Damage failure of cemented backfill and its reasonable match with rock mass

In order to study the failure mechanism of backfill and the reasonable matches between backfill and rock mass, and to achieve the object of safe and efficient mining in metal mine, four types of backfills were tested under uniaxial compression loading, with cement?tailing ratios of 0.250:1, 0.125:1, 0.100:1 and 0.083:1, respectively. With the help of the stress?strain curves, the deformation and failure characteristics of different backfills with differing cement?tailing ratios were analyzed. Based on the experimental results, the damage constitutive equations of cemented backfills with four cement?tailing ratios were proposed on the basis of damage mechanics. Moreover, comparative analysis of constitutive model and experimental results were made to verify the reliability of the damage model. In addition, an energy model using catastrophe theory to obtain the instability criteria of system was established to study the interaction between backfill and rock mass, and then the system instability criterion was deduced. The results show that there are different damage characteristics for different backfills, backfills with lower cement?tailing ratio tend to have a lower damage value when stress reaches peak value, and damage more rapidly and more obviously in failure process after peak value of stress; the stiffness and elastic modulus of rock mass with lower strength are more likely to lead to system instability. The results of this work provide a scientific basis for the rational strength design of backfill mine.

Development and application of novel high‐efficiency composite ultrafine cement grouts for roadway in fractured surrounding rocks

The fractured surrounding rocks of roadways pose major challenges to safe mining.Grouting has often been used to reinforce the surrounding rocks to mitigate the safety risks associated with fractured rocks.The aim of this study is to develop highly efficient composite ultrafine cement(CUC)grouts to reinforce the roadway in fractured surrounding rocks.The materials used are ultrafine cement(UC),ultrafine fly ash(UF),ultrafine slag(US),and additives(superplasticizer[SUP],aluminate ultrafine expansion agent[AUA],gypsum,and retarder).The fluidity,bleeding,shrinkage,setting time,chemical composition,microstructure,degree of hydration,and mechanical property of grouting materials were evaluated in this study.Also,a suitable and effective CUC grout mixture was used to reinforce the roadway in the fractured surrounding rock.The results have shown that the addition of UF and US reduces the plastic viscosity of CUC,and the best fluidity can be obtained by adding 40%UF and 10%US.Since UC and UF particles are small,the pozzolanic effect of UF promotes the hydration reaction,which is conductive to the stability of CUC grouts.In addition,fine particles of UC,UF,and US can effectively fill the pores,while the volumetric expansion of AUA and gypsum decreases the pores and thus affects the microstructure of the solidified grout.The compressive test results have shown that the addition of specific amounts of UF and US can ameliorate the mechanical properties of CUC grouts.Finally,the CUC22‐8 grout was used to reinforce the No.20322 belt roadway.The results of numerical simulation and field monitoring have indicated that grouting can efficaciously reinforce the surrounding rock of the roadway.In this research,high‐performance CUC grouts were developed for surrounding rock reinforcement of underground engineering by utilizing UC and some additives.

Theoretical analysis of a new segmented anchoring style in weakly cemented soft surrounding rock

According to the tensile failure of rock bolt in weakly cemented soft rock, this paper presents a new segmented anchoring style in order to weaken the cumulative effect of anchoring force associated with the large deformation. Firstly, a segmented mechanical model was established in which free and anchoring section of rock bolt were respectively arranged in different deformation zones. Then, stress and displacement in elastic non-anchoring zone, elastic anchoring zone, elastic sticking zone, softening sticking zone and broken zone were derived respectively based on neural theory and tri-linear strain softening constitutive model of soft rock. Results show that the anchoring effect can be characterized by a supporting parameter b. With its increase, the peak value of tangential stress gradually moves to the roadway wall, and the radial stress significantly increases, which means the decrease of equivalent plastic zone and improvement of confining effect provided by anchorage body. When b increases to 0.72, the equivalent plastic zone disappears, and stresses tend to be the elastic solutions. In addition, the anchoring effect on the displacement of surrounding rock can be quantified by a normalization factor δ.

