Rock damage and fracturing induced by high static stress and slightly dynamic disturbance with acoustic emission and digital image correlation techniques

A series of coupled static-dynamic loading tests is carried out in this study to understand the effect of slightly dynamic disturbance on the rocks under high static stress.The acoustic emission(AE)and digital image correlation(DIC)techniques are combined to quantitatively characterize the damage and fracturing behaviors of rocks.The effects of three influencing factors,i.e.initial static stress,disturbance amplitude,and disturbance frequency,on the damage and fracturing evolution are analyzed.The experimental results reveal the great differences in AE characteristics and fracturing behaviors of rocks under static loads and coupled static-dynamic loads.Both the Kaiser effect and Felicity effect are observed during the disturbance loading process.The crack initiation,stable and unstable propagation in the highly-stressed rocks can be triggered by cyclic disturbance loads,and more local tensile splitting cracks are found in the rocks subjected to coupled static-dynamic loads.The damage and fracturing evolution of rocks during cyclic disturbances can be divided into two stages,i.e.steady and accelerated stages,and the increase rate and proportion of each stage are greatly affected by these influencing factors.High initial static stress,low disturbance frequency,and high disturbance amplitude are considered to be adverse factors to the stability of the rocks,which would induce a high increase rate of the steady stage and a high proportion of the accelerated stage within the whole disturbance period.Based on the two-stage damage evolution trend,a linear-exponential damage model is employed to predict the instability of the rocks under coupled static-dynamic loads.

Probabilistic estimate of rock mass static and dynamic demands for underground excavation stabilisation

Excavation damage under high in situ stress depends largely upon the potential block size associated with any violent ejection.The size and shape of the dynamic instability are largely controlled by the location,orientation and extent of the pre-existing geological discontinuities.A new methodology is presented in which the rock mass demand can be expressed in terms of the mass in tonnes of unstable rock that is ejected per unit area of the excavation surface where failure occurs.A probabilistic approach has been implemented to estimate the potential rock mass instabilities and their associated static and dynamic demands.The new methodology considers that the strain energy released by the rock mass during violent stress-driven failure is largely converted into kinetic energy of ejection for blocks.The estimated dynamic demand has been favourably compared with observations of rock mass damage in a number of underground excavations.

Crack propagation mechanism of compression-shear rock under static-dynamic loading and seepage water pressure

To reveal the water inrush mechanics of underground deep rock mass subjected to dynamic disturbance such as blasting, compression-shear rock crack initiation rule and the evolution of crack tip stress intensity factor are analyzed under static-dynamic loading and seepage water pressure on the basis of theoretical deduction and experimental research. It is shown that the major influence factors of the crack tip stress intensity factor are seepage pressure, dynamic load, static stress and crack angle. The existence of seepage water pressure aggravates propagation of branch cracks. With the seepage pressure increasing, the branch crack experiences unstable extension from stable propagation. The dynamic load in the direction of maximum main stress increases type I crack tip stress intensity factor and its influence on type II crack intensity factor is related with crack angle and material property. Crack initiation angle changes with the dynamic load. The initial crack initiation angle of type I dynamic crack fracture is 70.5°. The compression-shear crack initial strength is related to seepage pressure, confining pressure, and dynamic load. Experimental results verify that the initial crack strength increases with the confining pressure increasing, and decreases with the seepage pressure increasing.

Caustic study on blast-induced wing crack behaviors in dynamic–static superimposed stress field

This paper studies blast-induced wing crack behavior in a dynamic–static superimposed stress field using high-speed photography in combination with the optical method of caustics. With a static–dynamic loading setup, four PMMA plate specimens with pre-existing cracks under different static loading and the same dynamic loading were tested to observe the mechanical characteristics and the kinematic characteristics of blast-induced wing cracks during the propagation process, including crack length, crack velocity and dynamic stress intensity factor(SIF) at the crack tip. The results show that the behavior of the blast-induced wing crack is affected by the explosion stress wave and initial static stress, and the initial static stress with the direction being perpendicular to the wing crack propagation direction hinders crack propagation. Furthermore, the boundary constraint condition of the specimen plays an important role on the behavior of the crack propagation in the experiment.

