Anchor Cable Research Articles

Elastoplastic coupling analysis of surrounding rock-prestressed yielding anchor bolts/cables based on unified strength theory

A whole-process analytical theory for the coupled deformation of deep circular tunnel surrounding rock and prestressed yielding anchor bolt (cable) system is derived based on the unified strength theory and non-associated flow rule. This theory considers the strain softening characteristic of rock mass, the yielding reinforced characteristics of anchor bolt (cable), and the support timing. An analytical method is proposed to calculate the difference in displacement of anchor bolts (cables). This study highlights the importance of monitoring anchor bolts (cables) elongation rate in high-stress tunnels by integrating theoretical analysis with engineering practice. The displacement difference that occurs during the coordinated deformation of the bolts (cables) and the surrounding rock provides the support resistance. Therefore, the safety margin standard of elongation rate can be used to assess the integrity and effectiveness of the support structure during the real-time bolts (cables) action. The present study aims to validate the rationality of the analytical theory by conducting numerical simulations using ABAQUS software. Specifically, we focus on analyzing the ground response curves (GRC) underthe bolt (cable) support and the elongation rate of the bolt (cable). Various factors such as prestress, yielding amount, support timing, intermediate principal stress coefficient, radial/longitudinal spacing, and length are considered tocompare and analyze their effects on the GRC. The results showed that anchor bolts (cables) can significantly reduce the surrounding rock convergence. With prestressed bolt (cable) support, the GRC exhibits a stepwise drop, significantly and timely reducing the support force required for the surrounding rock equilibrium. After setting the yielding structure, the increase in anchor cable stress was limited, thereby slightly increasing the surrounding rock displacement. However, the anchor cable elongation rate significantly decreased, thereby greatly enhancing the support structure safety. The support timing affects the starting point of bolts (cables) function. The displacement control effect is more pronounced when support is provided earlier. However, this also leads to an increase in the elongation rate of the bolt (cable). The intermediate principal stress coefficient reflects the self-bearing capacity of the surrounding rock, and increasing this value can improve the deformation control performance of the surrounding rock under anchor bolt (cable) support as a whole and reduce the elongation rate through the coupled function of the surrounding rock–anchor bolt (cable) system. The spacing between anchor cables significantly impacts the convergence control of surrounding rock. Smaller spacing leads to better control of the surrounding rock deformation and lower stress of the anchor cables. As the length of the anchor cables increases, the elongation rate and stress of the anchor cables continuously decrease. However, the surrounding rock deformation exhibits an initially decreasing and increasing pattern. This paper presents a theoretical and computational approach to analyze the effect of prestressed yielding anchor bolt (cable) support and the safety of support structures in tunnel engineering. The findings of this study can serve as a valuable reference for the convergence analysis of circular tunnels in underground engineering.

Numerical simulation of mechanical characteristics and tension-torsion coupling effect of tension-type anchor cable

PurposeThe purpose of this paper is to simulate the tension process of tension-type anchor cable and to explore the mechanical characteristics and tension-torsion coupling effect of anchor cable subjected to tension.Design/methodology/approachABAQUS numerical software is applied to construct the numerical models of tension-type anchor cables with different diameters. Through explicit contact, the characteristics of contact between grouting body-anchor cable and grouting body-rock mass are determined. Confining pressure is applied to the model through surface pressure, and drawing force is applied to the model by displacement loading so as to simulate the tension process of the anchor cable.FindingsThe results show that the stress is transmitted in both axial and radial directions in the anchorage section and distributed in a cone. The shear stress in the grouting body is unevenly distributed, and its peak value increases with the rise in confining pressure and anchor cable diameter. The stress characteristics of torque and axial force are basically consistent and evenly distributed in the free section; they gradually decrease in the anchorage section. Due to the tension-torsion coupling effect, the internal stress characteristics of the anchor cable structure vary. On average, the anchorage performance of each anchor cable model is improved by 6.19%.Originality/valueThe proposed method of numerical modelling is effective in addressing the interface contact between the anchor cable and the grouting body and in solving the problem with convergence of calculation. Compared with the indoor test, this method is more suited to collecting the internal mechanical data of the anchor body.

