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1.
Rock bolts are widely used for rock reinforcement in hard-rock mining and civil engineering since a long time. However the use of fully grouted rock bolts and cable bolts is limited in coal mines. In order to improve performance of the rock bolts as a supplementary roof support system for any type of roof condition in coal measured formations, it is necessary to have a good understanding of the behavior of the bolt–grout and grout–rock interactions as well as the mechanism of load transfer in rock bolts.As the performance of grouted bolts depends on bond strength, extensive laboratory pullout as well as pushout tests were conducted in the present investigations with the variations in the bolt diameters, length and cement–water mixing ratios of grout. The load–displacement curves were developed and were verified with the numerical results obtained from finite element analysis using ALGOR software.Numerical models were validated for pushout tests and a detailed analysis was carried out to know the displacement, stress, strain distribution along the bolt. 相似文献
2.
Load testing of anchors for wire mesh and cable net rockfall slope protection systems 总被引：1，自引：0，他引：1
Shanzhi Shu Balasingam Muhunthan Thomas C. Badger Robert Grandorff 《Engineering Geology》2005,79(3-4):162-176
This study presents results of field tests conducted on anchors used to support wire mesh and cable net rockfall protection systems. The load transfer and failure characteristics of these anchors are different from those used in most civil applications in that loads are often applied transversely to the top of tendon rather than axially. The study included vertical as well as horizontal series of tests conducted on some anchors widely used in wire mesh and cable net rockfall protect systems. It was found that the deformation characteristics of these anchors under vertical loading are nonlinear. They are approximated by a hyperbolic formulation and used to calculate the ultimate capacity. Top-downward progressive cracking of the grout was observed during loading and influences the deformation characteristics of these anchors under horizontal loading. The anchors deflected excessively before they could attain their ultimate capacity in the horizontal direction. Based on the field tests, it appears that the deformation under horizontal loading in the systems can be limited by using an enlarged grout zone at the top. 相似文献
3.
Performance of D-bolts Under Static Loading 总被引：1，自引：0，他引：1
D-bolt is a type of energy-absorbing rock bolt. It is made of a smooth steel bar with anchors spaced along the bolt length.
A typical section between adjacent anchors is approximately 1-m long, but it can be adjusted to adapt to the rock conditions.
The bolt is fully encapsulated with either cement or resin grout in a borehole. The anchors are firmly fixed into the grout,
while the smooth bolt sections can freely deform to absorb deformation energy. Full-scale static pull tests were carried out
at different testing facilities in two laboratories. The tests show that a smooth bolt section between anchors may elongate
by 110–167 mm depending on the section length. Field trials of the D-bolt were conducted in deep metal mines. The measurements
showed that the D-bolts were equally loaded within every anchor-between section, avoiding load peaks and premature bolt failure
due to stress concentrations caused by fracture/joint opening. The field trials of rebar and D-bolts in a largely deformed
mine tunnel showed that the D-bolts behaved satisfactorily, with only a few failed bolts, while a number of the rebar bolts
failed at the thread. 相似文献
4.
海洋能源开发不断向深海迈进,大型深水海上平台对锚泊结构的承载力提出了更高的要求。针对传统鱼雷锚承载比不足的问题,提出了一种新型深水注浆锚。锚体带动连接其尾部的注浆管贯入海床,然后在外部注浆设备驱动下向海床注浆,浆液挤压土体并在锚体周围形成注浆固结块,从而大幅增加锚体抗拔力。采用自主设计的海洋锚注浆和拉拔试验系统进行了模型试验,研究了不同注浆量对浆液扩散特性以及锚体承载特性的影响规律。结果表明：浆液可以较好地包裹锚体,浆块呈倒锥形与锚体紧密黏结为一体,共同承受上部荷载,浆块承载比可达 24.6,远高于传统鱼雷锚的 2.4～4.1,从而验证了深水注浆锚的可行性。随注浆量的增加,浆块端部截面积和整体高度增加,注浆锚整体承载力也不断增大。 相似文献
5.