Degradation and breakdown behaviors of SGTs under repetitive unclamped inductive switching avalanche stress

The repetitive unclamped inductive switching(UIS)avalanche stress is conducted to investigate the degradation and breakdown behaviors of conventional shield gate trench MOSFET(C-SGT)and P-ring SGT MOSFETs(P-SGT).It is found that the static and dynamic parameters of both devices show different degrees of degradation.Combining experimental and simulation results,the hot holes trapped into the Si/SiO_(2) interface and the increase of crystal lattice temperature should be responsible for the degradation and breakdown behaviors.Moreover,under repetitive UIS avalanche stress,the reliability of P-SGT overcomes that of C-SGT,benefitting from the decreasing of the impact ionization rate at bottom of field oxide caused by the existence of P-ring.

Research progress of monitoring, forecasting, and prevention of rockburst in underground coal mining in China

As one of the dynamic disasters of coal mines,rockburst seriously affects underground safe coal mining.Based on the laboratory test,field test,and theoretical analysis,this study proposed the principle of the rock burst induced by the combination of dynamic and static stresses and divided such rock burst into three types,including induced by primary dynamic stress,mainly induced by dynamic stress,and by dynamic stress in low critical stress state.The expressions of the static stress induced by coal mining and dynamic stress induced by mining tremors were obtained.Moreover,theories and technologies at home and abroad were summarized concerning the monitoring,forecasting,and preventing of rockburst.These mainly include the zoning and leveling forecasting method,electromagnetic radiation technology,elastic wave and seismic wave computed tomography technologies in aspect of rockburst monitoring,as well as the intensity weakening theory,the strong-soft-strong structure effect,the directional hydraulic fracturing technology,the roadway support system in regards of rockburst prevention.The prospect of rockburst development suggested that researches concerning the rockburst mechanism should be quantitatively developed around the roadway and coalface surrounding coal-rock mass.It should be focused on the rockburst mechanism and prevention technology of mining with over 1,000 km deep and mining in large tectonic zone.In addition,the monitoring and prevention of rockburst should be based on rockburst mechanism.

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.

Dynamic failure risk of coal pillar formed by irregular shape longwall face:A case study

Irregular shape workface would result in the presence of coal pillar, which leads to high stress concentration and possibly induces coal bumps. In order to study the coal bump mechanism of pillars, static and dynamic stress overlapping(SDSO) method was proposed to explain the impacts of static stress concentration and tremors induced by mining activities. The stress and deformation in surrounding rock of mining face were analyzed based on the field case study at 1303 workface in Zhaolou Coal Mine in China.The results illustrate that the surrounding rock of a workface could be divided into four different zones,i.e., residual stress zone, stress decrease zone, stress increase zone and original stress zone. The stress increase zone is prone to failure under the SDSO impact loading conditions and will provide elastic energy for inducing coal bump. Based on the numerical modelling results, the evolution of static stress in coal pillar as the size of gob increasing was studied, and the impact of dynamic stress was investigated through analyzing the characteristics of tremor activities. The numerical results demonstrate the peak value of vertical stress in coal pillar rises from about 30 MPa with mining distance 10 m to 52.6 MPa with mining distance 120 m, and the location of peak stress transfers to the inner zone of coal pillars as the workface moves forward. For the daily tremor activities, tremors with high energy released indicate high dynamic stress disturbance on the surrounding rock, therefore, the impact of dynamic stressing is more serious during workface extension period because the tremor frequency and average energy after workface extension are higher than those before the workface extension.

