Mechanical behaviour of fiber-reinforced grout in rock bolt reinforcement

Grouted rock bolts subject to axial loading in the field exhibit various failure modes,among which the most predominant one is the bolt-grout interface failure.Thus,mechanical characterization of the grout is essential for understanding its performance in ground support.To date,few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout(FRG)in rock bolt reinforcement.Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression,indirect tension,and direct shear loading conditions.We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG.FRG was developed using 15%silica fume(SF)replacement of cement(by weight)and steel fiber to achieve highstrength and crack-resistance to overcome drawbacks of the conventional grout.Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality.The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined.Our experimental results showed that the addition of SF and steel fiber by 1.5%fiber volume proportion could lead to the highest compressive,tensile,and shear strengths of the grout.The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%.The scanning electron microscopy(SEM)analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout.Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar’s load carrying capacity.Therefore,FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.

STUDY ON MESO-MECHANICAL SIMULATION OF GROUTING FOR UNFAVORABLE GEOLOGICAL CONDITIONS

The numerical simulation program of PFC2D(Particle Flow Code in 2 Dimension)particle flow based on the flow-solid coupling principle and,on its built-in FISHTANK function library and FISH language,defines the flow equation and pressure equation of fluid domain respectively,and carries out numerical simulation calculations on the diffusion process and,on the morphology and particle displacement of slurry during the slurry injection process.By adjusting the parameters of hist,n_bond,s_bond and measure in the PFC command flow,the tracking of granular body displacement changes is achieved,and the mesoscopic mechanism such as the diffusion law of soil slurry at different depths and the change of formation porosity is revealed.The numerical calculations show that:the grouting pressure has a significant effect on the alteration and destruction of the formation structure,and the fracturing effect becomes gradually worse with increasing adhesive strength,while the porosity increases significantly with increasing grouting pressure.Based on the elastic-plastic theory of the Mohr-Colomb criterion to theoretically derive the stress field of the soil around the borehole,it is pointed out that the mechanical mechanism of annular tension and radial compression is the fundamental reason for the appearance of fracturing grouting action mode.The increase of slurry viscosity is beneficial to improve the grouting effect of fracturing-compacting grouting,while the increase of friction coefficient has little effect on the grouting effect.The comparative analysis of the laboratory tests shows that the PFC2D simulation of the grouting process is feasible.

Experimental study on the mechanical properties and consolidation mechanism of microbial grouted backfill

Backfill mining technology is the practice of returning waste materials underground for both disposal and geotechnical stability,however,a challenge with current technologies is that they commonly require cement-based binders which have a relatively high environmental impact.Finding alternatives to cement-based binders can improve environmental performance and this paper proposes microbial grouted backfill(MGB)as a potential solution.In this paper,the effects of the cementation solution concentration(CSC),volume ratio of bacterial solution to cementation solution(VRBC),particle sizes of the aggregates,and the number of grouting batches on the mechanical properties of MGB are studied.The experimental results show that MGB strength increased,up to a peak value,as CSC was increased,before decreasing as CSC was increased further.The results also show that MGB strength increased,up to a peak value,as VRBC decreased,before decreasing as the VRBC was decreased further.The peak strength was achieved at a CSC of 2 mol/L and a VRBC of 1:9.The strength of the MGB also increased as the number of grouting batches increased.Graded MGB samples showed the highest UCS,25.12 MPa,at particle sizes of 0.2 to 0.8 mm,while full(non-graded)MGB samples displayed mean UCS values ranging from1.56 MPa when the maximum particle size was 0.2 mm,up to 13 MPa when the maximum particle size was 1.2 mm.MGB samples are consolidated by the calcium carbonate that is precipitated during microbial metabolism,and the strength of MGB increases linearly as calcium carbonate content increases.The calcium carbonate minerals produced in MGB materials are primarily calcite,with secondary amounts of vaterite.

Investigation of the Mechanism of Grout Penetration in Intersected Fractures

To study the penetration mechanism of cement-based slurry in intersected fractures during grouting and the related pressure distribution,we have used two different variants of cement,namely,basic cement slurry and fast-setting cement slurry.The influence of a retarder,time-varying viscosity,fracture width and location of injection hole is also considered.A finite element software is used to implement two and three-dimensional numerical models for grouting of intersected fractures in hydrostatic conditions.Results show that there are significant differences in the diffusion morphology and pressure distribution depending on the considered cement slurry.Retarder can effectively slow down the rising rate of injection pressure and extend the diffusion distance of grout.The influence of the branch fracture is more important when basic cement slurry is considered,indicating that the change of grout pressure is correlated with the slurry viscosity.The faster the viscosity increases,the less evident is the effect.

