Strength evolution and deformation behaviour of cemented paste backfill at early ages： Effect of curing stress, filling strategy and drainage

In this study, a pressure cell apparatus is developed to investigate the early age evolution of the strength and deformation behaviour of cemented paste backfill(CPB) when subjected to various loading conditions under different curing scenarios. The different curing scenarios that are simulated include:(1)drained and undrained conditions,(2) different filling rates,(3) different filling sequences, and(4) different curing stresses. The findings show that drainage, curing stress, curing time and filling rate influence the mechanical and deformation behaviours of CPB materials. The coupled effects of consolidation, drainage and suction contribute to the strength development of drained CPB subjected to curing stress. On the other hand, particle rearrangement caused by the applied pressure and suction development due to self-desiccation plays a significant role in the strength gain of undrained CPB cured under stress.Furthermore, curing stress induces slightly faster rate of cement hydration, which can contribute to strength acquisition.

Investigation of the short-term stress distribution in stopes and drifts backfilled with cemented paste backfill

Cemented paste backfill(CPB) is largely used in underground mines worldwide.A key issue associated with application of CPB is to estimate the stresses in backfilled stopes and on barricades.Recent numerical and experimental results show that arching effect is absent shortly after the placement of CPB in stopes.However,stress decreases in barricade drift with increasing distance between the measurement points and drawpoint have also been observed,demonstrating arching effect shortly after the pouring of CPB.To explain these paradoxes,CPB is considered as Bingham fluid having a yield shear stress.Three dimensional analytical solutions are proposed to evaluate the short-term total stresses in backfilled stopes and on barricades,accounting for the CPB's yield shear stress-induced arching effect.Stress diminution due to such arching effect in the backfilled stopes and on barricades is indeed obtained.But the reduction becomes insignificant using typical yield shear stress and stope geometry.More analyses indicate that the typical yield shear stress values do not fully correspond to field conditions where the yield shear stress would increase exponentially due to apparent consolidation(loss of water by drainage,a phenomenon similar to the desiccation of overly saturated fine-grained materials).

High strain rate compressive strength behavior of cemented paste backfill using split Hopkinson pressure bar

The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinson pressure bar(SHPB)was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4,0.8,and 1.2 MPa.And the failure modes were determined by macro and micro analysis.CPB with different cement-to-tailings ratios,solid mass concentrations,and curing ages was prepared to conduct the SHPB test.The results showed that increasing the cement content,tailings content,and curing age can improve the dynamic compressive strength and elastic modulus.Under an impact load,a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading.And the dynamic compressive strength of CPB has an exponential correlation with the strain rate.The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading.The local damage was enhanced,and fine cracks were formed in the interior of the CPB.This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.

Physical model investigation on effects of drainage condition and cement addition on consolidation behavior of tailings slurry within backfilled stopes

Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes.This process requires a good understanding of self-weight consolidation behaviors of the tailings slurry within practical stopes,where many factors can have significant effects on the consolidation,including drainage condition and cement addition.In this paper,the prepared tailings slurry with different cement contents(0,4.76wt%,and 6.25wt%)was poured into1.2 m-high columns,which allowed three drainage scenarios(undrained,partial lateral drainage near the bottom part,and full lateral drainage boundaries)to investigate the effects of drainage condition and cement addition on the consolidation behavior of the tailings slurry.The consolidation behavior was analyzed in terms of pore water pressure(PWP),settlement,volume of drainage water,and residual water content.The results indicate that increasing the length of the drainage boundary or cement content aids in PWP dissipation.In addition,constructing an efficient drainage boundary was more favorable to PWP dissipation than increasing cement addition.The final stable PWP on the column floor was not sensitive to cement addition.The final settlement of uncemented tailings slurry was independent of drainage conditions,and that of cemented tailings slurry decreased with the increase in cement addition.Notably,more pore water can drain out from the cemented tailings slurry than the uncemented tailings slurry during consolidation.

