深部开采底板岩体卸荷损伤的强扰动危险性分析

为研究深部高应力岩体强烈的卸荷效应扰动底板破坏并诱发突水的危险性,根据卸荷力学理论,研究了深部开采卸荷对底板扰动破坏的影响,运用离散元软件计算了深部开采底板卸荷损伤的强扰动特征,基于三轴卸荷试验及损伤因子概念推导了卸荷量与损伤因子的关系,获得了底板岩体卸荷的扩展破坏条件,划分了底板卸荷扰动分区,分析了深部开采底板岩体卸荷损伤破坏的强扰动危险性。结果表明：随采深增加,底板卸荷起点及卸荷应力增加,卸荷量却降低,而深部开采较小的卸荷量便造成底板严重损伤破坏;岩体卸荷量越大,卸荷速率、位移量及渗透系数越高,越易致其扩展破坏;裂隙倾角及水平应力与垂直应力比值越小,越易满足底板岩体卸荷的扩展破坏条件。     

深井开采地质灾害及矿山地震研究

矿山地震，又称为“矿震”，是深井开采中的地质灾害。它具有震源浅，震级小，烈度大，破坏性强等特点。文章基于地球动力区划的理论和方法，以北票台吉矿的实际研究资料为例，对地质动力引起的矿山灾害及矿震的发生规律进行了研究。认为“矿震”的发生是受区域构造应力场的影响，与地下采矿活动密切相关的一种地质动力突变现象，一般发生在地质构造比较复杂、断裂新活动比较显著的地区。文中还讨论了矿山地质动力的作用特征、井下活动断裂的变形与错动规律和对岩层与地表移动的影响。研究了“矿震”的震源机制、断裂错动及其与构造应力场和区域地方震之间的关系。     

Regional prediction of landslide hazard using probability analysis of intense rainfall in the Hoa Binh province, Vietnam

The main objective of this study is to assess regional landslide hazards in the Hoa Binh province of Vietnam. A landslide inventory map was constructed from various sources with data mainly for a period of 21 years from 1990 to 2010. The historic inventory of these failures shows that rainfall is the main triggering factor in this region. The probability of the occurrence of episodes of rainfall and the rainfall threshold were deduced from records of rainfall for the aforementioned period. The rainfall threshold model was generated based on daily and cumulative values of antecedent rainfall of the landslide events. The result shows that 15-day antecedent rainfall gives the best fit for the existing landslides in the inventory. The rainfall threshold model was validated using the rainfall and landslide events that occurred in 2010 that were not considered in building the threshold model. The result was used for estimating temporal probability of a landslide to occur using a Poisson probability model. Prior to this work, five landslide susceptibility maps were constructed for the study area using support vector machines, logistic regression, evidential belief functions, Bayesian-regularized neural networks, and neuro-fuzzy models. These susceptibility maps provide information on the spatial prediction probability of landslide occurrence in the area. Finally, landslide hazard maps were generated by integrating the spatial and the temporal probability of landslide. A total of 15 specific landslide hazard maps were generated considering three time periods of 1, 3, and 5 years.     

A logistic regression classifier for long-term probabilistic prediction of rock burst hazard

Rock burst is a complex dynamic process can lead to casualties, to failure and deformation of the supporting structures, and to damage of the equipment on site; hence, its prediction is of great importance in underground construction. We present a novel empirical method to predict rock burst based on the theory of logistic regression classifiers. An extensive database collected from the literature, which includes observations about rock burst occurrence (or not) in underground excavations in projects from all over the world, is used to train and validate the model. The proposed approach allows us to compute new class separation lines (or planes) to estimate the probability of rock burst, using different combinations of five possible input parameters—tunnel depth, H; maximum tangential stress, MTS; elastic energy index, W _et; uniaxial compressive strength of rock, UCS; uniaxial tensile strength of rock, UTS—among which it was found that the preferable model could be developed in H–W _et–UCS space. The proposed model is validated with goodness-of-fit tests and nine-fold cross-validation; results show that its predictive capability compares well with previously proposed empirical methods and confirm that, as expected, the probability of rock burst increases with excavation depth, and that both W _et and UCS have a similarly significant influence on rock burst occurrence. Finally, expressions are proposed for identification of conditions associated with several reference values of rock burst probability, which can be employed in preliminary risk analyses.     

