Numerical simulation on rockburst of underground opening triggered by dynamic disturbance

The dynamic disturbance, which is termed as the time-dependent loading such as explosion, vibration, stress impact from neighboring rockbursts, earthquakes, may trigger the rockbursts around the underground opening at depth. A numerical model capable of studying the dynamic failure process of rock under coupled static geo-stress and dynamic disturbance is proposed, and it is implemented into the Rock Failure Process Analysis (RFPA), a general finite element package to analyze the damage and failure process of engineering materials such as rock and concrete. Based on the consideration of the static geo-stress, the RFPA-Dynamics is used to simulate the rockburst that is deemed to be triggered by dynamic disturbance around the deep underground opening. The effect of lateral pressure coefficient and dynamic disturbance waveform on the development of failure zone around the underground opening is numerically simulated. The numerical results indicate that the dynamic disturbance is one of the most important mechanisms that trigger the rockbursts around underground opening. Therefore, it is of theoretical and practical significance to investigate the effect of dynamic disturbance on the rockbursts of underground opening, especially for the underground excavation at depth where the surrounding rockmass is highly stressed. The numerical results also reveal that the contribution of the dynamic disturbances is closely pertinent to both the static geo-stress condition and the waveforms of the dynamic disturbance. In general, dynamic disturbance brings about the greater influences on the stability of underground opening with its increasing magnitude and prolonged duration. However, with regard to the specific static geo-stress condition and characteristics of dynamic disturbance, the contribution of dynamic disturbance to trigger the rockbursts must be examined based on numerical analysis according to the specific geo-stress conditions and characteristics of the dynamic disturbance.     

动态扰动触发深部巷道发生失稳破裂的数值模拟

处于深部的岩体内部积累了大量的弹性应变能，在外部动力扰动下这些能量以非常猛烈的方式释放，从而导致岩爆的发生。模拟不同侧压力系数条件下动态扰动触发深部巷道发生失稳破裂的整个过程，并揭示动态扰动触发巷道岩爆的力学机制。数值模拟结果表明，动态扰动对巷道变形与破裂的触发与地应力状态密切相关；动态扰动应力波的波形也是影响巷道破裂的重要因素，随着应力波幅值和应力波作用时间的加长，动态扰动给巷道稳定性带来的影响越大。因此，对动态扰动触发巷道破坏的研究具有非常重要的理论价值和现实意义。     

Assessment of strain bursting in deep tunnelling by using the finite-discrete element method

Rockbursting in deep tunnelling is a complex phenomenon posing significant challenges both at the design and construction stages of an underground excavation within hard rock masses and under high in situ stresses. While local experience, field monitoring, and informed data-rich analysis are some of the tools commonly used to manage the hazards and the associated risks, advanced numerical techniques based on discontinuum modelling have also shown potential in assisting in the assessment of rockbursting. In this study, the hybrid finite-discrete element method (FDEM) is employed to investigate the failure and fracturing processes, and the mechanisms of energy storage and rapid release resulting in bursting, as well as to assess its utility as part of the design process of underground excavations. Following the calibration of the numerical model to simulate a deep excavation in a hard, massive rock mass, discrete fracture network (DFN) geometries are integrated into the model in order to examine the impact of rock structure on rockbursting under high in situ stresses. The obtained analysis results not only highlight the importance of explicitly simulating pre-existing joints within the model, as they affect the mobilised failure mechanisms and the intensity of strain bursting phenomena, but also show how the employed joint network geometry, the field stress conditions, and their interaction influence the extent and depth of the excavation induced damage. Furthermore, a rigorous analysis of the mass and velocity of the ejected rock blocks and comparison of the obtained data with well-established semi-empirical approaches demonstrate the potential of the method to provide realistic estimates of the kinetic energy released during bursting for determining the energy support demand.     