Investigation of the Effect of Using Different Fly Ash on the Mechanical Properties in Cemented Paste Backfill

In the cemented paste backfill(CPB)method,which can also be used for fortification purposes in mines,different additive materials with pozzolanic properties can be employed as substitutes instead of cement that is the main binder.One of the most popular pozzolanic materials that can be employed instead of cement is fly ash,which is thermal power plant tailings.But the compositions of fly ash and tailings used in high amounts in the CPB method,as well as the chemical structures that these materials form by interacting with the cement binder,affect the mechanical properties of the material depending on time.In this study,fly ash with 4 different chemical compositions(TFA,SFA,YFA,and CFA)was used as a cement substitute in CPB.By substituting fly ash with different chemical compositions in different proportions,CPB samples were created and their strength was elucidated according to 28,56,and 90-day curing times.The results of the study revealed that TFA with the highest CaO/SiO_(2) and SO_(3) ratios remained stable at the strength values of 6 MPa(total 9% binder)and 10 MPa(total 11% binder)in the long term.However,CFA with the lowest CaO/SiO_(2),SO_(3),and the highest SiO_(2)+Al_(2)O_(3)+Fe_(2)O_(3) ratios resulted in the greatest strength increase at a 20%substitution rate(11% of the total binder).Nevertheless,it was found that the SFA,which is in Class F,increased its strength in the early period based on the CaO rate.

Numerical simulation on thermal accumulation of cemented tailings backfill

Based on the collaborative exploitation of deep mineral resources and geothermal resources, the thermal accumulation process of cemented tailings backfill(CTB) was studied by numerical simulation. The effects of thermal accumulation time, slurry proportions and temperature conditions on the thermal accumulation of backfill are analyzed, the influence of the heat conduction between backfill and surrounding rock, the heat convection between backfill and airflow on thermal accumulation were compared simultaneously. The results show that the total thermal accumulation capacity increases by approximately 85% within 10-90 d. The influence of surrounding rock temperature and initial temperature on total thermal accumulation capacity is more significant and it is approximately 2 times of the influence of slurry proportions under the conditions of this study. It is clear that the rise of surrounding rock temperature and the decrease of initial temperature can improve the thermal accumulation capacity more effectively. Moreover, the heat conduction accounts for a considerable proportion in the process of thermal accumulation, the average heat conduction capacity is approximately 25 times of the heat convection capacity. This study can provide the theoretical basis and application reference for the optimization of thermal accumulation process of CTB in the exploitation of geothermal resources.

Mill tailings based composites as paste backfill in mines of U-bearing dolomitic limestone ore

This paper elaborates on the development of paste backfill using mill tailings generated during the processing of a uranium ore deposit hosted in dolomitic limestone. The tailings have been characterized in terms of the physical, chemical and mineralogical properties. Time-dependent rheological behaviors and geotechnical properties of cemented paste backfill(CPB) are also determined. The studies show that the mill tailing has the potential to form paste and the CPB has adequate strength to provide support to mine pillars, roofs, and walls.

Chemically induced changes in the geotechnical response of cementing paste backfill in shaking table test

Cemented paste backfill(CPB)is extensively used for underground mine support and/or tailings management.However,CPB behavior under cyclic loadings might be affected by the chemistry of its porewater,which often contains sulphate ions.Till today,no studies have addressed the effect of sulphate on the response of CPB to cyclic loadings by using shaking table technique.This study presents new findings of assessing the effect of the sulphate in the pore water of CPB on its geotechnical response to cyclic loading by using shaking table.CPB mixtures were prepared(with and without sulphate),poured into a flexible laminar shear box,cured to 4 h,and then exposed to cyclic loading using one-dimensional(1D)shaking table.Several parameters(e.g.pore water pressure,settlement,lateral deformation,acceleration,electrical conductivity,effective stress,and liquefaction susceptibility)were monitored or determined before,during,and after shaking.Obtained results indicate that the sulphate-bearing CPB cured to 4 h can be prone to liquefaction under the studied conditions.However,sulphate-free CPB samples are resistant to liquefaction.These results are expected to contribute to a better understanding of the effect of water chemistry on the cyclic behavior of CPB,consequently enhancing the cost-effective design of CPB structures.

