Mechanism of high-preload support based on the NPR anchor cable in layered soft rock tunnels

The control of large deformation problems in layered soft rock tunnels needs to solve urgently.The roof problem is particularly severe among the deformation issues in tunnels.This study first analyzes the asymmetric deformation modes in layered soft rock tunnels with large deformations.Subsequently,we construct a mechanical model under ideal conditions for controlling the roof of layered soft rock tunnels through high preload with the support of NPR anchor cables.The prominent roles of long and short NPR anchor cables in the support system are also analyzed.The results indicate the significance of high preload in controlling the roof of layered soft rock tunnels.The short NPR anchor cables effectively improve the integrity of the stratified soft rock layers,while the long NPR anchor cables effectively mobilize the self-bearing capacity of deep-stable rock layers.Finally,the high-preload support method with NPR anchor cables is validated to have a good effect on controlling large deformations in layered soft rock tunnels through field monitoring data.

Seismic stability of expansive soil slopes reinforced by anchor cables using a modified horizontal slice method

Earthquake-induced slope failures are common occurrences in engineering practice and pre-stressed anchor cables are an effective technique in maintaining slope stability,especially in areas that are prone to earthquakes.Furthermore,the soil at typical engineering sites also exhibit unsaturated features.Explicit considerations of these factors in slope stability estimations are crucial in producing accurate results.In this study,the seismic responses of expansive soil slopes stabilized by anchor cables is studied in the realm of kinematic limit analysis.A modified horizontal slice method is proposed to semi-analytically formulate the energy balance equation.An illustrative slope is studied to demonstrate the influences of suction,seismic excitations and anchor cables on the slope stability.The results indicate that the stabilizing effect of soil suction relates strongly to the seismic excitation and presents a sine shape as the seismic wave propagates.In higher and steeper slopes,the stabilizing effect of suction is more evident.The critical slip surface tends to be much more shallow as the seismic wave approaches the peak and vice versa.

Case study on the mechanics of NPR anchor cable compensation for large deformation tunnel in soft rock in the Transverse Mountain area,China

A study was conducted to analyze the deformation mechanism of strongly weathered quartz schist in the Daliangshan Tunnel,located in the western Transverse Mountain area.A large deformation problem was experienced during the tunnel construction.To mitigate this problem,a support system was designed incorporating negative Poisson ratio(NPR)anchor cables with negative Poisson ratio effect.Physical model experiments,field experiments,and numerical simulation experiments were conducted to investigate the compensation mechanical behavior of NPR anchor cables.The large deformations of soft rocks in the Daliangshan Tunnel are caused by a high ground stress,a high degree of joint fracture development,and a high degree of surrounding rock fragmentation.A compensation mechanics support system combining long and short NPR anchor cables was suggested to provide sufficient counter-support force(approximately 350 kN)for the surrounding rock inside the tunnel.Comparing the NPR anchor cable support system with the original support system used in the Daliangshan tunnel showed that an NPR anchor cable support system,combining cables of 6.3 m and 10.3 m in length,effectively prevented convergence of surrounding rock deformation,and the integrated settlement convergence value remained below 300 mm.This study provides an effective scientific basis for resolving large deformation problems in deeply buried soft rocks in western transverse mountain areas.

Three-dimensional limit variation analysis on the ultimate pullout capacity of the anchor cables based on the Hoek-Brown failure criterion

Only simplified two-dimensional model and a single failure mode are adopted to calculate the ultimate pullout capacity(UPC)of anchor cables in most previous research.This study focuses on a more comprehensive combination failure mode that consists of bond failure of an anchorage body and failure of an anchored rock mass.The three-dimensional ultimate pullout capacity of the anchor cables is calculated based on the Hoek-Brown failure criterion and variation analysis method.The numerical solution for the curvilinear function in fracture plane is obtained based on the finite difference theory,which more accurately reflects the failure state of the anchor cable,as opposed to that being assumed in advance.The results reveal that relying solely on a single failure mode for UPC calculations has limitations,as changes in parameter values not only directly impact the UPC value but also can alter the failure model and thus the calculation method.