Water-resisting ability of cemented broken rocks

Using the self-designed testing system, the seepage tests for cemented broken rocks were conducted, and the impact of different factors on water-resisting ability was analyzed. The results show that(1) seepage process of the cemented broken rocks can be divided into two categories: in one category, seepage instability occurs after a period of time, in the other, the permeability decreases slowly and tends to be stable,and seepage instability does not occur;(2) cementing performance of cementing agent and grain size distribution are the decisive factors for water-resisting ability, with the increase of cementing performance and the mass percentage of large grains, the water-resisting ability of the specimen strengthens;(3)aggregate type has little effect on seepage stability, for the specimens with different aggregate types,the permeability and the duration of seepage instability have small difference;(4) initial porosity has a certain effect on the water-resisting ability of the specimen, but has no decisive role. With the increase of the initial porosity, the duration of seepage instability decreases.

Finite element analysis of thermal residual stresses at cemented carbide rock drill buttons with cobalt-gradient structure

The aim of this study is to apply the concept of functionally graded materials(FGMs) to cemented carbides and to develop high-performance rock drill buttons. Cobalt-gradient structure was introduced to the surface zone of the buttons by carburizing process. Finite element method and XRD measurement were used to decide the distribution of thermal residual stress. Constitutive parameters were determined by constraint factor. Numerical results show that residual stresses of gradient buttons mainly concentrate in cobalt-gradient zone. There is compressive stress in the surface zone and tensile stress in the cobalt-rich zone. The maximum value of surface compressive stress is 180 MPa for WC-6Co cemented carbides. And the numerical results agree with the results of XRD measurement.

The Cemented Material Dam： A New, Environmentally Friendly Type of Dam

The first author proposed the concept of the cemented material dam （CMD） in 2009. This concept was aimed at building an environmentally friendly dam in a safer and more economical way for both the dam and the area downstream. The concept covers the cemented sand, gravel, and rock dam （CSGRD）, the rockfill concrete （RFC） dam （or the cemented rockfill dam, CRD）, and the cemented soil dam （CSD）. This paper summarizes the concept and principles of the CMD based on studies and practices in projects around the world. It also introduces new developments in the CSGRD, CRD, and CSD.

Measuring dynamic fracture toughness of cement rock using a short rod specimen

As Daqing Oilfield is developing oil layer with a big potential, the requirement for the quality of well cementation is higher than ever before. Cement rock is a brittle material containing a great number of microcracks and defects. In order to reduce the damage to cement ring and improve sealed cementing property at the interface, it is necessary to conduct research on the modification of the cement rock available. According to the principle of super mixed composite materials, various fillers are added to the ingredients of cement rock. Dynamic fracture toughness of cement rock will be changed under the influence of filler. In this paper, short rod specimens of cement rock are employed in the experiments to investigate the dynamic fracture toughness of cement rocks with different ingredients using split Hopkinson Pressure Bar, and partial experimental results are given. The results indicate that fiber reinforcement is an effective way to improve the impact resistance of cement rock.

Research of dynamic mechanical performance of cement rock

As Daqing Oilfield is developing oil layer with a big potential, the requirement for the quality of well cementation is higher than ever before. Cement rock is a brittle material containing a great number of microcracks and defects. In order to reduce the damage to cement ring and improve sealed cementing property at the interface, it is necessary to conduct research on the modification of the cement rock available. According to the principle of super mixed composite materials, various fillers are added to the ingredients of cement rock.Dynamic fracture toughness of cement rock will be changed under the influence of filler. In order to study the damage mechanism of the cement circle during perforation and carry out comprehensive experiments on preventing and resisting connection, a kind of comprehensive experiment equipment used to simulate perforation and multi-functional equipment for testing the dynamic properties of the material are designed. Experimental study of the dynamical mechanical performance of original and some improved cement rock and experiment used to simulate the well cementation and perforation are carried out. Standard for dynamical mechanical performance of the cement rock with fine impact resistance and mechanical properties of some improved cement rock are also given.