Key theory and technology of cemented paste backfill for green mining of metal mines

To reduce or eliminate environmental damage during mining processes,green mining practices have emerged as a focal point in China's metal mining research.Cemented paste backfll technology plays a pivotal role in promoting green mining within the metal industry.The technology allows safely backflling of surface tailings into underground mining airspaces,effectively addressing the challenges associated with tailings storage and underground goaves.In this paper,we introduce the paste rheology theory system,which forms the theoretical backbone of cemented paste backfll.We delve into key technologies such as paste thickening,mixing,transportation,and the use of economical,low-carbon materials.Additionally,we analyze macro and micromechanical properties,in-situ performance monitoring,barricade construction,intelligent control,and numerical simulations of the process.We establish several demonstration projects,both domestic and international,that utilize cemented paste backfill technology to foster greener mining practices.Cemented paste backfill technology is widely used all over the world.It has evolved from its initial stages to being recognized as an advanced application by various ministries and commissions:Ultimately,we propose future research directions for cemented paste backfill technology in the context of eco-friendly metal mining.These perspectives encompass theory,technology,equipment,and mode,which can strongly contribute to the sustainability of the mining industry in China.

Temperature variation characteristics in flocculation settlement of tailings and its mechanism

Rapid flocculation and settlement(FS)of mine tailings is significant for the improvement and development of the filling process,whereas the settlement velocity(SV)of tailings in FS has been recognized as a key parameter to evaluate the settlement effect.However,the influence of temperature on the SV and its mechanism have not been studied.FS experiments on tailings with various ambient temperatures were carried out.The SVs of tailings with a solid waste content of 10wt%and an anionic polyacrylamide content of 20 g·t^−1 were measured at different temperatures.The SV presented an“N”-shaped variation curve as the temperature changed from 5 to 40℃.The mechanism of these results can be explained from the perspective of the electric double-layer repulsive force,molecular dynamics,and the polymer flocculation principle,as revealed from the scanning electron microscopy of floc particles.The findings will be beneficial in the design of tailings dewatering processes and save costs in the production of cemented paste backfill.

Carbonate-activated binder modified by supplementary materials for mine backfill and the associated heavy metal immobilization effects

Cemented paste backfill(CPB)is one of the effective methods for resource utilization of tailings,but the high cost of ordinary Portland cement(OPC)limits its utilization.Considering the poor performance of Na_(2)CO_(3)-activated binders,in this work,supplementary materials,including CaO,MgO,and calcined layered double hydroxide(CLDH),were used to modify their properties with the aim of finding an alternative binder to OPC.Isothermal calorimetry,X-ray diffraction,and thermogravimetric analyses were conducted to explore the reaction kinetics and phase assembles of the binder.The properties of the CPB samples,such as flowability,strength development,and heavy metal immobilization effects,were then investigated.The results show that the coupling utilization of MgO and CLDH showed good performance.The strength of the Mg_(2)-CLDH_(3) sample was approximately 2.94 MPa after curing for 56 d,which was higher than that of the OPC-based sample.Moreover the cost of the modified Na_(2)CO_(3)-activated binder was lower than that of the OPC-based binder.Modified sample showed satisfactory heavy metal immobilization effects.These findings demonstrate that carbonate-activated binder modified by supplementary materials can be suitable in CPB.

