Experimental and numerical studies on progressive debonding of grouted rock boltsOA

Understanding the mechanism of progressive debonding of bolts is of great significance for underground safety. In this paper, both laboratory experiment and numerical simulation of the pull-out tests were performed. The experimental pull-out test specimens were prepared using cement mortar material, and a relationship between the pull-out strength of the bolt and the uniaxial compressive strength(UCS) of cement mortar material specimen was established. The locations of crack developed in the pul...     

Flotation of copper oxide minerals: A reviewOA

Copper oxide minerals are important copper resources, which include malachite, azurite, chrysocolla,cuprite, etc. Flotation is the most widely used method for the enrichment of copper oxide minerals in the mineral processing industry. In this paper, the surface properties of copper oxide minerals and their effects on the mineral flotation behavior are systematically summarized. The flotation methods of copper oxide minerals and the interaction mechanism with reagents are reviewed in detail. Flot...     

Coupled GIMP and CPDI material point method in modelling blast-induced three-dimensional rock fractureOA

Three-dimensional rock fracture induced by blasting is a highly complex problem and has received considerable attention in geotechnical engineering. The material point method is firstly applied to treat this challenging task. Some inherent weaknesses can be overcome by coupling the generalized interpolation material point(GIMP) and the convected particle domain interpolation technique(CPDI). For the media in the borehole, unchanged GIMP-type particles are used to guarantee a homogenous blast pre...     

Cyclic constitutive equations of rock with coupled damage induced by compaction and crackingOA

In this paper, the cyclic constitutive equations were proposed to describe the constitutive behavior of cyclic loading and unloading. Firstly, a coupled damage variable was derived, which contains two parts,i.e., the compaction-induced damage and the cracking-induced damage. The compaction-induced damage variable was derived from a nonlinear stress–strain relation of the initial compaction stage, and the cracking-induced damage variable was established based on the statistical damage theory.Seco...     

Compensation excavation method control for large deformation disaster of mountain soft rock tunnelOA

In recent years, the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China. It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling. Hence, the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation. It uses supportive...     

Selective depression action of taurine in flotation separation of specularite and chloriteOA

Chlorite, as the most representative gangue mineral associated with specularite, of which the separation of these two minerals is difficult. This paper investigated the depression effect of taurine on specularite/chlorite separation via flotation experiments, adsorption tests, contact angle measurements, Zeta potential detection, FT-IR measurements, and XPS analyses. The results of single mineral flotation indicated that chlorite could be depressed selectively by taurine with the recovery of les...     

Spatiotemporal evolution of thermo-hydro-mechanical-chemical processes in cemented paste backfill under interfacial loadingOA

Cemented paste backfill(CPB) and rock interface interaction causes the formation of an interfacial loading and affects the thermal, hydraulic, mechanical, and chemical processes in bulk CPB and thus its in-situ behavior. In this study, a new meter-sized column model is developed to systematically investigate the multiphysics processes in CPB under interfacial loading. The obtained results discover that for the mechanical process, the interfacial loading leads to a reduced settlement and a weaken...     

Effect of deep oxidation of chalcopyrite on surface properties and flotation performanceOA

In this study, chalcopyrite was oxidized in hydrogen peroxide(H₂O₂) solutions of different concentrations to simulate different degrees of oxidation in real ores, and the effects of H₂O₂ treatment on chalcopyrite surface properties and flotation performance were investigated by surface analysis techniques and floatation experiments, which implied the reason for the poor grade and recovery of oxidized chalcopyrite concentrate in the production process o...     

Lateral compression and energy absorption of foamed concrete-filled polyethylene circular pipe as yielding layer for high geo-stress soft rock tunnelsOA

Foamed concrete as energy absorption material for high geo-stress soft rock tunnels has been proven to be feasible due to its high compressibility and lightweight. However, the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain unsolved. In this study, we propose a novel energy absorber composed of foamed concrete-filled polyethylene(FC-PE) pipe and analyze its deformation and energy absorption capacity via quasi-static lateral compres...     

