Large-scale model testing of high-pressure grouting reinforcement for bedding slope with rapid-setting polyurethane

Bedding slope is a typical heterogeneous slope consisting of different soil/rock layers and is likely to slide along the weakest interface.Conventional slope protection methods for bedding slopes,such as retaining walls,stabilizing piles,and anchors,are time-consuming and labor-and energy-intensive.This study proposes an innovative polymer grout method to improve the bearing capacity and reduce the displacement of bedding slopes.A series of large-scale model tests were carried out to verify the effectiveness of polymer grout in protecting bedding slopes.Specifically,load-displacement relationships and failure patterns were analyzed for different testing slopes with various dosages of polymer.Results show the great potential of polymer grout in improving bearing capacity,reducing settlement,and protecting slopes from being crushed under shearing.The polymer-treated slopes remained structurally intact,while the untreated slope exhibited considerable damage when subjected to loads surpassing the bearing capacity.It is also found that polymer-cemented soils concentrate around the injection pipe,forming a fan-shaped sheet-like structure.This study proves the improvement of polymer grouting for bedding slope treatment and will contribute to the development of a fast method to protect bedding slopes from landslides.

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.

Determination of construction art and parameters for passenger dedicated line grouting test within karst area

There are many karst areas within Wuhan-Guangzhou route. Karst grouting is one of the main construction procedures of the sub-grade construction. Through construction art tests,construction principles,water and cementation ratio,grouting construction key points and quality check requirements were determined. Grouting quantity and pressure can be determined according to different geology conditions. Recommendations for quality problems such as bad practicability of grouting,unexpected dissipation of slurry,slurry belching,and overfeeding of slurry going to non-grouting area were proposed.

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.

Thickness regression for backfill grouting of shield tunnels based on GPR data and CatBoost&BO-TPE:A full-scale model test study

Ground penetrating radar(GPR)is a vital non-destructive testing(NDT)technology that can be employed for detecting the backfill grouting of shield tunnels.To achieve intelligent analysis of GPR data and overcome the subjectivity of traditional data processing methods,the CatBoost&BO-TPE model was constructed for regressing the grouting thickness based on GPR waveforms.A full-scale model test and corresponding numerical simulations were carried out to collect GPR data at 400 and 900 MHz,with known backfill grouting thickness.The model test helps address the limitation of not knowing the grout body condition in actual field detection.The data were then used to create machine learning datasets.The method of feature selection was proposed based on the analysis of feature importance and the electromagnetic(EM)propagation law in mediums.The research shows that:(1)the CatBoost&BO-TPE model exhibited outstanding performance in both experimental and numerical data,achieving R^(2)values of 0.9760,0.8971,0.8808,and 0.5437 for numerical data and test data at 400 and 900 MHz.It outperformed extreme gradient boosting(XGBoost)and random forest(RF)in terms of performance in the backfill grouting thickness regression;(2)compared with the full-waveform GPR data,the feature selection method proposed in this paper can promote the performance of the model.The selected features within the 5–30 ns of the A-scan can yield the best performance for the model;(3)compared to GPR data at 900 MHz,GPR data at 400 MHz exhibited better performance in the CatBoost&BO-TPE model.This indicates that the results of the machine learning model can provide feedback for the selection of GPR parameters;(4)the application results of the trained CatBoost&BO-TPE model in engineering are in line with the patterns observed through traditional processing methods,yet they demonstrate a more quantitative and objective nature compared to the traditional method.

Comparative experimental investigation of chemical grouting into a fracture with flowing and static water

We present a series of experimental tests on chemical grouting into a fracture with flowing and static water,using a transparent fracture grouting experimental device.Variations of seepage pressure and grout propagation were compared in our investigation.The results show that flowing water results in drops of seepage pressure,development of penetration radii in the upstream side and drops of propagation area during the same period,compared with grouting in static water.The propagation area in static water is always round before grouts reach the joint boundaries.However,the propagation shape changes from round to an elliptic shape for grouting into a fracture with flowing water.A theoretical model for the grout penetration radius in a fracture considering flowing velocity was developed and validated by our experimental results.These results are helpful in improving understanding of fracture grouting mechanism and in guiding engineering practices.

