Comprehensive assessment on dynamic roof instability under fractured rock mass conditions in the excavation disturbed zone

The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine, China. The rock mass was particularly weak and fractured. There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone （EDZ） with the collapsing volume of 216 m^3. First, the field detailed geological environment, regional seismic dynamics, and dynamic instability of roadways were generally investigated. Second, the field multiple-index monitoring measurements for detecting the deep delamination of the roof, convergence deformation, bolt-cable load, acoustic emission （AE） characteristic parameters, total AE events, AE energy-releasing rate, rock mass fracture, and damage were arranged. Finally, according to the time-space-strength relations, a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.

Predicting the excavation damaged zone within brittle surrounding rock masses of deep underground caverns using a comprehensive approach integrating in situ measurements and numerical analysis

Excavation Damaged Zone(EDZ)scope is important for optimizing excavation and support schemes in deep underground caverns.However,accurately predicting the full EDZ scope within the surrounding rock masses of deep underground caverns during excavation remains a pressing problem.This study presents a comprehensive EDZ scope prediction approach(CESPA)for the brittle surrounding rock masses of deep underground caverns by coupling numerical simulation with quantitative analysis of borehole wall images and ultrasonic test results.First,the changes in both P-velocity(V_(p))and joint distribution of the surrounding rock masses before and after excavation damage are captured using ultrasonic tests and borehole digital cameras.Second,the quality Q-parameters of the surrounding rock mass before and after excavation damage are preliminarily rated with the rock mass descriptions provided by borehole wall images,and the rock mass V_(p)-parameter values are determined according to the V_(p)-borehole depth curves.Third,the Q-parameter ratings are further finely adjusted by updating the related Q-values to be similar with the Q-values estimated by V_(p)-parameter values.Fourth,the initial and residual mechanical parameters for the rock mass deterioration model(RDM)are estimated by the adjusted Q-parameter ratings based on the modified Q-based relations,and the elastic modulus deterioration index(EDI)threshold to describe the EDZ boundary is determined with the V_(p)-parameter values.Finally,EDZ scope is predicted using the elastoplastic numerical simulation with RDM and EDI based on the mechanical parameter estimates and EDI threshold.Analyses of applications in Sub-lab D1 in Jinping II project show that CESPA can provide a reliable and operable solution for predicting full EDZ scopes within the brittle surrounding rock masses of deep underground caverns.

Numerical Analysis on Displacement Law of Discontinuous Rock Mass in Broken Rock Zone for Deep Roadways

On the basis of the characteristics of broken rock zone, using the program of "discontinuous deformation analysis(DDA)", the changing law of influential factors of discontinuous rock mass in large broken rock zone was researched quantitatively for the first time. Based on the results of computation, the concept of "key part"of roadways and its stability criterion were brought forward, and it was pointed out that in inclined coal and rock seams the"key parts"of roadways are the upper side and the floor of surrounding rocks, especially the former.

Petrology of an Arc-Oceanic Crust Contact Zone in the Laohushan Back-arc Basin, the Eastern Section of the North Qilian Mountains, NW China

A contact zone sandwiched between an arc and an oceanic crust was discoveredin the Laohushan area in the present study. It consists of a series of north-dipping imbricatedthrust sheets and is exposed on the surface as a narrow arcuate belt, which extends for about 30 kmin an E-W direction and measures about 1-3 km wide. Lithologically, it can be divided into foursubzones. Subzone 1 consists of meta-andesite and metasandstone; subzone 2, psammitic schists;subzone 3, psammitic and pelitic schists, quartz diorite and hornfelses; and subzone 4, metagabbro,epidote amphibolite and pelitic schists. The metamorphism has the following grading sequence: lowgreenschist facies in subzone 1 - > high greenschist facies in subzone 2 - > low amphibolite fadesin subzone 3 - > epidote amphibolite facies in subzone 4. Petrographic and geochemical evidenceshows that rocks in subzones 1, 2 and 3 are arc rocks, whereas those of subzone 4 are oceaniccrustal rocks. The metamorphic mineral assemblages and especially mineral chemistry of the bluishgreen amphibole from the pelitic schists and epidote amphibolite of subzone 4 suggest that the rocksof the contact zone were metamorphosed at a pressure of up to 0.69 GPa. It is thought that theLate-Mid Ordovician oceanic lithosphere of a back-arc basin was underthrust northerly beneath an arcto a depth of 20-23 km, where the basaltic rocks and gabbro were converted to epidote amphiboliteand metagabbro respectively. Then, the root rocks of the arc and these metamorphosed oceanic rockswere brought up to shallower depths by thrust faults to form a contact zone between the arc and theoceanic crust in the Laohushan area.