Burden prediction in blasting operation using rock geomechanical properties

Burden prediction is a vital task in the production blasting. Both the excessive and insufficient burden can significantly affect the result of blasting operation. The burden which is determined by empirical models is often inaccurate and needs to be adjusted experimentally. In this paper, an attempt was made to develop an artificial neural network (ANN) in order to predict burden in the blasting operation of the Mouteh gold mine, using considering geomechanical properties of rocks as input parameters. As such here, network inputs consist of blastability index (BI), rock quality designation (RQD), unconfined compressive strength (UCS), density, and cohesive strength. To make a database (including 95 datasets), rock samples are used from Iran’s Mouteh goldmine. Trying various types of the networks, a neural network, with architecture 5-15-10-1, was found to be optimum. Superiority of ANN over regression model is proved by calculating. To compare the performance of the ANN modeling with that of multivariable regression analysis (MVRA), mean absolute error (E _a), mean relative error (E _r), and determination coefficient (R ²) between predicted and real values were calculated for both the models. It was observed that the ANN prediction capability is better than that of MVRA. The absolute and relative errors for the ANN model were calculated 0.05 m and 3.85%, respectively, whereas for the regression analysis, these errors were computed 0.11 m and 5.63%, respectively. Moreover, determination coefficient of the ANN model and MVRA were determined 0.987 and 0.924, respectively. Further, a sensitivity analysis shows that while BI and RQD were recognized as the most sensitive and effective parameters, cohesive strength is considered as the least sensitive input parameters on the ANN model output effective on the proposed (burden).     

Study of microseismic activity associated with a longwall coal mining operation using a near-surface array

Microseismic studies associated with a longwall coal mining operation are described. The mine under study was located some 600 ft. below surface. Seismic events associated with controlled roof failure, and with stress development in both the roof and adjacent pillars were monitored by a seven-station near-surface array. The studies were carried out over a 6-month period during which the longwall face moved horizontally some 800 ft. below the area defined by the seismic array. Brief details are presented of the mobile monitoring system and the analysis techniques employed. Typical results obtained during the study are discussed along with suggestions for improving future studies of this type.     

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。     

矿区深部隐伏矿体三维可视化预测方法

针对深部隐伏矿定位难题,经多年研究,提出以定位模型-成矿信息-三维预测为主线的隐伏矿体三维可视化预测方法。矿体定位概念模型实现成矿规律到矿化分布规律的转换,获得矿体空间定位量化指标;采用形态分析、距离场或缓冲区分析、蚀变场分析等空间分析方法,分析和定量提取成矿信息指标;采用非线性多元回归、三维模糊证据权等方法,建立矿体三维预测模型,对深部立体单元的品位、金属量和含矿性进行预测。以安徽铜陵凤凰山铜矿和金川铜镍硫化物矿床为例,展开矿区深部三维可视化预测研究。结果显示,该方法能够适用于不同类型矿床的深部找矿工作,对于深部找矿具有重要意义。     

煤矿深部开采动力灾害区域应力效应监测与前兆特征研究

动力灾害的孕育及诱发与区域应力场的力学行为密切相关,煤矿开采扰动作用下区域局部应力场不断调整变化。为了研究区域应力场变化特征对动力灾害的前兆响应,采用变分模态分解和希尔伯特变换的方法对鲍店煤矿采集数据进行时频分析,识别和提取钻孔应变数据中反映动力异常变化的固有模态分量。研究结果表明,钻孔应变观测数据能够有效记录开采扰动相关区域岩体内部的微小变化,解析原始数据滤去干扰信号后获得表征动力异常的特定频段,分解变换后固有模态分量异常波动特征早于动压事件前2~7天出现,表现出形变稳定变化阶段向快速变化阶段“突跳”、形变快速变化阶段 “震荡”以及失稳阶段“跌落”的显著特征。依据地震形变三阶段理论,判别动力灾害发生前形变异常开始时刻和“突跳”—“震荡”—“跌落”作为煤矿动力灾害发生的前兆判据。基于钻孔应变仪对区域应力场的精确观测,构建了应用于煤矿动力灾害超前预警的判据方法,可为煤矿相似开采环境下工作面的安全高效回采提供借鉴和参考。     

Earthquake-induced liquefaction hazard mapping at national-scale in Australia using deep learning techniques