Super-absorbent swellable polymer as grouting material for treatment of karst water inrush

Grouting is the most commonly used method to control water inrush in underground engineering.Traditional cement-based materials are easy to dilute and hard to coagulate under the influence of large flow and high-velocity water inrush.To address these deficiencies,a new type of polymer grouting material with an excellent expansion ratio was synthesised.The material quickly absorbs water and has an expansion ratio of 1:300.The material is composed of a superabsorbent polymer(SAP),glycerol,and ethanol.The effects of water quality on the expansion ratio and expansion rate of the material were examined,and the best solid–liquid ratio for the slurry was determined by fluidity measurements.A karst specially designed pipeline water inrush test device showed that 800 g of SAP can achieve 0.6 m/s water flow blockage in the smooth pipeline,demonstrating that the ability of the SAP slurry to block water inrush is superior to those of other materials.This study provides a reference for water inrush plugging,and has important implications for the reduction and control of karst pipeline-type water inrush disasters,ensuring the safety of construction sites and preventing loss of life and damage to property.

Retention of clay-solidified grouting curtain to Cd^(2+), Pb^(2+) and Hg^(2+) in landfill of municipal solid waste

The effects of components and their ratio of grouts on anti-seepage capability of clay-solidified grouting curtain and its permeability of heavy metal cations were investigated by permeating experiments, using reactive solute transport model to study the permeation of heavy metals (Cd2+, Pb2+ and Hg2+). The study of permeating for different mixture ratios of cement and clay indicates that hydraulic conductivity of clay-solidified grouting curtain with different ratios of solid to liquid or with the same ratio of solid to liquid but with different ratios of cement to clay is changed. The laboratory simulation test results also show that precipitates produced in heavy metal cation migration process in curtain block up water flowing passage which makes the hydraulic conductivity of the solution-permeated curtain decrease with the leakage time. The permeation velocities for different heavy metal cations vary with ionic concentration, exchange capacity and ion radius etc. The test results indicate that the permeation rapidity order of heavy metals cations in clay-solidified grouting curtain is Hg2+>Pb2+ in the same experimental circumstance. In addition, permeability for different mixture ratios and antisepsis capabilities of clay-solidified grouting curtain were studied in tests.

Water shutoff model test in water-rich sandy stratum by phosphoric acid-water glass grout

The rheological behavior of phosphoric acid-water glass grout in different mixing ratios was studied. Grout made of water glass with Baume degree of 20° and 13.4% phosphoric acid by 1:1 volume ratio is found to be more effective in stopping water. Laboratory model test of water shutoff by grouting was conducted. Test results show that the diffusion length and water cutoff effect of the grout are significantly improved as the grout head is raised, due to the dilution of underground water, and it takes the grout longer than its gel time to cut off water.

Property changes of anchor grout calcined ginger nuts admixed with fly ash and quartz sand after accelerated ageing tests

Calcined ginger nuts admixed by fly ash and quartz sand (CGN-(F+S)) has been validated to be basically compatible to earthen sites as an anchor grout. Accelerated ageing tests including water stability test, temperature and humidity cycling test, soundness test and alkali resistance test are conducted with the objective to further research the property changes of CGN-(F+S) grout. Density, surface hardness, water penetration capacity, water permeability capacity, soluble salt, scanning electron microscopy (SEM) images and energy dispersive spectrometry (EDS) spectrum of these samples have been tested after accelerated ageing tests. The results show that densities of samples decrease, surface hardness, water penetration capacity and water permeability capacity of samples increase generally. Besides, soluble salt analysis, SEM and EDS results well corroborate the changes. Based on the results it can be concluded that property changes are most serious after temperature and humidity cycling test, followed by water stability, soundness and alkali resistance test in sequence. But in general, CGN-(F+S) still has good durability.