Exploring the feasibility of prestressed anchor cables as an alternative to temporary support in the excavation of super-large-span tunnel

Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages.However,these internal supports generally impose spatial constraints,limiting the use of large-scale excavation equipment and reducing construction efficiency.To address this constraint,this study adopts the“Shed-frame”principle to explore the feasibility of an innovative support system,which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions.To evaluate its effectiveness,a field case involving the excavation of a 24-m span tunnel in soft rock is presented,and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system.The results revealed that prestressed anchor cables integrated the initial support with the shed,creating an effective“shed-frame”system,which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds.Moreover,the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly.In summary,the proposed support system balances construction efficiency and safety.These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.

Instability mechanism of mining roadway passing through fault at different angles in kilometre-deep mine and control measures of roof cutting and NPR cables

The angle α between the fault strike and the axial direction of the roadway produces different damage characteristics. In this paper, the research methodology includes theoretical analyses, numerical simulations and field experiments in the context of the Daqiang coal mine located in Shenyang, China. The stability control countermeasure of "pre-splitting cutting roof + NPR anchor cable"(PSCR-NPR) is simultaneously proposed. According to the different deformation characteristics of the roadway, the faults are innovatively classified into three types, with α of type I being 0°-30°, α of type II being 30°-60°, and α of type III being 60°-90°. The full-cycle stress evolution paths during mining roadway traverses across different types of faults are investigated by numerical simulation. Different pinch angles α lead to high stress concentration areas at different locations in the surrounding rock. The non-uniform stress field formed in the shallow surrounding rock is an important reason for the instability of the roadway. The pre-cracked cut top shifted the high stress region to the deep rock mass and formed a low stress region in the shallow rock mass. The high prestressing NPR anchor cable transforms the non-uniform stress field of the shallow surrounding rock into a uniform stress field. PSCR-NPR is applied in the fault-through roadway of Daqiang mine. The low stress area of the surrounding rock was enlarged by 3-7 times, and the cumulative convergence was reduced by 45%-50%. It provides a reference for the stability control of the deep fault-through mining roadway.

Numerical simulation of rockburst disaster and control strategy of constant resistance and large deformation anchor cable in Gaoloushan tunnel

The Gaoloushan Tunnel in Longnan City,Gansu Province,China,frequently experiences rockburst disasters due to high in-situ stress.Managing rockburst in deep-buried tunnels remains a challenging issue.This paper employs RFPA(Rock Failure Process Analysis)software to establish a calculation model of constant resistance and large deformation(CRLD)anchorages and analyzes the effects of different support methods and pre-stress levels on rockburst.We simulate the process of tunnel rockburst disasters and find that ordinary anchor support incurs rockburst on the right arch waist and arch top,forming a V-shaped explosion pit.CRLD anchor support has several advantages in rockburst control,such as more uniform stress distribution in the surrounding rock,a uniform distribution of plastic zones,less noticeable damage to the tunnel,and effective control of the arch top displacement.The effectiveness of the CRLD anchor support under varying pre-stress conditions shows that a higher prestress results in a smaller plastic zone of the surrounding rock and arch top displacement and a lower number of acoustic emission signals,which better explains the excavation compensation effect.Moreover,adding long anchorages in the deep surrounding rock area can better control rockburst and reduce surrounding rock deformation.Based on these findings,we propose a comprehensive control system that combines long and short anchorages and provides the optimal scheme based on calculations.Therefore,by using high-prestress CRLD anchor support and the combination of long and short anchorages at critical positions,we can enhance the integrity of the surrounding rock,effectively absorb the energy released by the surrounding rock deformation,and reduce the incidence of rockburst disasters.

