Theory,technology and application of grouted bolting in soft rock roadways of deep coal mines

The grouted bolt,combining rock bolting with grouting techniques,provides an effective solution for controlling the surrounding rock in deep soft rock and fractured roadways.It has been extensively applied in numerous deep mining areas characterized by soft rock roadways,where it has demonstrated remarkable control results.This article systematically explores the evolution of grouted bolting,covering its theoretical foundations,design methods,materials,construction processes,monitoring measures,and methods for assessing its effectiveness.The overview encompassed several key elements,delving into anchoring theory and grouting reinforcement theory.The new principle of high pretensioned high-pressure splitting grouted bolting collaborative active control is introduced.A fresh method for dynamic information design is also highlighted.The discussion touches on both conventional grouting rock bolts and cable bolts,as well as innovative grouted rock bolts and cables characterized by their high pretension,strength,and sealing hole pressure.An examination of the merits and demerits of standard inorganic and organic grouting materials versus the new inorganic–organic composite materials,including their specific application conditions,was conducted.Additionally,the article presents various methods and instruments to assess the support effect of grouting rock bolts,cable bolts,and grouting reinforcement.Furthermore,it provides a foundation for understanding the factors influencing decisions on grouted bolting timing,the sequence of grouting,the pressure applied,the volume of grout used,and the strategic arrangement of grouted rock bolts and cable bolts.The application of the high pretensioned high-pressure splitting grouted bolting collaborative control technology in a typical kilometer-deep soft rock mine in China—the soft coal seam and soft rock roadway in the Kouzidong coal mine,Huainan coal mining area,was introduced.Finally,the existing problems in grouted bolting control technology for deep soft rock roadways are analyzed,and the future development trend of grouted bolting control technology is anticipated.

Experimental Study on Mechanical Characteristics of Cracked Rock Mass Reinforced by Bolting and Grouting

The stress hardening characteristics of the reinforced rock mass in uniaxial compression tests were revealed by means of the experimental study on mechanical characteristics of cracked rock mass reinforced by bolting and grouting. And the load-beating mechanism of the reinforced rock mass was perfectly reflected by the experiment. The results can offer some useful advice for support design and stability analysis of deep drifts in unstable strata.

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.

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.

Laboratory pull-out tests on fully grouted rock bolts and cable bolts:Results and lessons learned

Laboratory pull-out tests were conducted on the following rock bolts and cable bolts:steel rebars,smooth steel bars,fiberglass reinforced polymer threaded bolts,flexible cable bolts,IR5/IN special cable bolts and Mini-cage cable bolts.The diameter of the tested bolts was between 16 mm and 26 mm.The bolts were grouted in a sandstone sample using resin or cement grouts.The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample.In most tests,the rate of displacement was about 0.02 mm/s.The tests were performed using a pull-out bench that allows testing a wide range of parameters.This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response(rock bolts and cable bolts).It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole,which cannot be neglected when the test results are used to assess the bolt-grout or the grouterock interface.

Optimization of the fully grouted rock bolts for load transfer enhancement

The purpose of this study is to investigate the role of bolt profile configuration in load transfer capacity between the bolt and grout.Therefore,five types of rock bolts are used with different profiles.The rock bolts are modeled by ANSYS software.Models show that profile rock bolt T_3 and T_ with load capacity 180 and 195 kN in the jointed rocks,are the optimum profiles.Finally,the performances of the selected profiles are examined in Tabas Coal Mine by FLAC software.There is good subscription between the results of numerical modeling and instrumentation reading such as tells tale,sonic extensometer and strain gauge rock bolt.According to the finding of this study,the proposed pattern of rock bolts,on 7 + 6 patterns per meter with 2 flexi bolt(4 m) for support gate road.

A new analytical solution for calculation the displacement and shear stress of fully grouted rock bolts and numerical verifications

In presence of difficult conditions in coal mining roadways, an adequate stabilization of the excavation boundary is required to ensure a safe progress of the construction. The stabilization of the roadways can be improved by fully grouted rock bolt, offering properties optimal to the purpose and versatility in use. Investigations of load transfer between the bolt and grout indicate that the bolt profile shape and spacing play an important role in improving the shear strength between the bolt and the surrounding strata. This study proposes a new analytical solution for calculation displacement and shear stress in a fully encapsulated rock bolt in jointed rocks. The main characteristics of the analytical solution consider the bolt profile and jump plane under pull test conditions. The performance of the proposed analytical solution, for three types of different bolt profile configurations, is validated by ANSYS software. The results show there is a good agreement between analytical and numerical methods. Studies indicate that the rate of displacement and shear stress from the bolt to the rock exponentially decayed. This exponential reduction in displacement and shear stress are dependent on the bolt characteristics such as: rib height, rib spacing, rib width and grout thickness, material and joint properties.

