Rock mass damage induced by rockbursts occurring on tunnel floors: a case study of two tunnels at the Jinping II Hydropower Station

Rockbursts occurring on tunnel floors are a special form of failure encountered in tunnel projects, where the failure is characterized by uplift, fracturing, and severe shocks of the tunnel floor. Extremely intense rockbursts were encountered during the excavation of the headrace tunnels 2 and 4 at the Jinping II Hydropower Station. In this study, results of comprehensive analysis conducted using the combination of numerical methods, experiments, and onsite survey to analyze the occurrence and development process of the rockburst are presented. In addition, the degree and extension range of the surrounding rock mass damage were estimated using the failure approaching index and the local energy release rate. The results of the analysis presented in this study are expected to advance the existing knowledge of special rockburst forms and may also serve as a reference for the design of resistant measures for other similar rockbursts.     

A Top Pilot Tunnel Preconditioning Method for the Prevention of Extremely Intense Rockbursts in Deep Tunnels Excavated by TBMs

The headrace tunnels at the Jinping II Hydropower Station cross the Jinping Mountain with a maximum overburden depth of 2,525 m, where 80% of the strata along the tunnels consist of marble. A number of extremely intense rockbursts occurred during the excavation of the auxiliary tunnels and the drainage tunnel. In particular, a tunnel boring machine (TBM) was destroyed by an extremely intense rockburst in a 7.2-m-diameter drainage tunnel. Two of the four subsequent 12.4-m-diameter headrace tunnels will be excavated with larger size TBMs, where a high risk of extremely intense rockbursts exists. Herein, a top pilot tunnel preconditioning method is proposed to minimize this risk, in which a drilling and blasting method is first recommended for the top pilot tunnel excavation and support, and then the TBM excavation of the main tunnel is conducted. In order to evaluate the mechanical effectiveness of this method, numerical simulation analyses using the failure approaching index, energy release rate, and excess shear stress indices are carried out. Its construction feasibility is discussed as well. Moreover, a microseismic monitoring technique is used in the experimental tunnel section for the real-time monitoring of the microseismic activities of the rock mass in TBM excavation and for assessing the effect of the top pilot tunnel excavation in reducing the risk of rockbursts. This method is applied to two tunnel sections prone to extremely intense rockbursts and leads to a reduction in the risk of rockbursts in TBM excavation.     

岩爆类型及其防治

本文将在水电洞室、交通隧洞、矿山坑道岩体或矿体中发生的急剧猛烈释放弹性变形能的动力破坏现象统称为岩爆。在讨论岩爆与其他动力现象之间的区别和岩爆含义基础上,按照地应力作用方式,将其分为水平应力型、垂直应力型以及混合应力型3种主要类型,并分别讨论了各类岩爆的具体特征以及防治措施。     

深埋隧洞不同开挖方式下即时型岩爆微震信息特征及能量分形研究

基于锦屏二级水电站深埋隧洞钻爆法及隧道掘进机（TBM）开挖过程中大量微震监测数据及不同等级的岩爆案例,对不同开挖方式下即时型岩爆的孕育及发生过程的能量释放展开研究,并运用分形几何原理研究微震能量分布的变化规律,得到以下结论：（1）即时型岩爆的孕育及发生过程中,岩爆区围岩岩体处于破坏加速集聚并不断扩展的过程;（2）钻爆法开挖过程中储存在岩体内的弹性应变能消耗于岩体破裂过程大于TBM开挖,而转化为岩体动能小于TBM开挖;（3）钻爆法开挖微震能量分形维度在即时型岩爆的孕育过程不断增加,岩爆临近前会增加到某个临界值以上;（4）TBM开挖即时型高等级岩爆能量分形维度值大于钻爆法开挖,并且其分形维度值可以反映低等级岩爆伴随发生的特征。     

Buckling mechanism of pillar rockbursts in underground hard rock mining

The objective of this paper is to investigate the buckling mechanism of pillar rockbursts in underground hard rock mines from an innovative point of view. By considering rockbursts as a buckling (instability) problem of structures, rockbursts are classified into three categories: induced rockburst, triggered rockburst and inherent rockburst, in accordance with the magnitude of the dynamic stimulation force from large to null. Rigorous mathematical models are set up for these three rockbursts. For induced and triggered rockbursts, mechanism of parametric resonance is found and perturbation effect is observed. For inherent rockbursts, the condition of critical static loads is obtained. Various examples of rockbursts in Dongguashan Copper Mine are analysed. The limitations of the approach are addressed. Contrary to conventional methods where only rock materials or rock specimens were used for investigation of rockbursts, this study attaches more attention on the structural effect on rockbursts, which may appeal to practising engineers.     