Australia is a relatively stable continental region but not tectonically inert, having geological conditions that are susceptible to liquefaction when subjected to earthquake ground motion. Liquefaction hazard assessment for Australia was conducted because no Australian liquefaction maps that are based on modern AI techniques are currently available. In this study, several conditioning factors including Shear wave velocity (Vs30), clay content, soil water content, soil bulk density, soil thickness, soil pH, distance from river, slope and elevation were considered to estimate the liquefaction potential index (LPI). By considering the Probabilistic Seismic Hazard Assessment (PSHA) technique, peak ground acceleration (PGA) was derived for 50 yrs period (500 and 2500 yrs return period) in Australia. Firstly, liquefaction hazard index (LHI) (effects based on the size and depth of the liquefiable areas) was estimated by considering the LPI along with the 2% and 10% exceedance probability of earthquake hazard. Secondly, ground acceleration data from the Geoscience Australia projecting 2% and 10% exceedance rate of PGA for 50 yrs were used in this study to produce earthquake induced soil liquefaction hazard maps. Thirdly, deep neural networks (DNNs) were also exerted to estimate liquefaction hazard that can be reported as liquefaction hazard base maps for Australia with an accuracy of 94% and 93%, respectively. As per the results, very-high liquefaction hazard can be observed in Western and Southern Australia including some parts of Victoria. This research is the first ever country-scale study to be considered for soil liquefaction hazard in Australia using geospatial information in association with PSHA and deep learning techniques. This study used an earthquake design magnitude threshold of M_w 6 using the source model characterization. The resulting maps present the earthquake-triggered liquefaction hazard and are intending to establish a conceptual structure to guide more detailed investigations as may be required in the future. The limitations of deep learning models are complex and require huge data, knowledge on topology, parameters, and training method whereas PSHA follows few assumptions. The advantages deal with the reusability of model codes and its transferability to other similar study areas. This research aims to support stakeholders’ on decision making for infrastructure investment, emergency planning and prioritisation of post-earthquake reconstruction projects.     

Role of attenuation relationship in shaping the seismic hazard

Attenuation relationships are commonly used for engineering studies to estimate the peak ground acceleration values. This paper presents the role of attenuation relationship in defining the seismic hazard in an area. It is seen that the seismic hazard in an area, which is calculated using attenuation relationships, is mostly controlled by the type of attenuation relationship used in the study. The present work aims to study the effect of attenuation relationship on seismic hazard study. In the present work, seismic hazard maps have been prepared in the seismically very active northeast Himalaya using the approach given by Joshi and Patel (Tectonophysics 283:289–310, 1997). The attenuation relationships of Jain et al. (2000), Sharma (2000), Joyner and Boore (Bull Seism Soc Am 71:2011–2038, 1981) and Abrahamson and Litehiser (Bull Seism Soc Am 79:549–580, 1989) have been considered in the present study. Among all considered attenuation relationships, the Abrahamson and Litehiser (Bull Seism Soc Am 79:549–580, 1989) attenuation relationship gives the least root mean square error between the recorded and calculated peak ground acceleration values. Therefore, the same has been used to define attenuation characteristic of the region. The mean and standard deviation of peak ground acceleration values at all the observation points due to above-mentioned attenuation relationships in the NE Himalayas are calculated. The study shows that the Zone III covers an area of 81,000 km² and Zone II of 96,000 km² in the map prepared using the mean peak ground acceleration values, whereas the area of Zone IV increases by 40,000 km² when the map is prepared by adding the standard deviation values in the mean peak ground acceleration values, and only Zone II is left with 183,000 km² when the standard deviation values are subtracted from the mean. This high standard deviation is due to the difference in the peak ground acceleration values obtained from different events. This study shows that a rigorous test needs to be done for selecting attenuation relationship for any hazard study in a given area.     

深部开采上覆岩层采动裂隙网络演化的分形特征研究

借助相似模拟材料模型试验,模拟了在深部开采条件下上覆岩层采动岩体裂隙分布状态,运用分形几何理论研究了采动岩体裂隙网络分形维数随开采宽度、采场矿山压力、岩层沉降的动态演化规律,并分析了断层对采动岩体裂隙网络分布演化的影响以及采动岩体裂隙网络在三带的分布特征。结果表明：随开采宽度增加,采动岩体裂隙网络分形维数呈现总体增大趋势,在断层影响下表现出降维特点;分形维数与超前工作面压力和岩层沉降均具有非线性关系;三带采动岩体裂隙网络均具自相似性,冒落带、裂隙带、弯曲带分形维数比为1.082 3:1.139 4:1。     