The load response of a rock-socketed steel H-pile can be strongly influenced by the nonlinear interfacial behavior between the grout and the steel H-pile, and between the pile and the rock mass. This paper focuses on the load-transfer mechanism of the former interface through experimental push-out tests and numerical simulation of the tests. The study is divided into two parts. In the first part, a series of push-out tests have been carried out on four types of specimens (with studs + confinement (Case I); no stud + confinement (Case II); no stud + no confinement (Case III); and studs + no confinement (Case IV)). The second part is a numerical study based on three-dimensional finite element technique, which takes into account possible damage and cracking in grout, as well as bond-slip along the interface. It is shown that the numerical predictions of the four cases compare favorably with the corresponding test results, including the load–displacement response and the development of cracks. Furthermore, parametric study has been carried out to investigate the influence of various factors, including the studs, the casing confinement, the grout fracture energy, and the dilation property of steel-grout interface. Lastly, some implications, based on the test and numerical results, on the design of socketed steel H-piles are discussed. 相似文献
6.
The objective of this study is to improve the understanding of load transfer mechanism of Geogrid-Reinforced Pile-Supported Embankments (GRPS) via a new 3D analytical approach and comprehensive field tests. A full-scale embankment was built over a silty clay of medium compressibility as a part of the Liuzhou-to-Nanning High-speed Railway (LNHR) in China. Six sections of the embankment have been heavily instrumented producing comprehensive data of high quality. Field measurements evidence the existence of soil arching, membrane contribution and ground reaction, phenomena that are all contributing to load transfer mechanism. The new 3D analytical arching model accounts for a triangular arrangement of piles and, unlike existing methods, accounts for all relevant components of load transfer mechanisms. In addition, two key parameters were introduced in the model: an elastoplastic state parameter of soil arching (α) and a coefficient of equivalent uniform stress (β). The former was used to satisfy the load equilibrium in case of partial arching while the latter was adopted to allow possible nonuniform vertical stress acting on the ground surface. The so-called ground reaction method was incorporated in an innovative manner to take into account the reactive support of the subsoil beneath geogrid-reinforced layer when estimating the tension development in the geogrid. Finally, the performance of the proposed model was assessed against several existing models and field measurements. Results showed that the new model presented herein outperforms existing models and satisfactorily predicts both the pile efficiency and tension development within the geogrid. 相似文献
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Composite element model for the bonded anchorage head of stranded wire cable in tension 总被引：1，自引：0，他引：1 
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下载免费PDF全文 An elasto‐viscoplastic model is formulated using composite element technique for the bonded anchorage head of stranded wire cable in rock mass. This composite element contains sub‐elements corresponding to the rock material, the grout material, the stranded wire material, the rock/grout interface, and the grout/stranded wire interface, respectively. The displacement in each aforementioned sub‐element is interpolated from the corresponding nodal displacements of the composite element. In this manner, the mesh generation taking into account of tension cable anchors may be highly facilitated. By the application of the virtual work principle, the governing equation for solving the nodal displacements of the composite element is established. The proposed model has been incorporated into the conventional finite element algorithm and implemented in the program CORE3, in which the anchorage head is embedded within the composite elements. The comparative study concerning the pull‐out test has been carried out for the validation of the proposed model and algorithm. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
9.
A model was developed, to describe miscible grout propagation in a saturated deformable porous medium, based on Bear's statistical model with spatial volume averaging. In a previous paper, the model was first successfully confronted to one‐dimensional laboratory experiments. In the present paper, the numerical model is used to simulate practical grouting operation in a cylindrical injection model. The cylindrical injection model lends itself to study main flow and propagation character istics for a dispersed suspension‐type grout, under axisymmetric conditions close to real scale conditions. Comparison between numerical solutions and experimental results is essential to confirm the validity and accuracy of the proposed model from a phenomenological standpoint. The numerical model performances show that the underlying mathematical model constitutes a realistic predictive model reproducing most prominent features during injection of a suspension‐type grout into a deformable porous medium. The basic mechanism by which injected miscible grout permeates a soil mass is discussed in detail. Such a tool leads to quality control criteria for grouting on a theoretical basis, which complements existing criteria acquired through engineering practice. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
10.
The paper presents a simplified design procedure to evaluate the loads in piles and prestressed anchors when simultaneously used in foundations under tension loads and high overturning moments. Although involving some necessary simplifications for the sake of design, the procedure keeps the main features of load transfer from piles and anchors to the surrounding soil. The approximate method has been adopted by the authors in relevant projects in Brazil, whose long term satisfactory performance indicates its appropriate performance. Two practical examples have been selected to illustrate the application of the proposed method. It is shown that anchor prestressing plays an important role in limiting tension loads on the piles and controlling foundation eccentricity. The importance of monitoring for replacement of occasional prestress losses to prevent long-term pile overstressing is illustrated. 相似文献
11.
