Rock mass structural recognition from drill monitoring technology in underground mining using discontinuity index and machine learning techniques

A procedure to recognize individual discontinuities in rock mass from measurement while drilling(MWD)technology is developed,using the binary pattern of structural rock characteristics obtained from in-hole images for calibration.Data from two underground operations with different drilling technology and different rock mass characteristics are considered,which generalizes the application of the methodology to different sites and ensures the full operational integration of MWD data analysis.Two approaches are followed for site-specific structural model building:a discontinuity index(DI)built from variations in MWD parameters,and a machine learning(ML)classifier as function of the drilling parameters and their variability.The prediction ability of the models is quantitatively assessed as the rate of recognition of discontinuities observed in borehole logs.Differences between the parameters involved in the models for each site,and differences in their weights,highlight the site-dependence of the resulting models.The ML approach offers better performance than the classical DI,with recognition rates in the range 89%to 96%.However,the simpler DI still yields fairly accurate results,with recognition rates 70%to 90%.These results validate the adaptive MWD-based methodology as an engineering solution to predict rock structural condition in underground mining operations.

Characteristics of microseismic b-value associated with rock mass large deformation in underground powerhouse caverns at different stress levels

Rock mass large deformation in underground powerhouse caverns has been a severe hazard in hydropower engineering in Southwest China.During the development of rock mass large deformation,a sequence of fractures was generated that can be monitored using microseismic(MS)monitoring techniques.Two MS monitoring systems were established in two typical underground powerhouse caverns featuring distinct geostress levels.The MS b-values associated with rock mass large deformation and their temporal variation are analysed.The results showed that the MS bvalue in course of rock mass deformation was less than 1.0 in the underground powerhouse caverns at a high stress level while larger than 1.5 at a low stress level.Prior to the rock mass deformation,the MS b-values derived from both the high-stress and low-stress underground powerhouse caverns show an incremental decrease over 10%within 10 d.The results contribute to understanding the fracturing characteristics of MS sources associated with rock mass large deformation and provide a reference for early warning of rock mass large deformation in underground powerhouse caverns.

Key issues in water sealing performance of underground oil storage caverns: Advances and perspectives

Water sealing performance is important for underground water-sealed oil storage(UWSOS).The key issues concerning water sealing performance mainly include the permeability of fractured rock mass(FRM),water-sealed safety(WSS),water curtain performance,and prediction and control of water inflow.This paper reviews the progress of above four key issues on water sealing performances.First,the permeability of an FRM is the basis of water sealing performance,and several commonly used permeability test methods and spatial variation characteristics of permeability are outlined.Second,the current water sealing criteria are compared,and the evaluation methods of WSS are summarized.Third,the design parameters and efficiency evaluation of water curtain systems(WCSs)are introduced.The water inflow of oil storage caverns(OSCs)can reflect the water sealing effect,and the prediction methods and control measures of water inflow are also summarized.Finally,the advantages and disadvantages of the current research are discussed,and the potential research directions are pointed out,such as optimization of water sealing criteria and FRM model,quantitative evaluation of WCS efficiency,accurate prediction of water inflow,and improvement of grouting technology.

Some Mass Migration Underground Found in Beijing Area

The relationship between the change of a local gravity field and the mass migration underground is discussed by means of using a point-source disturbed body as a substitute for the mass migration underground. Some significant local gravity field changes in Beijing area have been found, from which the three parameters of the disturbed bodies, location, depth and mass, have been derived successfully from the observations of a gravimetric network. In order to determine the depth of a body, a new approach is suggested in which the gravity change difference is used instead of the gravity change itself. The mass of a disturbing body has been estimated properly. Astronomical PZT is suggested for this kind of survey. The results provide us a picture of the underground mass migration with which the gravity changes on the ground surface may be interpreted in a better way. This additional information may be useful in seismological studies.