圆形巷道两帮水平切槽对围岩卸压的数值分析

处于深部高应力的岩体中储存有大量的弹性应变能,它是引发深部硬岩巷道发生岩爆的内因。卸压法可以用于改变巷道和洞室附近围岩的应力场,使这部分围岩处于应力降低区,从而达到保持其稳定性的目的。本文用岩石破裂过程分析RFPA系统模拟圆形巷道周边开卸压槽前后巷道围岩的变形、损伤与破坏过程,分析了不同原岩应力状态(侧压力系数)和切槽长度条件下围岩的应力和损伤区的分布特征,揭示了围岩中开槽卸压的力学机理。数值模拟结果表明,数值模拟证实了当卸压槽深度为巷道直径的0.5倍左右时,围岩的卸压效果明显,但过长的卸压槽长度会导致整个巷道围岩结构体的承载力降低和变形过大。该项研究对于巷道卸压的工程实践具有一定的理论指导意义。     

动力扰动下侧压系数对卸压孔与锚杆支护的研究

为探讨各因素对深部巷道卸压孔与锚杆联合支护的影响机制,利用岩石破裂过程分析系统RFPA^2D-Dynamic模拟了巷道支护模型在动力扰动作用下围岩应力场的分布规律、巷道破坏形态特征。通过分析得到动静组合加载下不同侧压的巷道围岩应力重分布的一般规律,并从破坏单元声发射能量释放的角度分析了动静组合加载对围岩的损伤效应。研究指出,侧压系数λ是静态和动态扰动作用下巷道围岩应力重分布的主控因素;高围压条件下,动力扰动成为触发巷道破裂失稳的主要诱因,且动力扰动作用对不同围压的巷道围岩破坏形态的影响各不相同。     

主应力对洞室围岩失稳破坏行为的影响研究

 针对复杂应力环境三向应力状态下地下洞室围岩破坏条件和破裂机制,采用统计损伤理论和数值模拟方法,建立三维非均匀性地质模型,考虑应力的三维效应,引入强度折减法,一方面在保持模型边界条件的同时实现洞室围岩的逐步破坏,另一方面以此定量评价不同应力场中洞室安全稳定状况,探讨不同侧压力系数和轴向应力条件下洞室围岩破坏模式,探究中间主应力对洞室稳定性的影响以及深部岩体分区破裂化现象产生条件和破裂规律等。结果表明,侧压力系数影响洞室围岩初始破裂形成部位和发展趋势;不同的轴向应力使得洞室围岩破裂区域和范围显著不同,在不同的侧压力系数条件下,轴向应力影响洞室稳定的规律存在差异;不同方向中间主应力对洞室围岩安全稳定状况的影响是不同的;当洞室轴线方向与最大水平应力方向平行时,较大的轴向应力会使洞室围岩产生分区破裂化现象,围岩破坏的区域也是拉应变集中的区域等。这些结果对进一步揭示地下洞室围岩非线性变形破坏行为,评价岩土工程安全稳定性,采取合理的支护措施等均具有重要意义。     

Discussions on rockburst and dynamic ground support in deep mines

The paper is a summary of discussions on four topics in rockburst and dynamic ground support.Topic1 is the mechanisms of rockburst.Rockburst events are classified into two categories in accordance with the triggering mechanisms,i.e.strain burst and fault-slip burst.Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks.Fault-slip burst is triggered by fault-slip induced seismicity.Topic 2 is prediction and forecasting of rockburst events.Prediction for a rockburst event must tell the location,timing and magnitude of the event.Forecasting could simply foresee the probability of some of the three parameters.It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies,but forecasting is possible,for example the possible locations of strain burst in an underground opening.At present,the approach using seismic monitoring and numerical modelling is a promising forecasting method.Topic 3 is preconditioning methods.The current preconditioning methods are blasting,relief-hole drilling and hydrofracturing.Defusing fault-slip seismicity is difficult and challenging but has been achieved.In very deep locations(3000 m),the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required.Topic 4 is dynamic ground support against rockburst.Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass.The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps.Yielding props and engineered timber props are also used for dynamic support.     

Principles of rockbolting design

This article introduces the principles of underground rockbolting design.The items discussed include underground loading conditions,natural pressure zone around an underground opening,design methodologies,selection of rockbolt types,determination of bolt length and spacing,factor of safety,and compatibility between support elements.Different types of rockbolting used in engineering practise are also presented.The traditional principle of selecting strong rockbolts is valid only in conditions of low in situ stresses in the rock mass.Energy-absorbing rockbolts are preferred in the case of high in situ stresses.A natural pressure arch is formed in the rock at a certain distance behind the tunnel wall.Rockbolts should be long enough to reach the natural pressure arch when the failure zone is small.The bolt length should be at least 1 m beyond the failure zone.In the case of a vast failure zone,tightly spaced short rockbolts are installed to establish an artificial pressure arch within the failure zone and long cables are anchored on the natural pressure arch.In this case,the rockbolts are usually less than 3 m long in mine drifts,but can be up to 7 m in large-scale rock caverns.Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch.In addition to the factor of safety,the maximum allowable displacement in the tunnel and the ultimate displacement capacity of rockbolts must be also taken into account in the design.Finally,rockbolts should be compatible with other support elements in the same support system in terms of displacement and energy absorption capacities.     