Study on the Stress Evolution and Strengthening Support Timing of the Retracement Channel under the Super-Thick Nappe

The superposition effect of the advanced support pressure of the working face in the final mining stage and the lateral support stress of the roadway is a key factor affecting the stability of the retracement channel. To study the stress evolution of the retracement channel under the super-thick nappe and the timing of strengthening support, this paper takes the mining of the 360808 working face in Xinji No. 1 Mine as the engineering background, analyzes the occurrence conditions of the working face and the measured rock pressure law, and constructs a roof structure model of the retreat area. The UDEC discrete element numerical simulation software was used to analyze the evolution characteristics of concentrated stress and the failure law of surrounding rock around the retracement channel under gradual excavation conditions. Based on the relationship between the position of the main roof fracture and the stability of the surrounding rock of the retracement channel, the instability mechanism of the surrounding rock of the retracement channel was revealed. A mechanical model of the surrounding rock of the retracement channel under the condition of a gradient coal pillar was established, and the energy criterion K for the instability of the surrounding rock was obtained. The method of adding anchor cables to strengthen the support of the surrounding rock of the retracement channel was proposed. The results indicate that the accumulation of energy in the surrounding rock of the retracement channel is greater than the internal consumption of energy, which is the direct reason for the instability of the surrounding rock of the retracement channel. The time to strengthen the support of the roof is when the working face is 15 m away from the retracement channel. According to the analysis of on-site monitoring results, the roof convergence and the two-sides convergence before and after strengthening the support were reduced by 90 mm and 140 mm, respectively. Under the strengthening of support, the slope of the retracement channel in the 360808 working face is slight, without roof fall, and the surrounding rock of the channel is effectively controlled, which is of great significance for ensuring the safe application of the retracement channel. It has reference value for the safety production of surrounding mines and is conducive to promoting the sustainable development of local resource-based society and economy.

Analysis and Design of Protection Device for Anchor Cable Pull-Out in High-Stress Roadways

In regions with high-stress roadway stress, anchor cables frequently experience damage, leading to risky pull-outs and ejections. This study aimed to determine the dynamics of such incidents, refine protective devices, and validate their efficacy in enhancing safety. Drawing from an ejection accident in the 1632 (3) roadway of Pan San Mine, a combination of laboratory experiments, theoretical analysis, simulations, and field applications was utilized. The kinetic energy and speed of cable ejections were determined from single-axis tension test data. Based on these insights, a spring-based protection device was conceptualized. Subsequent experiments and simulations evaluated the energy absorption and deformation characteristics of these devices with different diameters. The results included the following: A cable, during ejection, moved at 48 m/s. Spring protective devices of 4 mm can absorb more energy than the 5 mm, but the anti-ejection effect is poor respectively. Increasing the device diameter improved its performance, especially in controlling spring deformation rate and preventing cable lock-ups. This devised protection mechanism showed promising results when implemented in the 1511 (1) roadway of Zhangji Mine.

Anchorage Performance of Multiple Split Grouting of Prestressed Anchor Cable

Anchorage Performance of Multiple Split Grouting of Prestressed Anchor Cable

Research on the coupled support technology of a composite rock beam-retained roadway roof under close coal seams

IntroductionThe technology of gob-side entry retaining without coal pillars in close (distance) coal seams is still immature, and the roof control and support technology in this case is not perfect.MethodsIn this paper, the coupled support technology of a composite rock beam roof under close coal seams is systematically studied by using theoretical analysis, numerical simulation and field test.ResultsBoth the floor slip calculation results and numerical simulations indicate that the vertical failure depth in the plastic zone of the #8 coal seam has not penetrated the roof of the #9 coal seam after mining, which is consistent with the field electronic imaging results. A theoretical formula for a composite rock beam model anchored by high-prestressed anchor cables was derived, and a formula for the optimal spacing of anchor cables under noncompressive shear failure of the roof was obtained. Identification of the internal stress hazard region of the rock beam provides a basis for determining the locations of vertical support. Through numerical simulation of different support schemes, including roof cutting, arrangement of high-prestressed anchor cables, and setting up of vertical supports, roof cutting was found to effectively reduce the stress of supporting structure and roof pressure. Setting up of vertical supports can reduce the roof convergence by 25.2%, and coupling with anchor cables can reduce the convergence by more than 49.1%. The feasibility of this support scheme was verified through field tests, with a maximum convergence of 99 mm between the roof and floor.DiscussionThis two-way verification approach, in which the damage degree of the roof of a close coal seam is analyzed through multiple means, targeted support plans are proposed, the support mechanisms are explored, and feedback is conducted through field tests, plays a certain guiding role in solving roof control of the gob-side entry retaining under similar geological conditions.