Relationship between the Classification of Rock Surrounding Underground Chambers and the Initial Damage Variations in Rock Masses

On the basis of the relationship between each classification index for underground chambers and the elastic wave velocity of rock mass, a corresponding relationship between the classification of rock surrounding underground chambers and the initial damage variable is established by using the wave velocity definition of the initial damage variable of rock masses. Calculation and analysis of relevant data from a hydropower dam located in Southwest China show that the initial damage variable obtained by means of surrounding rock classification has a close relationship with that calculated by wave velocity, which verifies the rationality of the relationship of the two classification indices. This study establishes a foundation for further damage mechanics and stability analysis on the basis of surrounding rock classification.

Displacement-based back analysis of mitigating the effects of displacement loss in underground engineering

Displacement-monitoring-based back analysis is a popular method for geomechanical parameter estimation.However,due to the delayed installation of multi-point extensometers,the monitoring curve is only a part of the overall one,leading to displacement loss.Besides,the monitoring and construction time on the monitoring curve is difficult to determine.In the literature,the final displacement was selected for the back analysis,which could induce unreliable results.In this paper,a displacement-based back analysis method to mitigate the influence of displacement loss is developed.A robust hybrid optimization algorithm is proposed as a substitute for time-consuming numerical simulation.It integrates the strengths of the nonlinear mapping and prediction capability of the support vector machine(SVM)algorithm,the global searching and optimization characteristics of the optimized particle swarm optimization(OPSO)algorithm,and the nonlinear numerical simulation capability of ABAQUS.To avoid being trapped in the local optimum and to improve the efficiency of optimization,the standard PSO algorithm is improved and is compared with other three algorithms(genetic algorithm(GA),simulated annealing(SA),and standard PSO).The results indicate the superiority of OPSO algorithm.Finally,the hybrid optimization algorithm is applied to an engineering project.The back-analyzed parameters are submitted to numerical analysis,and comparison between the calculated and monitoring displacement curve shows that this hybrid algorithm can offer a reasonable reference for geomechanical parameters estimation.

某地下大型洞室群开挖变形特性及参数敏感性分析

地下工程施工顺序的选择和支护措施的实施,直接关系到洞室群的整体稳定性和安全性。文章以某水电站大型地下洞室群开挖为例,通过建立三维数值模型,研究了主厂房、主变室和尾水调压室3种不同的开挖顺序下洞室群开挖后洞周围岩的变形特性,分析了参数的敏感性,并给出了洞室群开挖支护设计。结果表明:方案2(并行与顺序开挖相结合)在控制位移和塑性区面积方面表现更优,建议施工时优先选择;侧压力系数是影响洞室稳定性的关键因素,侧压力系数较小时,边墙为重点支护部位,而侧压力系数较大时,顶拱位移就较大;围岩破碎面的黏聚力、内摩擦角和抗拉强度对围岩的稳定性具有决定性的影响。洞室的主厂房顶拱采用锚喷支护和注浆的方法控制围岩的位移量,其余部位采用锚杆和锚索共同支护的方式,支护后锚固使洞室的主厂房顶拱、上、下游边墙的位移值减小幅度为10%~25%,而塑性区的面积也减小了40%~50%。

某水电站尾调室高湿环境散湿量分析和半经验预测方法

地下水电站尾调室内环境常年高湿,对尾调室合理除湿,保障室内人员和机组设备的安全成为亟待解决的关键问题。其中,尾调室内散湿量的分析和预测是开展除湿工作必不可少的一步。基于实测数据、理论推导和数值分析,总结了某水电站尾调室各项空气参数的变化规律,计算对比了短期测试和长期测试的散湿量,确定了高湿环境下大空间对流传质系数(以空气含湿量差为基准)的影响因素,建立了某水电站尾调室的散湿量预测模型。结果显示:11月底至次年1月,在入口风速较低的情况下,入口空气温度与围岩换热至出口时上升1.5~2.2℃,入口低湿度空气至出口时接近饱和状态;尾调室内的散湿量是动态变化过程,在11月底处于峰值28~32g/(m^(2)·h),至次年1月不断下降至7~10g/(m^(2)·h);将对流传质系数视为风速和含湿量差的双因素函数具有较高的相关性,并给出了拟合计算式。