THE THEORY OF SUPPORTING BROKEN ZONE IN SURROUNDING ROCK

The first topic discussed in this paper is to evaluate the present supporting theories,among which the typical two are collapse arch and elasto-plastic theories. The former is rather limited in practical application,and the latter is built up on some assumptions which is inconsis-tent with the reality,for it is of no need to support a roadway of which the surrounding rock is in elasto-plastic state. The second topic is to prove the objective existence of the broken zone in surrounding rock(BZSR) by a series of laboratory experiments and field measurements. The paper indicates that the object to be supported mainly is the bulking or expanding force resulted from the development of BZSR. This is remarkably different from the existing points of view which have been generally recognized nowadays. So far ,this theory has been tested in supporting more than ten thousand meters roadways located in various strata and has proved itself to have a great technoeconomical benefit.

Mechanics analysis on the conditions of rock burst occurrence in the coal mass of roadway rib

According to the rock burst features occurred in the coal mass of roadway rib in one mine,the mechanics model of coal mass and roof structure system along the edge of goaf was founded to analyze the stress of roof rock layer,so the subside curve of roof rock layer was deduced.Furthermore,the stability of coal and rock system were analyzed,the critical load and critical resistance zone were used to judge the danger degree of rock burst occurrence.The influence of coal mass strength,brittleness degree,coal seam thickness,roof thickness,suspending length,equivalent shear module on the critical load, critical resistance zone was confirmed.So the rock burst occurrence conditions of coal mass in roadway rib mainly depend on mining depth,coal seam thickness and hard roof and floor,which are decided by the above studies,and successfully applied in prediction and prevention of rock burst in this mine.

In-situ observations of damage-fracture evolution in surrounding rock upon unloading in 2400-m-deep tunnels

The damage-fracture evolution of deep rock mass has obvious particularity,which is revealed in 2400-mdeep tunnels by field tests.The evolution of the excavation damaged zone depth is consistent with that of the fractured zone depth.The ratio of the excavation damaged zone depth to the excavation fractured zone depth is greater than 2.0 in a rock mass with both high strength and good integrity,but less than1.5 in a rock mass with lower strength or poor integrity.Zonal disintegration in a rock mass with high strength and fair integrity is more likely to occur when it contains more than two groups of primary fractures in damaged zones.Fractures develop outward in zonal disintegration but are totally different from the single-zone fracture,in which the fractures develop inward,and it is the starting position of the fractured zone when the excavation surface of the middle pilot is 7–9 m close to the pre-set borehole and it stops after the excavation surface of the baseplate is 11–14 m away.The most intense evolution occurs around 2–4 m from the pre-set borehole in the sidewall expansion stage.The research results provide a reference for the monitoring scheme and support design of CJPL-Ⅲin its future construction.