Analysis and treatments of primary support failure in large-span tunnel under a soft-hard interbedded surrounding rock mass

The construction of large-span tunnels inevitably involves traversing uneven strata. Due to the influence of the flatness of the large-span tunnel structure and asymmetric surrounding rock loads, concrete cracking and excessive deformation of steel arches occur frequently. Taking a large-span highway tunnel with uneven rock strata as an example, the mechanical behavior, failure causes, failure mechanisms, and treatment techniques of the tunnel's initial support structure were studied. Firstly, field monitoring and systematic analysis of typical sections revealed that the displacement of tunnels on the soft rock side and the contact pressure between the surrounding rock and the support were significantly greater than on the hard rock side. Then, combined with the field test results, a similar model test was designed based on the tunnel structure performance testing platform developed by the research team to study the deformation and failure modes of conventional initial support systems for large-span tunnels under geological unbalanced pressure. Finally, an innovative technique is proposed to adjust external loads and optimize internal forces of the structure by locally adding long anchor rods or cables, and the treatment effects of various schemes are evaluated and compared. The results show that the initial support system exhibits a state of biased pressure in the presence of weak surrounding rock on one side. The maximum bending moment of the soft rock side spandrel bearing structure, the spandrel and vault on the soft rock side are the most vulnerable positions of the structure. By implementing local long anchor or bolts, the stress distribution within the initial support structure of a large-span tunnel can be effectively enhanced. This method offers significant practical value and flexibility, addressing the issue of initial support failure caused by a soft-hard interbedded surrounding rock mass in large-span tunnels.

Support Optimization of Open TBM Tunneling in Luohe Formation Sandstone by CT Test and Numerical Simulation

As underground engineering extends into the western and deeper regions of China, more and more Luohe Formation sandstone layers will be encountered, which have weak cementation and high water content. It is a significant challenge to apply the open TBM, and the support system is crucial in determining whether TBM can excavate quickly and safely. Therefore, in order to optimize the support scheme, this paper analyzes the pore structure and porosity through CT scanning, the results indicate that the volume percentage of pores ≥34 μm is 2.3% and 1.5%, respectively, the large pore apertures are predominant, the surrounding rock has strong permeability, and there is a high risk of rock burst and roof collapse accidents, hence requiring reinforced support measures. On this basis, numerical simulations were conducted to evaluate the support effectiveness. The results show that replacing the “bolt + mesh” with a “bolt + cable + mesh + steel belt”, and replacing the top three bolts with 7.3 m anchor cables, can better control the deformation and provide sufficient thrust force for the TBM, ensuring excavation speed. After the implementation of this scheme at the Kekegai coal mine in Shaanxi, China, the TBM excavation speed increased by 70%, from the previous 10 m/day to 17 m/d, significantly reducing the project duration and construction costs.

Dynamic properties of micro-NPR material and its controlling effect on surrounding rock mass with impact disturbances

A novel meta steel with negative Poisson’s ratio effect (termed as micro-NPR steel) is developed for rock support in deep underground engineering. It possesses high strength, high ductility, and high energy absorption characteristics. In this paper, static tension and modified dynamic drop hammer tests are performed on this novel material to investigate its mechanical properties first. Then based on this material, a new generation of micro-NPR anchor cable is developed and applied in field tests subjected to blasting dynamic loads. The results of laboratory tests reveal that the ultimate elongation of micro-NPR steel under dynamic impacts is more than 30% and it is over 1.5 times that of Q235; the plastic and total energy absorption of micro-NPR are both significantly higher than that of Q235. Field test indicates the fine controlling effect of micro-NPR anchor cable on surrounding rock mass under dynamic loads. Axial force confirms that micro-NPR cables can distribute and absorb the dynamic energy uniformly around the supported rock when subjected to dynamic disturbance, avoiding local failure induced by excessive stress concentration. The excavation compensation principle and energy-absorbing characteristics are used to explain the support mechanisms. Thus, micro-NPR material and anchor cable can control and prevent dynamic disasters in deep underground engineering effectively.