Characterisation, Analysis and Design of Hydrated Cement Treated Crushed Rock Base as a Road Base Material in Western Australia

Hydrated Cement Treated Crushed Rock Base （HCTCRB） is widely used as a base course in Western Australian pavements. HCTCRB has been designed and used as a basis for empirical approaches and in empirical practices. These methods are not all-encompassing enough to adequately explain the behaviour of HCTCRB in the field. Recent developments in mechanistic approaches have proven more reliable in the design and analysis of pavement, making it possible to more effectively document the characteristics of HCTCRB. The aim of this study was to carry out laboratory testing to assess the mechanical characteristics of HCTCRB. Conventional triaxial tests and repeated load triaxial tests （RLT tests） were performed. Factors affecting the performance of HCTCRB, namely hydration periods and the amount of added water were also investigated. It was found that the shear strength parameters of HCTCRB were 177 kPa for cohesion （c） and 42~ for the internal friction angle （~）. The hydration period, and the water added in this investigation affected the performance of HCTCRB. However, the related trends associated with such factors could not be assessed. All HCTCRB samples showed stress-dependency behaviour. Based on the stress stages of this experiment, the resilient modulus values of HCTCRB ranged from 300 MPa to 1100 MPa. CIRCLY, a computer program based on the multi-layer elastic theory was used in the mechanistic approach to pavement design and analysis, to determine the performance of a typical pavement model using HCTCRB as a base course layer. The mechanistic pavement design parameters for HCTCRB as a base course material were then introduced. The analysis suggests that the suitable depth for HCTCRB as a base layer for WA roads is at least 185 mm for the design equivalent standard axle （ESA） of 10 million.

The Feasibility of Basalt Rock Powder and Superfine Sand as Partial Replacement Materials for Portland Cement and Artificial Sand in Cement Mortar

The research gap on the feasibility of basalt rock powder(BRP)and superfine sand(SS)in preparation of cement mortar is significant.This study examines probable changes occurred in the modified cement mortar due to incorporation of certain quantity of basalt rock powder and superfine sand in mixture proportion.The cement mortar included Portland cement,artificial sand and water as principal mixture constituents.Then,basalt rock powder and superfine sand were added as partial replacement materials for Portland cement and artificial sand respectively.Therefore,replacement percentages were 10%,15%,20%,25%and 30%when the basalt rock powder replaced Portland cement and in case the artificial sand was replaced by superfine sand,10%,20%,30%,40%and 50%.Then,the strength indexes such as flexural strength,compressive strength,ultrasonic pulse velocity and dynamic elastic modulus were investigated.The results show that the presence of basalt rock powder in mixture proportion increased the flexural and compressive strengths of cement mortar however the cement mortar that contained superfine sand illustrated inadequate mechanical performance as flexural and compressive strengths decreased remarkably.Moreover,when basalt rock powder and superfine sand were included together in mixture proportion,the cement mortar’s mechanical performance declined compared to that of the reference cement mortar.Despite the fact that basalt rock powder and superfine sand weakened the cement mortar’s mechanical properties,it was found that they can be added into the cement mortar as partial replacement of Portland cement and artificial sand in the following ratios:from 10%to 25%when basalt rock powder replaces Portland cement and from 10%to 20%when artificial sand is replaced by superfine sand.

伊犁四矿弱胶结软岩巷道围岩控制技术研究及应用

以新疆伊犁四矿21113工作面为工程背景,通过理论分析、数值模拟以及现场实测等手段,围绕浅埋弱胶结软岩巷道破坏特征及控制技术展开了一系列研究,研究结果表明:伊犁四矿弱胶结软岩巷道围岩变形特点为自稳时间短、应力释放明显,泥岩遇水易软化、出现无征兆冒顶,岩体自重大、顶板出现下沉,支护结构受力不耦合、支护单元破坏等。根据围岩变形特点提出了对巷道围岩及时支护、喷浆封闭、拱形断面、加长支护的联合支护技术,经过现场工业性试验以及观测数据证明,该联合支护方案,能够很好地控制巷道变形,21113上顺槽巷道从开始回采到结束未出现瞬发变形、顶板切落、锚杆(索)断裂及钢带撕裂等情况,巷道变形及维护满足工作面顺槽的使用要求。可为伊犁矿区弱胶结软岩巷道支护设计和施工提供指导作用。

