Bolt-grouting combined support technology in deep soft rock roadway

Analyzing the mineral composition, mechanical properties and ground stress testing in surrounding rock,the study investigated the failure mechanism of deep soft rock roadway with high stress. The boltgrouting combined support system was proposed to prevent such failures. By means of FLAC3D numerical simulation and similar material simulation, the feasibility of the support design and the effectiveness of support parameters were discussed. According to the monitoring the surface and deep displacement in surrounding rock as well as bolt axial load, this paper analyzed the deformation of surrounding rock and the stress condition of the support structure. The monitor results were used to optimize the proposed support scheme. The results of field monitors demonstrate that the bolt-grouting combined support technology could improve the surround rock strength and bearing capacity of support structure, which controlled the great deformation failure and rheological property effectively in deep soft rock roadway with high stress. As a result, the long term stability and safety are guaranteed.

Experimental investigation on behaviors of bolt-supported rock strata surrounding an entry in large dip coal seam

In order to investigate the behaviors and stability of rock strata surrounding an entry with bolt supporting in large dip coal seams (LDCSs) dipping from 25° to 45°, a self-developed rotatable experimental frame for similar material simulation test was used to build the model with the dip of 30°, based on analyses of geological and technological conditions in Huainan mine area, Anhui, China. The strata behaviors, such as extracting- and mining-induced stresses development, deformation and failure modes, were synthetically integrated during working face advancing. Results show that the development characteristics of mining-induced stress and deformation are asymmetrical in the roadway. The strata behaviors are totally different in different sections of the roadway. Because of asymmetrically geometrical structure influenced by increasing dip, strata dislocating, rock falling and breaking occur in roof. Then, squeezing, collapsing and caving of coal happen in upper- and lower-rib due to shearing action caused by asymmetrical roof bending and dislocating. Owing to the absence of supporting, floor heaving is very violent and usually the zone of floor heaving develops from the lower-rib to upper-rib. Engineering practices show that, due to the asymmetrical characteristics of rock pressure and roadway configuration, it is more difficult to implement bolt supporting system to control rock stability of roadways in LDCSs. The upper-rib and roof of entries are the key sections. Consequently, it is reliable to use asymmetrical bolt-mesh-cable supporting system to control rock stability of roadways based on the asymmetrical characteristics of roadway configuration and strata behaviors.

Study on Repairing Permanent Transportation Roadway in Deep Mining by Bolt-Shotcrete and Mesh Supporting

The roadway support in many places of Jiulongkou Colliery, Fengfeng Mining Bureau, such as in the Permanent transportation roadway, was failed or locally caved, which seriously affected the colliery’s coal production performance and safety. Based on analysis of supporting objects for roadway repairing, this paper proposes the supporting parameters and condruction technics. The industrial ted of 70m long roadway repairing shows that the proposed parameters and technics of bolt shotcrete and mesh support for roadway repairing are reasouable, bring good technical and economic results for the colliery, and the repairing is successful.

Numerical simulation of creep characteristics of soft roadway with bolt-grouting support

Based on the engineering background of a soft rock roadway in Qinan Coal Mine 82 Area,Huaibei Mining Group,three creep models with different support patterns in soft rock roadway were established by using geotechnical software of FLAC2D.According to the calculation results of different models,the change law of mechanical properties with the time of bolt-grouting support structure was obtained.Furthermore,for the test bolt-grouting support roadway,the deformation law of surrounding rock got by underground industrial experiment and field observation accords with the creep law got by numerical calculation.The results of numerical calculation and field observation show that,compared with other supports,the creep of bolt-grouting support roadway enters the steady-state creep stage from tertiary creep stage ahead,the deformations of roof,floor and two sides are decreased greatly,the plastically deforming area in surrounding rock is reduced obviously,and the distribution ranges of maximum and minimum principal stress are shrank obviously.All those fully show that the bolt-grouting support has its remarkable advantages in controlling surrounding rock creep and improving the whole strength of surrounding rock and self-bearing capacity.