A mathematical model for ATP-mediated calcium dynamics in vascular endothelial cells induced by fluid shear stress

In consideration of the mechanism for shear-stress-induced Ca^2＋ influx via ATP（adenosine triphosphate）-gated ion channel P2X4 in vascular endothelial cells, a modified model is proposed to describe the shear-stress-induced Ca^2＋ influx. It is affected both by the Ca^2＋ gradient across the cell membrane and extracellular ATP concentration on the cell surface. Meanwhile, a new static ATP release model is constructed by using published experimental data. Combining the modified intracellular calcium dynamics model with the new ATP release model, we establish a nonlinear Ca^2＋ dynamic system in vascular endothelial cells. The ATP-mediated calcium response in vascular endothelial cells subjected to shear stresses is analyzed by solving the governing equations of the integrated dynamic system. Numerical results show that the shear-stress-induced calcium response predicted by the proposed model is more consistent with the experimental observations than that predicted by existing models.

爆破扰动高应力巷道围岩力学响应特征研究

为研究深井厚硬顶板采场巷道围岩在高静载和强动载耦合作用下的力学响应,基于相似模拟试验分析原岩应力、采动应力及爆破扰动三阶段的巷道围岩应力场与位移场,结合光纤环向应变场研究巷道围岩破坏特征,探索爆破扰动应力波在不同煤岩体中的传播规律及巷道动力响应机制。研究结果表明:巷道开挖后顶底板卸压明显,两帮产生应力集中区,采动应力阶段应力集中区范围增加50%,爆破后顶板围岩沿垮落角大范围卸压,应力沿巷道左肩窝逆时针逐渐增大;浅部巷道围岩呈现向自由面膨胀–变形,受巷道肩窝处剪切滑移错动影响,锚杆、锚索支护场产生相反的位移量,应力波扰动后,巷道左帮产生拉伸裂纹并与锚杆支护场连成宏观裂纹,裂纹发育高度大于锚杆支护场高度;巷道围岩顶底板呈现明显的张拉破坏特征,左右肩角呈现张拉及剪切复合破坏形式;应力波由小阻抗介质进入大阻抗介质的衰减速度最快,在同种介质中衰减速度次之,由大阻抗介质进入小阻抗介质中应力波峰值反而增大,应力波峰值强度衰减后仍大于巷道顶板极限抗拉强度,导致巷道围岩大变形失稳并产生一定程度的动力响应。基于应力波连续穿过层状岩体理论模型,结合动静载叠加理论,可优化爆破参数从而实现减冲抗冲主被动联合支护。

静态应力扰动对走滑断层阶区附近地震破裂传播影响的二维数值模拟

动态破裂在走滑断裂带上阶区附近的传播能力控制了地震破裂的可能规模,而非均匀应力场对动态破裂的传播有显著影响。在本研究中,我们通过整合动态破裂模型和静态应力扰动模型,构建了走滑断层上的非均匀应力场,对走滑断层阶区附近前次动态破裂所产生的静态应力扰动对后续破裂传播行为的影响进行了二维动态破裂模型研究。模拟结果表明,当考虑到走滑断层上的地震复发行为时,即使前序地震破裂传播被阶区所阻挡,其所产生的静态应力扰动也可显著提升下次地震跨该阶区传播的能力。另外,不同的初始均匀应力使得动态破裂能够跨大致相同宽度的阶区传播。较大的应力降或者较小的断层强度比(S)能够使得动态破裂在相对较宽的阶区上传播。因此,在研究走滑断裂带不同分段的级联破裂模式时,需要考虑前序地震所造成的静态应力扰动影响。

扰动诱发高应力岩石动力响应及岩爆灾变机制

为揭示深部矿山岩爆发生机制,以硬质红砂岩为研究对象,利用岩石动静组合加载试验系统开展了无轴向静压及4个轴压条件下的不同入射能冲击试验,获得了纯动载及动静组合加载下岩样的力学行为与破坏特征。结果表明:试样最终形态分为完整、轴向劈裂、表面剥离、即时型粉碎和滞后型粉碎五类,其中,表面剥离和滞后型粉碎两类破坏模式表现出“岩爆”特征,即Ⅰ型应力−应变曲线、峰后释放能量、岩石自身静应变储能驱动碎片弹射、明显压剪破坏面;根据碎片弹射与动力加载的相对时间,进一步将表面剥离与滞后型粉碎破坏分别对应深地工程中的“即时型”和“滞后型”岩爆;动力扰动是岩爆的关键诱发因素,触发岩爆的临界扰动能随轴压比升高而逐渐降低。

