Location Of Critical Slip Surface Research Articles

Stability analysis of heterogeneous infinite slopes under rainfall-infiltration by means of an improved Green–Ampt model

Rainfall infiltration analysis has a great significance to the mitigation and risk assessment of rainfall-induced landslides. The original Green–Ampt (GA) model ignored the fact that a transitional layer exists in infiltration regions of soils under the rainfall permeation; moreover, it cannot effectively analyze the rainfall-infiltrated heterogeneous slope considering the spatial variability of saturated hydraulic conductivity ( ks ). In this study, an improved GA model is proposed for the rainfall-infiltration analysis of heterogeneous slopes. Four common slope cases are investigated to validate the effectiveness of the proposed model. An infinite slope model is taken as an illustrative example to investigate the distributions of volumetric water content and slope stability under the rainfall infiltration. The results show that the distributions of volumetric water content and factor of safety ( Fs) obtained from the proposed model are in very good agreement with the numerical results of the Richards' equation. In contrast, the modified GA model obtains biased distributions of volumetric water content and smaller Fs for the same cases. The results show that the proposed GA model can accurately identify the location of critical slip surface of the slope, and as such it provides an efficient method for risk analysis and control of slopes susceptible to landslide.

A new perspective on determination of the critical slip surface of three-dimensional slopes

In the traditional slope stability analysis, the shape and location of critical slip surface (CSS) are identified by an objective function with the minimum safety factor (SF). However, the method cannot identify the true CSS when the minimum SFs of different critical slip surfaces are equal or extremely close. In order to solve the issue, the idea of slip surface with the maximum sliding direction (SD) as the CSS is proposed in this paper. The shape of CSS is regarded as a rotational ellipsoid with 6 parameters, and the genetic algorithm (GA) is adopted to search for the location of CSS. The three-dimensional (3D) slope stability analysis is performed based on the minimum potential energy principle, which provides an analytical formulation of SD as well as SF without iteration. Two benchmark slopes and a practical engineering case are employed to verify the rationality of the proposed method. The parametric analysis reveals that the larger SD the smaller SF. The developed method is a useful technique support for determining the CSS and the shape of 3D slope.

Evaluation of 3D slope stability based on the minimum potential energy principle

Based on the minimum potential energy principle, a novel method is proposed to determine the global sliding direction (GSD), the critical slip surface and the corresponding safety factor (SF) of three-dimensional (3D) slopes with arbitrary-shaped slip surface. The resistance direction at one point on the failure surface is determined based on the relationship between the mobilized shear strength and the virtual displacement which minimizes the total potential energy of failure mass system. The GSD is considered to be the opposite to the composition of resistance on failure surface. Meanwhile, the critical slip surface of 3D slope is generated by two random curves with 8 parameters. Three benchmark slopes and a slope from practice engineering are analyzed to test the validity and accuracy of the present model. The results from the developed method match well with the classical solutions, and the obtained SFs demonstrate that some factors (e.g., local surcharge, composite failure surface, slope geometry and so on) can cause slope instability and failure. The location of critical slip surface and the SF provided by the present method are in good agreement with other solutions. Finally, the influence of failure body volume, shear strength parameters, unit weight, slope angle, surcharge and slope height on the GSD is revealed. This study provides a useful guideline for landslide prediction and reinforcement management in slope engineering.

Critical slip surface and landslide volume of a soil slope under random earthquake ground motions

Finding the critical slip surface and estimating the landslide volume are of primary importance for slope seismic design. However, this may be difficult due to the uncertainty of ground motions. To address this problem, a new method for calculating uncertainties is recommended in this paper, especially for the critical slip surface and landslide volume under random earthquake ground motions. Firstly, a series of intensity–frequency nonstationary random earthquake ground motions were generated based on an improved orthogonal expansion method. A given number of potential slip surfaces were set in a soil slope. Subsequently, the factor of safety (FOS) of each slip surface for all ground motions was calculated and the minimum FOS curves were obtained. It was found that the critical slip surfaces and failure times are uncertain under different earthquakes. The Monte Carlo method was used to verify the accuracy of probability density evolution method (PDEM), and the results of the PDEM and the Monte Carlo method are consistent, meaning that the PEDM has higher computational efficiency. Moreover, the distributions of earthquake-triggered landslide volume and landslide depth were analyzed by considering equivalent extreme events. Both landslide volume and depth exhibit a normal distribution for a homogeneous soil slope. The framework of this study is meaningful for slope seismic design in engineering, for example, the location of critical slip surface can be used for slope reinforcement, and the distribution of sliding volume can be used for disaster assessment.