Anchoring mechanism and application of hydraulic expansion bolts used in soft rock roadway floor heave control

Comparing with the resin bolt, the hydraulic expansion bolt has different anchoring mechanism and application advantage. According to the working mechanism of the hydraulic expansion bolt, its anchoring force is expressed in four forms including support anchoring force, tension anchoring force, expansion anchoring force and tangent anchoring force, and their values can be obtained on the basis of each calculation formula. Among them, the expansion anchoring force, which is the unique anchoring force of the hydraulic expansion bolt, can provide confining pressure to increase the strength of rock. Aiming at solving the problem of stability control in the soft rock roadway in Jinbaotun Coal Mine which has a double layer of 40 U-type sheds and cannot provide enough resistance support to control floor heave, the study reveals the mechanism of floor heave in the soft rock roadway, and designs the reasonable support parameters of the hydraulic expansion bolts. The observed results of floor convergence indicate that the hydraulic expansion bolts can prevent the development and flow of the plastic zone in the floor rock to control floor heave. Research results enrich the control technology in the soft rock roadway.

Mechanical properties and supporting effect of CRLD bolts under static pull test conditions

A device for supporting soft rock masses combined with a constant resistance structure characterized by constant resistance and large deformation at the end of a steel bar, known as the constant resistance and large deformation（CRLD） bolt, has recently been developed to counteract soft rock swelling that often occurs during deep mining. In order to further study the mechanical properties of the CRLD bolt, we investigated its mechanical properties by comparison with the conventional strength bolt（rebar） using static pull tests on many aspects, including supporting capacity, elongation, radial deformation, and energy absorption. The tests verified that the mechanical defects of the rebar, which include the decrease of bolt diameter, reduction of supporting capacity, and emergence and evolution of fracture until failure during the whole pull process, were caused by the Poisson＇s ratio effect. Due to the special structure set on the CRLD bolt, the bolt presents a seemingly unusual phenomenon of the negative Poisson＇s ratio effect, i.e., the diameter of the constant resistance structure increases while under-pulling. It is the very effect that ensures the extraordinary mechanical properties, including high resistance, large elongation, and strong energy absorption. According to the comparison and analysis of numerical simulation and field test, we can conclude that the CRLD bolt works better than the rebar bolt.

An experimental study of a yielding support for roadways constructed in deep broken soft rock under high stress

A rationally designed support for deep roadways excavated in broken soft rock under high stress was investigated. The deformation and failure characteristics and the mechanism of ''yielding support'' was studied for anchor bolts and cables. The rail roadway of the 2-501 working face in the Liyazhuang Mine of the Huozhou coal area located in Shanxi province was used for field trials. The geological conditions used there were used during the design phase. The new ''highly resistant, yielding'' support system has a core of high strength, yielding bolts and anchor cables. The field tests show that this support system adapts well to the deformation and pressure in the deep broken soft rock. The support system effectively controls damage to the roadway and ensures the long term stability of the wall rock and safe production in the coal mine. This provides a remarkable economic and social benefit and has broad prospects for fur- ther application.

Non-destructive testing and pre-warning analysis on the quality of bolt support in deep roadways of mining districts

The bolt support quality of coal roadways is one of the important factors for the efficiency and security of coal production. By means of a self-developed technique and equipment of random non-destructive testing, non-destructive detection and pre-warning analysis on the quality of bolt support in deep roadways of mining districts were performed in a number of mining areas. The measured data were obtained in the detection instances of abnormal in-situ stress and support invalidation etc. The corresponding relation between axial bolt load variation and roadway surrounding rock deformation and stability was summarized in different mining service stages. Pre-warning technology of roadway surrounding rock stability is proposed based on the detection of axial bolt load. Meanwhile, pre-warning indicators of axial bolt load in different mining service stages are offered and some successful pre-warning cases are also illustrated.The research results show that the change rules of axial bolt load in different mining service stages are quite similar in different mining areas. The change of axial bolt load is in accord with the adjustment of surrounding rock stress, which can consequently reflect the deformation and stability state of roadway surrounding rock. Through the detection of axial bolt load in different sections of roadways, the status of real-time bolt support quality can be reflected; meanwhile, the rationality of bolt support design can be evaluated which provides reference for bolting parameters optimization.