基于工程岩体起裂判据的岩爆破坏区研究

随着深部地下工程的兴建,岩爆发生的概率大大增加,工程建设中常遇到的岩爆类型为应变型岩爆,确定岩爆破坏区范围和深度对地下工程支护设计和施工安全有着重要的指导意义。本文根据秦岭终南山混合片麻岩单轴压缩变形实验结果,采用裂纹体积应变法和侧向应变响应法,得到混合片麻岩的裂纹起裂应力。在分析混合片麻岩的起裂机制基础上,建立了基于裂纹起裂应力的工程岩体起裂判据,并根据围岩二次应力Kirsch计算公式,采用弹性理论推导了岩爆破坏区范围和深度的计算公式。岩爆破坏区的计算结果与秦岭终南山公路隧道2号通风竖井实际情况有很好的一致性,对类似地下工程有一定参考价值。     

Numerical study on failure mechanism of tunnel in jointed rock mass

During underground excavation many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this paper, a numerical code called RFPA was used to study the influence of different dip angle of layered joints and the lateral pressure coefficient on the stability of tunnel in jointed rock mass. Numerical analysis indicated that both the dip angle of joints and the lateral pressure coefficient have significant impacts on the failure mode and displacement characters of tunnel. The progressive failure processes of tunnel in jointed rock mass were presented and the mechanisms were discussed. The applicable condition of geographical method by Goodman is also discussed. These results offer a guideline in support design.     

一维动静组合加载下砂岩动力学特性的试验研究

 基于对深部岩石承受高地应力并在动力开挖扰动下发生破坏这一问题的科学认识,利用改造的劈裂霍普金森压杆动静组合加载试验装置,开展一维动静组合加载下砂岩的动力学特性试验研究。选取无轴压和3个典型轴压水平4种情形,开展不同应变率下的冲击试验。研究结果表明,相同应变率下岩石对外界冲击的响应受轴压比影响很大,冲击强度会随着轴压比的增加出现先增加后减小的趋势,在轴压比为0.6～0.7时达到最大值。相同轴压下,冲击强度会随着应变率的增加而增加,呈现指数函数关系。在一定的轴压比范围内,随着入射能的递增,岩石在加载破坏试验中先后会经历“吸收能量–释放能量–吸收能量”3个阶段。这3个阶段可以较好的解释高应力下岩石的动态强度递增、岩爆发生和诱导致裂三者之间的互相转化机制,对深部岩石工程的实践可以提供理论上的指导。     

双护盾TBM在软弱地层中的掘进模式选择

 双护盾岩石掘进机(TBM)采用双护盾模式掘进时,支撑靴的支撑压力常会造成围岩的破坏进而引发其他事故,针对青海“引大济湟”工程中双护盾TBM在软弱地层中掘进模式的选择问题,提出模拟双护盾TBM掘进过程的三维有限元模型,分析支撑压力作用下围岩的破坏机制及不同地应力分布情况下支撑压力对软弱围岩的影响。分析结果表明,支撑压力作用下围岩的破坏形式主要为剪切破坏和拉裂破坏。在浅埋自重应力场下,当侧向压力系数l＜1时,支撑压力一般会使软弱围岩的塑性区有较大程度的扩展,且在隧洞埋深较小时还可能造成大面积拉裂区的出现;其次,对支撑压力导致塑性区扩展的围岩临界强度的分析表明：在自重应力场下应采用单护盾模式或掘进参数降低的双护盾掘进模式掘进。在埋深较大且地应力侧向压力系数l≥1时,支撑压力对围岩的影响相对有限,一般不会导致新塑性区的产生,但可能造成旧塑性区的进一步破坏,此时,可谨慎地采用双护盾模式掘进。     

