Basic mechanism of elastic jacking and impact of fracture aperture change on grout spread,transmissivity and penetrability

One of the most important parameters in the grouting of rock fractures is the applied pressure. This produces the driving force on the Bingham group material that causes it to penetrate the fracture. However, deciding the optimum pumping pressure is challenging. Using too high a pressure not only causes the grout to spread beyond the desired area, but, if it exceeds the minimum in situ stress in the rock mass, may also cause jacking of the fractures. This may lead to uncontrolled uplift. With a lower grout pressure, this “ultimate state” (jacking) can be avoided, although the pressurized grout still may induce smaller elastic deformations during pumping, and these may become irreversible when the grout has hardened. In previous studies, various theoretical approaches to distinguish the onset of these elastic and non-elastic deformations have been described and evaluated. However, the merits and disadvantages of theoretical approaches in general have been questionable. In the current study, the basic mechanism of elastic jacking is described, and its negative consequences are analyzed and quantified. These are the prolongation of grouting time, and the reduction in sealing efficiency. The role of an increased grouting pressure is evaluated by considering its positive effect in improving the penetrability and comparing this with the potential negative consequences. Case studies from two projects (the THX and Citybanan projects) are studied to examine the efficiency of the work that was carried out on site. The results indicate a high-applied pressure can have negative effect on the grouting procedure, and that this effect is significant in fractures situated in weak rock at shallow depth. It is concluded that unwanted fracture deformations and their negative consequences can be eliminated by defining appropriate stop criteria in advance of grouting, and confirming their suitability during pumping by the use of theoretical approach presented here. In general, this will allow the use of lower pump pressure and allow better control of the grout spread.     

Design of grouting with silica sol in hard rock – New design criteria tested in the field, Part II

An extensive field test was conducted in spring 2005 in the Törnskog Tunnel and consisted of design, execution and evaluation of a grouting campaign for 100 m of tunnel. The field test was part of the normal construction of the tunnel. This paper describes how the design of the grouting was coupled with the actual grouting procedure. A preliminary investigation of the tunnel showed that the location where this field test was conducted had a large fracture zone. A drill-core was taken in this zone and hydraulic tests were performed. From the evaluation of the rock core a fracture aperture distribution was assessed and the grouting design was focused on this part of the tunnel. The evaluation showed that apertures down to 14 μm needed to be sealed to cope with stipulations set for leakage into the tunnel (2 l/min and 100 m of tunnel). A design was made based on silica sol, where a critical penetration length was decided and the layout of the grouting fan could be determined. A new design was chosen, with a specific pumping time of 30 min at a grouting pressure of 1.1 MPa. The design worked well and the water ingress was reduced. A drip characterisation in both tunnel tubes was made. One tube was grouted with silica sol and the other with cement following a more traditional approach. The drips were both larger and more frequent in the cement-grouted tube than in the silica sol-grouted tunnel. Eight out of nine fans grouted with silica sol showed a significant sealing effect. For one fan the design was not followed. Instead, the workers used the more traditional method, i.e. only pumping until the design pressure was reached, which produced a poor result. This paper demonstrates the efficiency of design methodology that takes into account the hydraulic apertures and that the required minimum penetration length can be coupled to the apertures when formulating the grouting criteria.     

Sealing narrow fractures with a Newtonian fluid: Model prediction for grouting verified by field study