Rock Mass Characterization and Support Design for Underground Additional Surge Pool Cavern—A Case Study, India

For better rock mass characterization and support design, 3D engineering geological mapping was carried for the heading portion of the under construction 200.00 m long, 68.75 m high and 20.20 m wide underground additional surge pool cavern of a Pranahitha-Chevella Sujala Sravanthi lift irrigation scheme package 8, India. To study cavern behavior, 3D geologic mapping of heading portion is very important for large cavern for predicting geologic conditions in benching down up to invert level, planning support system, selecting inclination for best location of supplemental rock bolt and choosing strategic locations for various types of instrumentation. The assessment of Tunnel Quality Index “Q” and Geomechanics classification for the granitic rock mass was done based on the information available of the rock joints and their nature and 3D geological logging. Hoek-Brown parameters were also determined by the statistical analysis of the results of a set of triaxial tests on core samples. On basis of geological characteristics and NMT Q-system chart, support system is recommended which includes rock bolt, steel fibre reinforced shotcrete and grouting. To evaluate the efficacy of the proposed support system, the capacity of support system is determined.

Modification of rock mass rating system:Interbedding of strong and weak rock layers

Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.

锚杆钢-木组合托盘极限承载力学性能研究

为降低动压冲击对支护系统的破坏,适应大变形巷道的需要;基于球壳结构理论构建锚杆拱形钢托盘承载力学模型,给出钢托盘最大承载力计算式,分析钢托盘各参数尺寸对其承载力的影响关系,研究木托盘压缩实验特征;通过Abaqus软件对钢托盘与组合托盘开展有限元静态力学强度实验,对比分析钢托盘与组合托盘受压状态下的不同特征,分析让压距离对组合托盘承载性能的影响规律。结果表明:对钢托盘承载力的影响顺序为拱高>拱底圆半径>孔口半径,拱高与承载力服从对数增加关系,拱底圆半径、孔口半径与托盘承载力基本成线性增加关系;钢-木组合托盘中木托盘先受力,并经历了压密阶段、弹性变形阶段和塑性变形阶段,木托盘被压缩可降低钢托盘30.03%的承载受力,组合托盘的应力-位移曲线右移,组合托盘的极限承载力增加;钢托盘受压破坏从孔口处开始,基本成圆形向四周扩展,托盘底部四边中间区域与四角区域形成的高应力差是导致托盘四角破坏的主要原因。

巷帮煤体整体滑脱型冲击地压锚杆防冲支护原理及工程实践

冲击地压是目前严重影响煤炭安全有效开采的灾害之一,研究锚杆防冲支护原理和技术对防治巷道冲击地压灾害具有重要意义和价值。通过对巷帮煤体整体冲入型冲击地压发生的地质条件以及破坏特征进行总结分析,认为坚硬顶板与坚硬煤层是此类型冲击地压的重要地质特征,而巷帮煤体整体滑脱是其主要冲击破坏特征。在此基础上,以巷帮滑脱煤体为研究对象,建立了顶板-巷道-底板复合结构体力学模型,建立了巷帮煤体发生水平滑移的极限平衡方程,并对各个参数进行分析。结果表明:由于顶板反弹使巷帮煤体竖直方向压力降低,巷帮煤体被构造应力推入巷道发生冲击地压。基于该发生机制模型,认为目前的锚杆支护设计体系在防治巷帮煤体冲入型冲击地压存在不足,并基于其发生和破坏特征,建立了针对巷帮煤体整体滑脱型冲击地压的锚杆防冲支护设计原则,即将顶和底帮锚杆锚固端分别穿层打入稳定的顶底板内,并使用长锚索取代中部帮锚杆,提供锚杆支护的防冲作用。基于新建立的锚杆防冲支护设计方法,以大屯矿区孔庄煤矿7305工作面防冲支护为工程背景,在宽煤柱段巷帮锚杆支护采取了防冲设计,帮顶、底部锚杆及补强锚索均锚固于顶底板内部,能够有效吸收煤体滑动动能,提高安全性。