A local homogenization approach for simulating the reinforcement effect of the fully grouted bolt in deep underground openings

Fully grouted bolts are a key component of the support system for underground openings.Although considerable effort has been made in the simulation of the reinforcement effect of the fully grouted bolts on the rock masses surrounding underground openings,most of the work has limited significance since the structural element approach is used.This study proposes a local homogenization approach(L-H approach)that integrates elastoplastic mechanics,composite mechanics,and analytical approaches with numerical simulation to effectively simulate the reinforcement effect of the fully grouted bolt on deep surrounding rock masses.In the L-H approach,the representative volume of bolted rock mass(RVBRM)with a fully grouted bolt is established based on the original mesh model utilized in the rockbolt element approach.The RVBRM is a regular quadrangular prism with a cross-sectional size equal to the bolt spacing and a length equal to the bolt length.The RVBRM is homogenized by the L-H approach from a unidirectional bolt-reinforced composite into a homogeneous transversely isotropic medium whose mechanical properties are described by a new transversely isotropic elastoplastic model.The L-H parameters for the RVBRM are obtained using analytical approaches,composite mechanics,and known parameters of the rock mass and bolt.Using the L-H approach,the reinforcement effect of the fully grouted bolt on the bolted rock specimen and the surrounding rock mass in Jinping II Diversion Tunnel#2 with a depth greater than 2000 m is simulated.The results show that the predictions of the L-H approach are more in agreement with the physical model results of bolted rock specimen and provide a more realistic response of the bolted surrounding rock mass.The L-H approach demonstrates that fully grouted bolts with common bolt spacings and diameters substantially enhance the elastic modulus,shear strength,and tensile strength of the rock mass in the direction of the bolt axis.

Utilizing a novel fiber optic technology to capture the axial responses of fully grouted rock bolts

Rock bolts are one of the primary support systems utilized in underground excavations within the civil and mining engineering industries. Rock bolts support the weakened rock mass adjacent to the opening of an excavation by fastening to the more stable, undisturbed formations further from the excavation. The overall response of such a support element has been determined under varying loading conditions in the laboratory and in situ experiments in the past four decades; however, due to the limitations with conventional monitoring methods of capturing strain, there still exists a gap in knowledge associated with an understanding of the geomechanical responses of rock bolts at the microscale. In this paper, we try to address this current gap in scientific knowledge by utilizing a newly developed distributed optical strain sensing(DOS) technology that provides an exceptional spatial resolution of 0.65 mm to capture the strain along the rock bolt. This DOS technology utilizes Rayleigh optical frequency domain reflectometry(ROFDR) which provides unprecedented insight into various mechanisms associated with axially loaded rebar specimens of different embedment lengths, grouting materials, borehole annulus conditions, and borehole diameters. The embedment length of the specimens was found to be the factor that significantly affected the loading of the rebar. The critical embedment length for the fully grouted rock bolts(FGRBs) was systematically determined to be430 mm. The results herein highlight the effects of the variation of these individual parameters on the geomechanical responses FGRBs.

Effects of different pull-out loading rates on mechanical behaviors and acoustic emission responses of fully grouted bolts

Due to the influence of mining disturbance stress,it is of great significance to better understand the bearing characteristics of fully grouted bolts under different pull-out loading rates.For this purpose,a series of laboratory pull-out tests were conducted to comprehensively investigate the effects of different pull-out loading rates on the mechanical performance and failure characteristics of fully grouted bolts.The results show that the mechanical performance of the anchored specimen presents obvious loading rate dependence and shear enhancement characteristics.With the increase of the pull-out loading rates,the maximum pull-out load increases,the displacement and time corresponding to the maximum pull-out load decrease.The accumulated acoustic emission(AE)counts,AE energy and AE events all decrease with the increase of the pull-out loading rates.The AE peak frequency has obvious divisional distribution characteristics and the amplitude is mainly distributed between 50-80 dB.With the increase of the pull-out loading rates,the local strain of the anchoring interface increases and the failure of the anchoring interface transfers to the interior of the resin grout.The accumulated AE counts are used to evaluate the damage parameter of the anchoring interface during the whole pull-out process.The analytical results are in good agreement with the experimental results.The research results may provide guidance for the support design and performance monitoring of fully grouted bolts.