Seismic Evaluation of Existing Earth-Cored Fill Dams based on Pseudostatic and FE-Newmark Approaches

등가정적해석은 댐의 지진 시 사면 안정성을 평가하기 위한 방법으로 여전히 널리 사용되고 있는 기법이다. 2011년 개정 댐설계기준에 의하면 등가정적 지진계수값은 설계 PGA의 약 70% 수준을 채택하고 있으며, 허용 안전율은 1.2를 취하고 있다. 그러나 댐의 성능을 지배하는 것은 영구 변형량이라 할 수 있다. 본 연구에서는 국내의 기존 21개 중심코어형 필댐에 대하여 개정 기준을 적용한 내진성능평가를 수행하였다. 등가정적해석과 유한요소법 및 Newmark 변형해석을 수행하여 등가정적 지진계수와 허용 안전율의 타당성에 대해 검토하였다. 해석을 위해서 등가정적 한계평형해석과 더불어 정상침투 해석, 등가선형 지진동 해석 및 Newmark 변형 해석을 차례로 적용하였으며, 최신 물리탐사 기술을 적용한 전단파속도 주상도를 구하여 현장의 동적물성을 반영한 평가를 수행하였다. 연구 결과, 현재의 등가정적 지진계수와 허용 안전율 채택 기준은 대단히 보수적인 것으로 판단되었으며 향후 기준 개정시 이에 대한 고려가 필요할 것으로 검토되었다. 유한요소 및 Newmark 변형해석 결과, 기존 필댐들은 상향된 내진성능을 모두 만족하였으며, 추가적인 민감도 해석을 통해 지진파의 증폭 양상, 임계 활동면의 위치, 쉘존의 내부마찰각 등이 영구 변형량에 지배적인 영향 인자로 판명되었다. The pseudostatic approach is still in widespread use in industry to evaluate seismic slope stability of dams. According to the revised seismic design guideline of dams in Korea (2011), the pseudostatic seismic coefficient for dams is defined as about 70% of design PGA, and an allowable factor of safety (FS) is taken as 1.2. However, in terms of serviceability, permanent deformation matters rather than the FS. In this study, the seismic safety of 21 existing earth-cored fill dams in Korea was re-evaluated using updated design criteria. Accordingly the suitability of pseudostatic coefficient and allowable FS was studied. A systematic procedure was applied in a row of pseudostatic limit equilibrium analyses, steady state FE (finite element) seepage analyses, equivalent-linear dynamic response analyses, and Newmark type deformation analyses. In order to reflect in-situ dynamic soil properties as input parameters, innovative in-situ shear wave velocity profiles were adopted using up-to-date geophysical surveys. A comparison between pseudostatic limit equilibrium and FE-Newmark deformation analyses yielded that for a pseudostatic method with horizontal seismic coefficient of 70% design PGA and the allowable FS of 1.2 were found to be significantly conservative, which is believed to be considered in the revision of design guideline in the future. As a result of FE-Newmark type analyses, existing earth-cored fill dams showed a reasonably satisfactory performance under the updated design PGA. Additional sensitivity analyses showed that the amplification of ground motion within the sliding mass, the location of critical slip surface, and the internal friction angle of shell materials are the dominant factors governing permanent displacements.

Stability analysis of sandy slope considering anisotropy effect in friction angle

This paper aims to investigate the effect of anisotropy of shear strength parameter on the stability of a sandy slope by performing the limit equilibrium analysis. Because of scarcity of mathematical equation for anisotropic friction angle of sand, at first, all results of principal stress rotation tests are processed by artificial neural network and a computational procedure is developed for determining sand friction angle subjected to various loading directions. By implementing this procedure, slope stability analysis is performed in both isotropic and anisotropic conditions. The results indicate that while isotropic slope stability overestimates the factor of safety between 5 and 25% which the deviation is more for flatter slope, the location of critical slip surface is coincident in both conditions. Also in specific slip surface, the parameters of face angle, geometry of slip surface and soil properties relating to anisotropy are the main factors governing the result of anisotropic slope stability.