A novel asymmetric stress unloading technology in two sides of coal roadway in deep mine: A case study

The existing stress unloading technology using dense equal-diameter large drilling usually results in damaging the load-bearing structure of the shallow surrounding rock of the roadway. Therefore, this study, while providing full anchor cable strong anchorage support for the roadway sides, proposes an asymmetric stress unloading technology on the two sides of a coal roadway. Small-diameter holes are directly drilled in the shallow low-stress area, and the large-diameter stress unloading hole (LSUH) is excavated in the deep stress concentration peak area for the right side of the roadway; utilizing the floor rock roadway, by drilling upward through the rock stratum, excavating the LSUH in the deep stress concentration peak area for the left side of the roadway. Full anchor cable reinforcement technology for the shallow surrounding rock of roadway sides forms a thick layer anchorage load-bearing structure, avoiding cracks further development of the shallow coal seam of the roadway side and creating a quality stress environment for the implementation of the LSUH in the deep area of the roadway side. The small drilling and the coal slag discharge of the roadway left side does not pass through the shallow anchorage area of the roadway left side, and the shallow small drilling on the roadway right side is supported reinforcement by the steel pipe, which minimize the impact of hole-manufacturing on the shallow anchorage area to the greatest extent possible. Large-diameter weak structural stress unloading holes are arranged in the deep stress concentration peak area of far away from anchorage area of the roadway side, making the high concentration stress areas around the roadway be transferred to deeper area without affect the stability of the shallow anchorage area, also making the plastic deformation of the surrounding rock in the stress concentration area of the roadway side be transferred to the weak structural area of the stress unloading holes. A numerical model for the asymmetric stress unloading technology on the two sides of a coal roadway is established to investigate the influence of different stress unloading parameters on the roadway side stress. Engineering practice shows that this technology can ensure the long-term stability of the roadway.

Analysis of Maximum Economic Length of Soil Nail for Slope Stability

Slope stability is of utmost importance in geotechnical engineering, necessitating effective reinforcement methods to mitigate failures. This study examined the advantages, limitations, and overall suitability of soil nails and cable anchors in stabilizing slopes. Numerical modeling and analysis were performed using the Rocscience Slide2 program. The study analyzed soil nails and cable anchors for slopes of 10 m to 60 m height, slope angle from 35° to 90°, and friction angle from 27° to 36°. The findings reveal that the maximum economic length of soil nails decreases as slip surface depth, slope height, and slope angle increase. Additionally, the friction angle of the soil has a negligible effect on the maximum economic length of the soil nail.

Simulations of Deformation Failure Process and Refinement of Reinforcement Scheme in the Dabenliu Quarry Slope Using Discontinuous Deformation Analysis

For this study, the geological engineering features and possible failure modes of the Dabenliu quarry slope in the Jinping-I Hydropower Station were qualitatively analyzed before a method for setting viscous boundary and an algorithm for modeling pre-stressed cables were embedded into a DDA (Discontinuous Deformation Analysis) computer code to analyze the deformation of the slope under seismic loading. Our simulation results revealed that the middle and upper parts of the slope slipped along the bedding joints (interlayer shear zones) and that the lower part buckled and collapsed after the slope was excavated. This is a typical slipping–buckling failure mode characterized by upper-slipping followed by lower-buckling. Based on the distribution of the simulated internal force of the anchor cables, the reinforcement scheme was adjusted by strengthening the support for the middle and lower parts of the slope, whereas the length and pre-stress of the anchor cables were reduced for the upper part of the slope. The adjusted reinforcement scheme can ensure the stability of the slope under the action of a magnitude 7 earthquake, and the slope may lose stability with no evident collapse under the action of a magnitude 8 earthquake. Finally, the simulation results were verified via a comparison with the monitoring data regarding the slope.

SANACIJA NESTABILNE KOSINE TOKOM IZGRADNJE VIJADUKTA UVAČ 4 NA DIONICI AUTOPUTU SMOKOVAC – MATEŠEVO U CRNOJ GORI

The rock slide that occurred in Montenegro in May 2019, damaged the support of the Uvač 4 highway viaduct under construction. The rock sliding happened in the mountain section, where the terrain is composed of tectonically crushed flysch sediments represented by sandstones, marlstones, and siltstones. Initially, deformations appeared on the ground with the formation of a 90m long scar, that after four weeks the movement of the L2O1 support of the Uvac 4 viaduct by more than 40 cm was registered. Additional geological investigation works were carried out and the sliding plane was registered with inclinometer measurements at a depth of 18m. Rehabilitation works included the formation of the new deep foundation supporting structures and securing the slope with cable anchors. The paper analyzed the values of flysch sediment shear parameters given in the rehabilitation project, as well as the adopted rock mass disturbance factor. The assessment is that the main reason for sliding terrain is caused by stress relief.