The increased demand for efficiency when sealing tunnels by grouting has led to a need to seal narrow fractures. The more conductive fractures are sealed by cement-based grouts, however, the limitations in penetrability make these grouts less useful for low permeable rock. Silica sol is an inorganic grouting material with high potential to penetrate narrow fractures. Its two components, silica sol and a salt solution, are both considered harmless. The salt solution (CaCl₂) is the accelerator. The field study investigates whether the penetration of a Newtonian fluid (silica sol) can be predicted and verified using numerical models, based on grout properties and hydraulic tests. The field study was conducted, in 2004, on a pillar located at 0/670 m at Äspö Hard Rock Laboratory (Äspö HRL).One, well characterised and grouted fracture was selected to be grouted with silica sol and analysed. To check the conditions of the fracture hydraulic tests were used, namely, constant head tests with single packer and they were directly followed by pressure logging in the recovery phase. The transmissivity, T, was estimated from the recovery phase of single-hole injection tests using Jacob’s method. Further, the hydraulic aperture was estimated using the well-known cubic law. For the design of the grouting parameters, gel time, injection pressure, and injection time were determined from a one-dimensional model with the penetration length set to 2.2 m. The grout was mixed with optical brightener to make the grout easier to see in the six cores drilled. The grouted borehole was over-cored, and specimens from the grouted fracture were analysed by microscope. Hydraulic tests were made after grouting to estimate the sealing efficiency of the rock mass. The penetration was also estimated in a two-dimensional model to verify length for selected grouting times.Visual observation and the hydraulic properties of two boreholes show that the penetration length is at least 1.0 m. For the numerical model in 2D, a good agreement is found. The final penetration is underestimated by the model underestimates. The hydraulic tests show that at least two boreholes were sealed with silica sol within the predicted penetration radius. The sealing efficiency was approximately 70%.     

Application of the pressure grouting in the hydraulic tunnels

Present paper presents the application of pressure grouting in hydraulic tunnels subjected to high internal pressure of water. Structural analysis of the pressure grouting used for pre-stressing of concrete lining is shown along with the methods used to control the pressure grouting effects. The paper also presents a new experimental method for measuring the loss of water along the complete tunnel under operating conditions and a mathematical model for the evaluation of tunnel impermeability and functionality. All presented test methods have been developed and all measurements were performed by the “Jaroslav Cerni” Institute for Development of Water Resources in Belgrade (Serbia). These methods are presented on the example of a hydraulic tunnel of the “Bajina Basta” pumped storage plant in Serbia, during the stages of its construction and operation.     

考虑浆液扩散路径的多孔介质渗透注浆机理研究

多孔介质注浆的扩散方式以渗透注浆为主,传统的多孔介质渗透注浆往往忽略了浆液渗透过程中的扩散路径,导致理论结果与实际偏差较大。基于对多孔介质浆液渗透过程中扩散路径分析,根据浆液扩散运动方程,建立了考虑浆液扩散路径的多孔介质渗透注浆模型,设计了一套多孔介质渗透注浆扩散模拟实验装置,并采用常规注浆材料-水泥浆液,获得不同被注介质渗透率及不同注浆速率下的注浆压力的时空变化规律。研究结果表明:考虑浆液扩散路径的多孔介质浆液渗透注浆模型计算值为试验值的1.1~1.3倍,计算值与试验值误差在允许的范围之内,所建模型可较好的描述了浆液渗透扩散过程;不考虑浆液扩散路径的多孔介质渗透注浆模型计算值为试验值的1.8~3.2倍,显著高估了注浆扩散过程的浆液压力。研究成果成功用于青岛地铁砂层治理工程,因此,在多孔介质渗透注浆扩散设计中应充分考虑浆液扩散路径。     

考虑注浆压力影响锚–土界面剪切蠕变Kriging模型

锚–土界面剪切蠕变特性直接关系到锚杆支护系统的长期锚固性能,而工程锚杆施工中通常采用的压力注浆对锚固体–土体界面蠕变特性有重要影响。为研究不同注浆压力下的锚–土界面剪切蠕变特性,本文利用自主研制的压力注浆装置制作了不同注浆压力下的锚杆微元体试样,利用自行设计制作的锚–土界面剪切蠕变特性测试系统对试样进行分级加载,获得了不同注浆压力下的锚-土界面剪切蠕变全过程曲线,利用"陈氏加载法"将蠕变全过程曲线转化为分别加载蠕变曲线,并采用等时曲线法获得不同注浆压力下的锚–土界面长期抗剪强度。为提高建模精度,提出了将蠕变试验曲线经对数转换后来建立蠕变模型的方法,并引入Kriging法,建立了考虑注浆压力影响的锚–土界面剪切蠕变Kriging模型。通过所建模型的预测结果与试验结果对比分析发现,本文方法建立的锚–土界面剪切蠕变模型,其拟合和预测精度均很高。     

Effect of grout pressure and grout flow on soil physical and mechanical properties in jet grouting operations