Newmark 기반 변형해석에 의한 필댐의 내진저항성 연구

Newmark-type deformation analysis has rarely been done in Korea due to the popularity of simple pseudo-static limit equilibrium analysis and detailed time-history FE/FD dynamic analysis. However, the Korean seismic dam design code updated in 2011 prescribes Newmark-type deformation analysis as a major dynamic analysis method for the seismic evaluation of fill dams. In addition, a design PGA for dynamic analysis is significantly increased in the code. This paper aims to study the seismic evaluation of four existing large fill dams through advanced FEM/Newmark-type deformation analyses for the artificial earthquake time histories with the design PGA of 0.22g. Dynamic soil properties obtained from in-situ geo-physical surveys are applied as input parameters. For the FEM/Newmark analyses, sensitivity analyses are performed to study the effects of input PGA and <TEX>$G_{max}$</TEX> of shell zone on the Newmark deformation. As a result, in terms of deformation, four fill dams are proved to be reasonably safe under the PGA of 0.22g with yield coefficients of 0.136 to 0.187, which are highly resistant for extreme events. Sensitivity analysis as a function of PGA shows that <TEX>$PGA_{30cm}$</TEX> (a limiting PGA to cause the 30 cm of Newmark permanent displacement on the critical slip surface) is a good indicator for seismic safety check. CFRD shows a higher seismic resistance than ECRD. Another sensitivity analysis shows that <TEX>$G_{max}$</TEX> per depth does not significantly affect the site response characteristics, however lower <TEX>$G_{max}$</TEX> profile causes larger Newmark deformation. Through this study, it is proved that the amplification of ground motion within the sliding mass and the location of critical slip surface are the dominant factors governing permanent displacements.

Rigorous back analysis of shear strength parameters of landslide slip

A rigorous back analysis of shear strength parameters of landslide slip was presented. Kinematical element method was adopted to determine factor of safety and critical failure surface, which overcomes the disadvantage of limit equilibrium method. The theoretical relationship between the combination of shear strength parameters and stability state was studied. The results show that the location of critical slip surface, F/tan ϕ and F/c depend only on the value of c/tan ϕ. The failure surface moves towards the inside of slope as c/tan ϕ increases. According to the information involving factor of safety and critical failure surface in a specific cross-section, strength parameters can be back calculated based on the above findings. Three examples were given for demonstrating the validity of the present method. The shear strength parameters obtained by back analysis are almost consistent with their correct solutions or test results.

Slope seismic stability analysis on kinematical element method and its application

In this paper, kinematical element method (KEM) is extended to the solution of seismic slope stability with the pseudo-static approach. Analytical expressions are derived to calculate the factor of safety of slopes subjected to seismic loading and pore-water pressure. KEM is adopted to assess seismic stability of slope and some examples show that the results obtained from KEM, limit equilibrium method (LEM), variational method and strength reduction method (SRM) are generally in good agreement. And then the seismic slope stability charts are developed on the basis of KEM and pseudo-static approach, providing a rapid and reliable way to calculate the factor of safety and the location of critical slip surface without iteration. Based on the above seismic slope stability charts, a new back analysis method is presented. KEM and pseudo-static approach are applied to study the effect of blasting on the stability of open pit slope, and the approach to determine the relationship between critical explosive weight and distance is presented.

Influence of Anisotropic Internal Friction Angle on the Stability of Uniform Soil Slopes

The effect of anisotropy of friction angle in natural deposited soil on the stability of soil slopes was studied in this paper. Stability analysis was performed on a uniform soil slope with anisotropic friction angle. Spencer’s method was used, and the variation of friction angle was assumed to be linear to the change of direction of the slip surface. It was shown that 7-10 percent of change in safety factor might achieve within a 10m-highed anisotropic soil slope. It was also found from the analysis that that frictional anisotropy had no obvious effect on the location of critical slip surface.

