Failure evaluation and control factor analysis of slope block instability along traffic corridor in Southeastern Tibet

The instability of slope blocks occurred frequently along traffic corridor in Southeastern Tibet(TCST),which was primarily controlled by the rock mass structures.A rapid method evaluating the control effects of rock mass structures was proposed through field statistics of the slopes and rock mass structures along TCST,which combined the stereographic projection method,modified M-JCS model,and limit equilibrium theory.The instabilities of slope blocks along TCST were then evaluated rapidly,and the different control factors of instability were analyzed.Results showed that the probabilities of toppling(5.31%),planar(16.15%),and wedge(35.37%)failure of slope blocks along TCST increased sequentially.These instability modes were respectively controlled by the anti-dip joint,the joint parallel to slope surface with a dip angle smaller than the slope angle(singlejoint),and two groups of joints inclined out of the slope(double-joints).Regarding the control effects on slope block instability,the stabilization ability of doublejoints(72.7%),anti-dip joint(67.4%),and single-joint(57.6%)decreased sequentially,resulting in different probabilities of slope block instability.Additionally,nearby regional faults significantly influenced the joints,leading to spatial heterogeneity and segmental clustering in the stabilization ability provided by joints to the slope blocks.Consequently,the stability of slope blocks gradually weakened as they approached the fault zones.This paper can provide guidance and assistance for investigating the development characteristics of rock mass structures and the stability of slope blocks.

Application of cusp catastrophe theory to reliability analysis of slopes in open-pit mines

A method of slope reliability analysis was developed by imposing a state equation on the limit equilibrium theory, given the basis of a fixed safety factor technique. Among the many problems of reliability analysis, the most important problem is to find a performance function. We have created a new method of building a limit state equation for planar slip surfaces by applying the mathematical cusp catastrophe theory. This new technique overcomes the defects in the traditional rigid limit equilibrium theory and offers a new way for studying the reliability problem of planar slip surfaces. Consequently, we applied the technique to a case of an open-pit mine and compared our results with that of the traditional approach. From the results we conclude that both methods are essentially consistent, but the reliability index calculated by the traditional model is lower than that from the catastrophic model. The catastrophe model takes into consideration two possible situations of a slope being in the limit equilibrium condition, i.e., it may or may not slip. In the traditional method, however, a slope is definitely considered as slipping when it meets the condition of a limit equilibrium. We conclude that the catastrophe model has more actual and instructive importance compared to the traditional model.

Investigation on long-term progressive deformation of engineering slope based on comprehensive monitoring

A landslide always results from a progressive process of slope deformation. In recent years, an increasing number of slope instabilities have occurred with regard to human engineering activities such as hydropower or traffic construction in mountainous area, which cause even greater casualties and economic loss compared with the natural hazards. The development of such earth surface process may hold long period with mechanisms still not fully understood. Using monitoring technology is an effective and intuitive approach to assist analyzing the slope deformation process and their driving factors. This study presents an engineering slope excavated during the construction of Changheba Hydropower Station, which is located in the upper reaches of Dadu River, Sichuan Province, southwest China. The engineering slope experienced and featured a five-year continuous deformation which caused continuous high risks to the engineering activities. We conducted in-depth analysis for such a long-term deformation process based on ground and subsurface monitoring data, collected successive data with a series of monitoring equipment such as automated total station, borehole inclinometers and other auxiliary apparatus, and identified the deformation process based on the comprehensive analysis of monitoring data as well as field investigation. After analyzing the effects of engineering activities and natural factors on the continuous deformation, we found that the overburden strata provided deformable mass while the excavation-produced steep terrain initiated the slope deformation in limit equilibrium state over a long period of time;afterwards, the intense rainwater accelerated slope deformation in the rainy season.

Time-variant reliability analysis of three-dimensional slopes based on Support Vector Machine method

In the reliability analysis of slope, the performance functions derived from the most available stability analysis procedures of slopes are usually implicit and cannot be solved by first-order second-moment approach. A new reliability analysis approach was presented based on three-dimensional Morgenstem-Price method to investigate three-dimensional effect of landslide in stability analyses. To obtain the reliability index, Support Vector Machine （SVM） was applied to approximate the performance function. The time-consuming of this approach is only 0.028% of that using Monte-Carlo method at the same computation accuracy. Also, the influence of time effect of shearing strength parameters of slope soils on the long-term reliability of three-dimensional slopes was investigated by this new approach. It is found that the reliability index of the slope would decrease by 52.54% and the failure probability would increase from 0.000 705% to 1.966%. In the end, the impact of variation coefficients of c andfon reliability index of slopes was taken into discussion and the changing trend was observed.