A Pull-Out Test Study on the Working State of Fully Grouted Bolts

The present study examines the working conditions of fully grouted bolts used for the construction and expansion of high slopes.On the basis of a pull out destructive test,the work load and the ultimate load are obtained on site,and the Flac3d numerical simulation method is employed to determine the axial force distribution and the effective anchor length.The test results show that(1)the Q-S(load-displacement)curve of the bolt displays a certain degree of deformation coupled with the creep of the surrounding rock;(2)the working load of the bolt is closely related to the sliding deformation trend of the slope,while the ultimate load depends on the design parameters of the bolt and the lithology of the slope;(3)the distribution of bolt axial force is characterized by a single peak along the bolt length and the effective anchorage length of the bolt is 3 m;(4)after 20 years,the bolt’s ultimate load has a maximum loss of 31.94%.

盾构壁后注浆窜浆模型试验及发生条件研究

全断面围岩管片壁后注浆因向开挖面方向的窜浆现象会引起盾尾空隙注浆不饱满,管片上浮、错台及开裂,螺机喷涌等事故常有发生,已经引起广泛重视。通过设计自制壁后注浆液窜浆模型装置进行试验,分析浆液性质、缝隙厚度、注浆压力差对是否发生窜浆及窜浆量的影响,并探讨了不发生窜浆的临界条件。结果表明:(1)浆液压力与窜浆距离呈线性衰减,当浆液稠度较低时,窜浆量与缝隙厚度、浆液稠度呈近似线性正相关、与浆液的剪切屈服应力呈近似线性负相关,窜浆距离与注浆压力差呈近似线性正相关;当浆液稠度增大时,以上关系将逐渐转化为非线性关系;(2)通过极差分析表明浆液的窜浆量受盾壳与岩层间缝隙厚度影响最大,注浆压力与开挖面压力差影响其次,最后是浆液本身的性质;(3)建立了窜浆临界分析模型和计算公式,得到了窜浆发生条件和判别方法,可用于指导稳定围岩地层中盾构掘进时浆液的配制。

侧部注浆对已建盾构隧道受荷变形影响试验研究

采用侧部注浆法整治盾构隧道横椭圆变形超限过程中,盾构隧道周围附加土压力及隧道变形特性暂不明晰。通过几何相似比为1∶10的缩尺寸模型试验开展了侧部注浆对已建盾构隧道的影响试验研究,试验结果分析表明:在注浆挤压作用下,将导致隧道周围的土压力在注浆点处局部增大,两边有一定程度的减小,产生了明显的水平被动土拱现象;在注浆附加荷载影响下,模型盾构隧道在注浆点附近发生了竖椭圆变形,而在离注浆点较远处则发生了横椭圆变形,且隧道发生了反弯现象;注浆过程中发生了“渗透→挤密→劈裂”扩散模式与“挤密→劈裂→渗透”扩散模式,并阐明了两种浆液扩散模式的扩散机制;隧道外壁附加荷载主要由浆液通过渗透扩散与劈裂扩散的浆液压力所形成,同时浆液挤压土体变形对隧道周围的浆液也将形成一定的挤压荷载。

含水率影响下黄土盾构隧道壁后注浆浆液扩散特性试验研究

为了揭示黄土盾构隧道壁后注浆浆液在地层中的扩散形式和规律,考虑盾构隧道盾尾间隙特征,建立含水率、渗流压力、土压力可实时监测以及扩散过程可视的模型试验系统。考虑黄土不同含水率,通过试验研究浆液扩散形式以及注浆过程中的含水率、渗流压力和土压力变化规律。研究结果表明:在相同干密度下,不同含水率对壁后注浆浆液扩散形式影响显著;含水率为10%时,浆液未发生明显扩散,浆-土形成了明显的分界面,仅分界面处的含水率发生显著变化,各分层土体土压力较大;含水率为20%和30%时,浆液扩散范围增大,各分层土体含水率均有变化,土压力和渗流压力出现了阶跃曲线,土体中形成了明显的浆脉。黄土盾构隧道壁后注浆中浆液的扩散形式主要为压密扩散、压滤扩散和劈裂扩散。

长外露锚杆无损检测技术应用研究

常规锚杆无损检测是依据一维杆体理论对锚杆注浆质量进行快速检测。对于长外露锚杆(长自由端),弹性波在外露端的多次反射严重影响锚杆长度与注浆密实度的判定。采用通截取法、辅助钢筋法和辅助套环法对长外露锚杆进行现场处理,对采集的数据进行对比分析,应用结果表明3种方法均能解决长外露锚杆无损检测难题,在某些特定条件下,辅助套环法比辅助钢筋法和截取法具有更多的优势,具有一定的推广价值。