Jet grouting is a method for improving soil characteristics. In this method, grouting of cement slurry with high pressure and velocity causes damage to soil structure. Excavated grains of soil are then removed from the borehole and are replaced with cement slurry. The grains that remain around the borehole mix with cement slurry and produce an improved soil mass of soil. This mass is called “soilcrete”. Soilcrete has special characteristics such as high strength, low deformability and very low permeability. The jet grouting process and its results are affected by various parameters of the soil material and jet grouting system. This paper discusses the effects of jet grouting process on the soil properties before and after the operations, and the effects of grout pressure and grout flow on soilcrete's uniaxial compression strength (UCS). For these purposes, five types of the laboratory tests have been done on the jet grouted soil: uniaxial compression, triaxial compression, direct shear, Brazilian indirect tension, and Schmidt hammer tests. According to the numerical results obtained from experiments, by increasing the grout pressure and flow, the UCS (MPa) of soil increases logarithmically. In addition, jet grouting dramatically increases properties such as cohesion and friction angle.     

Effect of grout properties on the pull-out load capacity of fully grouted rock bolt

This paper represents the result of a project conducted with developing a safe, practical and economical support system for engineering workings. In rock engineering, untensioned, fully cement-grouted rock bolts have been used for many years. However, there is only limited information about the action and the pull-out load capacity of rock bolts, and the relationship between bolt–grout or grout–rock and the influence of the grout properties on the pull-out load capacity of a rock bolt. The effect of grout properties on the ultimate bolt load capacity in a pull-out test has been investigated in order to evaluate the support effect of rock bolts. Approximately 80 laboratory rock bolt pull-out tests in basalt blocks have been carried out in order to explain and develop the relations between the grouting materials and untensioned, fully grouted rock bolts. The effects of the mechanical properties of grouting materials on the pull-out load capacity of a fully grouted bolt have been qualified and a number of empirical formulae have been developed for the calculating of the pull-out load capacity of the fully cement-grouted bolts on the basis of the shear strength, the uniaxial compressive strength of the grouting material, the bolt length, the bolt diameter, the bonding area and the curing time of the grouting material.     

岩石地基上扩展式基础基底反力分布数值分析

通过用ANSYS对影响岩石地基上扩展式基础基底反力分布的各因素分析,绘制了各自的基底反力分布曲线,总结出不同因素变化时,基底反办分布曲线的规律,为岩石地基上基础工程的研究和实际应用提供一定的参考价值。     

考虑浆液自重的盾构隧道管片注浆浆液渗透扩散模型

为研究盾构隧道管片注浆的渗透扩散模型,以宾汉姆浆液流体为研究对象,基于广义达西定律(毛管组理论),并运用相关流体力学理论,推导了考虑浆液自重的盾构隧道管片注浆渗透扩散模型的计算公式,并分析了其适用范围及各参数的确定方法。结合具体计算案例,讨论了注浆参数(注浆压力、注浆时间)、地层特性(地层渗透系数)等主要因素对浆液扩散半径的影响及浆液对管片总压力的影响。结果表明:考虑浆液自重后,浆液的扩散范围呈椭球形;相同的注浆压力下,顶部注浆孔的浆液扩散范围小于底部注浆孔浆液扩散范围(顶部注浆孔出现最小扩散半径,底部注浆孔出现最大扩散半径);注浆压力、注浆时间及地层渗透系数增大,浆液扩散半径也增大,但其增长速率均减小;注浆压力增大,管片所受的注浆压力增大,单位管片所受的浆液压力呈线性增长,考虑浆液自重后,上部单位管片所受的浆液压力大于下部单位管片所受的浆液压力;注浆压力越大,注浆时间越长,地层渗透系数越大,最大扩散半径与最小扩散半径的差值越大,即浆液自重对浆液扩散半径的影响越大。     

顶推梁设计、施工中有关张拉、压浆问题的分析与处理——兼介一种新型钢绞线联接器

总结多座顶推梁预应力张拉和压浆的基础上,对有关问题的分析与处理进行了详细介绍。同时介绍了一种新型钢绞线联接器。     

考虑时间因素的岩体灌浆参数设计研究

水泥灌浆常被用来提高岩体的完整性和降低其渗透性,其工艺参数的设计目前主要依赖于灌浆工程师的经验和类似工程的类比,灌浆时间一般不包括在灌浆设计参数中。根据水泥浆液在光滑顺直裂隙中的扩散运动方程,考虑水泥浆液的宾汉体流变性质和其颗粒特性,并在给出灌浆特征时间概念的基础上推导出灌浆过程中浆液扩散比与灌浆时间比的关系,提出了基于灌浆时间的灌浆结束标准,并结合岩体裂隙开度分布规律对其在灌浆设计和施工中的运用进行了分析,可为灌浆工程的设计和施工提供有益的参考。     

