Rock brittleness indices and their applications to different fields of rock engineering:A review

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst proneness.As such,it is of high practical value to correctly evaluate rock brittleness.However,the definition and measurement method of rock brittleness have been very diverse and not yet been standardized.In this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly discussed.The development and role of rock brittleness in different fields of rock engineering are also studied.Eighty brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are discussed.The results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock brittleness.On the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness.It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness.This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.     

急倾斜极薄矿脉削壁充填法开采采动压力监测

二道沟金矿为急倾斜极薄矿脉,采用削壁充填法与浅孔留矿法开采,随着采深的增加,发生了多起采场岩爆。为研究岩爆发生所需高应力的来源,特对开采过程进行了采动压力监测。采用巷道变形收敛监测的方法,实测了1530采场削壁充填法回采过程中,穿脉监测巷道顶底板和两帮的收敛变形。监测结果表明:随着回采高度的增加,监测巷道顶底板间距呈减小的趋势,而两帮间距则呈增大的趋势,且两帮的变形幅度比顶底板的变形要大。并根据两帮各监测点最大收敛值,绘制了采动压力特性曲线。由该曲线可知,采动压力在距上部采场上盘回采边界约7 m的范围内形成波峰,再往上盘侧则趋于平缓。对于这种比较集中的采动压力分布特点,适合采用卸压的方法对其进行控制,从而达到阻止岩爆发生所需外部高应力条件的形成。     

基于模糊物元理论的岩爆倾向性等级评价

岩爆倾向性等级评价是研究岩爆发生机理的基础。本文以脆性岩爆指标(B)、Barton岩爆指标(α)、弹性变形能岩爆指标(Wet)和冲击能岩爆指标(Wcf)为基础建立岩爆倾向性评价指标体系,建立了基于模糊物元理论的岩爆倾向性等级评价模型。采用该模型对小厂坝矿区典型岩石的岩爆倾向性等级进行评价,结果表明:矿岩和黑云母石英片岩均为强岩爆倾向性。灰岩随着埋深增加,由弱岩爆倾向性向中岩爆倾向性过渡。矿体的上盘(黑云母石英片岩)为强岩爆倾向性,矿体的下盘(灰岩)为中岩爆倾向性,在实际开采过程中,应尽量将采矿工程布置于下盘。矿体为强岩爆倾向性,这与实际开采中频繁出现岩爆征兆现象一致。建议开采过程中应加强地压监测,合理布置卸压工程。     

岩爆分级预测的粗糙集-多维正态云模型

准确有效的岩爆分级预测对避免或减少岩爆灾害具有重要意义。选取围岩最大切向应力σθ、岩石单轴抗压强度σc、岩石单轴抗拉强度σt和岩石弹性变形能指数Wet作为岩爆评价指标，将多维正态云模型作为岩爆等级的预测方法，利用粗糙集确定评价指标权重，以国内外15组岩爆实例作为模型构建样本，建立了粗糙集-多维正态云岩爆分级预测模型。首先采用模糊集聚类后再通过粗糙集逐级筛选评价指标的方法确定评价指标权重，根据多维正态正向云发生器计算得到评价指标的确定度；然后利用评价指标权重和评价指标确定度计算评价样本的综合确定度，根据最大隶属度原则，判定评价样本的岩爆等级。采用鑫华矿业矿岩样本对粗糙集-多维正态云岩爆分级预测模型进行了有效性验证，计算结果与工程实际相吻合，表明该模型具有较好的实用性。     

三山岛金矿深井采矿卸压孔卸压数值模拟分析

三山岛金矿深井开采岩爆问题突出，为了保障作业面安全，提出了卸压孔卸压方案，建立了三维数学模型对卸压效果进行了分析，并通过三山岛金矿深部-780 m采场进行了实施。应力测试结果表明，卸压孔可以有效形成一定范围的降压区，降低了岩爆发生几率。     

深部巷道开挖加卸荷诱发围岩失稳的模拟研究

为研究深部巷道开挖引起的加卸荷现象及其诱发的围岩失稳,以埋深为1 275m的云南某矿山8#矿体1261中段沿脉巷道为背景,采用FLAC3D软件对巷道的应力场、位移场和塑性破坏区的演化规律进行模拟分析,探究开挖引起的加卸荷情况及其对巷道围岩稳定性的影响。结果表明:开挖结束后,巷道围岩应力重新调整,其帮部、斜底脚以及斜拱顶处加卸荷现象明显;随着开挖的进行,巷道斜底脚处围岩应力逐渐增加,而其余位置的围岩应力逐渐减少。8#矿体有着中等至强烈岩爆倾向,主要危险区域为巷道折角处;巷道围岩位移量:拱顶帮部底板斜拱肩拱肩斜底脚。     

Rock support in strainburst-prone ground

Strainburst is the most frequently encountered type of rockburst in underground mines. Strainburst occurs when the stress near the excavation boundary reaches the peak strength of the rock mass causing it to fail suddenly and violently. To mitigate strainburst damage risk, effective rock support is needed. In strainburst-prone grounds, it is critical to have rock support components to fulfill the role of rock reinforcement first to prevent rock failure. On the other hand, well-retained and reinforced rock masses may be excessively deformed and fail violently. In such a case, yielding elements are needed in the rock support system to absorb the excess strain energy released due to rock failure. The conventional method to support strainburst-prone grounds is to install rock reinforcement system using rebar and mesh first and then install yielding support system using dynamic rockbolts at a later stage. This two-stage rock support installation process is not effective because it can adversely impact mine production schedule.This paper presents a new, patented dynamic rockbolt, which is called superbolt and is developed for rock support in burst-prone grounds. Laboratory testing confirmed that the superbolt has superb capacity to achieve the goal of reinforcing and holding rock masses. The superbolt is characterized by high dynamic energy absorption capacity, consistent performance, and the ability to withstand repeated dynamic loading. The new rockbolt can be used in a one-pass rock support system to facilitate rapid drift development in underground mines and increase mine safety and productivity.     

Directional hydraulic fracturing to control hard-roof rockburst in coal mines

Hard roof is the main factor that induces rock-burst.In view of the present obvious weakness of control measures for hard roof rockburst in domestic collieries,the mechanism and field application of di...     

弓长岭井下矿地应力现场实测及应用

为掌握弓长岭井下矿的地应力赋存状态,采用实现完全温度补偿并考虑岩体非线性的地应力测量技术,对弓长岭井下矿3个水平3个测点进行了地应力现场实测,利用Lab VIEW编制的地应力计算程序对测量结果进行分析。3个测点的地应力赋存状态:(1)每个测点均有2个主应力接近水平方向,另1个主应力接近垂直方向;(2)3个测点的最大主应力均为最大水平主应力,垂直主应力为最小主应力,说明矿区地应力场以水平构造应力为主导;(3)3个测点最大水平主应力的走向总体上为南东东—北西西方向;(4)最大水平主应力、最小水平主应力和垂直主应力均随深度呈增长关系。地应力测量结果在弓长岭井下矿的应用主要有3个方面:(1)巷道走向应根据矿山的工程地质条件和采矿生产作业的要求,尽可能与最大主应力方向一致(113.96°);(2)提供数值分析必需的力学边界条件;(3)为弓长岭井下矿预测岩爆发生的地点和级别提供了可能。