DETERMINATION OF MICROCRACK BOUNDARY RESULTING FROM ROCK BLASTING WITH SEISMIC TRAVELTIME TOMOGRAPHY

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Fluid-rock interaction and mass balance of deformed rock in deformation——Taking the Eritx tectonic zone,northern Xinjiang

The Irtish techonic zone,as an example,is presented to study fluid-rock interactions during overthrusting the deformation process at the depth of middle-lower earth crust.The results show that there were compicuous fluid actions in the meantime of deformation and many deformational and differential microstructures related to fluid-rock interactions provided direct evidence of fluid actions.Fluid,as a medium of mass transfer,played an important role in the loss and getting of chemical compositions in deformed rocks during tectono-dynamic lithogeneous processes in which rock alterations from protolith(volcanics)through mylonite to migmatite and finally to migmatitic granite took place.The loss and getting of chemical compositions can he calculated by means of major and trace elements.Using the calculated results and SiO_2 solubility,the calculation fluid(mass)/rock(volume)ratio is 10~3-10~5g fluid/m^3 rock.The possible fluid resources are dehydration reactions of pore water and mineral water within protoliths(marine mid-acid volcanics)and foodwaU rocks during tectono-rise pressure and temperature processes.The fluid flow migrated from deep to shallow positions of the earth crust along the large-scale thrusting fault,penetrative cleavage,and S-C foliation.Fluid mass transportation resulted in chemical composition alterations in deformed rocks. Within overthrusting zone under the compressive orogenic background,the major mechanism of mass transportation is infiltration or advection in the open system.

热湿循环作用下节理砂岩重复剪切力学特性及本构模型

乌东德、白鹤滩等大型水库处于金沙江典型干热河谷内,其岸坡消落带岩土体除经受库水位每年大幅升降以及汛期小幅频繁变化的影响外,还包括干热河谷高温低湿气候条件以及区域高频地震和水库地震的影响。为研究干热河谷地区消落带节理岩体的损伤劣化特性,在前期水-岩作用的研究基础上,以乌东德库区典型岸坡节理砂岩为研究对象,开展了热湿循环作用下节理砂岩重复剪切试验,分析了节理岩体的剪切力学特性劣化规律和劣化机理,并分段建立了考虑热湿循环作用损伤的节理砂岩剪切本构模型。研究表明:(1)在热湿循环以及重复剪切作用下,节理砂岩的抗剪强度、剪切刚度、剪切重点剪胀值和屈服点剪切位移均呈现“快-缓-稳”的劣化趋势,其中在前3个循环周期内劣化幅度显著,劣化占比近70%,3~8个循环周期内劣化速率放缓,8个循环周期后劣化速率趋稳;(2)相比于干湿循环,热湿循环对岩石孔隙度和纵波波速的影响更大,且岩石颗粒间的连接作用在较高温度的影响下更易遭受破坏;(3)根据剪切应力-剪切位移曲线特征,建立了以Goodman模型和Clough-Duncan双曲线模型分段修正描述的本构模型,模型曲线与试验结果能够较好吻合。研究成果及方法可为干热河谷水库岩质岸坡消落带稳定分析提供参考。

煤岩变形破坏电荷感应规律试验研究及现场应用

准确掌握岩体受载破坏过程电荷感应规律,对于冲击地压等动力灾害预测具有重要意义。在电荷监测仪采集精准度优化提升基础上,对砂岩试样单轴压缩受载破坏电荷感应规律进行了实验室监测试验,并进行井下监测试验,详细分析了不同加载速率下砂岩电荷感应与应力降以及裂纹扩展的关系和超前工作面支承压力影响区电荷感应特征。结果表明:岩样受载破坏过程中裂纹的多次形成、发育与扩展均伴随着电荷感应信号,前兆电荷信号的产生早于岩样受载破裂出现的应力降;在0.005、0.015、0.020 mm/s 3种加载速率条件下,岩样破坏过程的电荷信号规律随加载速率的变化显现出差异性,主要表现为加载速率越大,电荷信号越丰富,超前应力突变前兆电荷信号越发提前出现;现场各测点平均感应电荷量最大值均位于超前支承压力影响区内,且平均感应电荷量大小与工作面超前支承压力分布趋势一致。