Stress analysis of full-length grouted bolt under shear deformation of anchor interface

The bolt anchoring force is closely related to the shear properties of the anchor interface. The shear stress distribution of full-length grouted bolts is analyzed based on the stress-strain relationship among the bolt, grout, rock mass and bond interface,considering the shear properties of the grout and contact interface bonding behavior. In this case, the interfacial shear stress of the grout and rock mass and the bolt axial force are obtained under pull-out and normal working conditions. The results show that the peak shear stress of the interface with the shear deformation of the bond interface is significantly lower than that without it when the pull-out force is applied. When designing bolt parameters of grade IV and V rock mass, the relative deformation between the rock mass and anchor should be considered, with a “unimodal” to “bimodal” shear stress distribution.In the case of a low elastic modulus of rock masses,both the shear stress concentration and distribution range are obvious, and the neutral point is near the bolt head. As the elastic modulus increases, the shear stress concentration and distribution range are reduced, and the neutral point moves towards the distal end. As a result, the optimum length of fulllength grouted bolts can be determined by in-situ pull-out tests and decreases with the increased elastic modulus of the rock mass.

Study on strata control by delay grouting in soft rock roadway

The properties of broken rock before and after grouting reinforcement are studied. Testing results show that grouting can raise the residual strength of broken rock, and the broken rockness by grouting can keep the steady supporting capacity within a relatively large deformation range. Revealing of the characteristics of stage deformation and damage process comes to the conclusion that the supporting of soft rock roadway should be analyzed in a dynamic view, and the grouting should be delayed at a proper occasion. Based on the above, the stepwise reinforcement technology characterized by immediate shotcreting, timely bolting and delay grouting is put forward and illustrated with a successful engineering practice.

Analysis profile of the fully grouted rock bolt in jointed rock using analytical and numerical methods

The purpose of this study was to investigate the effect of bolt profile on load transfer mechanism of fully grouted bolts in jointed rocks using analytical and numerical methods. Based on the analytical method with development of methods, a new model is presented. To validate the analytical model, five different profiles modeled by ANSYS software. The profile of rock bolts T3 and T4with load transfer capacity,respectively 180 and 195 kN in the jointed rocks was selected as the optimum profiles. Finally, the selected profiles were examined in Tabas Coal Mine. FLAC analysis indicates that patterns 6+7 with2 NO flexi bolt 4 m better than other patterns within the faulted zone.

Development and application of an interface constitutive model for fully grouted rock-bolts and cable-bolts

This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results.A database was created combining published experimental data with in-house tests.By means of a comprehensive framework,a Coulomb-type failure criterion accounting for friction mobilization was defined.During the elastic phase,in which the interface joint is not yet created,the proposed model provides zero radial displacement,and once the interface joint is created,interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints.The results predicted by the proposed model are in good agreement with experimental results.The model has been implemented in a finite element method(FEM)code and numerical simulations have been performed at the elementary and the structural scales.The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.

NUMERICAL SIMULATION ANALYSES ON REINFORCEMENT FUNCTION OF THE TENSIONED AND GROUTED BOLTS

The purpose of the paper is to calculate the equivalent mechanics parameters of reinforced surroundings, which is based on the assume that the reinforcement of bolts is equivalent to the improvement of mechanics parameters of surroundings and combines with site engineering practice. Use numerical simulation analysis to study the reinforcement mechanism of full length bolts, thus to provide theoretical bases for bolting design.

新型承插式螺栓连接柱-柱节点抗拉性能研究

为实现模块化钢结构单元房间的上下连接,提出一种新型承插式螺栓连接柱-柱节点,以有无注浆、承插深度为参数设计并制作3个足尺节点试件,并对其进行抗拉试验,分析了各节点的破坏形态、应变分布以及承载能力等,探讨了该新型节点的抗拉性能.建立了数值分析模型,进行了轴拉荷载作用下的受力性能参数化分析,研究了承插深度、螺栓直径及内套筒厚度对节点抗拉承载力的影响.基于高强螺栓的抗剪承载力,提出了适用于该新型节点的抗拉承载力计算公式.研究结果表明:该新型节点可将轴向拉力有效传递至高强螺栓,试件破坏时均出现高强螺栓群被剪断,灌浆节点试件发生破坏时,出现钢材与灌浆料界面的黏结破坏及螺栓周围局部灌浆料的压碎;高强螺栓群在拉力荷载作用下呈端部螺栓受剪较大、中心螺栓受剪较小的分布,试件破坏时,各螺栓承受的剪力趋于相等;灌浆节点与无浆节点相比,灌浆料与高强螺栓协同工作性能良好,弹性阶段最大摩擦力平均值提高64.4%,极限抗拉承载力提高14.1%;承插深度由300 mm增至500 mm,节点极限抗拉承载力提高80.9%;承插深度和螺栓直径对节点抗拉承载力影响较大,内套筒厚度对节点抗拉承载力的影响较小;根据提出的节点抗拉承载力计算公式得到的计算值与有限元模拟值吻合良好.