既有隧道不同扩挖宽度下锚杆参数的优化

以黄山洞隧道工程为依托,通过对现场数据的监测和利用有限元分析软件Midas GTS NX进行数值模拟,分析了不同扩挖宽度下隧道拱顶沉降值、周边收敛值和围岩有效应力变化的规律,并改变锚杆的长度和锚杆间距,分析在不同锚杆长度下围岩有效应力、衬砌应力以及锚杆应力的变化规律,确定了不同扩挖宽度下最优的锚杆长度和锚杆间距.研究结果表明:随着扩挖宽度的增加,围岩有效应力由大至小依次为拱脚处压应力、拱腰处压应力、拱顶处压应力和仰拱处拉应力;拱顶处压应力随扩挖宽度的增大而减小,拱腰处压应力随扩挖宽度的增大而增大,但增大趋势不明显;受单侧扩挖方式的影响,扩挖侧的应力大于非扩挖侧;拱脚处受到应力集中的影响,其压应力随着扩挖宽度的增大而增大;扩挖宽度为1.5~2.5 m时的最优锚杆长度和间距分别为2.5 m和1.7 m,扩挖宽度为3.5~4.5 m时二者分别为3.0 m和1.2 m.

节理发育区巷道锚杆支护参数优化研究

在节理发育区的地下硐室和巷道开挖过程中,锚杆支护会对巷道围岩应力分布有显著影响。为研究锚杆对巷道围岩主应力状态的影响,采用FLAC3D软件对锚杆支护下的巷道围岩稳定性进行了模拟研究。基于HYPERWORKS软件开发了一种分析应力重分布结果的处理方法,以克服在应力分布图中难以直接观察锚杆支护影响的问题。结果表明:锚杆支护作用能提高最小主应力,围岩承载性能明显增加;对于在硐室顶板、底板和四周侧墙安装的3种支护形式,最大主应力增量分别为3.61、6.28、6.88 MPa;锚杆预应力、长度和数量均会对围岩应力重分布造成影响。根据数值模拟结果对巷道锚杆支护参数进行了优化,优化后的锚杆预应力、长度和数量分别为60 kN、2.0 m和5根,优化后的锚杆支护设计能够有效提高巷道围岩稳定性。

软土地层隧道围岩分区初期支护技术研究

软土地层通常具有较低的承载力和较高的压缩性,隧道开挖过程中极易发生变形和坍塌。为了控制围岩的变形和破坏,确保施工安全,提出软土地层隧道围岩分区初期支护技术。通过合理规划围岩压力监测点,采集压力数据;利用简化的锚杆、钢架及岩体结构面,构建初期支护本构模型;计算锚杆与钢架的最佳间距和长度,并以此为依据设计复合支护结构,实现围岩分区初期支护。结果表明:所提方法隧道沉降位移较小、塑性区分布面积较小。体现了支护技术的有效性,具有较好的应用价值。

浅埋大跨岩质隧道主动支护作用机制研究与应用

预应力锚杆主动支护技术在隧道工程的应用日益增多,但其对浅埋大跨岩质隧道的适用性及作用机制尚未明确。以青岛地铁暗挖车站为依托工程,开展调研分析、数值计算和模型试验,对比分析预应力锚杆与非预应力锚杆对块状围岩的支护作用,从围岩应力补偿、块体围岩挤压成拱和危险块体控制3个方面研究浅埋大跨岩质隧道主动支护作用机制及理论模型,并进一步开展现场应用。结果表明:原支护方案主要沿用了土质隧道支护理念,对岩质围岩自承能力的认识和利用不充分;锚杆预应力(100 kN)使围岩拉应力区消失、塑性区大幅度减小,并使围岩结构面的法向挤压接触应力提高约0.2~0.3 MPa,有效控制结构面两侧岩体的滑移错动,提升了隧道围岩整体稳定性;建立的主动支护理论模型将传统主动支护应力补偿对象由开挖面聚焦至岩体结构面;主动支护新方案较原支护方案的支护材料减量约30%,工期缩短约17%,隧道沉降量减小约50%。