Mechanism of Pendulum-type wave phenomenon in deep block rock mass

Pendulum-type ( μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse waves propagated in continuum media and is also a phenomenon of the sign-variable reaction of deep block rock masses to dynamic actions, besides the Anomalous Low Friction (ALF) phenomenon. In order to confirm the existence of the μ wave and study the rule of variation of this μ wave experimentally and theoretically, we first carried out one-dimensional low-speed impact experiments on granite and cement mortar blocks and continuum block models with different characteristic dimensions, based on the multipurpose testing system developed by us independently. The effects of model material and dimensions of models on the propagation properties of 1D stress wave in blocks medium are discussed. Based on a comparison and analysis of the propagation properties (acceleration amplitudes and Fourier spectra) of stress wave in these models, we conclude that the fractures in rock mass have considerable effect on the attenuation of the stress wave and retardarce of high frequency waves. We compared our model test data with the data of in-situ measurements from deep mines in Russia and their conclusions. The low-frequency waves occurring in blocks models were validated as Pendulum-type wave. The frequencies corresponding to local maxima of spectral density curves of three-directional acceleration satisfied several canonical sequences with the multiple of 2～(1/2), most of those frequencies satisfied the quantitative expression (2～(1/2))i V p/2△ .

Triaxial shear behavior of a cement-treated sand——gravel mixture

A number of parameters,e.g.cement content,cement type,relative density,and grain size distribution,can influence the mechanical behaviors of cemented soils.In the present study,a series of conventional triaxial compression tests were conducted on a cemented poorly graded sandegravel mixture containing 30% gravel and 70% sand in both consolidated drained and undrained conditions.Portland cement used as the cementing agent was added to the soil at 0%,1%,2%,and 3%(dry weight) of sandegravel mixture.Samples were prepared at 70% relative density and tested at confining pressures of 50 kPa,100 kPa,and150 kPa.Comparison of the results with other studies on well graded gravely sands indicated more dilation or negative pore pressure in poorly graded samples.Undrained failure envelopes determined using zero Skempton’s pore pressure coefficient (= 0) criterion were consistent with the drained ones.Energy absorption potential was higher in drained condition than undrained condition,suggesting that more energy was required to induce deformation in cemented soil under drained state.Energy absorption increased with increase in cement content under both drained and undrained conditions.

Study of Fractal Characteristics of the Cementation Index in Shale Gas

The description of pores and fracture structures is a consistently important issue and certainly a difficult problem, especially for shale or tight rocks. However, the exploitation of so-called unconventional energy, such as shale methane and tight-oil, has become more and more dependent on an understanding of the inner structure of these unconventional reservoirs. The inner structure of porous rocks is very difficult to describe quantitatively using normal mathematics, but fractal geometry, which is a powerful mathematical tool for describing irregularly-shaped objects, can be applied to these rocks. To some degree, the cementation index and tortuosity can be used to describe the complexity of these structures. The cementation index can be acquired through electro-lithology experiments, but, until now, tortuosity could not be quantitatively depicted. This research used the well-logging curves of a gas shale formation to reflect the characteristics of the rock formations, and the changes in the curves to indicate the changes of the rock matrix, the pores, the connections among the pores, the permeability, and the fluid type. The curves that are affected most by the rock lithology, such as gamma ray, acoustic logging, and deep resistivity curves, can provide significant information about the micro-or nanostructure of the rocks. If the rock structures have fractal characteristics, the logging curves will also have fractal properties. Based on the definition of a fractal dimension and the Hausdorff dimension, this paper presents a new methodology for calculating the fractal dimensions of logging curves. This paper also reveals the deep meaning of the rock cementation index, m, through the Hausdorff dimension, and provides a new equation to calculate this parameter through the resistivity and porosity of the formation. Although it represents a very important relationship between the saturation of hydrocarbons with pores and resistivity, the Archie formula was not available for shale and tight rock. The major reason for this was an incorrect understanding of the cementation index, and the calculation of saturation used a single m value from the bottom to the top of the well. Unfortunately, this processing method is clearly inappropriate for the intensely heterogeneous material that is shale and tight rock. This paper proposes a method of calculating m through well-logging curves based on a fractal geometry that can change with different lithologies, so that it would have more agreement with in situ scenarios than traditional methods.