Filtration and penetrability of cement-based grout: Study performed with a short slot

Filtration of cement-based grout during penetration through fractures in rock is an important issue while sealing the rock around tunnels. Whether a type of grout could be designed to penetrate a fracture of a certain aperture without filtration is an interesting question that needs to be further investigated. This study examines the question of whether grout penetration can be measured using our designed measuring method as well as which factors and processes influence the penetrability and filtration of the grout.The penetration and filtration of grout are complex processes influenced by many factors such as the grain-size curve of the cement, hydration and flocculation, pressure, grain concentration, and the geometry of constriction.The measured results were in agreement with the predicted results, indicating that the filtration process in the given geometry describes correctly.     

中空注浆锚索技术在软岩高地应力巷道的应用

针对清水营煤矿软岩巷道围岩失稳变形严重现象,本文主要对失稳原因进行分析总结,提出以中空注浆锚索补强加固为主的支护方案。文章介绍了中空注浆锚索支护原理,进行了中空注浆锚索支护试验,发现巷道顶板和帮的位移变形明显减小,变形量得到有效控制,减小了围岩的松动不稳定范围提高了巷道的持续承载能力和稳定性取得了良好的支护效果。     

桩底劈裂注浆扩散半径和注浆压力研究

在幂律型浆液平板窄缝流动模型的基础上,推导出了劈裂注浆时浆液流速、流量、注浆压力差、最大扩散半径的计算公式。计算分析了注浆压力差随稠度系数、流变参数、裂隙高度的变化情况以及裂隙高度对最大扩散半径的影响。注浆压力差随稠度系数的增大呈线性增大,随流变参数的增大呈非线性增大。裂隙高度的减小使所需注浆压力差迅速增大,并使扩散半径迅速减小,这种影响随着水灰比的增大而减小。通过建立能量平衡方程,详细讨论了不同注浆压力对整个注浆过程的影响。结合本文计算结果对工程实例进行分析,阐述了注浆压力与注浆量的变化规律。     

桩端压力注浆在人工挖孔灌注桩中的应用

论述了桩端压力注浆的作用机理，结合某建筑物场地的工程概况，经分析确定了人工挖孔桩的施工方案，介绍了桩端压力注浆在人工挖孔灌注桩中的应用，取得了良好的施工效果。     

围压对破裂岩体注浆加固效果影响分析

破裂岩体注浆加固技术广泛应用于土木工程各个建设领域。室内试验研究是推动理论研究的主要手段,在注浆加固理论研究过程中,常规的室内注浆试验难以考虑地应力的影响,本文采用自行设计加工的、能够实现垂向和水平向不同加压水平的注浆系统进行了多项承压条件下破裂岩体注浆加固试验,该试验方法更加贴近真实的破裂岩体应力状态,并通过KH-3000数字式三维视频显微镜对注浆固结体进行了分析,试验结果表明,这项注浆加固技术具有重要的推广价值。     

实用矿山压力传感器综述

针对矿山压力监测的实际特点,综合介绍了几种常见的矿山压力监测传感器的原理、结构及特点,为矿山压力监测传感器的选择提供了参考依据,从而达到为煤矿企业节省成本,提高经济效益的目的。     

低压注浆与旋喷桩技术在岩溶塌陷治理中的应用

龙厦铁路象山隧道岩溶突水,导致某水泥厂大面积地面塌陷,厂区建(构)筑物发生开裂和不均匀沉降,其中一期、二期烧成窑头墙体及地面出现起拱及裂缝。经研究决定采用高压旋喷桩结合低压注浆方案进行加固。即采用高压旋喷桩对窑头篦冷机基础进行加固处理,加固区域地基土则采用低压注浆进行加固,取得了较好的加固效果。