with values measured using 96 dielectric soil moisture probes over the same time period. Additional results illustrate how water can be confined within the FCL and monitored through an aFO-DTS protocol serving as a practical means to measure soil moisture at an industrial capacity.

The effects of high temperature on the compaction behaviour of waste rock backfill materials in deep coal mines

To study the mechanical properties of backfill materials during compaction at high ground temperature in deep backfill mining, the WAW-1000D electro-hydraulic servo universal machine was used to conduct compaction testing of crushed sandstones heated to different temperatures. The stress–strain curves of crushed sandstones with four particle sizes heated to different temperatures were obtained. In this way, this study analysed the influence of temperature on the stress–strain relationship, porosity changes, and deformation mechanisms during the compaction of crushed sandstones. The experimental results demonstrate the following: (1) At the same particle size, with increased heating temperature, the strain in crushed waste rock decreased at a given applied stress. (2) After heating to the same temperature, the final strains in crushed waste rock samples of different particle size distributions decreased with particle size. (3) As heating temperature increased, the porosities of crushed waste rock samples heated to 100 °C, 200 °C, 300 °C, and 25 °C are ranked thus (in descending order) at the same stress. (4) After compaction of the samples at 25 °C, the number of large blocks decreased, while that of smaller blocks increased slightly. After compaction of heated samples of crushed waste rock, the amount of large blocks gradually reduced, while that of medium- and small-sized blocks gradually increased with increasing temperature. The temperature affects the deformation mechanisms during compaction of the samples of crushed waste rock, thus affecting their stress–strain relationships and porosity.

Calculation and monitoring analysis of stress distribution in a coal mine gob filled with waste rock backfill materials

Crushed backfill materials are used to backfill the gob during solid backfill mining (SBM). Thus, the stress distribution in the coal mine gob is different from that found when using other methods including caving and paste backfill mining. The compaction properties of crushed waste rock backfill materials (WRBM) with different particle sizes were tested using a test machine and a self-made compaction device in order to analyze the stress distribution in the coal mine gob. Moreover, based on the stress-strain relationship for such WRBM, a method for calculating the stress distribution in a gob filled with backfill materials was proposed and a stress calculation model was established. In addition, taking engineering practice as a case study, stresses in the gob of an SBM-worked panel were calculated, measured on site, and analyzed. The calculated result is consistent with that measured on site, thus verifying the feasibility of the research. In addition, the influences of four primary factors including backfill material particle size, mining height, mining depth, and coal seam dip angle on the stress distribution in the gob were analyzed.

Recycling of crushed waste rock as backfilling material in coal mine: effects of particle size on compaction behaviours.

Crushed waste rocks can be used as materials for backfilling goafs, so as to achieve the simultaneous goals of processing solid waste and controlling surface subsidence; however, particle size distribution directly affects the compaction of crushed waste rocks. Therefore, by employing a self-designed bidirectional loading test system for granular materials, this study tested compaction characteristics of crushed waste rocks with four different particle size distributions. Moreover, this research tested the changes of parameters in lateral and axial loading of crushed waste rocks and analysed the influence of particle size distribution on lateral strain, axial strain, porosity, lateral stress, and lateral pressure coefficient during compaction. The test results show that (1) particle size distribution affects porosity, strain, and lateral pressure coefficient of crushed waste rocks under lateral and axial loading. (2) For the samples under particle size distribution ranging from 0 to 10mm, the initial porosity is low and deformations are small under axial loading, so that particles can make contact and bear effective stress in grain-grain contact. Therefore, more stress is transferred to the lateral direction. (3) After compaction, the curves of the samples of crushed waste rocks under four particle size distributions all shift upwards in comparison with those before compaction, indicating that particles are crushed and the proportion of small particles constantly increases. (4) A reasonable particle size distribution can significantly improve stress characteristics, reduce crushing of particles in the samples, and increase the stiffness of the samples, so as to achieve better compaction effects.

Effect of Cyclic Lateral Loading on the Compaction Behaviour of Waste Rock Backfill Materials in Coal Mines

Crushed waste rock (CWR) can be used as backfill for goafs allowing disposal of solid waste and control of surface subsidence. Waste rocks for backfilling (WRBs) have a certain density before use if cyclic lateral loads are applied to CWRs, therefore, by employing a self-designed bidirectional loading test system for granular materials, the influence of the number of lateral loading cycles on the compaction characteristics of WRBs was explored. Through testing, changes in mechanical parameters of WRBs during lateral and axial loading were attained to analyse the influence of lateral loading on lateral strain, axial strain, porosity, and lateral pressure coefficient during their compaction. The test results showed that: (1) the lateral loading exerted a significant influence on the porosity, strain, and lateral pressure coefficient of crushed WRBs during lateral and axial loading; (2) under lateral load, the more cycles of lateral loading applied, the greater the lateral strain and the reduction in lateral porosity of samples; (3) during axial loading, for samples subjected to multiple cycles of lateral loading, owing to the porosity of WRBs having been decreased in advance to improve their density, the final axial strain was low; (4) after compaction, the particle size distributions of CWR samples after different numbers of cycles (1, 3, 5 and 7) of lateral loading all shifted upwards compared with those obtained before compaction, implying that rock particles were crushed. However, the number of cycles of lateral load did not affect crushing of particles before, and after, compaction.