MICP技术在地下水封油库渗控注浆中的应用潜力

地下水封油库在建设及运营过程中洞室涌水量大小是影响洞库水封安全和运营成本的重要因素。目前地下水封油库工程建设中采用传统的注浆方式难以将围岩渗透性降低到设计要求,因此洞室涌水量得不到很好的控制。微生物诱导碳酸钙沉淀(MICP)技术具有注浆黏度低、环境适应性强、生成矿化物质稳定等显著优点,引起了学术界与工程界广泛的兴趣和研究。本文首先分析了地下水封油库涌水量控制中存在的相关问题,然后阐述了MICP技术对裂隙渗流控制的机理、影响因素以及对裂隙渗透性的影响效果,最后探讨了MICP技术在地下水封油库中应用的关键问题。通过分析表明,MICP作为地下水封油库渗流控制的一种辅助注浆方式,可以较为准确地控制围岩渗透性变化,达到对洞室涌水量有效控制的目的。

煤矿采空区破损煤岩层的渗透性研究

利用矿井资源修建地下储库有助于实现“碳达峰,碳中和”战略目标,保障国家能源安全。掌握矿井储存空间内煤岩层渗透特性,是确定地下储库储存容量,保障储能系统稳定性和安全性的前提。本文以灵新煤矿矿井浓盐水地下储库工程为背景,开展现场原位压水试验,对采掘完成的矿区煤岩层渗透特性进行研究,探明了矿区遗留煤柱、采区顶、低板的渗透特性和透水能力。试验结果表明各煤层遗留煤柱的稳定流量值为1.0~6.12 L/min,15和16煤顶板稳定流量为1.76~8.82 L/min,16煤的底板稳定渗流量为1.971~8.82 L/min。在此基础上,计算了各层煤柱透水率为0.046~0.261 Lu,顶板透水率为0.07~0.162 Lu,底板透水率为0.042,其中16煤煤柱透水率最大,为0.261 Lu。煤岩层透水性较差,有利于修建地下储库工程。

露天转地下挂帮矿崩落法开采边坡安全防控技术研究

露天转地下过渡期崩落法开采挂帮矿,会引起边坡的岩移和陷落,威胁露天矿的安全生产。以大孤山铁矿为工程背景,分析边坡岩移机理,得出挂帮矿持续冒落跨度为临界冒落跨度的1.25~1.65倍,第一分段进路布置在矿体厚度大于3.3l的位置,能够保证露天开采的安全。研究陷落散体所需的回采体积,得出回采体积先随着保安矿柱宽度的增加而减小,后又随着保安矿柱宽度的增加而增大,当保安矿柱的宽度为88.45 m时,所需回采体积最小。采用散体滑落试验,得出了防护坝设置在露天坑底的上一个台阶,保证了露天开采的安全。研究成果能够实现大孤山铁矿露天转地下过渡期的产能衔接和安全生产,对于矿山的未来发展具有重要意义。

考虑流固耦合的露天坑积水下边坡与巷道协同稳定性研究

露天矿边坡与巷道协同稳定性是影响矿山安全开采的关键因素。开展矿区边坡与巷道协同稳定性研究是保证矿山能进行安全施工的重要工作之一。针对矿区Ⅵ号矿组露天坑目前存汇水问题,分析论证后续井巷开采、工程力学、汇水等因素对Ⅳ号矿组、Ⅶ号矿组深部井巷工程是否有影响;采用3Dmine建立了露天矿三维地质模型,截取风险边坡剖面并建立数值模型,结合COMSOL Multiphysics多场耦合分析软件,对建立的剖面模型的渗流场与应力场进行耦合,通过精细化划分网格对其进行稳态求解,得到剖面模型的损伤区、应力场及位移变化云图,其中,边坡5号剖面区域基坑存在积水问题,在求解过程中考虑渗水条件。分析结果表明:Ⅵ号露天边坡、Ⅶ号露天边坡岩体损伤对地下工程均未造成影响,Ⅵ号矿坑积水的渗透速度分布在10^(-7)~10^(-6)m/s,由于渗透速度较低,Ⅵ号矿坑汇水并未对附近地采工程稳定性造成显著影响;建议对Ⅵ号矿坑汇水进行及时抽排,并加强Ⅶ号露天边坡位移监测。该研究结果为论证边坡与巷道协同稳定提供了新思路和参考。