以预应力锚杆复合土钉支护体系受力变形为分析对象,假定潜在滑裂面为平面,并考虑土体分层开挖过程,将施加预应力作为一个施工工况,建立了预应力锚杆复合土钉支护体系受力变形的增量解析方法。锚杆预应力和设置位置影响分析表明,随着锚杆预应力值的增加,潜在滑裂面的倾角逐渐减小,对基坑整体稳定性的贡献先增大后减小;锚杆设置越低,增加预应力对基坑整体稳定性的贡献越大。通过实际基坑支护工程的数值模拟分析与施工过程监测结果的对比分析,验证了考虑预应力锚杆施工过程特点的复合土钉支护体系增量解析方法的合理性。 相似文献
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This paper reports the limitation of the conventional Bishop's simplified method to calculate the safety factor of slopes stabilized with anchors, and proposes a new approach to considering the reinforcing effect of anchors on the safety factor. The reinforcing effect of anchors can be explained using an additional shearing resistance on the slip surface. A three‐dimensional shear strength reduction finite element method (SSRFEM), where soil–anchor interactions were simulated by three‐dimensional zero‐thickness elasto‐plastic interface elements, was used to calculate the safety factor of slopes stabilized with anchors to verify the reinforcing mechanism of anchors. The results of SSRFEM were compared with those of the conventional and proposed approaches for Bishop's simplified method for various orientations, positions, and spacings of anchors, and shear strengths of soil–grouted body interfaces. For the safety factor, the proposed approach compared better with SSRFEM than the conventional approach. The additional shearing resistance can explain the influence of the orientation, position, and spacing of anchors, and the shear strength of soil–grouted body interfaces on the safety factor of slopes stabilized with anchors. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
14.
A numerical study incorporating three-dimensional Eulerian large deformation finite element analyses is performed to investigate the pullout process of horizontal square plate anchors in both hypothetical weightless soil and soil with self-weight. The validity of the numerical model is established through verification against published experimental and numerical results. The failure mechanisms during the pullout process under different conditions are then investigated. Three types of failure mechanism are observed; of which only two have been reported in the literature. The third mechanism identified in this study, which is a partially localized flow mechanism, is operative when the soil overburden ratio is not high enough to mobilize the full flow mechanism. The influence of soil self-weight is directly investigated by incorporating the density of the soil in the finite element model and maintaining the gravitational acceleration field throughout the analysis. The critical overburden ratio corresponding to the full transition to a localized plastic flow mechanism is identified in this study. The effect of the soil rigidity index (E/su) on the anchor uplift capability has not been systematically investigated in earlier studies. Contrary to the general failure mechanism and the full flow mechanism described in the literature, the capacity factor corresponding to this new mechanism increases with increasing E/su. The capacity factors for square plate anchors corresponding to different anchor embedment ratios, overburden ratios and E/su are provided in the form of design charts. 相似文献
15.
The ultimate capacity of anchors is determined using the material point method (MPM). MPM is a so‐called meshless method capable of modelling large displacements, deformations and contact between different bodies. A short introduction to MPM is given and the derivation of the discrete governing equations. The analysis of a vertically loaded anchor and one loaded at 45° is presented. The load–displacement curves are compared to that obtained from experiments and the effect of soil stiffness and anchor roughness is investigated. The results of the vertically loaded anchor are also compared to an analytical solution. The displacement of the soil surface above the anchor was measured and compared to the numerical predictions. Convergence with mesh refinement is demonstrated and the effect of mesh size and dilatancy angle on the shear band width and orientation is indicated. The results show that MPM can model anchor pull out successfully. No special interface elements are needed to model the anchor–soil interface and the predicted ultimate capacities were within 10% of the measured values. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
16.