Influence of Lateral Loading on Compaction Characteristics of Crushed Waste Rock Used for Backfilling

Crushed waste rock can be used as backfill in goafs to allow re-use of otherwise solid waste and to control surface subsidence. If a certain lateral stress is applied to crushed waste rocks beforehand, they are densified. Therefore, this research investigated the effects of lateral stress on compaction characteristics of waste rocks for backfilling by utilising a self-designed bidirectional loading test system for granular materials. Furthermore, this study tested the changes in the mechanical parameters on lateral and axial loading of waste rocks for backfilling and measured the influence of lateral stress on lateral strain, axial strain, porosity, and lateral pressure coefficient during compaction. The test results demonstrate that (1) lateral stress affects porosity, strain, and the lateral pressure coefficient of crushed waste rocks for backfilling in lateral and axial loading. (2) In lateral loading, the greater the lateral stress, the larger the lateral strain and the reduction in lateral porosity. (3) Under axial loading, for the samples on which a high lateral stress is applied, because the porosity of waste rocks is decreased in advance, the density increases, thus finally resulting in a lower axial strain. (4) After compaction, the particle size distributions of the samples of the crushed waste rocks under four lateral stresses all shift upwards compared with those before compaction, implying that particles are crushed. However, lateral stress does not reach the crushing strength of waste rock particles, which exerts only a small influence on the crushing of particles before and after compaction.

Application of Quebec recycling guidelines to assess the use feasibility of waste rocks as construction aggregates

The mining industry generates large volumes of solid wastes, which are potentially suitable for recycling in the construction sector. Serious issues are mostly connected to the sustainable management of these wastes from a technical, environmental and policy levels. In the present study, the recycling potential of gold mining waste rocks as construction materials has been investigated according to Quebec (Canada) recycling guidelines of non-hazardous inorganic wastes based on a scientific point of view. Waste rocks were collected from a gold mining site (Quebec, Canada) and prepared using crushing and sieving methods. Acid generation potential, chemical analysis, mineralogy and pollution potential of waste rocks were assessed. Concrete mixtures were then prepared using crushed waste rocks and their mechanical performances and environmental properties were evaluated. The results showed that waste rocks sample contains 46% of coarse material similar to the normalized concrete aggregates. The toxicity characteristic leaching procedure (TCLP) highlighted the nonhazardous character of the studied gold waste rocks. The concentrations of leached pollutants were significantly lower than the limits fixed by the environmental protection agency (US-EPA). The same sample is classified as non-acid generating material. Considering the measured technological and environmental properties, concretes with good mechanical performances could be manufactured using gold mining waste rocks.

Atmosphere Interaction and Capillary Barrier in Filtered Tailings

The filtered tailings technology consists in reducing the water content of tailings ahead of their final disposal and later storing them in stacks with no containment structures. Since the stability of the waste storage facility (WSF) partly relies on the increase of strength due to suction, the unsaturated condition should be always preserved. Therefore, limiting the water content by the time of burying the tailings under the next lifts of the stack and preventing the infiltration of rainfall water into the already buried tailings becomes essential. This paper presents two field column tests performed with the Casposo Mine tailings material. The initial desiccation process and the effects of a number of rainfall events at the actual mine site conditions were observed during a period of 14 months. The columns were 1 m high and the water content was monitored at five different depths. In one of the columns, a gravel layer made of crushed waste rock was intercalated between tailings layers, simulating the layered structure of the actual WSF. In this case, capillary barrier effect developed at the tailings layer-waste rock interphase. This effect is availed in the WSF design for preventing the infiltration of rain water into the lower layers, keeping it close to the deposit top surface for ease of evaporation and preserving the unsaturated condition of the deposit. The water storage capacity of the top tailings layer is evaluated, both analytically and experimentally, in order to study how likely would be the infiltration of water into the deep layers of the deposit.

Effect of Particle Size on the Energy Evolution of Crushed Waste Rock in Coal Mines

Effect of Particle Size on the Energy Evolution of Crushed Waste Rock in Coal Mines