An improved particle swarm optimization algorithm with harmony strategy for the location of critical slip surface of slopes

The determination of optimal values for three parameters required in the original particle swarm optimization algorithm is very difficult. It is proposed that two new parameters simulating the harmony search strategy can be adopted instead of the three parameters which are required in the original particle swarm optimization algorithm to update the positions of all the particles. The improved particle swarm optimization is used in the location of the critical slip surface of soil slope, and it is found that the improved particle swarm optimization algorithm is insensitive to the two parameters while the original particle swarm optimization algorithm can be sensitive to its three parameters.

Effects Analysis of Expansive Soil Slope Reinforced with Geogrid Considering Long Term Weathering

Considering the long-term atmospheric weathering effects on expansive soil strength, geogrid reinforcement effects of expansive soil slope are analyzed with FLAC3D. The research in this paper shows that: (1) when the reinforcement is deeper than the weathered layer, the inhibition effect of soil stress and displacement increases with increasing length of geogrid, in this case a critical slip arc moves away from the slope surface, and the maximum safety factor of slope stability increases approximately 50 percent; the grid stress decreases with the increasing height of grid location; (2) when the reinforcement depth exceeds the weathered layer 1 m, the denser geogrid in the vertical direction, the smaller shear stress and horizontal deformation in reinforced region, so that the slope safety factor increase and the critical slip arc moves towards the slope back. However,if the geogrid length exceeds the weathered layer more than 3 m, the vertical grid distance change has no significant influence on the safety factor and the location of critical slip surface.

Performance studies on six heuristic global optimization methods in the location of critical slip surface

Recently, many heuristic global optimization algorithms have evolved with success for treating various types of problems. Majority of these algorithms have not been applied to slope stability problem for which the presence of soft band and convergence problem (discontinuity of the objective function) may create difficulties in the minimization process. In this paper, six heuristic optimization algorithms are applied to some simple and complicated slopes. The effectiveness and efficiency of these algorithms under different cases are evaluated, and it is found that no single method can outperform all the other methods under all cases, as different method has different behavior in different types of problems. For normal cases, the particle swarm method appears to be effective and efficient over various conditions, and this method is recommended to be used. For special cases where the objective function is highly discontinuous, the simulated annealing method appears to be a more stable solution.

Geosynthetic Reinforced Slopes: Limit Equilibrium and Finite Element Analyses

ABSTRACT This note presents a comparative study of geosynthetic reinforced slope analyses. The comparison is between predictions of a finite element (FE) method and a limit equilibrium (LE) method. The comparisons are limited to the potential failure surface and the maximum tensile force developed in the geosynthetic reinforcement layers. These two items signify the design output in the LE analysis of geosynthetic reinforced slopes. The agreement between EE and LE methods is found to be reasonably good in terms of both location of critical slip surfaces and required strength of reinforcement.

Location of critical slip surfaces in slope-stability problems: Thompson, R J J S Afr Inst Min MetallV93, N4, April 1993, P85–95

Location of critical slip surfaces in slope-stability problems: Thompson, R J J S Afr Inst Min MetallV93, N4, April 1993, P85–95

Location of critical slip surfaces in coal mine spoil piles : Williams, D J; Zou, J Z Proc 6th Australia-New Zealand Conference on Geomechanics, Christchurch, 3–7 February 1992P468–473 Publ New Zealand: New Zealand Geomechanics Society, 1992

Location of critical slip surfaces in coal mine spoil piles : Williams, D J; Zou, J Z Proc 6th Australia-New Zealand Conference on Geomechanics, Christchurch, 3–7 February 1992P468–473 Publ New Zealand: New Zealand Geomechanics Society, 1992

Applications of the technique of rational approximation in geotechnical analysis

Rational approximation is a numerical technique which involves the interpolation of a function by a rational polynomial. Although the technique has been developed for a long time, it is seldom used in geotechnical analysis. This paper explores applications of rational approximation in geotechnical analysis. Examples are presented to demonstrate use of rational approximation in geotechnical reliability analysis, calculation of factor of safety and location of critical slip surface. The results clearly illustrate the efficiency and accuracy of the numerical technique.