葫芦素煤矿上覆岩体运移规律及“上三带”发育高度

为研究大采宽条件上覆岩体运移与离层空间发育规律及“上三带”的关系,以内蒙葫芦素煤矿21406工作面与21101工作面为研究对象。采用多种方法如理论预测、建立模型进行数值模拟、钻探取芯观测岩性与裂隙发育、注水测量漏失量与窥视等方法研究了回采面开采后上覆岩层移动与变形规律与“上三带”发育关系。21406工作面位移呈“中间大、两边小”的分布态势,其运动速度先增加后减小,并在推过钻孔138 m处取得极大值;工作面推过138~178 m的范围内,为离层演化和发育的核心区间,并在322 m开始减弱并发生闭合;离层空间分布在距离煤层约260 m向上区域。21101工作面随着推进距离的增加,裂隙发育范围由“拱形”逐步演化为“马鞍形”,其发育的高度在推进80 m时达到61.6 m的最大值;注水实测导水裂隙带高度为65.39 m,裂采比为22.54倍。离层空间含水层发育在煤层上方260 m以上,远离导水裂隙带范围。本文研究结果为离层注浆与顶板疏放水提供了较为扎实的设计依据。

露天矿高陡边坡岩体参数获取与稳定性评价方法研究

针对露天矿高陡边坡岩体参数难获取和稳定性易变化的问题,以攀枝花露天矿高陡边坡为研究对象,采用非接触式无人机摄影测量技术获取研究区域的三维模型,统计结构面的分布情况,结合室内岩石力学试验数据,采用《工程岩体分级标准》(GB/T 50218—2014)进行岩体质量分级,并给出边坡岩体强度力学参数建议值。在此基础上,通过有限单元法分析了矿区在开采条件下边坡的稳定性动态演化特征,并对开挖过程边坡的稳定性做出了评价。结果表明:随着矿区的开采,边坡在开挖面附近由于卸荷作用发生位移回弹,最大位移增量为33.2 mm;塑性区主要集中在断层和矿岩界面附近,以剪切屈服为主;边坡稳定性随着矿区的开采逐渐降低,直至达到临界稳定状态。采用锚索对边坡进行加固,并采用塑性区面积占比对加固前后的稳定性进行评价,评价系数α由加固前的0.4降低至加固后的0.05,证明了加固措施的有效性。研究成果可为露天矿高陡边坡岩体参数取值和稳定性评价提供参考。

针对双目摄像技术的岩体结构面非接触调查评述

为准确评估岩体质量的优劣,以及了解其在稳定性方面的差异,进行岩体质量分级工作是必要的,其中最关键的部分是调查岩体的结构面。现阶段,对于岩体质量分级中的岩体结构面的调查方法主要有现场接触法、钻孔测量以及非接触扫描测量3类方法。随着科技发展,基于双目摄像技术的岩体结构面非接触调查法在识别准确率上有质的提升,同时大大节省人力物力成本。该文结合基于双目摄像技术的岩体结构面非接触调查法的基本原理、采集过程及数据处理过程对这项技术进行详细介绍,同时通过应用实例对该技术的实用性进行评述。该技术符合现场实际条件,能够快速评价岩体质量,为矿山企业提供重要依据来选择工程结构参数,并有效指导生产。

程潮铁矿崩落法开采对上覆岩体变形的影响研究

针对程潮铁矿开展工程地质调查,采用离散元分析软件UDEC建立其二维地质剖面模型,在假设其上部水平矿房未开采的条件下,模拟了程潮铁矿无底柱分段崩落法开采-480m、-500m相邻分段的过程,研究单一分段及相邻分段开采导致的围岩“冒落带、导水裂隙带”的分布规律及范围,探索程潮铁矿单分段矿房开采时其上覆岩体形成的导水裂隙带高度范围y随采长x的变化函数,分析无底柱分段崩落法不同分段矿房开采对于上覆岩体变形及影响机理,为类似开采技术条件矿山安全生产提供参考。