锚杆锚固区承载层范围影响因素研究

针对锚杆支护中锚固区承载层范围与其影响因素之间的关系问题,采用理论分析与数值模拟开展了相关研究。首先,采用理论分析明确了锚杆锚固区承载层厚度b与锚固承载层边界的支护强度P ib呈正比关系,即锚固承载层越厚巷道围岩越稳定;其次,采用FLAC^(3D)数值模拟软件分析了预紧力分别为50、100、150、200 kN,锚杆间距分别为0.8、1.0、1.2、1.5 m时锚固区承载层厚度和体积的变化规律。研究结果表明,随着锚杆预紧力的增加、锚杆间距的减小,锚固区承载层的厚度和体积也随着增大;锚杆预紧力与锚固区体积呈指数关系;锚杆间距存在临界值,当间距大于该临界值时锚固区体积急剧下降。研究成果可为锚杆支护参数设计及工程技术开发提供理论依据与参考。

锚杆-围岩结构的耦合振动和减振

锚杆支护是隧道施工中常见的支护手段,而随着施工工况日趋复杂,锚杆与围岩的组合结构也承受着各类动力荷载的影响。针对隧道中单根锚杆的受力特性有较多研究,而对于锚杆和围岩组合体的动力特性研究较少。对锚杆-围岩结构进行整体分析,简化出一种巷道顶板锚杆支护模型,结合动力学双梁理论,建立并求解出模型动力学方程;运用MATLAB软件进行数值模拟,研究不同支护参数下结构的自振特性以及在外荷载作用下的动力响应,提出减振措施;利用有限元软件GTS NX建立二维模型,验证支护体系的安全性。结果表明:锚杆-围岩结构的动力特性与锚固段长度、锚杆间距和锚杆直径有关。在所建模型中,随着锚固段长度与锚杆间距的适当增加,结构动力响应明显减弱;随着锚杆直径的变化,结构动力特性的变化情况较复杂,结构不同部位的动力响应变化趋势差别较大。

高延伸率锚索动态力学特性及工程应用

传统锚索延伸率低、抗冲击能力差,在强冲击载荷作用下易出现脆性破断失效,导致巷道出现冒顶、冲击地压事故等问题。基于此,自主开发了具有高强度、高延伸率及高抗冲击等特性的锚索,采用实验室试验、理论分析及现场试验等综合手段,分析了高延伸率锚索的静、动载力学性能,研究了高延伸率锚索化学成分、金相组织和夹杂物与普通锚索的差异,提出了高延伸率锚索支护吸能原理,并将高延伸率锚索在现场进行了应用。研究结果表明:静载作用下,高延伸率锚索抗拉强度为1790 MPa,最大力总延伸率8.1%,是普通锚索的1.61~2.25倍;动载作用下,高延伸率锚索钢丝不易散开,破断载荷与普通锚索基本相同,断后伸长率分别是锚索A、B、C的1.82倍、1.68倍和1.52倍,单位长度吸能量分别是锚索A、B、C的2.54倍、1.99倍和1.70倍,高延伸率锚索塑性变形能力更强,吸能能力更高。高延伸率锚索通过在冶炼和轧制工艺过程中控制有害化学元素和有益化学元素含量、细化金相组织及减少夹杂物尺寸和数量等方式提高了钢丝的塑性变形能力,进而提高锚索整体的抗冲击性能。高延伸率锚索在现场应用过程中经受了多次大能量冲击后,巷道支护效果良好,高延伸率锚索未出现破断,有效控制了巷道冲击破坏。

急倾斜极薄矿脉破碎软岩支护技术研究

针对某矿山采场片帮频发、超挖严重和采矿损失贫化较大等问题,结合极薄矿脉作业空间受限等问题,提出了采用锚杆+双筋条的支护技术,其实质是双筋条支护的时效性和柔韧性,在支护过程中使整排的锚杆群在托板作用下协同起作用,从而使可能冒落的关键块体处于稳定状态。该支护技术很好地解决了极薄矿脉支护难题,有利于提高采场安全性,并降低矿石贫化率,从而提高矿山的经济效益。