考虑充填高度和龄期的超细尾矿胶结充填体强度演变模型

目的:受固结应力的影响,采场不同位置的充填体强度存在较大差异。为精细化指导矿山充填作业,需构建考虑充填高度和龄期的充填体强度演变模型。方法:以超细尾矿胶结充填体为研究对象,通过提取不同充填高度处的充填体试样,分析了弹性模量、泊松比及抗压强度随充填高度和龄期的变化规律。结果:充填体的弹性模量随着充填高度和龄期的增长而逐渐增大,而泊松比相反;充填体弹性模量、泊松比和抗压强度随充填高度和龄期的变化均符合指数函数的发展规律;考虑充填高度和龄期的充填体抗压强度演变模型可以用相乘模式的双指数模型进行评估,模型计算值与试验值的误差在10%以内。结论:该强度演变模型的建立,可为矿山充填结构的稳定性评估提供更精确的模型参数。

Time- and temperature-dependence of compressive and tensile behaviors of polypropylene fiber-reinforced cemented paste backfill

The understanding of compressive and tensile behaviors of polypropylene fiber-reinforced cemented paste backfill(FR-CPB)play crucial roles in the successful implementation of reinforcement technique in underground mine backfilling operations.However,very limited studies have been performed to gain insight into the evolution of compressive and tensile behaviors and associated mechanical properties of FR-CPB under various curing temperatures from early to advanced ages.Thus,this study aims to investigate the time(7,28,and 90 d)-and temperature(20°C,35°C,and 45°C)-dependence of constitutive behavior and mechanical properties of FR-CPB.The obtained results show that pre-and post-failure behaviors of FR-CPB demonstrate strongly curing temperature-dependence from early to advanced ages.Moreover,the pseudo-hardening behavior is sensitive to curing temperature,especially at early ages.Furthermore,the mechanical properties including elastic modulus,material stiffness,strengths,brittleness,cohesion,and internal friction angle of FR-CPB show increasing trends with curing temperature as curing time elapses.Additionally,a predictive model is developed to capture the strong correlation between compressive and tensile strength of FR-CPB.The findings of this study will contribute to the successful implementation of FR-CPB technology.

银山矿超细全尾砂精细化絮凝沉降实验研究

银山矿全尾砂−19μm颗粒约占51%,属于超细全尾砂,处理过程中面临浓密脱水难度大的问题,且深锥浓密效果受到季节变化以及尾砂入料质量浓度的显著影响。因此,为提升银山矿深锥浓密机沉降效果,通过室内物化性质检测、室内絮凝沉降实验、现场半工业实验,开展了超细全尾砂精细化絮凝实验研究。结果表明:优选出的DR1030絮凝剂,在尾砂浆质量浓度10%时絮凝剂单耗为30.0 g/t(夏季)、33.0 g/t(其他季节),尾砂浆质量浓度15%时絮凝剂单耗为35.0 g/t(夏季)、38.0 g/t(其他季节)。半工业实验条件下,DR1030絮凝剂的实际单耗34.0 g/t,与现场絮凝剂相比,低4.4 g/t;DR1030对应的底流质量浓度波动性更小,质量浓度更高,平均值提高2.6百分点;扩展度测试表明DR1030对料浆流动性无明显影响。本次实验为提升银山矿充填质量提供了重要的工艺参数,对其他相似矿山也具有一定的借鉴意义。

某金矿全尾砂膏体充填优化配比及性能研究

为解决某金矿尾矿库库容不足及环境污染问题,计划采用全尾砂膏体充填采矿法进行地下开采。为提供经济合理的最优配比方案,以该矿山膏体物料为试验材料,设计对比试验来研究不同配比、不同料浆浓度、不同减水剂掺量对膏体强度和流动性的影响。试验结果表明:水泥、粉煤灰和尾砂的质量比,料浆浓度和减水剂掺量是影响膏体强度与流动性的重要因素;少量的减水剂能明显提高膏体的强度,适当地控制料浆浓度与减水剂掺量可以达到更好的充填效果;粉煤灰的添加有助于减水剂增强膏体的强度;最终综合考虑料浆流动性与试样的强度,推荐充填最优配比为水泥、粉煤灰和尾砂质量比1∶0.5∶8,料浆浓度为66%,可适当添加1%左右的减水剂。该研究也可为矿山未来的全尾砂膏体充填工程提供理论依据。