深部地下实验室扩挖岩爆监测与动态防控技术研究

中国锦屏地下实验室二期(CJPL-Ⅱ)扩挖工程建设潜在高等级岩爆风险。为此,建立了深部地下实验室相邻同向短洞室固定式和单侧相向扩挖移动式微震传感器阵列优化布置方法,构建了基于岩爆风险程度的岩爆预警频次优化原则,提出了针对性的CJPL-Ⅱ扩挖岩爆防控措施,实现了CJPL-Ⅱ扩挖过程岩爆实时监测、动态预警与防控,岩爆预警与实际情况吻合良好,保障了CJPL-Ⅱ扩挖顺利完成。分析了CJPL-Ⅱ扩挖各洞段开挖过程微破裂时空演化规律及其差,研究结果表明新增通道微震活动较扩挖段更为活跃,岩爆风险亦更高,扩挖微震活动活跃程度与空间集聚特征受扩挖断面尺寸,扩挖深度以及结构面影响。研究成果可为类似深埋工程安全建设提供借鉴。     

基于微震信息的硬岩新生破裂面方位特征矩张量分析

为了更清晰直观地了解高应力下硬岩破坏（岩爆、片帮、应力型塌方等）孕育过程中岩石破裂演化过程,根据岩石破裂面的特点,依据微震监测数据的矩张量结果,推导并得到了岩体破裂面空间方位计算方法,在此基础上给出了根据运动夹角? 来判断岩石破裂类型的确定方法。借助此方法,在实例研究中进一步证明了深埋隧洞矩张量分解判断破裂类型分析方法的可靠性。依托锦屏二级水电站深埋引水隧洞这一典型工程,依据破裂面的方位角、倾角特征和岩爆宏观破坏情况,初步探究了即时性应变-结构面滑移型岩爆的孕育过程：在岩爆孕育初期,以张拉破裂为主,由于硬性结构面的存在,在开挖扰动应力调整初期,破裂面由岩体浅层往岩体较深层硬性结构面扩展,张拉破裂面尖端接近硬性结构面时,硬性结构面上发生剪切滑移,若较深层岩体内部还有其他硬性结构面存在,则在该硬性结构面尖端,除随着岩体浅层切向应力的持续增大,往开挖面扩展外,继续以张拉破裂面型式往深层扩展,至较深层硬性结构面上剪切破裂产生,最终以剪切滑移面为破坏面边界往开挖面发展,并最终将岩体抛掷而出。     

凡口铅锌矿狮岭南深部矿床地质特征及找矿方向

广东韶关凡口铅锌矿狮岭南区段的开拓工程已延伸至-550m中段,矿体呈现尖灭趋势。为查明深部区域地层矿化特征、构造控矿特点,并指导深部寻找盲矿体,通过收集分析中上部各中段地质资料,并与地质勘查资料对比,利用坑道设计并施工了9个孔深300 m左右的坑内探矿钻孔,进一步查明了狮岭南深部地质特征,并在F3断裂下盘探获多条盲矿体。F3断裂既是导矿构造,也是重要控矿构造,其下盘至F203断裂之间的夹持带为狮岭南深部有利成矿空间     

岩溶地区地下水位变动带隧道涌水问题的思考

通过鸡冠山隧道涌水实例及广泛收集岩溶地区隧道涌水案例,总结出岩溶地区隧道季节变动带涌水具有反应时间快、水量大、泥沙重的特点,并综合分析地下水季节变动带隧道的水文地质特征,将其划分为一般山岭隧道及向斜构造地下水位变动带两种类型,且对两种类型涌水机理进行了阐述。岩溶地区隧道前期勘察应重点划分隧道岩溶地下水系统及地下水动力分带,查明岩溶发育特征与规律;施工期和运行期应结合岩溶揭露情况和涌水情况开展针对性的补充勘察,做好降雨、涌水过程和涌水压力监测,判断和预测最大外水压力和涌水量。针对涌水问题,提出封堵和排泄两种处理思路:施工开挖揭露的岩溶现象不可盲目封堵,需尽可能维持原通道的通畅,针对可能涌水的隧道衬砌设计不可仅考虑围岩结构,应充分考虑外水压力,做好围岩固结灌浆;常规隧道“环形排水系统+中心沟”排水系统可靠性差,针对大流量涌水,多采用泄水洞排水。      