Mechanical Behaviors and Deformation Properties of Retaining Wall Formed by Grouting Mould-Bag Pile

The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displacement monitoring,deep horizontal displacement(inclinometer)monitoring,soil pressure monitoring and seepage pressure monitoring in the lower reaches of Wuan River regulation project in Shishi,Fujian Province.The mechanical behavior and deformation performance of mould-bag pile retaining wall formed after controlled cement grouting in the silty stratum of the test section are analyzed and compared.The results show that the use of controlled cement grouting mould-bag pile technology is to strengthen the soft stratum for sealing water and reinforcement,so that it can rock into a retaining wall,which can both retain soil and seal water with excellent effect.The control of cement grouting technology not only makes the soft soil rock in the range of retaining wall of mould-bag pile,but also makes a wide range of soil around the mould-bag pile squeeze and embed to compaction;and its cohesion and internal friction angle increased,so as to achieve the purpose of reducing soil pressure and improving mechanical and deformation properties of retaining wall.

Theoretical and experimental study on the rheological properties of WIS grout and the dispersion and sealing mechanism

Recently a new grout material called water inflow sealing(WIS) was invented for sealing water inflow in tunneling and underground constructions. In this study, a special experimental method called intubated counter grouting(ICG) was proposed to investigate the influence of water dispersion on the rheological properties of the grout during the grouting process, and to testify the sealing performance of the grout,such as instant gelling ability(IGA) and anti-dispersion ability(ADA). In the experiment, dispersion was restricted in the downstream of the channel with a high turbulence intensity. The influences of ADA and IGA were therefore decoupled and evaluated separately. Experimental results revealed two distinctive sealing mechanisms of WIS. For a low initial velocity of water, WIS turned the shear flow of water into an overall movement of a plug by absorbing water into the particles. For a high initial velocity and the situation that the particles reached the outlet before sufficiently expanding, WIS modified the rheology of the water in the channel and reduced its velocity till the static state. The distinctive feature of WIS brings a reformation on the sealing mechanism and provides an effective way to control water inflow with high pressure and velocity.

Stress evolution and support mechanism of a bolt anchored in a rock mass with a weak interlayer

By applying experimental method, the bolt stress and supporting mechanism is studied during the deformation process of a rock mass containing a weak interlayer. The force measuring bolt is installed manually and instrumented five pairs of symmetrical strain gauges. The experimental results show that the fully grouted bolt suffers tensile, compressive, bending and shear stress at the same time. The bolt stress evolution is closely related to the deformation stages of the rock mass which are very gradually varying stage, gradually varying stage at the pre-peak and suddenly varying stage at the post peak stage.The axial compressive stress in the bolt is mainly induced by the moment. Thus, in most cases the axial compressive stress is distributed on one side of the bolt. For axial stresses, induced by the axial force and the bending moment at the post-peak stage, three types of changing are observed, viz. increasingincreasing type, decreasing-increasing type and increasing-decreasing type. The stress characteristics of the bolt section in the weak interlayer are significantly different from those in the hard rock. The failure models of the anchored bolt are tensile failure and shear failure, respectively. The bolt not only provides constraints on the free surface of the rock mass, but also resists the axial and lateral loading by the bending moment. This study provides valuable guidelines for bolting support design and its safety assessment.

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.

Reinforcement of Clay Soils through Fracture Grouting

Fracture grouting is widely used for building foundation reinforcement,however the underpinning mechanisms are still not clear.Using numerical results about a single-hole fracture grouting process as a basis,a model composed of soil and grouting veins has been created to analyze the reinforcement mechanism.The influence weights of the grouting vein skeleton and compaction effect have been studied,thereby obtaining relevant information on the compressive modulus of the considered composite soil.The research results show that the compaction effect plays a leading role in the soil fracture grouting reinforcement.The grouting pressure,the hardened grouting vein modulus,and the shape of the grouting veins all influence the compressive modulus of the composite soil.