考虑围压影响的深埋圆隧围岩应变软化与剪胀特性分析

 不同围压下岩石应变软化与剪胀特性不同,若在隧洞开挖中考虑围岩塑性区域内变化围压影响,其应力–应变场求解方式将区别于既有文献中的传统方法。根据围压影响下应变软化围岩的临界塑性剪切应变变化特征,给出改进的判断围岩是否进入塑性残余区域的规则;引入考虑围压与临界塑性剪切应变的非线性剪胀模型。基于Hoek-Brown屈服准则,根据一定径向应力增量将围岩塑性软化与残余区域分层,采用有限差分法对围岩应力–应变场进行求解;为分析围压对围岩稳定性的影响,根据临界塑性剪切应变与剪胀系数变化与否,设定4种非线性力学模型,深入分析并比较4种力学模型下临界塑性剪切应变、剪胀系数与围岩变形等在塑性软化与残余区域的分布规律。研究结果表明：地质强度指标GSI较小时,考虑围压影响下的围岩应力–应变场与未考虑时差异明显;此时临界塑性剪切应变的减小对开挖边界的围岩剪胀性具一定抑制作用。     

坚硬顶板水压致裂控制理论与成套技术

煤矿坚硬顶板具有硬度大、整体性好、分层厚度大等特点,导致诸多围岩控制与安全难题。水压致裂可改造顶板岩体结构,控制工作面顶板的冒落;提出坚硬顶板水压致裂控制的理论与成套技术框架。采用真三轴实验系统等研究揭示水压裂缝的扁椭球体典型形态和空间转向扩展形态,给出围压主应力差、排量、层面与原生裂隙等对水压裂缝扩展的影响规律,考虑围岩的应力应变状态与控顶效果,阐明定向压裂临空坚硬悬顶的断顶线位置适当内错煤柱的原理。给出采动岩体水压致裂的时空关系及确定方法。针对裂缝形态的控制要求,提出定向水力割缝致裂等系统的控制致裂方法,在此基础上研制煤矿井下高压(60 MPa)水压致裂的成套装备。针对不同类型工程特点,控制水压主裂缝扩展、翼型裂纹扩展和吸水湿润作用,使顶板及时充分冒落,实现围岩弱化、应力转移、诱导矿压破煤等功能。研发了工作面端头悬顶、切眼及中部坚硬顶板、坚硬顶煤弱化、综放面初采瓦斯、临空巷道冲击地压和大变形等控制成套工艺技术。成套技术与装备已在大同矿区、神东矿区等推广应用。与传统爆破弱化顶板相比,水压致裂弱化顶板管理简单、扰动小、安全性高、工程量少、作用范围大、控制距离远,且经济成本不到其1/10,在深部开采中更具有优势。     

Laboratory-scale investigation of response characteristics of liquid-filled rock joints with different joint inclinations under dynamic loading

In underground rock engineering, water-bearing faults may be subjected to dynamic loading, resulting in the coupling of hydraulic and dynamic hazards. Understanding the interaction mechanism between the stress waves induced by dynamic loadings and liquid-filled rock joints is therefore crucial. In this study, an auxiliary device for simulating the liquid-filled layer was developed to analyze the dynamic response characteristics of liquid-filled rock joints in laboratory. Granite and polymethyl methacrylate (PMMA) specimens were chosen for testing, and high-amplitude shock waves induced by a split Hopkinson pressure bar (SHPB) were used to produce dynamic loadings. Impact loading tests were conducted on liquid-filled rock joints with different joint inclinations. The energy propagation coefficient and peak liquid pressure were proposed to investigate the energy propagation and attenuation of waves propagating across the joints, as well as the dynamic response characteristics of the liquid in the liquid-filled rock joints. For the inclination angle range considered herein, the experimental results showed that the energy propagation coefficient gently diminished with increasing joint inclination, and smaller coefficient values were obtained for granite specimens compared with PMMA specimens. The peak liquid pressure exhibited a gradually decreasing trend with increasing joint inclination, and the peak pressure for granite specimens was slightly higher than that for PMMA specimens. Overall, this paper may provide a considerably better method for studying liquid-filled rock joints at the laboratory scale, and serves as a guide for interpreting the underlying mechanisms for interactions between stress waves and liquid-filled rock joints.     