Evolution and effect of the stress concentration and rock failure in the deep multi-seam coal mining

Supports crushing accident occasionally occurs in the protected seam exploitation of deep multi-seam coal mining structure and results in adverse effect to the production. To prevent its recurrence in a newly developed working field, a 3D numerical extraction model was built based on the geologic and mining conditions of Jining coal mine to evolve the changes, state and characteristics of the reconstructed vertical and lateral stress in rock interlayer after protective seam exploitation. Stress release and increase zones of this mining structure were separated. Mining-induced localized stress concentration and the interlayer rock failure behavior were explored. The action of concentrated stress on the hydraulic supports in protected seam was discussed upon the major stress redistribution. Using the infinitesimal strain method, a mechanical model was created to further explore, from the vertical and lateral directions, the cause and mechanism of localized stress concentration and rock failure behavior in rock interlayer. The field investigation was finally performed to verify the numerical and mechanical results, and the essential control measures were proposed to prevent this accident. Key findings of this study bring some new insights into the deep multi-seam coal extraction and help to promote a more reliable underground mining.     

Regional characterisation of hydraulic properties of rock using air-lift data

 Hydrogeologic studies are commonly data-intense. In particular, estimations of hydraulic properties of hard rock often require large amounts of data. In many countries, large quantities of hydrogeologic data have been collected and archived over the years. Therefore, the use of existing data may provide a cost-efficient alternative to collecting new data in early stages of hydrogeologic studies, although the available data may be considered imprecise. Initially, however, the potential usefulness, i.e., the expected accuracy, of the available data in each specific case must be carefully examined. This study investigates the possibilities of obtaining estimates of transmissivity from hard-rock air-lift data in Sweden within an order of magnitude of results obtained from high-quality injection-test data. The expected accuracy of the results was examined analytically and by means of statistical methods. The results were also evaluated by comparison with injection-test data. The results indicate that air-lift data produce estimates of transmissivity within an order of magnitude compared to injection-test data in the studied examples. The study also shows that partial penetration and hydrofracturing may only affect the estimations approximately half an order of magnitude. Thus, existing data may provide a cost-efficient alternative to collection of new data in early stages of hydrogeologic studies. Received, January 1998 Revised, November 1998, December 1998 Accepted, December 1998     

分幅开挖方式下高应力硬岩地下洞室的微震特性及稳定性分析

高应力硬岩大型地下洞室开挖卸荷导致围岩片帮、塌方事故频发,严重威胁现场施工人员及设备的安全。从降低围岩局部破坏风险的角度考虑,白鹤滩水电站右岸主变室第Ⅳ层采用分幅开挖方案。通过构建微震监测系统,研究分幅开挖下岩体的微震特性及稳定性,监测结果表明：上游半幅开挖诱发的微震事件、能量大于下游半幅诱发的,且上、下游半幅开挖均表现出了掌子面贯通前微震事件、能量增大的特性,这主要受两相向掘进掌子面前方支承压力叠加的影响;上游半幅开挖诱发微震事件频发且出现了丛集现象,下游半幅开挖诱发的微震事件较少且事件空间分布离散,规律性不明显;采用Schmidt数、事件活动率与累积视体积、能量指数与累积视体积评价研究区域的稳定性,结果显示,较之于应变硬化阶段,处于应变软化阶段的岩体发生不稳定变形破坏的风险较大。研究结果可为白鹤滩水电站地下洞室施工方案的优化提供重要参考,同时也可为其他类似工程的施工提供借鉴。     