基于流变特性试验的充填料浆优化配比研究

针对安庆铜矿充填料浆的流变参数和影响规律,为了提升管道输送效率,保障矿山安全高效生产,主要开展了不同浓度充填料浆剪切流变特性试验研究。根据尾砂的粒度分布和料浆流动性要求,实验室设计了不同配比充填料浆的流变性试验、流动性试验,探究充填料浆质量浓度、灰砂比等因素对充填料浆流变特性的影响规律,测定不同充填料浆的剪切应力、黏性系数等参数。试验结果表明,较高的砂灰比和料浆浓度,流动性更好,74%为充填料浆的上限浓度。因此,浓度74%、砂灰比8是安庆铜矿充填料浆的最优参数。

矿山废石全尾砂充填研究现状与发展趋势

矿产资源开发过程中产生的废石、尾砂和冶炼渣,等占我国工业固体废料排放量的85%左右。大量矿山固体废料堆放地表,易造成严重污染,诱发泥石流、尾矿溃坝事故。固体废料充填工艺是解决矿山废尾排放的最有效途径。本文介绍了低浓度分级尾砂充填、全尾砂高浓度充填、膏体似膏体充填、块石胶结充填工艺的研究与应用现状,并分析了矿山废石全尾砂充填技术的研究与发展方向。

矿用尾砂固结粉在铁矿山全尾砂现场充填试验研究

为了分析和评价新型充填胶凝材料尾砂固结粉(简称矿尾粉)替代水泥用于铁矿全尾砂胶结充填法采矿的可行性与性价比,开展了矿尾粉的现场试验,测试了不同配比和浓度条件下的矿尾粉全尾砂充填体的单轴抗压强度,并与水泥和胶固粉胶凝材料进行了对比分析。结果表明:矿尾粉胶凝材料强度高、成本低、性价比高,替代水泥用于铁矿充填法采矿,不仅能大大降低充填采矿成本,而且还能实现铁矿全尾砂充填,为贫铁矿床的充填法采矿奠定基础。

基于BP网络的某矿山充填料浆配比优化

针对目前某矿山残矿回采充填体质量所存在的问题,提出采用分级尾砂胶结充填的方案。分析分级尾砂的物化特性,得出分级尾砂作为充填骨料的可行性。通过配比试验,初步确定影响料浆质量的因素。为了得到最优配比,采用神经网络进行优化,以料浆浓度及各组分添加量作为输入因子,塌落度、7 d抗压强度及28 d抗压强度作为输出因子,并以配比实验数据为训练和检验样本来建立BP神经网络预测模型。对比隐含层节点数对模型训练过程及预测精度的影响,选取最佳预测模型结构为4 9 3。将配比参数细化输入到预测模型中,从而搜索出优选样本,得到最优配比为m(水泥):m(粉煤灰):m(尾砂)=1:3:8。优化结果表明:在保证强度的前提下,粉煤灰的添加可有效地降低充填成本,经济效益显著。

高应变率下灰砂比对全尾胶结充填体力学性能影响

为研究采矿扰动下灰砂比对全尾胶结充填体力学响应,预制了三组不同灰砂比的全尾砂胶结充填体试件,利用ф50 mm SHPB试验系统,对预制试件进行单轴冲击试验,试验结果证明:全尾砂胶结充填体对弹性波传播有较强的反射和阻尼作用;在较高应变率下,试件强度则表现出快速软化;软化试件在18μs左右即达到峰值应力;试件动态抗压强度等参数变比均随应变率的增加而增大.灰砂比越高,试件的极限动态抗压强度等参数越大;在相同应变率下,试件的动态抗压强度等参数的增加反而降低.试件的破坏形式为压碎破坏,在相同应变率作用下,水泥含量越少,试件的破坏程度越高.