ZONAL DISINTEGRATION MECHANISM OF DEEP CRACK-WEAKENED ROCK MASSES UNDER DYNAMIC UNLOADING

Size and quantity of fractured zone and non-fractured zone are controlled by cracks contained in deep rock masses. Zonal disintegration mechanism is strongly dependent on the interaction among cracks. The strong interaction among cracks is investigated using stress superposition principle and the Chebyshev polynomials expansion of the pseudo-traction. It is found from numerical results that crack nucleation, growth and coalescence lead to failure of deep crack- weakened rock masses. The stress redistribution around the surrounding rock mass induced by unloading excavation is studied. The effect of the excavation time on nucleation, growth, interaction and coalescence of cracks was analyzed. Moreover, the influence of the excavation time on the size and quantity of fractured zone and non-fractured zone was given. When the excavation time is short, zonal disintegration phenomenon may occur in deep rock masses. It is shown from numerical results that the size and quantity of fractured zone increase with decreasing excavation time, and the size and quantity of fractured zone increase with the increasing value of in-situ geostress.

Experimental Study on Mechanical Characteristics of Cracked Rock Mass Reinforced by Bolting and Grouting

The stress hardening characteristics of the reinforced rock mass in uniaxial compression tests were revealed by means of the experimental study on mechanical characteristics of cracked rock mass reinforced by bolting and grouting. And the load-beating mechanism of the reinforced rock mass was perfectly reflected by the experiment. The results can offer some useful advice for support design and stability analysis of deep drifts in unstable strata.

THE CONSTITUTIVE RELATION OF CRACK-WEAKENED ROCK MASSES UNDER AXIAL-DIMENSIONAL UNLOADING

An accurate and efficient numerical method for solving the crack-crack interaction problem is presented. The method is mainly by means of the dislocation model, stress superposition principle and Chebyshev polynomial expansion of the pseudo-traction. This method can be applied to compute the stress intensity factors of multiple kinked cracks and multiple rows of periodic cracks as well as the overall strains of rock masses containing multiple kinked cracks under complex loads. Many complex computational examples are given. The dependence of the crack-crack interaction on the crack configuration, the geometrical and physical parameters, and loads pattern, is investigated. By comparison with numerical results under confining pressure unloading, it is shown that the crack-crack interaction under axial-dimensional unloading is weaker than those under confining pressure unloading. Numerical results for single faults and crossed faults show that the single faults are more unstable than the crossed faults. It is found from numerical results for different crack lengths and different crack spacing that the interaction among kinked cracks decreases with an increase in length of the kinked cracks and the crack spacing under axial-dimensional unloading.

Coordination and evolution mechanism of fractal crack network in mining rock mass destruction

Based on the natural characters of stratum, complicated geological mining conditions and the essence of mining rock mass destruction, the complexity of rock mass destruction caused by miningw as analyzed. The inner link between rock mass destruction phenomena caused by mining and nonlinear science was revealed. There are numerous cracks in natural rock mass. The cracks’ distribution is irregular and is of statistical fractal structure. Self-organizational nonlinear evolution of the inner structure flaws leads to the rock mass destruction with external force. The evolution includes single fault’s fractal development, formation and evolution of fractal crack network and coordination of fractal crack network, etc. The law of fractal crack network’s evolution was introduced, at the same time, the coordination of fractal crack network was analyzed. Finally, based on coordination the principal equation of mining-caused subsidence of structural rock mass was established and its steady-state solution and unsteady-state solution were found.