宁都县上横铀矿地质特征及控矿因素分析

上横铀矿位于江西省宁都县,是近年来江西省核地质工作少数取得突破的地区之一。该矿床所处的桃山铀矿田中,大多矿床为产于复式岩体内部的碎裂蚀变岩型,但上横铀矿产于岩体外接触带的区域断裂中,为花岗岩外带型,成矿规律与控矿因素的认识略有欠缺。本文利用野外专项地质测量、槽探、钻探揭露等手段,初步查明铀成矿条件和控矿因素,为今后该类型铀找矿提供新思路。研究认为,在成矿、容矿和保矿过程中,桃山复式岩体、南华系地层、红盆、上横断裂、脆性构造岩以及韧性构造岩等因素在不同程度上起到作用。

高水平应力矿岩接触带巷道稳定性分析

井下巷道在通过矿岩接触带时,由于接触带两侧岩性差异会在巷道两端和接触带上产生不同的变形和破坏。以杜达铅锌矿100 m中段矿岩接触带巷道为研究对象,采用Flac3D软件数值模拟和现场巷道收敛变形监测的方法,分析矿岩接触带巷道在未支护情况下的应力分布和变形情况,得出杜达铅锌矿在高水平应力下矿岩接触带巷道的变形和破坏规律。研究结果表明:高水平应力下矿岩接触带巷道形成后的破坏以剪切破坏为主,巷道变形和破坏在顶底板表现较为明显。矿岩接触带上剪切应力集中,使得接触带两侧矿(岩)体的变形存在明显的不对称非协调分布。岩体侧的变形破坏比矿体侧更为明显,且巷道两帮变形小于顶底板变形。研究结果可为类似条件下矿岩接触带巷道的支护提供理论依据。

基于ShapeMetrix 3D及修正BQ分级法的节理岩体稳定性分级

岩体稳定性分级是反映岩体完整性、判断岩体质量好坏、确保矿山开采安全的重要工作。为了准确高效地获得岩体节理产状信息,采用非接触式测量法调查岩体结构面。以大冶铁矿为工程背景,利用ShapeMetrix 3D系统对该矿现场19处节理裂隙进行了精确扫描和测量,并对节理裂隙的几何参数进行了统计分析,得到了岩体产状信息。利用测量数据,基于修正的BQ分级法对该矿岩体进行分级,并将此分级结果与Q分级法和RMR分级法的分级结果进行对比,结果表明:由3种分级方法得到的岩体质量等级基本一致,岩体稳定性基本为Ⅱ级,个别位置为Ⅲ级,稳定性较好。

甘肃省厂坝铅锌矿工程地质条件浅析

矿区土体按成因类型和土体结构可分为一般土和特殊土两大类,一般土主要为冲洪积砂砾卵石、碎石及粉土,特殊土有残坡积碎石土、崩滑碎石土和人工堆积矿渣,结构松散凌乱,孔隙大,透水性强,压缩性高,物理力学性质极不稳定。矿区矿石类型、结构构造、物质成分特征完全相同。矿床赋存在坚硬、半坚硬的碳酸盐岩及碎屑岩层中,可分为大理岩含矿系统和片岩含矿系统两大类,较坚硬中厚层状片岩岩组:主要包括黑云母石英片岩、黑云母片岩和石英片岩,岩石较坚硬,中厚层状结构为主,坚硬厚层状大理岩岩组:岩性主要为带状结晶灰岩、白云岩层组成,工程地质性质较好。厂坝铅锌矿床岩石一般完整-较完整,岩体结构类型主要为整体块状结构及层状结构,矿体及围岩较坚硬,陡倾斜,倾角75°~85°,岩石稳定性好,矿体顶、底板和采矿工程系统范围内岩、矿石大多数裂隙不甚发育,一般比较稳定,断裂带附近岩石破碎。综合考虑,确定矿区为工程地质条件中等的矿床。