A numerical study of the pullout behavior of grout anchors underreamed by pulse discharge technology
Pulse discharge technology (PDT) is an innovative construction method used to enhance the bearing capacity of piles and the resisting capacity of anchors by underreaming using a high-pressure shockwave induced by an underwater electric discharge. This study numerically analyzes the pullout behavior of a grout anchor underreamed by PDT. A series of finite element analyses were performed to examine the pullout behavior of the anchor based on successive simulations from underreaming to subsequent pullout tests. The electric blasting and shockwave generation by PDT was equivalently modeled using the underwater explosion (UNDEX) model, and the appropriate UNDEX parameters were determined by benchmarking the laboratory PDT tests. Full-scale PDT underreaming and the subsequent pullout tests in dry sand deposits reported in the literature were then simulated on the basis of fluid–structure interaction (FSI) analyses and static uplift analyses. The predicted expansion of the borehole and the pullout behaviors were compared with field test results to validate the numerical model. Moreover, the results from a parametric study conducted to investigate the influence of soil and anchor characteristics on the uplift behavior of the PDT underreamed anchor are discussed. 相似文献
17.
Qiong Wang Xinyu Ye Shanyong Wang Scott William Sloan Daichao Sheng 《Acta Geotechnica》2018,13(5):1129-1140
This paper presents a non-destructive, low-cost, photo-based, 3D reconstruction technique for characterizing geo-materials with irregular shapes of a relatively large size. After being validated against two traditional volume measurement methods, namely the vernier caliper method and the fluid displacement method for regular and irregular shapes, respectively, 3D photogrammetry was used to analyse the grout bulbs formed in laboratory pressure grouting tests. The reconstructed 3D mesh model of the sample provides accurate and detailed 3D vertex data, which allowed the volume, densification efficiency and bleeding behaviour of the grout bulbs to be analysed. Comparing the bulb section views at different grouting pressures also offers an intuitive observation of the grout development and propagation process. Moreover, the 3D vertex data and surface area included in the model are of great importance in validating numerical predictions of the pressure grouting process and analysing the interface shear resistance of grouted soil nails or anchors. Compared to existing approaches, the new 3D photogrammetry method possesses several key advantages: (a) it does not require expensive, specialized equipment; (b) samples are not destroyed or modified during testing; (c) it allows to reconstruct objects of various scales and (d) the software is public domain. Therefore, the adoption of this 3D photogrammetry method will facilitate research in the pressure grouting process and can be extended to other problems in geotechnical engineering. 相似文献
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桩-土相互作用问题是岩土工程桩基础问题的关键点与难点,目前针对桩身在循环温度荷载与上覆结构荷载双重作用下的能源桩承载特性研究较少。在传统理想弹塑性模型及双曲线模型的基础上,采用分段非线性的方法对桩-土荷载传递骨干曲线进行了修正,并基于Masing’s循环准则,提出了适用于能源桩的桩-土荷载传递模型。利用改进的桩-土荷载传递模型对能源桩承载特性进行数值分析,着重研究了桩-土荷载传递参数比R对能源桩受力情况的影响。此外,为了探究在上覆结构荷载及循环温度荷载双重作用下,能源桩与周围土体之间的真实荷载传递关系及其结构热力学特性,开展了针对能源桩与周围土体之间相互作用问题的室内模型试验,监测了其桩身轴向应力及侧摩阻力随温度及深度变化的趋势,并与基于改进荷载传递模型的数值计算结果进行了对比。室内模型试验监测及数值计算结果显示：能源桩在上覆结构荷载及温度循环荷载双重作用下,其受力行为受改进的桩-土荷载传递循环曲线控制;基于改进的桩-土荷载传递循环曲线而建立的数值模型计算结果与试验结果基本吻合,改进的桩-土荷载传递模型能够较好发地反映能源桩实际的承载特性。 相似文献
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通过块体集上限分析方法,研究锚板的抗拔承载力和破坏面特性,并将分析结果与Das[1]以及Rowe[2]的锚板模型试验结果进行详细对比,验证块体集上限法的有效性。分析斜坡地形条件下锚板抗拔承载特性,并与Khing等[3]的条形锚板抗拔承载力试验以及Rao和Prasad[4]的圆形锚板抗拔承载力试验进行详细对比,分析斜坡地形条件下锚板模型试验中采用拉杆加载的方式对于试验结果的影响。分析结果表明,斜坡地形条件下拉杆的存在对于锚板抗拔承载力影响较大,模型试验应优先采用Trapdoor模型。 相似文献