Deformation analysis of transversely isotropic coal-rock mass with porous and cracks

Coal-rock as a typical sedimentary rock has obvious stratification,namely it has transversely isotropic feature.Meanwhile,deformation leads to coal-rock mass having the characteristics of different porous and crack structures as well as local anisotropy.Equivalent axial and circumferential strain' formulas of the pure coal-rock mass specimen with a single crack were derived through the establishment of equivalent mechanical model of standard cylindrical coal-rock specimen,and have been widely used to a variety of media combined different structures containing multiple cracks.The complete stress strain curve of a real coal-rock specimen was obtained by the CTC test.Additionally,according to the comparison with the theoretical value,the theoretical mechanical model could well explain the deformation characteristics of coal-rock mass and verify its validity.Further,following features were analyzed:strain normalized coefficient and elastic modulus(Poisson's ratio) in vertical and parallel direction to the stratification,stratification angle,porosity,pore radius,normal and tangential stiffness of crack,and the relationship of different crack width with different tangential stiffness of crack.Through the analysis above,it substantiate this claim that the theoretical model with better reliability reflects the transversely isotropic nature of the coal-rock and the local anisotropy caused by the porous and cracks.

Effects of Rock Mass Conditions and Blasting Standard on Fragmentation Size at Limestone Quarries

The size distribution of fragmented rocks depends on not only the blasting standard but also the mechanical properties, joint system and crack density of rock mass. As, especially, the cracks in the rock mass are heavily developed at the limestone quarries in Japan, the joints and/or cracks in the rock mass have big impacts on the blasting effects such as the size of fragmented rocks. Therefore, if the joint system and/or crack density in the rock mass can be known and evaluated in quantity, the blasting operation can be done more effectively, efficiency and safety. However, the guideline for designing the appropriate blasting standard based on the rock mass condition such as mechanical properties, joint system and/or distribution of cracks, discontinuities, from the scientific point of view, has not been developed yet. Therefore, a series of blasting tests had been conducted in different mines and faces, geological conditions and blasting standards in order to know the impacts of each factor on the blasting effects. This paper summarizes the results of blasting tests and describes the impacts of rock mass conditions and blasting standard on the size of fragmented rocks.

冰充填裂隙对冻结岩体压缩破坏特征的影响研究

冻结岩体的力学性质是决定冻结地层工程施工与运营安全的核心因素,而冻结岩体的力学性质由裂隙结构和冻结温度等条件决定。本文在常温和冻结条件下开展了含预制裂隙砂岩的力学实验,通过高速摄影技术对试样表面的裂纹起裂和扩展过程进行了监测,基于实验结果着重讨论了冰充填裂隙对冻结岩体压缩破坏特征的影响机制。结果表明:(1)冻结没有改变试样强度随裂隙倾角的变化趋势,随裂隙倾角的增大,试样的强度均呈先减后增的趋势。强度最小值出现在裂隙倾角α=60°时,最大值出现在α=90°时;(2)在冻结状态下,试样的起裂模式随裂隙倾角的增加整体呈现“拉伸起裂→剪切起裂→拉伸起裂”的变化趋势,此外,相同裂隙倾角的试样在冻结状态下起裂的应力水平均高于在常温状态下;(3)冻结裂隙砂岩的力学性质受冻结作用和裂隙倾角双重控制。并进一步分析了冰填充裂隙对冻结岩体压缩破坏特征的影响,认为冰均起到了支撑、填充和黏结作用。在裂隙倾角较小时(0°~30°),裂隙冰的法向压力较高,强化效应主要来源于冰的支撑作用;当裂隙倾角较大(45°~75°)时,裂隙冰上的法向压力较低,强化效应主要来源于冰-岩界面黏结作用;裂隙倾角(近90°)与加载方向平行时,裂隙冰的法向应力变为拉应力,强化效应主要来源于冰-岩界面黏结作用。

破碎岩体隧道洞口开挖诱导滑坡与古滑坡耦合分析

以大栗树高速公路隧道洞口施工为工程背景,研究了在考虑古滑坡因素下洞口工作面边坡失稳及其加固技术。利用钻孔测斜数据(BCD)和Midas GTS折减强度有限元分析模型,分别推测了最危险滑动面,得知两者滑动面位置相似。并采用不平衡推力传递法,基于BCD推断滑动面计算安全系数。以BCD和有限元法的滑动面为基础,将滑动面近似假设为对数螺旋线,考虑地形因素,建立考虑多台阶边坡上限分析模型,研究了不同加固措施对边坡稳定的影响。结果表明,3种方法计算出的边坡安全系数结果相近。