花岗岩巷道岩爆过程红外辐射时空演化特征室内模拟试验研究

通过含孔花岗岩的双向加载试验模拟巷道岩爆过程,以红外热像仪为观测手段,利用红外热像和最低红外辐射温度作为监测指标,研究岩爆过程中的红外辐射温度时空演化特征。结果表明：岩爆过程红外辐射时空演化特征与岩爆孕育、发生过程具有良好的同步性。岩爆发生前红外热像上出现低温嵌套于高温条带间的温度场,其在空间上的延伸扩展则是岩爆孕育和发展过程在温度场中的反映,其出现的位置对应着岩爆发生的区域。最低红外辐射温度呈现出上升-短暂下降-上升-下降4个阶段性特征,岩爆发生前最低红外辐射温度出现3个突变转折点。试验结果对于巷道岩爆灾害的时空预测具有一定的理论意义。     

岩爆、冲击地压的定义、机制、分类及其定量预测模型

引述了若干国际权威学者关于岩爆的机制和定义的论述,在此基础上,依据岩爆发生的不同机制,将岩爆分为断层滑移或者剪切断裂所导致的断裂滑移型和岩石破坏导致的应变型岩爆,并结合事故案例,分析了应变型和滑移型两类岩爆及冲击地压的发生机制和特点。在机制分析的基础上,介绍了岩（煤）柱应变型岩爆和围岩应变型岩爆以及断裂滑移型岩爆定量预测的研究成果,其中,包括作者利用非欧几何模型研究非协调变形影响后对应变型岩爆进行了定量预测和数值模拟的新研究成果。     

多级水流系统耦合下深部岩溶分异研究——以川东隔挡式构造区中梁山背斜南段为例

新构造运动背景下,干、支流对地壳抬升反应速率的差异,导致具有不同排泄作用的河谷广泛组合,形成多级地下水流动系统,地下水作为岩溶含水系统发育的主要控制因素,多级水流系统的空间耦合影响岩溶发育分布规律。文章首先根据中梁山背斜南段岩溶槽谷横向沟谷的发育特征,将岩溶槽谷划分为渗流区、分流区、外流区;结合横向沟谷控排作用与地形指数,分析多级水流系统耦合的空间分异特征。其次通过隧道建设背景下地表水漏失、隧道涌水情况及隧道施工揭露岩溶现象验证在多级水流系统耦合效应下深部岩溶发育特征。结果表明:渗流区以区域水流系统为主,隧道涌水量巨大,水流通道连通性良好,地表水基本干涸,深部岩溶发育强烈;分流区除了近河谷地带以局部水流系统为主、深部岩溶发育较弱以外,宽缓分水岭地带的地下水流动仍然以区域性流动为主,深部岩溶较发育,隧道涌水量较大,地表水与深部岩溶地下水水力联系较好,隧道建设对地表水影响严重;外流区以局部浅循环为主,深部岩溶发育程度弱,深部岩溶水与地表水水力联系较弱,地表水漏失程度一般。本研究不但拓宽了托特多级水流系统的应用领域,为岩溶发育理论研究提供了新的角度,同时为深埋岩溶隧道建设的危险性评价及引发的环境负效应研究提供理论指导。     

二朗山公路隧道岩爆特征与预测研究

根据二郎山公路隧道施工中记录的２００多次岩爆资料,总结隧道的岩爆特征,并采用“地质超前预报法”和“σθ／Ｒｂ判断现场测定预测法”两种方法,对岩爆预测问题进行有益探讨。     

Tunnelling soils in South Auckland,New Zealand

The formation and occurrence of subterranean erosion tunnels is considered to be a more widespread phenomenon than has previously been recognised. The formation of erosion tunnels is related to the physico-chemical characteristics of soils and is dependent upon the concurrent occurrence of a number of factors, including soil characteristics, climate, topography, geology and hydraulic considerations.Of particular consideration is the comparatively widespread identification of erosion tunnels in sedimentary deposits in which the phenomena have previously been thought to be isolated occurrences.The methods for determining the propensity for tunnelling to develop within a soil are not well defined, and lead to apparently anomalous results. There is thus a need for continued research on the occurrence of these phenomena, and the development of suitable laboratory tests to better define soils which present a risk.     

Performance of a multi-face tunnel excavated in loess ground based on field monitoring and numerical modeling

In large-span tunneling projects, the mechanical behavior of the rock changes in response to different sequential excavation methods (SEMs) of advancing the tunnel face. The double side drift method (DSDM), which is a development of SEM, was widely used in loess tunnels with large cross sections in China for its ability to limit ground displacement. This paper presents the deformation characteristics of large-span loess tunnels of the high-speed railway line in China. Field monitoring and numerical simulations were conducted to determine the optimal construction approach and reveal the deformation properties of large-span loess tunnels in China. The construction approaches, support measures, ground surface, and subsurface deformation characteristics associated with DSDM are demonstrated. The ground surrounding the loess tunnel underwent vertical settlement at the arch part and at the ground surface because of the metastable structure of the loess. This study provides an in-depth illustration of the influence of face-advancing sequences on ground displacement induced by tunneling, which helps us implement the most effective SEMs.     