烧变岩富水特征与采动水量损失预计

自燃煤层围岩在不同高温作用下会引起不同程度的结构损伤,导致其物理力学性质和工程地质效应发生显著变化。为深入认识烧变过程中岩石的结构演化规律,以徐州某矿底板灰岩为研究对象,开展不同温度作用下的热破裂试验,从多尺度上探究岩石热破裂的规律,并结合数值模拟和微观结构测试揭示其发育机理。结果显示：(1)方解石填充裂隙、层理等相对软弱结构面的热破裂温度阈值在300~400℃,完整岩石结构的热破裂温度阈值在500℃左右;600℃之前的热破裂形态较简单,基本是直线型裂纹,且宽度较小、数量较少;700℃以上出现宽度和长度显著增大的弧形热裂纹,热裂纹两侧试样的颜色有明显区别,靠近热裂纹的白色部位还发育一些连通弧形裂纹的次级小裂纹;800℃时,试样颜色全部变白,结构完全破碎,成散体状。(2)从微观结构和热应力角度阐释灰岩热破裂发育机理,发现试验温度路径下试样的热破裂主要发育在降温过程中,且最大热应力差主要在靠近试样表面的近似环形带上分布。500℃以下的热破裂成因主要为热应力在试样的原始缺陷处集中,并超过了部分软弱结构的抗拉强度;500℃以上受热应力与矿物分解共同控制,500℃以上升降温过程中的最大热应力基本超过灰岩的抗拉强度,且菱镁矿、白云母、白云石等矿物逐渐分解,逐渐增多的内部缺陷为应力集中提供有利条件,加剧了热破裂的发育;当温度达到800℃时,热破裂发育程度很高,且白云石和方解石快速分解,生成CaO,部分CaO在冷却过程中与空气接触生成Ca(OH)₂,热裂纹与主体矿物分解共同导致试样结构的破碎。研究成果可为岩体破裂和地质结构演化分析奠定基础。

     

深埋隧洞微震活动区与岩爆的相关性研究

基于锦屏二级水电站深埋引水隧洞和排水洞大量微震监测数据及上百个不同等级岩爆实例,研究了深埋隧洞微震活动区与岩爆之间的关系。研究结果表明：（1）微震活动分布范围主要介于掌子面后方3倍洞径至前方1.5倍洞径之间,而岩爆高发区位于掌子面后方3倍洞径以内,表明岩爆高发区与微震事件主要分布范围相吻合;（2）隧洞工程岩爆潜在风险重点关注区域是掌子面后方3倍洞径已开挖范围,以及掌子面前方1.5倍洞径施工范围;（3）微震事件及岩爆分布呈区域性集结特点,其中一部分岩爆发生于微震事件集结区内部,另一部分岩爆发生于微震事件集结区边缘,这是岩体破坏过程中所固有的现象,与微震事件集结区边缘局部应力集中密切相关。     

Radiological hazard assessment for building materials incorporating phosphogypsum made using Eshidiya mine rock in Jordan

The mean activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K in Eshidiya phosphogypsum samples were measured as 351.4 ± 23.4, 3.8 ± 0.3, and 120.7 ± 8.3 Bq kg^?1, respectively. The results show that the mean values of activity concentration of ²²⁶Ra, ²³²Th, and ⁴⁰K are in the lower range of typical values reported for phosphogypsum samples collected worldwide. Radiological hazard indices such as the radium-equivalent activity (Ra_eq), the gamma index (I _γ ) alpha index (I _α ), the absorbed gamma dose rate (D _in), and the corresponding annual effective dose (E _in) were assessed for building materials for dwellings. The results of assessment exhibit that all phosphogypsum samples are higher than the recommended safe limit for building materials for dwellings, except for the radium-equivalent activity (Ra_eq). Overall assessment, it can be concluded that the possibility of using Eshidiya phosphogypsum in building materials in proportions lower than 100 % will be safe. The mixture of phosphogypsum with normal gypsum can dilute the concentrations of natural radionuclides allowing the use of the mixed building materials to be safe from a radiological point of view.     

深部大变形回采巷道围岩拉压分区变形破坏的模拟研究

为研究深部回采巷道围岩大变形破坏规律,在地质力学评估及矿压显现特征实测的基础上,采用真三轴相似模拟方法,模拟了不同加载梯度下巷道围岩应变特征。结果显示,在浅埋静水压力条件下,巷道围岩呈现“浅部拉应变、深部零应变”的特征;深埋静水压力及初掘采动应力下巷道围岩出现“径向应变拉压交替分布”现象;当采动应力集中系数大于2时,深埋巷道围岩应变进入非线性大应变状态。采用FLAC3D的应变软化模型与摩尔-库仑模型,对比研究了深部回采巷道围岩位移、塑性区分布规律。结果表明,应变软化条件下,巷道围岩产生拉、压分区破坏且软化后的围岩位移与实测结果更吻合。综合研究结果,揭示了深部回采巷道围岩拉、压分区的产生机制,初步提出了注浆、喷层等措施,防止过度应变软化引起深部回采巷道围岩大变形,为类似巷道稳定性控制提供了一定的参考。