基于数字图像相关方法的煤岩表面应变场及裂纹演化特征

基于数字图像相关方法,开展了煤岩体试样单轴压缩破坏的裂纹演化特征及破坏过程研究,分析了试样破坏过程的表面应变场、变形局部化带的拉伸位移演化和错动位移演化特征,精细化分析煤岩体变形破坏过程。研究结果表明:(1)根据试样的应力-应变曲线特征,将试样分为缓慢破坏型和瞬间破坏型。缓慢破坏型试样的破坏过程较为平稳,裂纹宽度较小。瞬间破坏型试样破坏过程较为剧烈,表面裂纹宽度增加,表现出明显的岩爆现象。(2)加载过程中,缓慢破坏型试样先产生应变集中后,裂纹沿变形局部化带扩展延伸并逐渐贯通;瞬间破坏型试样在应力峰值后试样表面瞬间产生宏观裂纹。(3)试样表面应变演化特征与加载过程中应力变化特征对应,反映了裂纹扩展规律。缓慢破坏型试样在加载过程中表面应变变化过程较为缓慢,并在后期呈现波动状态;瞬间破坏型试样在应力峰值点处,拉伸应变瞬间突增达到峰值,导致试样破坏。

三点弯曲载荷下岩体偏置斜裂隙的应力强度因子

地下巷道(硐室)顶板常因弯曲离层而破断,其破断位置与裂隙几何形态和位置密切关联。为揭示裂隙对岩层断裂的影响,建立了岩体偏置斜裂隙的三点弯曲模型,定义了裂隙的偏置系数和贯通率,分析了裂隙偏置系数、倾角和贯通率三者之间的关系,基于力学平衡原理和σ-K关系导出了偏置斜裂隙与偏置竖裂隙应力强度因子K的关系式。同时分析了裂隙倾角、贯通率和偏置系数对应力强度因子的影响规律。该方法可为裂隙影响下巷道(硐室)顶板的张拉断裂提供判定依据。

THE EFFECTS OF THREE-DIMENSIONAL PENNY-SHAPED CRACKS ON ZONAL DISINTEGRATION OF THE SURROUNDING ROCK MASSES AROUND A DEEP CIRCULAR TUNNEL

In this study, it was assumed that three-dimensional penny-shaped cracks existed in deep rock masses. A new non-Euclidean model was established, in which the effects of penny- shaped cracks and axial in-situ stress on zonal disintegration of deep rock masses were taken into account. Based on the non-Euclidean model, the stress intensity factors at tips of the penny- shaped cracks were determined. The strain energy density factor was applied to investigate the occurrence of fractured zones. It was observed from the numerical results that the magnitude and location of fractured zones were sensitive to micro- and macro-mechanical parameters, as well as the value of in-situ stress. The numerical results were in good agreement with the experimental data.

高地应力水平岩层隧道初期支护适应性研究

研究目的:蒙华铁路宜川县境内隧道地层多为水平砂泥岩互层地层,区域水平地应力高,在地应力和水平岩层共同作用下,隧道初期支护发生大面积起皮、开裂、掉块、钢架扭曲,对施工带来较大安全隐患,针对高地应力水平岩层采取什么类型的措施是亟须研究解决的问题。本次共研究了常规支护、加强型支护、加筋底板+长锚杆、限阻耗能型支护四种支护类型,结合3DEC离散元软件以及现场实际变形应力量测数据对四种支护类型效果进行对比分析,从而得出高地应力水平岩层应对工程措施。研究结论:(1)高地应力水平岩层开裂主要表现为拱顶喷混凝土剥皮、掉块、钢架扭曲;(2)单一加强支护参数方案、加筋底板+长锚杆支护方案对控制变形收敛具有效果,但拱部仍然存在开裂掉块现象,不能完全解决施工安全风险;(3)限阻耗能型支护可达到释放围岩压力的效果,限阻结构变形后初期支护未出现开裂现象;(4)在高地应力水平岩层中采用限阻耗能型支护在经济性、安全性上成效显著,推广应用效果良好。