某330kV地下变电站底板浇筑温度的影响参数分析

地下变电站建设中经常涉及大体积混凝土浇筑,控制施工时的混凝土温度非常关键。该文以某330kV地下变电站为工程实例,建立ANSYS有限元分析模型,对不同施工参数下的底板大体积混凝土进行温度场、应力场仿真分析,得出混凝土入模温度、保温层厚度、冷却水管相关参数和地基约束程度等施工参数对底板温度场、应力场的影响规律和影响程度,提出相应的施工优化建议。明确工程底板浇筑温度的影响参数,能够为地下变电站工程及大体积混凝土浇筑温度控制提供依据。

在倾倒边坡中建设地下调压室的工程地质研究

扎拉水电站调压室建在山体倾倒边坡内,对该边坡及围岩稳定性的系统研究至关重要。根据岩体结构和变形破坏类型的差异,采用岩体结构、岩层转角、风化等定性因素结合波速比定量因素进行综合分区;通过现场超常规原位试验,结合反演计算,综合提出各区适宜的岩体抗剪强度参数;采用数值分析法模拟倾倒边坡变形破坏模式,并通过多种解析法校验边坡稳定性。结果表明:边坡倾倒岩体可分为层状弯曲区、碎裂拉张区、散体坠覆区;厂后倾倒边坡的主要失稳形式为拉裂-滑移-剪断和块体卸荷崩落;在倾倒边坡稳定性评价中,安全系数应取现行技术标准规定范围内的较大值,有利于保障倾倒边坡滑移稳定和坡内洞室围岩变形稳定。研究成果解决了地质条件局限和水工结构要求之间的突出矛盾,在中国水利水电建设中具有开创意义,可为倾倒边坡中工程建设提供参考。

积水采空区破碎煤岩体渗流特性试验研究

掌握积水采空区破碎垮落带煤岩体渗流规律对矿井瓦斯安全高效开采至关重要。利用气水两相可调控流动试验系统,采用稳态渗透法开展了积水采空区破碎煤岩体应力-渗透率试验,得到了不同块径、不同积水量条件下渗透参数随轴向载荷的变化特征,揭示了积水采空区破碎煤岩体渗流规律。结果表明:煤样应变随着载荷应力的增加逐渐增大;相同积水量条件下,不同块径煤样渗透率随着载荷的增大呈指数式递减;相同块径条件下,不同积水量的煤样渗透率随载荷的增大呈减小的趋势,且随着载荷的增大,积水量对渗透率的影响逐渐减小。

Developments and prospects of microseismic monitoring technology in underground metal mines in China

Microseismic monitoring technology has become an important technique to assess stability of rock mass in metal mines.Due to the special characteristics of underground metal mines in China,including the high tectonic stress,irregular shape and existence of ore body,and complex mining methods,the application of microseismic technology is more diverse in China compared to other countries,and is more challenging than in other underground structures such as tunnels,hydropower stations and coal mines.Apart from assessing rock mass stability and ground pressure hazards induced by mining process,blasting,water inrush and large scale goaf,microseismic technology is also used to monitor illegal mining,and track personnel location during rescue work.Moreover,microseismic data have been used to optimize mining parameters in some metal mines.The technology is increasingly used to investigate cracking mechanism in the design of rock mass supports.In this paper,the application,research development and related achievements of microseismic technology in underground metal mines in China are summarized.By considering underground mines from the perspective of informatization,automation and intelligentization,future studies should focus on intelligent microseismic data processing method,e.g.,signal identification of microseismic and precise location algorithm,and on the research and development of microseismic equipment.In addition,integrated monitoring and collaborative analysis for rock mass response caused by mining disturbance will have good prospects for future development.