Research on the Energy Criterion for Rockbursts Induced by Broken Hard and Thick Rock Strata and Its Application

In this study, the occurrence conditions of rockbursts induced by broken hard and thick rock strata (HTRS) in fully mechanized longwall face are investigated by dividing the surrounding rock of a roadway rib into three zones: burst-resistance zone (BRZ), burst-inoculation zone, and stable zone. On this basis, the process of impact vibration energy (released by the broken HTRS) transformation in these zones was analyzed, and theoretical equations are presented to calculate the strain energy, dissipated energy and shock vibration energy. In addition, an energy criterion associated with the critical broken length of the HTRS, the width of burst-resistance zone, and the burst proneness index was proposed to predict rockbursts induced by broken HTRS in fully mechanized longwall face. Moreover, to control these types of rockbursts effectively, a quantitative method was proposed for determining the limit broken length of the HTRS and the BRZ. The research results show that the energy criterion may forecast these typical rockbursts, and rockburst hazards can be eliminated using the proposed method.     

The squeezing potential of rock around tunnels: Theory and prediction with examples taken from Japan

Summary Large deformations of surrounding media around tunnels are often encountered during excavations in rocks with squeezing characteristics. These deformations may sometimes continue for a long period of time. Predictions of deformations of tunnels in such grounds are urgently needed, not because of stability concerns, but also of their sevicability. In the present study, the squeezing phenomenon of rock around tunnels and its mechanism and associated factors are first clarified by carefully studying failures of tunnels, and a survey of tunnels in squeezing rocks in Japan is presented and its results are summarised. Then, a practical method is proposed to predic the squeezing potential and deformation of tunnels in squeezing rock and this method has beeen applied to actual tunnelling projects, where squeezing problems were encountered, to check its applicability and validity. Finally, an extension of this method to the time-dependent behaviour of squeezing rocks is given and an application of this method to an actual tunnel is presented.     

隧道围岩变形的尺寸效应研究

通过分析不同结构围岩的变形机制研究隧道变形的尺寸效应,研究结果表明隧道围岩变形的尺寸效应与围岩的变形机制存在密切的关系。围岩中由于结构面的存在使围岩的变形机制复杂多样,主要包括材料变形和结构变形两大类,围岩变形的尺寸效应也主要体现在材料变形和结构变形两方面。围岩材料变形包括弹性变形和塑性变形,均与围岩断面尺寸呈线性比例关系;围岩结构变形的尺寸效应表现为：（1）围岩结构类型随隧道断面尺寸的增大而发生改变,不同类型的围岩其变形机制不同,不同变形机制产生的围岩变形量相差较大;（2）在同一种围岩结构下,相同变形机制产生的围岩变形量也会随着隧道尺寸增大而呈现不同的变化规律,如在块状围岩中,隧道周边不可动块体会随着隧道断面尺寸的增大而转化成可动块体,从而发生滑动或者滚动变形,甚至坍塌;在层状围岩中,岩层的弯曲变形与隧道断面尺寸的平方成正比。     

隧道下穿既有结构物引起的地表沉降控制标准研究

解决好隧道下穿既有结构物引起的地表沉降问题,对城市地下交通和高速铁路的建设具有重要的意义.在调研国内大量隧道下穿开挖引起的地表沉降控制标准和方法的基础上,根据隧道下穿公路、铁路、隧道和建筑物时引起的地表沉降的不同特点,结合隧道的施工、开挖面积、埋深和工程地质条件等因素,对隧道下穿不同的结构物提出不同的控制沉降措施和建议...     

基于双岩模式的抚顺煤田矿震成因机理探讨

矿震是由采矿活动所引起的,产生于某些特定岩体,一定深度受高应力影响的微震.抚顺是我国著名的"煤都",但由于开采深度的加大,产生的矿震对城市的影响日益严重,并产生了强烈的破坏作用,影响了城区的发展和人们的正常生活.本文在介绍抚顺矿震特征类型基础上,提出了产生矿震的可能潜在条件,借用双岩模式对抚顺煤田矿震成因机理进行了探讨,并借鉴日本Miike煤矿认为矿震可能主要产生于1140 m以上,煤层中的巷道表面高应力集中地带为矿震发生的主要区域.