单节理深埋隧洞开挖瞬态卸荷响应机理数值模拟研究

采用颗粒流数值模拟重现深埋单节理隧洞瞬态卸荷过程,从应力状态、变形特征、裂纹扩展等多角度探析节理特征对双江口水电站进厂交通洞瞬态卸荷效应的影响,研究表明:节理对深埋隧洞瞬态卸荷的应力调整过程有着重要的影响,应力集中区将由硐室底角、拱顶转移至节理尖端。随着节理长度的增加,节理尖端应力集中区域离自由面距离逐渐增大,围岩损伤区逐步向岩体深部发生迁移。不同节理角度下,微裂纹数目差异性显著,其中60°和30°节理围岩中的微裂纹数量较多;此外,压剪裂纹所占比例随着节理角度的增大呈现先增大后减小的变化趋势,45°时达最大。研究成果对水工隧洞开挖卸荷作用下围岩破坏机制认识和评价具有指导意义。

三轴压缩下裂隙岩体破坏模式及能量演化研究

为研究不同围压条件下含不同长度单裂隙岩体的裂纹扩展特征和能量演化规律,基于室内三轴压缩试验结果标定细观参数,开展了PFC^(2D)颗粒流数值模拟试验。结果表明:拉伸裂纹先于剪切裂纹产生,两者呈指数增长,裂隙长度减小和围压增大使拉伸裂纹和剪切裂纹快速增长时间滞后;最终破坏时,随裂隙长度增加,拉伸裂纹和剪切裂纹减少。应力集中于裂隙两端,裂纹周围存在应力集中现象。相同围压下,裂隙长度增加,岩样破坏时块体数减少。岩体破坏本质为能量储存、耗散与释放的过程,在加载过程中,岩体能量转化被分为4个阶段。裂隙长度增加削弱岩样储存应变能的能力,总能量减少,围压增强岩样储存应变能的能力。岩样破坏时,耗散能大于应变能,随裂隙增长,耗散能减少。

截齿旋转破碎板状岩体性能研究

截齿是掘进机的关键刀具,截齿的破岩性能影响掘进机的破岩效率。通过建立截齿旋转破碎板状岩体数值模型,研究截齿不同截割深度和旋转速度对板状岩体裂纹、截齿峰值截割力和截割比能耗的影响。结果表明:随着截割深度的增大,截齿峰值截割力和截割比能耗逐渐增大,当截割深度为18~28 mm时,板状岩体横向裂纹扩展范围不断增大,当截割深度为30 mm时,板状岩体横向裂纹扩展范围相对较小,碎裂效果较差;随着旋转速度的增大,板状岩体横向裂纹扩展范围不断增大,峰值截割力和截割比能耗逐渐增大但截割比能耗增长速度减慢。研究通过优化截割参数,提高截齿破岩性能,得到更好的岩板碎裂效果。

基于LCEM-GFEM方法爆炸载荷作用下含缺陷岩体损伤机理研究

在爆破作业过程中,岩体缺陷对裂纹扩展具有显著影响。本研究基于全局有限元方法的局部黏结单元(LCEM-GFEM)方法构建数值模拟模型,研究爆破作用下含缺陷岩体的损伤演化和裂纹扩展模式。通过引入能量传递系数,定量分析了缺陷形态对应力波传播和衰减的影响。结果表明,缺陷形态对岩体的损伤特性和裂纹扩展具有显著影响。随着平行缺陷夹角的增加,爆破诱发的裂缝与衍生裂缝的合并路径从缺陷末端转移到了缺陷中间,能量传递系数增加,分形维度减小。随着平行缺陷之间的水平距离增加,平行缺陷之间的裂缝数目和能量传递系数相应减少。随着垂直缺陷之间的垂直距离增加,穿过缺陷C的主水平裂缝长度增加,能量传递系数和分形维度也增加。研究结果可为受到爆破荷载作用下含缺陷岩体的损伤特征提供指导。