Dynamic response of a slope reinforced by double-row antisliding piles and pre-stressed anchor cables

Large-scale shaking table tests were conducted to study the dynamic response of a slope reinforced by double-row anti-sliding piles and prestressed anchor cables. The test results show that the reinforcement suppressed the acceleration amplification effectively. The axial force time histories are decomposed into a baseline part and a vibration part in this study. The baseline part of axial force well revealed the seismic slope stability, the peak vibration values of axial force of the anchor cables changed significantly in different area of the slope under seismic excitations. The peak lateral earth pressure acting on the back of the anti-sliding pile located at the slope toe was much larger than that acting on the back of the anti-sliding pile located at the slope waist. The test results indicate an obvious load sharing ratio difference between these two anti-slide piles, the load sharing ratio between the two anti-sliding piles located at the slope toe and the slope waist varied mainly in a range of 2-5. The anti-slide pile at the slope waist suppressed the horizontal displacement of the slope surface.

Prestressed tensioning method and its application to testing anchor stress of anchor cables for side-slope stabilization

The anchor stress extent of a prestress anchor cable project has a direct relation with the project safety and performance. Prestressed tensioning method is a kind of nondestructive testing method, by which a reverse stretching load is applied on the external exposure section of anchor cable under construction or in service, and then the elongation variation of stress bars is measured to determine the anchor stress. We elaborated the theory and testing mechanism of prestressed tensioning method, and systematically studied key issues during the prestressed tensioning process of anchor cable by using physical model test, including the composition of tension stress-elongation curve, the variation of anchor stress, the compensation of locked anchor stress, and the judgment of anchor stress, and verified the theory feasibility of prestressed tensioning method. A case study on slope anchor cable of one highway project was conducted to further discuss on the test method, operation procedures and judgment of prestressed tensioning method on obtaining anchor stress, and then the test data of three situations were analyzed. The result provides a theoretical basis and technical base for the application of prestressed tensioning method to the evaluation of construction quality and operation conditions of anchor cable project.

Optical Fiber Grating Sensor for Force Measurement of Anchor Cable

The development of the sensor suitable for measuring large load stress to the anchor cable becomes an important task in bridge construction and maintenance. Therefore, a new type of optical fiber sensor was developed in the laboratory - optical fiber grating sensor for force measurement of anchor cable （OFBFMAC）. No similar report about this kind of sensor has been found up to now in China and other countries. This sensor is proved to be an effective way of monitoring in processes of anchor cable installation, cable cutting, cable force regulation, etc, with the accurate and repeatable measuring results. Its successful application in the tie bar cable force safety monitoring for Wuhan Qingchuan bridge is a new exploration of optical fiber grating sensing technology in bridge tie bar monitoring system.

Shaking table test of seismic responses of anchor cable and lattice beam reinforced slope

As a combined supporting structure,the anchor cable and lattice beam have a complex interaction with the slope body.In order to investigate the seismic behaviors of the slope reinforced by anchor cable and lattice beam,a largescale shaking table test was carried out on a slope model(geometric scale of 1:20)by applying recorded and artificial seismic waves with different amplitudes.The acceleration and displacement of the slope,the displacement of lattice beam and the axial force of anchor cable were obtained to study the interaction between the slope and the supporting structure.The test results show that:(1)the acceleration responses of the slope at different relative elevations display obvious nonlinear characteristics with increasing of the peak ground acceleration(PGA)of the inputted seismic waves,and the weak intercalated layer has a stronger effect on acceleration amplification at the upper part of the slope than that at the lower part of the slope;(2)the frequency component near the second dominant frequency is significantly magnified by the interaction between the slope and the supporting structure;(3)the anchor cables at the upper part of the slope have larger peak and residual axial forces than that at the lower part of the slope,and the prestress loss of the anchor cable first occurs at the top of the slope and then passes down;(4)the peak and residual displacements inside the slope and on the lattice beam increase with the increase of relative elevation.When the inputted PGA is not greater than 0.5 g,the combined effect of anchor cable and lattice beam is remarkable for stabilizing the middle and lower parts of the potential sliding body.The research results can provide a reference for the seismic design of such slope and the optimization of supporting structure.