变区段煤柱工作面诱冲机理及防治技术研究

针对某矿变区段煤柱工作面开采冲击危险性较高的问题,运用数值模拟方法对工作面采掘过程中煤柱区域垂直应力分布规律进行研究,分析了不同宽度区段煤柱应力积聚特征,揭示了变区段煤柱工作面诱冲机理,并制定了“近场-远场”协同卸压方案。研究结果表明,较宽的区段煤柱(30 m和55 m)受采空区侧向支承压力和超前支承压力影响,煤柱应力集中程度较高;受“近场高静载+远场动载”叠加影响,变区段煤柱工作面回采期间易诱发冲击地压;采取近场高承压煤体强卸压+远场高位坚硬顶板超前预裂断顶卸压协同控制方案后,微震能量事件始终维持在104J以下,表明控制方案能够有效降低工作面采掘期间的冲击危险性。

Complete Coulomb stress changes induced by the Ms7.6 earthquake in Lancang-Gengma, Yunnan and triggering of aftershocks by dynamic and static stress

The spatiotemporal evolution patterns of complete Coulomb stress changes caused by 1988 Ms7.6 earthquake in Lancang-Gengma, Yunnan, are calculated and studied. And the triggering problems of Ms7.2 Gengma shock occurring 13 minutes after the main shock and of Ms5.0―6.9 aftershocks within 24 days after the main shock are discussed. The results show that the spatial distribution patterns of complete Coulomb stress changes of the Ms7.6 main shock are strongly asymmetric. The areas of positive dynamic and static Coulomb stress are both coincident well with the strong aftershocks' loca-tions. The Ms7.2 Gengma shock and most of strong aftershocks are subjected to the triggering effect of dynamic and static Coulomb stresses induced by the Ms7.6 Lancang earthquake.

小山口水电站砂砾石面板坝三维静、动力有限元计算分析

鉴于小山口水电站为软岩基础,坝体较长,且混合坝接头部位非常复杂。为了解决该坝体面临的变形控制难、坝体抗震等级高等设计难题,结合砂砾石面板坝结构、坝壳料设计,通过构建三维有限元模型,该模型包括坝体、泥岩和沙质泥岩基础组成。在静力本构分析中,采用了非线性邓肯E-B模型,而在动力本构分析中,则使用了等效线性粘弹性模型。通过这个模型,对坝体的应力和变形进行了全面系统的研究和分析,同时对坝体的抗震性能和抗震稳定性进行了验证。结果表明,在各种工况下坝体所表现出的变形规律合理。同时在混凝土面板最大拉应力和压应力都符合所采用混凝土材料的允许应力要求,坝体的抗震性能和抗震稳定性满足规范要求。

静动力边界转换及其合理性验证方法的研究

繁琐复杂的静动力边界转换处理是进行静动力耦合模拟的关键步骤,为了研究黏弹性边界条件下传统静动力边界转换的合理性及其验证方法的适用性,本文首先根据弹性叠加原理提出了一种验证静动力耦合模拟分析中静动力边界转换合理性的方法(参考解法);然后基于有限元软件ABAQUS,并结合自行研发的适用于成层介质的黏弹性边界施加和等效节点力计算程序VBEA2.0,对多土层自由场静动力耦合模型和土-地下结构静动力耦合模型进行了地震反应分析,对参考解法的适用性进行了探究;最后使用本文提出的参考解法,对一种典型的未进行合理静动力边界转换的自由场模型进行了分析,探讨了静动力边界转换产生振荡的原因和机理。研究结果表明:用于验证静动力边界转换合理性的参考解法,既适用于多土层自由场静动力耦合计算模型,又适用于土-结构相互作用的静动力耦合模型;静动力边界转换后产?生的振荡是静动力耦合计算模型静力不平衡所导致,一般是因为未合理施加边界反力或单元应力。