Application of dynamic analysis of strength reduction in the slope engineering under earthquake

At present,the methods of analyzing the stability of slope under earthquake are not accurate and reasonable because of some limitations. Based on the real dynamic tensile-shear failure mechanism of slope,the paper proposes dynamic analysis of strength reduction FEM (finite element method) and takes the reduction of shear strength parameters and tensile strength parameters into consideration. And it comprehensively takes the transfixion of the failure surface,the non-convergence of calculation and mutation of displacement as the criterion of dynamic instability and failure of the slope. The strength reduction factor under limit state is regarded as the dynamic safety factor of the slope under earthquake effect and its advantages are introduced. Finally,the method is applied in the seismic design of anchors supporting and anti-slide pile supporting of the slope. Calculation examples show that the application of dynamic analysis of strength reduction is feasible in the seismic design of slope engineering,which can consider dynamic interaction of supporting structure and rock-soil mass. Owing to its preciseness and great advantages,it is a new method in the seismic design of slope supporting.

New algorithm of mine slope reliability based on limiting state hyper-plane and its engineering application

Due to the influence of joint fissure, mining intensity, designed slope angle, underground water and rainfall, the failure process of mine slope project is extremely complicated. The current safety factor calculation method has certain limitations, and it would be difficult to obtain the reliability index when the performance function of reliability analysis is implicit or has high order terms. Therefore, with the help of the logistic equation of chaos theory, a new algorithm of mine slope reliability based on limiting state hyper-plane is proposed. It is shown that by using this new reliability algorithm the calculation of partial derivative of performance function is avoided, and it has the advantages of being simple and easy to program. The new algorithm is suitable for calculating the reliability index of complex performance function containing high order terms. Furthermore, the limiting state hyper-plane models of both simplified Bishop's and Janbu's method adaptive to slope project are obtained, and have achieved satisfactory effect in the study of mine slope stability in Dexing copper open pit.

Excavation compensation theory and supplementary technology system for large deformation disasters

Given the challenges in managing large deformation disasters in energy engineering,traffic tunnel engineering,and slope engineering,the excavation compensation theory has been proposed for large deformation disasters and the supplementary technology system is developed accordingly.This theory is based on the concept that“all destructive behaviors in tunnel engineering originate from excavation.”This paper summarizes the development of the excavation compensation theory in five aspects:the“theory,”“equipment,”“technology,”the design method with large deformation mechanics,and engineering applications.First,the calculation method for compensation force has been developed based on this theory,and a comprehensive large deformation disaster control theory system is formed.Second,a negative Poisson's ratio anchor cable with high preload,large deformation,and super energy absorption characteristics has been independently developed and applied to large deformation disaster control.An intelligent tunnel monitoring and early warning cloud platform system are established for remote monitoring and early warning system of Newton force in landslide geological hazards.Third,the double gradient advance grouting technology,the two-dimensional blasting technology,and the integrated Newton force monitoring--early warning--control technology are developed for different engineering environments.Finally,some applications of this theory in China's energy,traffic tunnels,landslide,and other field projects have been analyzed,which successfully demonstrates the capability of this theory in large deformation disaster control.

Recent advances in high slope reinforcement in China: Case studies

This paper reviews a number of engineering technologies and workmanships for addressing the challenging issues concerning possible landslides in large-scale slope reinforcement projects in China.It includes:(1) the multi-point anchored piles with a depth of 64 m in the Jietai Temple rehabilitation project,(2) soil nailing strengthened by driven pipe grouting technique covering an area of530 m × 100 m(length × height) in the Xiluodu hydropower project,(3) the cantilever piles extending vertically from the slope toe to stabilize a 300 m high slope at the Xiaowan hydropower station,(4) a new and simple workmanship for building a pile with cross-sectional area of 20 m × 5 m in the Hongjiadu hydropower station,and(5) comprehensive reinforcement scheme proposed for excavation of a 530 m high slope in Jinping I hydropower station.These new technologies can provide valuable experiences for reinforcement of high slopes of similar projects in China and other regions and countries with similar geological conditions.

3D deformation effect and optimal excavated design of surface mine

The three-dimensional （3D） deformation effect of the slope engineering under the step-by-step excavation for the Antaibao surface mine was analyzed using the FLAC^3D technique. An optimal excavated scheme with a relatively steeper slope angle of 47° instead of 30° was successfully implemented at the west wall in the geological section 73200 of the mine area, where the 3D effect of the nonlinear large deformation of the slope was taken into account. Based on the above research conclusion, put forward the countermeasures of shortening mining length, excavating by different regions, timely foot backfilling to protect the excavated slope, and monitoring and feedback adjustment by studying the nonlinear effect. The results show that these countermeasures are effective in controlling maximum deformation and increasing the stability of the slope.

Cut slope reinforcement technique in open-pit mines

The design and practice in supporting the cut slope of an open-pit mine wereintroduced, in which the high pressure grouting method was used in reinforcing the weak formation inthe slopes. Based on a detailed geological survey of the slope, a theoretical analysis was carriedout, and the design parameters were proposed, where the Tresca or Mohr-Coulomb yield criteria wasemployed. A patent technology, named 'Technology of high pressure and multiple grouting in differentlevels within a single hole', was employed in the construction. Anchor bars were also installed asgrouting proceeds. This method combines anchoring and grouting comprehensively and was foundsuccessful in practice.