Negative Poisson's ratio and peripheral strain of an NPR anchor cable

Materials with a negative Poisson’s ratio effect perform significantly better than traditional materials for rock mass impact resistance,shear resistance,and energy absorption.Based on these advantages,a negative Poisson’s ratio anchor cable(NPR anchor cable)with high elongation and constant resistance was developed and successfully applied in the field of mine disaster control.However,theoretical and experimental research on the negative Poisson’s ratio effect and peripheral strain characteristics of NPR anchor cables is currently incomplete.This study used several theories and methods,such as static tensile,peripheral strain measurement,and static negative Poisson’s ratio measurement,to investigate the radial deformation law of an NPR anchor cable and the negative Poisson’s ratio characteristics.Experimental results elucidated constant resistance changes in an NPR anchor cable during operation,the motion of the constant resistance body in the constant resistance sleeve,and the deformation law of the constant resistance sleeve.Negative Poisson’s ratio characteristics of the NPR anchor cable and its superior energy absorption characteristics were verified and it provided a theoretical and experimental basis for energy absorption mechanisms of an NPR anchor cable.

Model test of negative Poisson’s ratio cable for supporting super-largespan tunnel using excavation compensation method

In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。

Optimization of Dead Load State in Earth-Anchored Cable-Stayed Bridges

In order to determine the reasonable completed dead load state in earth-anchored cable-stayed bridges,a practical method is proposed. The method is based on the rigidly supported continuous beam method and the feasible zone method,emphasizing on the mutual effect between the self-anchored structural parts and the earth-anchored ones. Three cable-stayed bridge models are designed with the main spans of 1 400 m,including a partially earth-anchored cable-stayed bridge,a cable-stayed-suspension bridge and a fully selfanchored cable-stayed bridge,in which the C50 concrete and Q345 steel are adopted. The partially earthanchored cable-stayed bridge and the cable-stayed-suspension bridge secure lower compressive force in the girder than the fully self-anchored cable-stayed bridge by 25 percent at least. The same is for the material consumption of the whole bridge. Furthermore,the anchor volume is more than 20% lower in the partially earthanchored cable-stayed bridge than that in the cable-stayed-suspension bridge. Consequently,the practical span of cable-stayed bridges can be accordingly extended.

Application of A New Anchor Cable Mounting Rod in the Lower Soft Coal Seam of Splitting and Merging Coal

To obtain the deep displacement of the coal seam in the working face,multi-point displacements were installed in the coal seam, but the installation of multi-point displacement is differen tunder different geological conditions. This paper is based on the splitting and merging of 7_1 coal and 7_2 coal in Huaibei Mining(Group) Co., Ltd., and analyzes properties of the roof andcoal in the 7_2 coal of the lower coal seam of bifurcation area, and calculates the damage depth of the floor in the process of 7_1 coal mining. The multi-point displacement meter installation is often challenged by hole collapse, stuck pole and broken installation rod in 7_2 coal of the soft coal seam of bifurcation area, as a result, the base points can't be installed in the specified location. In view of this, this paper adopts a new anchor cable mounting rod which can install the whole base points to the specified location without stuck pole or broken mounting stem. All the basic displacement data can be obtained, and the law of mine pressure appearance in stope and tunnel can be accurately controlled, which can be used to maintain the stability of roadway and the safety of stope.

ANALYSIS ON INCREMENTAL COHESION OF SURROUNDING ROCK DUE TO PRESTRESSED CABLE ANCHOR

A new method for determining the incremental cohesion △Cm of surrounding rock due to prestressed cable anchor is presented, and the formulas for △Cm are deduced and △Cm distributions also are discussed, based on the two anchorage effects, one is the effect with the prestressed vaIue △σ3 of cable anchor improving the stress state of surrounding rock and increasing the surrounding rock strength, the other is the fully encapsulated effect. The determined incremental cohesion △Cm is subiected to the model test and field measurement in the references, and coincides well with those tested results. The formulas for △Cm can be used in designing supoport parameters and related numerical analyses of prestressed cable anchor.