不同主横梁建模方式对弧门静动力学模拟结果影响

针对弧形闸门有限元分析中采用不同建模方式易造成数值模拟结果差异性的问题,以贵州乌江沙沱水电站大型露顶式弧形闸门为例,从计算原理角度探究了主梁翼缘采用节点耦合法、厚度叠加法两种建模方式对闸门静动力学计算结果(三维非线性静力学、模态分析和瞬态动力学)的影响。通过对比分析发现:采用厚度叠加的简化方式增加了构件的刚度,对闸门静力复核不利;两种建模方式对闸门干湿模态下的振型和自振频率影响较小;采用节点耦合法获取的支臂垂向振动程度较厚度叠加法结果略大,支臂与主横梁连接处敏感区域的动应力较厚度叠加法结果明显增大。两种建模方式对闸门整体结构属性影响有限,对支臂与主横梁连接处等敏感区域进行计算复核时应尽量采用节点耦合法,使计算结果更偏于安全。

某山谷贮灰场坝体静动力分析

燃煤发电的余灰一般都会堆放在灰场,随着堆灰高度的增加,灰场底部灰体和地基的应力会逐渐变大,部分灰体和地基土会进入塑性区域,且随着塑性区的加大会直接威胁到灰场的安全,因而高坝在安全方面的风险也随之加大,发生滑坡的可能性及滑坡造成的危害也会明显增加。根据规范要求,山谷干灰场最终贮灰高度超过100 m时应作专题研究。以龙王庙灰场为例,开展了灰场坝体的有限元静动力分析,得出了各工况下坝体的应力场和位移场,确定了坝体动剪应力、水平加速度和相对位移的分布规律,对同类工程有一定的参考价值。

强夯加固粉土地基的竖向附加动应力传递特性

强夯法在各类地基处理项目中得到了广泛应用,但其加固机理仍落后于实践,特别是强夯引起的地基内部竖向附加动应力传递特性。鉴于此,先基于Boussinesq应力解和动量定理推导强夯竖向附加动应力和附加剪应力拟静力解。然后,以新疆维吾尔自治区乌鲁木齐市机场北区扩建项目为工程背景,运用夯锤速度法,模拟1000~4000 kN·m能级间强夯引起的动力波传播过程、竖向附加动应力传递特性和夯后土体位移场。最后,将拟静力解与动力数值解的计算结果进行对比分析。研究结果表明:强夯引起的动力波传播呈半圆弧形,竖向附加动应力传递呈半椭圆形。动力波的传播距离决定了强夯影响范围,竖向附加动应力显著区边界决定了强夯有效加固区。由拟静力解得到的竖向附加动应力相比数值解沿深度方向的衰减更快。该研究结果可为强夯法地基处理工程提供重要参考。

深井断层切割煤柱冲击地压防治实践

针对大采深影响下断层切割煤柱区域冲击地压防治难题,采用理论分析、现场实测方式对断层切割煤柱区域冲击危险性进行了分析与研究,得到如下结论:断层切割煤柱区域在静载条件下趋近于失稳状态,推采过程中动静载应力叠加,煤柱冲击危险性升高;通过断层切割煤柱失稳模型和现场微震、应力及其它数据监测分析发现,工作面初采阶段及单、双工作面见方阶段,微震能量积聚显著,应力集中区域明显,在此过程中断层切割煤柱存在整体失稳现象,通过大直径钻孔卸压、爆破预裂顶板及加强支护等冲击地压防护措施加强对此区域的冲击地压监测与防治,实现断层切割煤柱区域的安全回采。