椰壳纤维加筋土遗址生态注浆材料的性能

为提升土遗址注浆料的力学性能,以椰壳纤维掺和糯米浆、烧料礓石以及黄土改性注浆料为研究对象,研究了椰壳纤维长度和掺量(质量分数)对土遗址注浆料流动性、收缩性、抗压强度和抗折强度的影响.结果表明:椰壳纤维的掺量和长度越大,浆体的流动性越低,而椰壳纤维的长度与浆体的收缩率无明显相关性;椰壳纤维良好的桥接能力可以有效提高浆体固化后的抗压强度、抗折强度和延性;椰壳纤维的长度和掺量均存在最优值,建议最优配比为纤维长度6 mm、掺量0.5%~0.6%,此时浆体固化后的抗压强度、抗折强度分别提升49.09%和32.08%;过多、过长的椰壳纤维易发生弯折、团聚,导致浆体的流动性和强度大幅降低.

铜尾矿改性水泥基地聚合物注浆材料性能与机理分析

为促进岩土工程绿色发展,提高尾矿资源化利用效率,选取铜尾矿制备铜尾矿改性水泥基地聚合物注浆材料,研究水固比、铜尾矿掺量、碱激发剂用量及碱激发剂模数对改性浆液各性能指标的影响规律及微观机理。研究结果表明:掺入尾矿有利于改善改性浆液力学性能,掺入碱激发剂能提高改性浆液整体的反应程度,减小改性浆液析水率;综合考虑各项性能指标,选取改性浆液最佳配比,即水固比为1.0,铜尾矿掺量为30%(质量分数,下同),碱激发剂用量为4%,碱激发剂模数为1.6;相较于纯水泥浆液,改性浆液最佳配比黏度减小11.1%,流动度增大22.3%,析水率减小29.7%,28 d结石体抗压强度仅减小9.5%,耐久性能良好;改性浆液发生地聚合物反应形成了具有三维空间网状结构的C-A-S-H凝胶和N-A-S-H凝胶等胶凝物质。本研究成果可为岩土工程提供高性能低成本的注浆材料,同时还将为尾矿等固废材料资源化利用提供参考。

钢纤维对海上风电灌浆料及灌浆连接段模型性能的影响研究

开展了不同体积掺量的钢纤维对海上风电灌浆料以及小型灌浆连接段模型力学性能影响的研究。结果表明:当钢纤维掺量为1.0%时,能在保障灌浆料工作性和微膨胀性能的基础上,灌浆料的28 d抗折强度和抗压强度相较于未掺钢纤维时分别提高了65.4%和31.0%,且灌浆连接段模型的极限承载力和极限位移分别提高了12.0%和15.5%,有效提高了灌浆料的延性;灌浆连接段模型在轴心荷载作用下,主要受力和变形部位为内筒上部剪力键和外筒下部,在今后的灌浆连接段设计中,可对该部位进行适当加强,以便充分发挥灌浆连接段的整体性能。

盾尾注浆材料硬化特性对隧道和地层力学响应影响的有限元模拟研究

为了探究注浆材料硬化和注浆压力的消散过程对软土地层和隧道衬砌受力变形的影响,以青岛某地铁隧道为背景,考虑盾构机与土体相互作用、衬砌-注浆层-土体相互作用,以及注浆材料硬化和注浆压力消散过程,基于ABAQUS有限元平台建立了盾构施工精细化的有限元数值仿真模型,并利用实测地层沉降和隧道衬砌的收敛变形验证了数值模型的合理性。同时,对注浆材料初凝时间分别为0、2、6、12 h的数值模型进行了计算,获得了地层和隧道衬砌受力变形随注浆材料硬化过程的发展规律,以及注浆材料硬化特性对地层和隧道衬砌受力变形的影响规律。模拟结果表明:盾尾注浆8 h以内,地层的沉降和水平位移以及隧道衬砌的围岩压力和内力增加显著,注浆时间超过8 h后增加变得缓慢;注浆材料的初凝时间越长,地表沉降、地层水平位移和竖向位移则越大;衬砌拱顶和拱腰的径向收敛越大,拱底径向收敛则越小;衬砌的轴力和弯矩在注浆8 h以内增加显著。