Influence of advanced engineering measures on displacement and stress field of surrounding rock in tunnels crossing active strike-slip faults

Based on significant improvements in engineering materials, three advanced engineering measures have been proposed—super anchor cables, high-strength concrete anti-fault caverns, and grouting modification using high-strength concrete-to resist fault dislocation in the surrounding rock near tunnels crossing active strike-slip faults. Moreover, single- or multiple-joint advanced engineering measures form the local rock mass-anti-fault (LRAF) method. A numerical method was used to investigate the influence of LRAF methods on the stress and displacement fields of the surrounding rock, and the anti-fault effect was evaluated. Finally, the mechanism of action of the anchor cable was verified using a three-dimensional numerical model. The numerical results indicated that the anchor cable and grouting modification reduced the displacement gradient of the local surrounding rock near the tunnels crossing fault. Furthermore, anchor cable and grouting modifications changed the stress field of the rock mass in the modified area. The tensile stress field of the rock mass in the modified anchor cable area was converted into a compressive stress field. The stress field in the modified grouting area changed from shear stress in the fault slip direction to tensile stress in the axial tunnel direction. The anti-fault cavern resisted the dislocation displacement and reduced the maximum dislocation magnitude, displacement gradient, and shear stress. Among the three advanced engineering measures, the anchor cable was the core of the three advanced engineering measures. An anchor cable, combined with other LRAF measures, can form an artificial safety island at the cross-fault position of the rock mass to protect the tunnel. The research results provide a new supporting idea for the surrounding rock of tunnels crossing active strike-slip faults.

Dynamic responses and evolution characteristics of bedrock and overburden layer slope with space anchor cable anti-slide piles based on large-scale shaking table test

The study focuses on the anti-slide pile structure with space anchor cable, designing and conducting the large-scale shaking table test of bedrock and overburden layer slope with space anchor cable anti-slide pile system. The dynamic characteristics of bedrock and overburden layer slope with space anchor cable anti-slide piles are systematically explored from aspects of the overall acceleration field of the slope, the interface between overburden layer and bedrock, and the different depths of overburden layer. The results show that in the design of anti-slide pile with space anchor cable, the strength of the bedrock is utilized to resist the sliding force generated by the overburden layer in order to give full play to the role of the strength of bedrock in slope safety protection. The surface of the overburden layer appears a concentrated area of acceleration amplification and as the increase of ground motion intensity, and the concentrated area gradually shifts from the trailing edge of slope to the anchor head segment of anti-slide pile. Under accelerations in different peaks, the peak accelerations in the direction of free face and vertical direction have the asymptotic amplification effect, and the former is stronger. With the increase of ground motion intensity, the peak acceleration magnification decreases exponentially in direction of free face, while the peak acceleration magnification in the vertical direction presents a wavy distribution that first increases and then decreases.

Grouting anchor cable active advanced support technology for mining roadways

Because of the deficiencies in safety and economy of the single hydraulic prop passive advanced support, the grouting anchor cable active advanced support technology is proposed with the Changping Coal Mine 53,081 roadway as the engineering background. By using a combination of theoretical analysis, laboratory tests, numerical simulation, and field tests, the influence of different grouting parameters on the diffusion law of grout is studied. Considering the effect of the stress field on grout migration, a grout seepage-stress coupling model is established. Grouting material ratio tests are carried out and grout parameters are tested. The grouting part of the advanced grouting anchor cable is modeled and solved using the COMSOL Multiphysics numerical software. The results show that the grouting material selected is Portland cement 42.5 and water glass double liquid grout, with a slurry ratio of 15% ACZ-1 type additive and 4% water glass content, and a water–cement ratio of 0.6. The grouting pressure for the 53,081 roadway grouting anchor cable advanced support is 5 MPa, the grouting time is 6 min, and the grouting anchor cable spacing is 2000 mm × 1000 mm. The engineering application shows that the maximum roof subsidence is 180 mm, the maximum separation value at a depth of 9 m is 24 mm, and the maximum separation value at a depth of 3 m is 90 mm. The research results have achieved effective advanced support for the 53,081 roadway, replacing the single hydraulic prop, and provided a theoretical basis for the subsequent design of advanced support parameters for mining roadways.