不均匀卵石持力层桩端后注浆效果试验研究

我国东南沿海尤其是温州地区广泛存在上覆深厚软土下覆不均匀卵石的地层。该区域的钻孔灌注桩常采用后注浆技术改善其承载性能。为了评价后注浆技术对这类地层中灌注桩承载力改善效果,开展了相应的模型试验,对比了不同注浆量对桩承载力的影响程度;并结合扫描电镜(scanning electron microscope,简称SEM)试验分析了浆液分布特点,探讨了浆液在卵石层中的扩散范围,研究了浆液扩散范围与桩承载力之间的关系。结果表明:浆液能够有效地填充桩端卵石层,注浆量的增加使得填充范围扩大,填充范围为3~4倍桩径时,桩的承载力改善最显著。在不均匀卵石持力层中存在一个最优注浆量,最优归一化注浆量约为2.8,若超过该最优注浆量归一化值,桩的承载力不再显著提高。单桩模型试验确定的最优注浆量与刘金砺公式[1]的预测结果接近。扫描电镜技术有助于评价桩的后注浆技术在上覆深厚软土下覆不均匀卵石的土层中的效果。

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%。

新线引入既有客运专线车站软土地基加固技术

以新线引入既有客运专线车站软土地基加固工程为依托,开展布袋注浆桩试桩研究,分析不同浆液配比布袋注浆桩复合地基加固效果,对布袋注浆桩施工工艺、质量检验进行了研究。结果表明:布袋注浆桩机械设备高度低,对既有线影响小,对于空间受限的邻近营业线地基加固工程适用性强;提高单位面积布袋质量、采用桶式钻头引孔等可解决碎石成分类填土地基应用布袋注浆桩技术时遇到的布袋破裂、塌孔等问题。浆液质量配比水泥∶水∶粉煤灰=0.70∶0.55∶0.45时桩身无侧限抗压强度平均值9.6 MPa,加固效果优于高压旋喷桩;采用低应变反射波法检测桩体完整性效果较差,工程应用中应加强桩身取芯检测。

新型波纹管连接方钢管混凝土拼接柱抗震性能试验研究

为研究一种新型波纹管连接方钢管混凝土拼接柱的抗震性能,以不同节点配筋率、不同节点锚固长度和轴压比为主要研究变量,对1个整浇柱和4个装配柱进行低周往复加载试验。研究分析了整浇柱与装配柱在破坏模式、滞回性能、位移延性等方面的抗震性能差异。结果表明:装配柱与整浇柱破坏模式类似,采用不同节点构造的装配柱与整浇柱在滞回曲线、骨架特性和刚度退化等方面差异不大,装配柱的耗能性能优于整浇柱。各装配柱极限位移角为1/16.7~1/25,满足规范设计要求。在较大轴压比下,装配柱的承载力提升,延性降低。在较大位移角下,装配柱节点抗震性能受焊缝质量的影响较大,建议实际工程中加强焊接质量管理,以保证构件具有足够的变形能力。

裂隙面起伏形态对注浆固结体剪切力学特性的影响

为研究裂隙面起伏形态对裂隙岩体注浆加固后剪切力学特性的影响,首先,通过3D打印技术生成不同起伏形态的裂隙模型,并采用类岩石材料浇筑成型,然后,对裂隙岩体进行注浆加固,最后,对含不同类型裂隙的注浆固结体进行常法向荷载直剪试验。结果表明:锯齿形固结体的剪切强度最大,波浪形次之,平直形最小;随着法向荷载的增加,平直形固结体的剪切强度增幅最大,波浪形次之,锯齿形最小。剪切过程中,平直形固结体仅发生沿浆-岩界面的剪切破坏;波浪形固结体的浆-岩界面在加载初期发生剪切破坏,随着浆脉与岩壁的啮合程度降低,剪切破坏面逐渐向浆脉和岩体的内部发展,而锯齿形固结体的剪切破坏面出现在浆脉和岩石内部。