Assessing geological uncertainty of a cement raw material deposit,southern Vietnam,based on hierarchical simulation

Resource modeling plays a crucial role in raw material quality management for cement manufacturing.Research has shown that geological uncertainty in resource modeling is inevitable and results in risk to future extraction planning and operations of the cement plant.This study aims to assess the geological uncertainty and associated risk in modeling a cement raw material deposit in southern Vietnam.For this deposit,soil,clay,laterite,and limestone are the four primary rock types,controlling the occurrence and spatial distribution of chemical grades.In this study,hierarchical simulation method was used to evaluate the uncertainty.Rock types were first simulated,and the chemical grades conditioning to the rock types were then generated.The results demonstrated the capability of the hierarchical simulation approach to incorporate the uncertainty of rock types in resource modeling and to allow evaluating the risks in providing the desired raw material for the cement plant in the form of grade-tonnage curves.

Methodology for the estimation of expansive cement borehole pressure

This work is part of a multi-phase project which aims to develop a sound methodology for rock fragmen-tation in underground mines using expansive cement.More specifically,it is the first phase of the project which focuses on laboratory tests to investigate the mechanical performance of expansive cement,also known as soundless chemical demolition agents(SCDA).This paper reports the results of laboratory tests conducted on instrumented thick-walled cylinders filled with expansive cement.Expansive pressure evo-lution and temperature variation with time are first examined for different borehole diameters.The clas-sical analytical method for expansive pressure estimation is validated with direct pressure measurement using high-capacity pressure sensor,and an empirical model is obtained.A new methodology based on iterative procedure is developed using axisymmetric finite element modelling and test results to derive the modulus of elasticity of the expansive cement at peak pressure.The results of this study show that the expansive pressure increases with borehole diameter when the rigidity of the steel cylinder is constant reaching 83 MPa for a 38.1 mm borehole.It is also shown that the expansive pressure decreases signif-icantly with increased cylinder rigidity for the same borehole diameter.The newly developed methodol-ogy revealed that the modulus of elasticity of expansive cement at peak pressure is estimated at 8.2 GPa.A discussion on the extension of the findings of this work to hard rock mining applications is presented.

基于RSM的超细水泥注浆材料配比及性能优化模型

注浆堵水技术已成为水害措施防范向工程治理不可缺少的技术之一,超细材料的研究也成为了目前注浆材料发展的新方向。为了解决矿井水害注浆治理工程中注浆材料优选和配比优化问题,采用单因素试验与响应曲面法(RSM)相结合的方法进行超细水泥注浆材料优化配比研究。首先通过单因素试验对不同水灰比、硅灰(SF)掺量及高效聚羧酸减水剂(PCS)掺量条件下浆液黏度、泌水率及7 d单轴抗压强度进行分析,以确定RSM最佳基准水平,其次构建以浆液黏度、泌水率及7 d单轴抗压强度为响应目标的二次多项式预测模型,结合方差、残差及响应曲面分析各响应变量对响应目标的影响规律,确定注浆材料最优配比。通过单因素试验结果对比分析,发现最优水灰比、SF掺量及PCS掺量分别为1∶1、35%及0.3%。通过RSM研究发现,浆液黏度、泌水率及7 d单轴抗压强度不仅受单一因素影响,且存在多因素交互作用。根据建立的二次多项式响应面回归预测模型可知,当水灰比、SF掺量及PCS掺量分别为0.7∶1、38%及0.2%时,注浆材料性能最优,其回归模拟预测浆液黏度、泌水率及7 d单轴抗压强度分别为210.82 mPa·s、1.0%及12.22 MPa。通过室内试验,其结果与预测模型结果吻合度较高,进一步验证了模型的可靠性,证明了该模型能够用于注浆材料优化配比设计研究。