Service life prediction of prestressed anchor cable exposed to a dry-wet cycling corrosion environment

The life of anchor cable will be shortened by corrosion in complex engineering environment, however at present there is no quantitative method available for predicting the service life of a prestressed anchor cable. Considering the key factor (dry-wet cycles) that causes the corrosion of anchor cables in an actual project, indoor dry-wet cycling corrosion test equipment and the electrolytic corrosion test device were developed in this work. Pseudo-environmental corrosion tests of the cables were performed. The variation of cable corrosion weight loss ratio with the number of dry wet cycles was revealed through the dry-wet cycling test, and based on this, a model for calculating the corrosion weight loss ratio was built. In addition, the change of the anchor force and breaking strength of the anchor cable with corrosion weight loss ratio was investigated through electrolytic corrosion tests and based on the findings an anchor force loss model and a breaking strength attenuation model were developed. On this basis, a life prediction method of anchor cable was established. The verification results of two engineering examples with anchor cable breakage show that the prediction life of this method is highly consistent with the actual life of the anchor cable, with a difference less than 1 year.

A Study of Anchor Cable and C-Shaped Tube Support for the Roadway of Shuangliu Coal Mine

Active support using highly prestressed cable bolts and anchor cables has become a mainstream support technology for coal mine roadways. However, the ability of bolts and anchor cables to withstand transverse shear decreases with the prestress level, jeopardizing mining safety. This study proposed a technical solution to this problem featuring anchor cables enclosed in an axisymmetrical tube with a C-shaped cross-section (ACC), which are highly prestressed and can withstand high transverse shear. The ACC mechanical performance was tested in the #318 gas extraction roadway of the Shuangliu Coal Mine, China, characterized by extensive deformation under original support conditions. Theoretical analysis, laboratory tests, numerical simulation, and field tests were performed to analyze the shear mechanical properties of the ACC and anchor cables alone. The double shear test results revealed that the proposed ACC scheme increased the transverse shear resistance and stiffness by 10–25% and 20–40%, respectively. The FLAC3D numerical simulation showed that the roof-and-floor and rib-to-rib convergences decreased by 9.53 and 25.11%, respectively. The area of the stress concentration zone also decreased. Field monitoring showed that the ACC achieved good support performance. During the monitoring period, the maximum roof-and-floor and rib-to-rib displacements were 40 and 49 mm, respectively. The ACC scheme offered adequate shear resistance and effectively controlled surrounding rock deformation in the gas extraction roadway under study, making it applicable to similar engineering scenarios.

Energy balance support method in soft rock tunnel with energy absorbing anchor cable

Deformation and failure phenomena in rock mass after excavation can be described from the energy perspective, i.e. the work done by external forces increases the energy, thereby exceeding the energy storage limit of rock mass, resulting in the release of residual energy. Currently, energy-absorbing anchor supports have been used for stability control of surrounding rocks to avoid engineering failure by large deformations of soft rocks. However, the design of energy-absorbing anchor support still depends on field experience and engineering tests. In particular, under the influence of structural plane, the characteristics of energy transfer of surrounding rock with energy-absorbing anchorage are still unclear. In this paper, a design method of energy anchorage considering the influence of structural plane based on the theory of energy balance is proposed, which is corroborated by numerical simulation, similar simulation, and engineering application. The study demonstrates that under the effect of ground stresses, the arch support alone cannot absorb the deformation energy produced by the surrounding rock, leading to a significant region of the plastic zone and deformation instability. Under the control of ordinary anchor cable, the deformation of surrounding rock and the extension of the plastic zone are further alleviated; however, some anchor cable tensile fractures still occur. The energy-absorbing anchor cable scheme is created following the energy balancing concept. The surrounding rock deformation is maintained in an ideal range, while the plastic zone area is substantially reduced. The final engineering application also validates the accuracy of the energy-absorption anchorage design based on the energy balance theory, which provides a theoretical and practical basis for the application in similar projects.

Global analysis approach of stability of deep foundation pit slopes reinforced by underground diaphragm walls and prestressed anchor cables

The stability evaluation of deep foundation pit slopes is crucial, including the solution of the factor of safety and the location of the critical slip surface. Prestressed anchor cables and underground diaphragm walls are commonly used to reinforce pit slopes. By means of the dimensional increase technique and the global analysis approach of slope stability, a nonlinear optimization problem is defined for the stability analysis of pit slopes. In the optimization problem, the ordinates of discrete points on the slip surface and the factor of safety are both the decision variables, the objective function is the factor of security, and the constraints are the equilibrium equations and the convexity of the slip surface. Because the objective function is linear and the constraint functions are polynomials of degree three at most, the optimization problem is a classical optimization one that conventional optimization techniques can solve without recourse to modern optimization techniques such as the AI technique. Examples suggest that the proposed procedure is far more efficient and stable than the optimization models based on the methods of slides. At last, applications are demonstrated to ongoing deep foundation pit slopes situated at Tong Zhou – Beijing sub-center.