特厚煤层大巷变形破坏特征及控制技术研究

针对特厚煤层大巷变形破坏特征分析及控制技术难题,以砚北煤矿二水平回风大巷为研究背景,在分析巷道围岩地质力学测试及围岩变形破坏特征与机理的基础上,提出了全断面注浆加固与高预应力支护综合围岩控制技术,制定了煤层大巷修复加固具体实施方案,并确定了相应的技术参数,开展了井下工业试验,试验结果表明:修复加固后35 d左右巷道变形趋于稳定,两帮最大位移量63.5 mm,顶底板最大移近量79.8 mm;注浆后水泥浆液与巷帮煤体裂隙及破碎区充分胶结,围岩裂隙明显减少,钻孔成型效果显著提高。研究表明采用高预应力锚杆支护及全断面注浆加固后,在巷道围岩内形成锚注加固体,提高了巷道围岩稳定性与抗变形能力以及浅部锚杆(索)锚固基础力学性能,巷道围岩变形得到有效控制。

高强螺栓锥孔灌浆连接的预制天沟抗剪性能试验研究

针对装配式混凝土建筑工程中多采用现浇天沟导致安装工序复杂的问题,为了探讨预制天沟替代现浇天沟的可行性,提出一种由预留锥形灌浆孔、高强螺栓、螺母、紧固件和高强灌浆料构成的预制构件连接方式,即“高强螺栓锥孔灌浆连接方式”,并对采用该种连接的简化天沟试件进行竖向力加载试验,研究预制天沟与预制混凝土剪力墙结合面的抗剪性能。结果表明:高强螺栓锥孔灌浆连接的预制天沟性能可靠,剪力作用下,试件未发生脆性破坏,螺栓未断裂;天沟等非结构预制构件,可以采用该种连接方式与预制结构构件连接;提出了该种构造下单个螺栓连接件的抗剪承载力计算公式,可为工程应用提供参考。

缓凝型水泥浆液配合比优化及锚孔浆岩界面特性影响研究

针对预应力锚杆后张法施工中自由段浆液流动性和缓凝效果差的工程难题,提出使用标准型聚羧酸减水剂作为掺加剂以实现水泥浆液缓凝并提高其工作性能,探究其对锚孔浆岩界面特性的影响。采用室内试验、SEM电镜扫描等手段,结合Matlab多目标优化等方法,对掺加减水剂的缓凝型水泥浆液的锚固性能及配合比优化展开研究,得出适用于预应力锚杆自由段的注浆材料及其最优配合比,并与现行规范推荐配合比进行锚孔横断面结石特性对比试验。研究结果表明:1)随着水灰比增大,水泥浆液的流动度和凝结时间增大,体积结石率和抗压强度减小;随着减水剂掺量的增大,水泥浆液的流动度和凝结时间增大,体积结石率减小,减水剂对浆液抗压强度影响较小;2)未掺加减水剂时,浆液结石体致密性随着水灰比的增大而降低,掺加减水剂使得浆液结石体表面局部存在相对较大尺度的孔或孔隙,对宏观结石体强度有一定影响;3)通过Matlab多目标优化方法推荐了缓凝型水泥浆液最优配合比为水灰比0.3,减水剂掺量1.85%,相关性能参数符合规范要求,且流动度与抗压强度较规范推荐配合比分别提升了72.3%和107%;4)浸水围岩会弱化浆岩界面的抗剪强度,因此在锚杆灌浆过程中保证横断面结石率有利于提高浆岩界面的抗剪强度,本文提出的最优配合比浆液抗剪强度优于规范推荐配合比浆液。

全长预应力锚注支护下深部巷道控制效果对比研究

本文基于后注浆的全长预应力锚注支护工艺,并通过对FLAC3D软件中内嵌PILE结构单元修正,提出了全长预应力锚注支护数值模拟方法。在此基础上,开展了地应力、原岩强度等级、支护构件长度、布设间距、注浆强化指数与预应力6种因素下巷道围岩控制效果数值模拟对比研究,揭示了各类因素对围岩变形量、塑性区演化的影响规律,构建了全长预应力锚注支护下控制效果敏感性评价指标,将影响因素依次划分为围岩强度、地应力、锚注支护构件设计3个层级,并根据各因素敏感性层级给出了工程措施建议。最后,以现场典型软弱破碎地层巷道为工程依托,研发了具有强度高、可施加预应力等优势的组合式高强注浆锚杆与高强中空注浆锚索。通过现场应用,验证了全长预应力锚注支护可有效增强软弱破碎围岩自承载能力,充分发挥锚固构件的支护潜力,限制巷道围岩变形破坏。