A comprehensive geomechanical method for the assessment of rockburst hazards in underground mining

Rockburst hazard in mining industry all over the world is one of the most severe hazards. It is becoming increasingly common because of the ever-growing depths of mining operations accompanied by the increasing strength of rocks. One of the most difficult issues is to predict this hazard before the mining operations, whether geophysical investigations have been conducted or not. Polish experience in this field shows that in such cases an effective solution can be the geomechanical method. Therefore, extensive studies on rockburst hazard should focus on three main aspects:(1) rock mass and rock(and coal)predisposition to rockburst–laboratory tests and empirical analyses based on lithology,(2) identification of the potential places with stress and elastic energy concentration in the rock mass within the area planned for exploitation, and(3) the assessment of the impact of mining tremors on the surface. This preliminary geomechanical analysis assesses the propensity of the rock mass to dynamic breakage and provides quantitatively the level of rockburst hazard. The paper presents Polish experience in rockburst hazard assessment with the use of geomechanical method, as well as some solutions and examples of such analyses.

Excavation of underground research laboratory ramp in granite using tunnel boring machine: Feasibility study

Underground research laboratory(URL)plays an important role in safe disposal of high-level radioactive waste(HLW).At present,the Xinchang site,located in Gansu Province of China,has been selected as the final site for China’s first URL,named Beishan URL.For this,a preliminary design of the Beishan URL has been proposed,including one spiral ramp,three shafts and two experimental levels.With advantages of fast advancing and limited disturbance to surrounding rock mass,the tunnel boring machine(TBM)method could be one of the excavation methods considered for the URL ramp.This paper introduces the feasibility study on using TBM to excavation of the Beishan URL ramp.The technical challenges for using TBM in Beishan URL are identified on the base of geological condition and specific layout of the spiral ramp.Then,the technical feasibility study on the specific issues,i.e.extremely hard rock mass,high abrasiveness,TBM operation,muck transportation,water drainage and material transportation,is investigated.This study demonstrates that TBM technology is a feasible method for the Beishan URL excavation.The results can also provide a reference for the design and construction of HLW disposal engineering in similar geological conditions.2020 Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Modified Mohr-Coulomb strength criterion considering rock mass intrinsic material strength factorization

With the increase of mining depth of mineral resources,the rock mass stress state is being more and more complex.The rock mass show different features,namely,with the increase of hydrostatic pressure,rock mass failure mode turns from brittle tension failure to structure ductile failure and its limit strength also increases.The restriction of minimal principal stress on the initiation and development of microcrack and the change of micro-unit stress state by the intermediate principal stress play a decisive role in the increase of rock mass limit strength.Based on the rock mass failure behavior law under complex stress state and the σ2-dependence on the rock mass strength,we proposed a Modified Mohr-Coulomb(M-MC) strength criterion which is smooth and convex.Finally,the M-MC criterion is validated by multiaxial test data of eight kinds of rock mass.We also compared the fitting results with Mohr-Coulomb criterion(MC).It shows that the new criterion fits the test data better than the Mohr-Coulomb criterion.So the M-MC strength criterion well reveals the rock mass bearing behavior and can be widely used in the rock mass strength analysis.The results can provide theoretical foundations for stability analysis and reinforcement design of complex underground engineering.

Multiscale Hierarchical Digital Rock Mass Models and Numerical Testing on Mechanical and Hydaulic Properties of Rock Mass

Underground space utilization and exploration is an irreversible trend for promoting sustainable development especially in megacities.Geotechnical engineering safety is always one of the most important issues in all phases,including planning,design, construction and operation,of the underground project.Engineering geological and hydro-geological characteristics of the foundation rock mass