岩石动静组合加载力学特性研究

 根据深部岩石力学研究的需要,在分析深部开挖中岩石受力特点的基础上,提出岩石动静组合加载问题。通过对多载荷凿岩机、INSTRON系统、SHPB装置的不断改进和尝试,研制出中高应变率段岩石动静组合加载试验系统,该系统可实现岩石轴向静压0～200 MPa、围压0～200 MPa和冲击动载0～500 MPa的同时加载。基于新研制的试验系统,对岩石在不同动静组合加载下的强度特性、破碎规律及吸能效率进行研究。结果表明：冲击动载一定,轴向静压从0增大到其单轴静压强度70%时,岩石的组合加载强度大于其纯静载强度或纯动载强度。轴向静压不变,随着冲击动载的增大,岩石的组合加载强度逐渐增大,表现出率相关性。动静组合加载下,岩石的破坏呈拉伸破裂模式,岩石的破碎块度在冲击动载或轴向静压增大时都向细粒端发展。岩石的吸能率随着动静组合加载的不同而不同,通过选择合适的动静组合加载,可使岩石的吸能率最大。     

隧道设计模型、理论与试验

本文作者把围岩应变法、孔洞位移法和衬砌内力法三种地下结构设计模型与圆形隧道的弹、塑、粘性三种衬砌计算理论结合起来,通过室内的模型试验和现场量测验证后,得到了地层压力与衬砌刚度以及地层本构关系有关的设计公式;得出了侧压力系数随衬砌与地层的刚度比而变化,且比静止侧压力系数大。将此法运用于新奥法或盾构法隧道设计中,即可减薄衬砌,节省投资。     

盐岩屈服–破坏特征的试验及理论研究

围岩塑性区及破坏区的范围是盐岩地下储气库群腔体间距设计的重要因素,盐岩屈服及破坏特性的精确描述对于减少腔体间距,以及在有限的盐岩建库区建设更多的储气库具有重要的意义。基于盐岩的单轴、三轴应力–应变试验曲线,分析盐岩的屈服–破坏特征,将腔体围岩分为弹性区、塑性区及破坏区。试验结果表明：盐岩的屈服表现出强烈的线性特征,能够用Tresca屈服准则来描述盐岩的屈服特性,以塑性应变第二不变量为硬化参数研究盐岩的硬化特征,发现盐岩为等向硬化材料。在屈服方面,盐岩表现出金属材料的特征;在破坏方面,盐岩表现出岩土材料的特性。试验观察到剪切破坏以及轴向劈裂破坏,并基于厚壁圆筒理论解释单、三轴压缩试验中出现的轴向劈裂破坏现象。同时发现盐岩的破坏特征具有强烈的围压相关性,当围压≥5 MPa时,盐岩即使达到很大的变形(20%)依然能够承载而不发生破坏。基于莫尔–库仑准则,引入一条与围压相关的坏准则,最终建立包括拉破坏、剪破坏以及不破坏的盐岩破坏准则,基于破坏准则将应力空间划分为3个区：拉破坏区、剪破坏区以及不破坏区。在FLAC中修改本构以及自定义状态参量,通过简单模型得到围岩的弹性区、塑性区以及破坏区,验证屈服准则、破坏准则以及围岩分区的正确性。     

考虑T应力下受压岩体水力压裂特性分析

自然状态下岩体多处于受压状态,分析受压岩体水力压裂性质对于完善和发展水力压裂技术有着重要意义。基于线弹性断裂力学的基本理论,对受压岩体水力压裂性质开展研究,通过最大周向应变准则,考虑裂隙尖端非奇异项即T应力的影响,推导出闭合和非闭合状态下临界水压和临界起裂角计算式。将该计算式用于某岩石水力压裂工程实例计算,所得计算值与实际值较为吻合。最后分析了闭合和非闭合情形下泊松比和侧压力系数对临界水压和临界起裂角的影响。该文研究可为实际水力压裂技术提供一定的理论参考。     

黄岛地下水封石油洞库场区地应力场模拟分析

地应力主要是指存在于地壳岩层中的未受工程干扰的天然应力,是影响地下洞室围岩稳定性的主要因素之一。利用FLAC3D数值计算软件的内嵌FISH语言编制了阻尼最小二乘拟合程序,将拟合计算与应力数值计算结合在一起,实现应力自动调整与拟合分析。将这套方法在黄岛地下水封石油洞库工程中进行应用,对场区内#Zk17钻孔的水压致裂地应力测试结果进行拟合,得出场区地应力分布:区内最大主应力值一般为10～12 MPa,中间主应力值为6～8 MPa,最小主应力基本受岩体自重控制,最大主应力方向为水平NWW向,最小主应力方向为竖直方向,库址区属于低-中地应力区。