纤维增强粉煤灰基地聚合物注浆材料力学性能与模拟研究

针对粉煤灰基地聚合物注浆材料韧性差的问题,研究了两种不同纤维对注浆材料抗压强度和抗折强度的影响,并利用扫描电镜对纤维增强地聚合物注浆材料微观形貌进行分析。为进一步揭示注浆材料内部纤维的受力状态,使用ABAQUS软件建立纤维增强地聚合物注浆材料的有限元模型,对模型开展三点抗折试验模拟,探究基体的损伤破坏形态与基体内部纤维的受力情况。结果表明:与聚丙烯纤维相比,玄武岩纤维对注浆材料抗折与抗压强度提升效果更好,当玄武岩纤维的掺量为0.60%时,相较于未添加纤维的空白组,注浆材料的抗折强度与抗压强度分别提升了33.54%与19.40%;纤维可以有效减小基体的损伤面积,玄武岩纤维与聚丙烯纤维掺量分别为0.60%与0.90%时,基体内部的纤维能够充分发挥自身的抗拉强度。

脱空混凝土管道纵向力学行为及自膨胀高聚物注浆修复性能提升

为揭示脱空混凝土管道的纵向力学行为以及自膨胀高聚物外部注浆修复性能提升效果,开展了密实、脱空和高聚物修复混凝土管道现场足尺试验和三维有限元数值仿真,并通过试验结果对数值模型进行了验证。以不同管基状态下混凝土管道的截面纵向弯曲弯矩和管顶竖向位移为分析对象,讨论了脱空宽度和脱空长度对混凝土管道力学行为的影响规律,并引入纵向弯矩和竖向位移修复指数ξM和ξU,对高聚物注浆修复脱空管道的性能提升效果进行了量化表征。研究表明:脱空管道正负纵向弯矩分别分布在脱空两侧的相邻管段和接头,峰值分别位于SgL2、SgR2和SgL3、SgR3处;脱空管道纵向弯矩在SgL1和SgR1处随脱空宽度的增大而减小,其余测点处随脱空宽度的增大而增大,在整个纵向随脱空长度的增大而增大;不同脱空宽度和脱空长度管道的纵向弯矩在SgL1和SgR1以外均高于密实管道;与密实管道相比,脱空管道竖向位移和接头剪切位移的最大增幅分别为155%和230%;修复管道的纵向弯矩略低于密实管道,竖向位移略高于密实管道,纵向弯矩和竖向位移最大修复指数分别为76.5%和83.7%。

采用大直径灌浆套筒连接的预制桥墩抗震性能研究

为探究墩台处采用大直径灌浆套筒连接的预制装配式桥墩抗震性能,进行拟静力试验及有限元分析。设计、制作2个采用大直径灌浆套筒(主筋直径40 mm)连接的预制装配式桥墩(预制桥墩)及1个现浇桥墩开展拟静力试验,对2类试件的试验现象、破坏形态、滞回曲线和承载能力进行对比分析,并采用有限元法对预制桥墩混凝土、套筒及连接钢筋的受力性能进行研究。试验结果表明:在水平循环荷载作用下,预制桥墩与现浇桥墩一致表现为弯剪破坏,但墩底区域破坏形式不同,现浇桥墩主要表现为柱脚混凝土大面积压碎,而预制桥墩的破坏现象更为严重,集中表现为套筒四周混凝土成块压碎剥落;相较于现浇桥墩,预制桥墩的承载能力平均值偏小5.2%,位移延性系数平均值偏小2.7%,预制桥墩力学性能与现浇桥墩相当。有限元分析结果表明:预制桥墩会在套筒顶部和桥墩底部出现2个塑性区,且预制桥墩中大直径灌浆套筒的受力状态以轴向受力为主,按照轴向受力进行套筒设计可满足其在桥墩结构中的受力要求;预制桥墩在墩底混凝土破坏后,其主筋和灌浆料仍保持可靠粘结,采用大直径灌浆套筒连接的预制桥墩抗震性能良好。

透明砂土基本特性及其在注浆模型试验中的应用

透明土技术为可视化监测土体内部变形、渗流提供了有效手段,充分认识透明土透明度的影响因素是该技术发展的基础,亦是实现注浆模型试验浆液扩散可视化的前提。采用熔融石英颗粒和混合矿物油配制透明砂土,通过调整混合矿物油配比、熔融石英颗粒粒径、环境温度获得透明砂土。配制与标准砂级配相近的透明砂土,测试了透明土与标准砂的基本物理力学性能,并开展了大尺寸透明砂土注浆模型试验。结果表明:混合矿物油配比、熔融石英颗粒粒径对透明砂土透明度影响显著;混合矿物油折射率对温度较敏感,折射率随温度的升高而降低;与标准砂级配相近的透明土透明度较高,物理力学特性与标准砂相近,该透明砂土实现了注浆模型试验浆液扩散过程的可视化。研究成果对促进透明土技术发展及其在注浆模型试验中的应用具有借鉴意义。