Investigation of a non-explosive directional roof cutting technology for self-formed roadwayOA

Traditional explosives have characteristics of high risk, large vibration, and poor directional fracturing.Consequently, an instantaneous expander with a single crack surface(IESCS), which is a novel nonexplosive directional rock-breaking technique, has been developed. The directional roof-cutting mechanism of the IESCS method, driven by high-pressure gas, was theoretically analyzed. Laboratory experiments and numerical simulations proved the directional slitting effect of the IESCS method to be...     

围岩与衬砌复合体的粘弹性分析

本文在平面应变条件下,对粘弹性圆形巷道和衬砌的耦合问题进行分析,衬砌(粘弹或弹性的)是在巷道开挖后,或巷道形成后经过一段时间蠕变才加上的。使用积分型粘弹本构关系——Boltzmann记忆积分求出围岩和衬砌的位移,然后根据它们交界面处的连续条件,得到位移围岩和衬砌交界面上支护反力为未知量的积分方程。最后,对一些具体情况由积分方程求得支护反力,从而得到围岩和衬砌的位移和应力,并对其进行了分析。     

复杂地层地下厂房围岩稳定性研究

本文介绍复杂地质条件下兴建大型地下洞室群时,围岩应力及变形状态的模型试验成果,就所揭示的围岩稳定问题,提出看法和建议。     

Domino instability effect of surrounding rock-coal pillars in a room-and-pillar gob

To discuss the domino instability effect and large area roof falling and roof accidents of surrounding rock-coal pillars in a room-and-pillar gob, the equilibrium equation for a roof-coal pillar-floor system with the influence of mining floor was developed based on the engineering conditions of the surrounding rock in a room-and-pillar gob in the 3^?2 coal seam of Tanggonggou mine. The conditions of system instability and the relationship between system stability and system stiffness were analyzed from an energetic point of view. Numerical simulation using the discrete element software UDEC was also carried out to simulate conditions causing the domino effect on surrounding rock-coal pillars in a 3^?2 room-and-pillar gob. The results show that: if we want the system to destabilize, the collective energy in roof-and-floor must be larger than that in the coal pillar. When the stiffness of the coal pillars and the roof-and-floor are both greater than zero, the system is stable. When the stiffness of the coal pillars is negative but the summed stiffness of the coal pillars and roof-and-floor is larger than or equal to zero, the system is statically destroyed. When the sum of the coal pillars and the roof-floor stiffness is negative, the system suffers from severe damages. For equal advance distances of the coal mining face, the wider coal pillars can reduce the probability of domino type instability. Conversely, the smaller width pillars can increase the instability probability. Domino type instability of surrounding rock-coal pillars is predicted to be unlikely when the width of coal pillars is not less than 8 m.     

Numerical investigation into pillar failure induced by time-dependent skin degradation

This paper focuses on the instability mechanism of an isolated pillar, caused by time-dependent skin degradation and strength heterogeneity. The time-dependent skin degradation is simulated with a non-linear rheological model capable of simulating tertiary creep, whereby two different pillar failure cases are investigated. The first case is of an isolated pillar in a deep hard rock underground mine and subjected to high stresses. The results show that pillar degradation is limited to the regions near the surface or the skin until two months after ore extraction. Afterwards degradation starts to extend deeper into the pillar, eventually leaving a highly-stressed pillar core due to stress transfer from the failed skin.Rockburst potential indices show that the risk increases exponentially at the core as time goes by. It is then demonstrated that the progressive skin degradation cannot be simulated with conventional strain-softening model assuming brittle failure. The parametric study with respect to the degree of heterogeneity reveals that heterogeneity is key to the occurrence of progressive skin degradation. The second case investigated in this study is pillar failure taking place in a very long period. Such failure becomes significantly important when assessing the risk for ground subsidence caused by pillar collapse in an abandoned mine. The analysis results demonstrate that the employed non-linear rheological model can simulate gradual skin degradation taking place over several hundred years. The percentage of damage zone volume within the pillar is merely 1% after a lapse of one days and increases to 50% after one hundred years, indicating a high risk for pillar collapse in the long term. The vertical displacements within the pillar also indicate the risk of subsidence. The proposed method is suitable for evaluating the risk of ground surface subsidence above an abandoned mine.     