含双垂直缺陷岩体爆生裂纹扩展行为试验研究

为探究在爆炸载荷作用下含两条垂直预制缺陷岩体的爆生裂纹扩展行为,采用数字激光焦散线方法开展了一系列双垂直裂隙模型爆破实验,展现了爆生裂纹演化过程,揭示了单孔装药量对含缺陷岩体裂纹扩展行为(裂纹扩展长度、应力强度因子、扩展速度和起裂时间等)的影响规律。研究结果表明:随着单孔装药量增加,双垂直裂隙端部的裂纹扩展长度、裂纹扩展速度、裂纹起裂韧度和应力强度因子均呈增加趋势。对于裂纹J_(u),单孔的药量对裂纹扩展速度影响较小,并且裂纹扩展极限速度约为横波速度的0.38倍;对于迎爆端裂纹D_(l)和背爆端裂纹D_(r),随着单孔药量的增加,裂纹D_(l)和D_(r)的起裂时间减小,但裂纹D_(l)和裂纹D_(r)的峰值应力强度因子增大。相比于裂纹D_(l),裂纹D_(r)的应力强度因子和扩展长度增加显著。当爆炸应力波作用于缺陷B两端部的能量足以使两侧裂纹扩展时,裂纹D_(l)比裂纹D_(r)先起裂。单孔药量的增加能够增大裂纹D_(r)的扩展速度,但是对裂纹D_(l)扩展速度影响较小。研究结果可为含缺陷岩体在爆破荷载作用下的断裂行为提供实验参考,有助于含缺陷岩体爆破安全设计工作。

基于实景三维建模和点云投影分析的岩体裂隙识别应用

本研究旨在探讨无人机(UAV)实景三维建模技术和点云投影分析在岩体裂隙识别中的应用。首先,利用无人机搭载高清摄像镜头,对岩体进行高精度的三维实景扫描,获取大量的岩体表面数据;然后,通过图像处理和三维重建算法,对获取的数据进行处理和分析,实现对岩体裂隙的准确识别和测量;最后,结合实地验证和地质勘探实际需求,验证该技术在岩体裂隙识别中的可行性和有效性。研究结果表明,无人机实景三维建模和点云投影分析能够实现对岩体裂隙的高精度识别和三维重建,裂缝识别准确率由83.4%提升至93.1%,漏提率由30.3%降低至15.4%。该技术不仅在提高识别精度和效率方面具有显著优势,同时也能够降低传统岩体勘探过程中的人力和物力成本。

动载下3条断续裂隙岩样的裂缝贯通机制

采用含3条断续预制裂隙的类砂岩模型试样进行单轴动力加载试验,对不同裂隙空间位置条件下断续裂隙岩体中裂隙的贯通机制进行了研究。静、动荷载下的对比研究成果显示:不同空间位置的裂隙贯通方式存在较大差异,且对动载的响应不同;动载下分支裂纹扩展及贯通具有惯性效应,即动载下裂尖次生共面、次生倾斜裂纹起裂后易朝原起裂方向快速发展,动载下易在两预制裂隙内端部产生直接贯通。这与静载下岩桥处的贯通常通过分支裂纹拐折扩展、相连不同,这也是导致裂隙试样中低应变速率下强度增大(即速率效应)的主要原因。同时,试验结果也表明:含裂隙试样静、动荷载下裂隙间的多次贯通是导致其呈现出渐进破坏特征的主要原因。

裂隙岩石拉伸断裂破坏理论分析试探

利用边界配置法对最大周向应力理论、有效应力理论进行了修正,建立了实验室尺度下拉剪裂纹的两种破坏准则,并通过相应的破坏准则建立起了岩石单轴拉伸强度与断裂韧度之间的关系,给出了量化裂隙岩石试件抗拉强度的无量纲量,分析了裂纹倾角、裂纹长度对裂纹尖端开裂角及裂隙岩石试件的抗拉断能力的影响。结果表明,开裂角以及裂隙岩石的抗拉断裂能力(抗拉强度)均随裂纹倾角的增大而增大;对于具有宏观裂隙的试件,开裂角及抗拉断能力随裂隙长度的增加而递减;试件的尺度对裂隙岩石的强度影响不容忽视。