卸围压下弱胶结软岩分数阶蠕变损伤本构模型

为研究地下硐室开挖卸荷诱发的软岩蠕变损伤特征,以西部矿区弱胶结软岩为研究对象,利用GDS HPTAS开展了分级卸围压蠕变试验,研究了不同含水条件下弱胶结软岩卸围压下蠕变特征和蠕变速率特征。基于稳态蠕变速率倒数的方法,确定了弱胶结软岩长期强度和含水率的数学指数函数关系。基于蠕变速率曲线特征提出了一种确定衰减蠕变与等速蠕变分界点t_1和等速蠕变与加速蠕变分界点t_2的新方法。引入Riemann-Liouville分数阶积分算子和负时间指数损伤演化变量,定义了非线性损伤Abel黏壶,建立了一个包括弹性元件、黏弹性损伤元件、黏性元件和非线性黏塑性损伤元件的六元件分数阶蠕变损伤本构模型。基于试验结果,采用Trust-Region算法进行了模型参数识别和敏感性分析。结果表明,所建立的模型具有物理意义明确、与试验值吻合度较高等特点,可较为准确地反映开挖卸荷条件下弱胶结软岩蠕变损伤特性,对保障地下工程长期稳定性具有重要的意义。

生物质混凝土在岩石表面增肥的研究

提出了人工提高岩面粗糙度,以提高其承载土壤能力,再结合客土喷播技术的岩面复绿方法。首先,在研究泥浆流动性的基础上,建立了岩面承载土壤能力的测量方法。然后分别利用水泥砂浆平铺、水泥砂浆微台阶、桔杆水泥砂浆微台阶法改造了岩面,并研究了改造后的岩面的承载土壤能力。结果表明水泥砂浆平辅法由于提高了岩面粗糙度而提高了承载土壤能力,水泥砂浆微台阶法由于岩面外形的改变为承载土壤提供了条件,因而大幅提高了承载土壤能力,桔杆水泥砂浆微台阶法不仅保留了水泥砂浆微台阶的优点,还由于桔杆的加入,形成了尖锐的突出物,能够留存树叶、杂草等从而进一步提高了岩面保持土壤、水分和肥力的能力。最后,提出了标准承载土壤能力的概念,解决了不同浓度泥浆测试结果不同的问题。

不同灰砂比岩充组合体疲劳损伤与破裂特性试验研究

为了揭示地下采场中岩充组合结构体在频发应力扰动作用下的损伤演化和破裂机制,对4种不同灰砂比的岩充组合体试样开展多级增幅疲劳试验并进行试验后CT扫描。结果表明:(1)充填体的灰砂比对岩充组合体的变形、刚度劣化、损伤扩展和破坏模式均有影响。灰砂比从1:4下降到1:12,体积膨胀增加,割线模量先增加后减小。(2)提出了基于不可逆轴向应变的累积损伤演化模型,该模型与试验数据拟合良好,灰砂比为1:4和1:8的岩充组合体累积损伤呈现2阶段增加模式,即最初稳定增加,随后急剧增加。灰砂比为1:10和1:12的岩充组合体呈现倒“S”形损伤累积模式,即初始、稳定和加速增加3个阶段。(3)随着灰砂比减小,岩充组合体的宏观破坏模式从拉伸−剪切混合破坏过渡为拉伸破坏。试验后的CT图像揭示了岩充组合体细观破裂演化模式,包括充填体中的剪切破坏、沿着岩石和充填体接触面的拉伸破裂以及岩石中的拉伸和剪切破裂。采用“柔性充填体”有利于防止岩石剥落、坍塌等灾害。研究成果可为矿山充填配比优化和深部矿产资源安全开采提供理论依据。