大型地下洞室开挖数值模拟分析

以某水电站调压井大型地下洞室群施工为例,通过典型断面关键点位移、小主应力及安全系数随开挖步的变化,分析了开挖对大型地下洞室群围岩稳定造成的影响．数值计算表明,开挖过程中,围岩整体稳定性较好,但是围岩位移、小主应力随开挖步的不断递进而持续增大,关键点安全系数持续减小,最大位移与最大拉应力均位于调压井下部,分别为10．57mm及1．10MPa,局部关键点最小安全系数不满足规范要求,所以洞室开挖后需及时支护．计算表明,当二次衬砌高程大于关键点所处高程,该点安全系数明显增大,满足规范要求,且通过支护方案比选,调压井混凝土浇筑至625．5111高程是该工程最经济合理支护方案．     

火灾时隧道临界风速及内力模拟研究

摘 要：火灾时的烟气控制在隧道防火安全设计中占有很重要的地位,而临界风速即隧道火灾过程中能有效控制烟气于火源下风方向而不发生逆流的最小纵向风速,是隧道火灾烟气控制的关键。利用CFD数值模拟软件对公路隧道不同火灾工况的烟气扩散进行了数值模拟,并运用SAP2000分别计算了火灾时不同火源位置不同临界风速下钢筋混凝土隧道的内力大小。经过对比分析得出,适当增大其临界风速可有效地控制烟气流的扩散避免产生回流,同时也有利于减小高温下隧道结构损伤。     

采场覆岩中复合关键层的形成条件与判别方法

在采场覆岩运动中起主要控制作用的岩层为关键层，而有时关键层是由2层或2层以上岩层形成的复合岩层所组成，我们称其为复合关键层．本文在深入揭示复合岩层形成机理的基础上，给出了形成复合岩层的力学条件与数学表达式，进而建立了采场覆岩中复合关键层的判别方法，并编写了复合关键层的判别程序．实例分析表明，复合关键层在岩层运动中是客观存在的，比同组岩层分开后的单一岩层的控制作用的线性叠加要大得多．本项研究是岩层控制的关键层理论研究的深入和发展，将有力促进岩层控制理论和技术的发展．     

破碎围岩浅埋偏压隧道衬砌荷载的计算方法

隧道洞口大都会面临围岩破碎、浅埋和偏压等不良地质地形情况,现行规范只给出了偏压隧道衬砌荷载的计算方法。对于破碎围岩浅埋偏压隧道,根据现场情况及实测的衬砌受力和变形特征表明其与规范假定不同,不宜直接利用规范方法。通过工程实例分析及隧道三维数值分析结果提出了浅埋偏压隧道破碎围岩的破坏模式,即隧道开挖后深埋侧岩体滑塌下落挤压支护结构使其向外侧变形,从而外侧支护受到被动土压力。根据提出的破坏模式,将隧道开挖后围岩主要分为滑塌区和被动区,在此基础上利用极限平衡法推导出了衬砌荷载的计算公式。将计算得到的结果与现场实测值对比发现,对于围岩极其破碎且存在较严重偏压的浅埋隧道工程,提出的计算方法比采用规范方法更接近实际情况。     

分析粘弹围岩稳定性的新方法—离散记忆积分法

提出一种新的数值方法——离散记忆积分法。它用于分析粘弹围岩在弹性衬砌支护下的稳定性问题。文中Boltzmann＇s积分,即积分型粘弹本构关系,在总的时间和空间上被离散,而在离散的每个时步内使用以微分型本构关系为基础的对应性原理。方法不受巷道断面形状和衬砌建成时间的限制,可求出围岩和衬砌内的应力、位移及两者交界面上的围岩压力,通过将圆形断面巷道的计算结果与解析解比较,证明本方法是有效的,并对直壁圆拱形巷道进行了数值分析。