托顶煤巷道易片冒顶板变形机理与超前导管预注浆控制技术研究

目的 为探究厚煤层易片冒区域托顶煤巷道顶板变形破坏机理,并对易片冒区托顶煤巷道顶板进行有效控制,方法 以常村煤矿2701工作面皮带运输巷为例,通过等截面梁理论分析托顶煤巷道顶板破断成因,研究托顶煤巷道顶板的稳定性与巷道宽度和顶煤强度的关系。通过极限平衡准则得到巷帮位移的计算公式,证明托顶煤巷道具有帮顶协同变形机制。建立托顶煤巷道数值模型,研究巷道埋深、侧压系数、顶煤厚度和顶煤强度与托顶煤巷道围岩稳定性的关系。结果 结果表明:巷道埋深越大,其对托顶煤巷道两帮稳定性的影响越大;侧压系数的增加对巷道两帮和底鼓量的影响更大,对顶板影响较小;顶板下沉量与顶煤厚度呈正相关,底鼓量则与顶煤厚度呈负相关;顶煤强度的增加使巷道顶板下沉量与两帮移近量均近似呈线性减小趋势,底鼓量基本保持不变。结论 通过幂律型流体柱形渗透注浆扩散理论得到超前导管注浆半径,由此提出托顶煤巷道超前导管预注浆帮顶联合控制技术,成功控制易片冒托顶煤巷道顶板冒落问题,可为类似地质条件的托顶煤巷道顶板控制提供借鉴。

超性能灌浆料微观水化机理与连接性能分析

文章通过微观扫描电镜和灌浆套筒连接件力学性能试验,验证超性能灌浆料微观水化机理与连接性能。SEM测试表明,超性能灌浆料内部形成大量的CH、AFt和C-S-H凝胶,胶凝体系内部密实,可以增强体系耐久性能;AFt形成的骨架抑制体系收缩,可以为后期抗压、抗折强度提供支持。采用套筒损伤试验验证连接件的连接性能,结果表明:灌浆套筒发生的损伤以端部钢筋拉断损伤为主,端部灌浆料有轻微的劈裂现象,但灌浆套筒的约束效应明显,阻止了灌浆料劈裂现象进一步出现;灌浆套筒发生损伤后,套筒内部匀直段和变形段与灌浆料的平均黏结应力均远小于损伤应力,灌浆套筒内灌浆料安全储备度高。

聚丙烯纤维改性超细水泥复合注浆材料性能研究

为获得高性能矿用水泥基注浆材料,拓展短切纤维在全长锚固领域的应用,以超细硅酸盐水泥为胶凝材料,速凝剂、膨胀剂、聚羧酸减水剂作外加剂,基于单因素试验,探究聚丙烯纤维(PPF)掺量对水泥注浆材料的力学性能、可注性、泌水性、凝结时间、体积收缩性及微观结构的影响规律,并筛选PP改性超细水泥浆液作锚固剂,研究相似实验拉拔条件下全长锚固系统的力学承载性能与声发射特征。结果表明:PPF掺量对超细水泥注浆材料的浆液特性与力学性能具有显著影响,可明显改善超细水泥注浆材料的抗压性能,缩短终凝时间,减小流动度,尤其抗折强度与PPF掺量呈正相关关系。当PPF掺量0.1%时,复合注浆材料S1的综合性能最佳,硬化结石体3 d和28 d抗压强度为60.1 MPa和83.7 MPa,比未添加PPF的参照组S0提高23.4%和23.2%;XRD、SEM及FTIR微观表征证实,适宜PPF不仅能促进水化反应,而且可改善结石体内部裂隙,发挥桥连作用并传递应力,延缓裂纹扩展;拉拔试验表明,基于该复合注浆材料的全长锚固体系力学性能、残余承载能力和最大变形量显著增强,最高拉拔强度是参照组S0的1.356倍,推迟了声发射事件的发生,提升巷道围岩稳定性,为类似全长锚固提供借鉴。