Applied on bolting-cable anchor support of full-seam roadway in weaker thick coal seam

The designing method and the supporting mechanism of both bolt and small cable anchor for full seam roadway in the weaker thick coal seam are systematically analyzed, and the construction technology and the supporting results are briefly summarized.

穿断层隧道NPR锚索支护体系抗震特性振动台试验研究

为研究具有负泊松比效应(negative Poisson’s ratio,NPR)的恒阻大变形锚索在地震作用下的吸能特性与动力响应规律,利用振动台开展含断层隧道使用普通锚索支护以及使用NPR锚索支护的振动台物理模型试验,对比分析地震作用下处于不同围岩条件中以及使用不同锚索进行支护时隧道结构的动力响应规律。研究结果表明:在同一地震波作用下,使用NPR锚索进行支护的隧道结构破坏程度与使用普通锚索进行支护的隧道结构相比有明显的改善,表明NPR锚索在地震作用下具有良好的吸能特性,能够为隧道结构提供有效支护;通过对比分析普通锚索与NPR锚索的锚索轴力时程曲线可知,在地震波作用下,普通锚索会发生破断现象,轴力突降至零,而NPR锚索的高恒阻力能够持续提供有效支护;分析隧道结构各测点的加速度、应变、土压力等动力响应可知,隧道断层区域在地震作用下的动力响应更为明显,隧道结构在地震作用下呈现出拱肩→拱腰→拱顶的破坏规律,这一研究成果为类似隧道工程的支护对策提供了理论参考。

千米深井切顶卸压自成巷支护技术及应用

为了解决深部复杂条件下的切顶卸压自成巷难题,以红阳三矿703工作面运输巷道为研究对象,从恒阻大变形锚索超前支护、切顶巷内支护、切顶巷旁支护三个方面研究了切顶卸压沿空成巷支护技术,并对现场试验巷道顶板受力以及巷道围岩变形量进行了监测。结果表明:在超前工作面实施爆破切顶能够极大降低巷道所受应力,成巷区巷道顶板整体下沉量较小,巷中顶板最大下沉量约385 mm,平均下沉量约280 mm,巷中底鼓最大值545 mm,碎石巷帮无明显侧鼓现象,实体煤帮无明显片帮现象,满足安全和使用要求,巷道围岩变形在可控范围内,留巷效果良好。

Negative Poisson's ratio anchor cable support for fault tunnels with different inclination angles under earthquake

It is inevitable to encounter fault zones in tunnel construction.These faults can lead to significant deformations and potential collapses of the surrounding rock in the tunnel.Therefore,it is crucial to study the influence of different fault angles on tunnel deformation.The Tabaiyi Tunnel,located in Yunnan Province of China passes through a multi-stage fault zone.The dynamic response characteristics of the surrounding rock in the Tabaiyi Tunnel were studied under various fault dip angles and the most unfavorable angle was identified.Physical model tests were conducted using two types of anchor cables with specific parameters.Additionally,a relationship between the engineering rock mass and energy absorption by the anchor cables was established,demonstrating the advantages of negative Poisson's ratio(NPR)anchor cables.Experimental results indicate that stress concentration tends to occur at the junctions between faults and the surrounding rock mass.Tunnels supported by NPR anchor cables effectively mitigate amplification effects,achieving energy absorption increases of up to 87%compared to positive Poisson's ratio(PR)anchor cables.Furthermore,the highest acceleration amplification was observed at a fault dip angle of 45°,with peak acceleration reaching twice that of the original input wave,indicating that this angle should be avoided in tunnel design.These findings provide valuable insights for the safe management of tunnels traversing fault zones.