Potential Slip Surface Research Articles

Study of Excavation Stability and Treatment Measures of the Side Slope of Anti-Dip Bedding Highway

In order to improve the slope safety of the side slope of anti-dip bedding highway, this paper analyzes the stability of the excavation by using the finite difference numerical simulation technique. The development process of the disaster under the three excavation conditions and the whole process of the slip surface of the anti dip bedding rock slope are revealed; The method of determining the potential slip surface is introduced, that is to say, the slope is unstable and slip by reducing the material parameters of the slope, and then the position of the slip surface is judged by the difference of the displacement value. The research results have important significance for understanding the development mechanism of slope disaster and adopting corresponding engineering measures for different stages of slope.

INFLUENCE OF DISTANCE BETWEEN A RETAINING WALL AND THE EXISTING BUILDING ON STRESS-STRAIN STATE OF THE SYSTEM «RETAINING STRUCTURES – SOIL MASSIF»

The results of work research of engineering protective structures in a densely built–up area with difficult engineering–geological conditions have been presented. The modeling of the geotechnical problem of deep excavation protection using a three-tier retaining wall has been performed. The task of mutual influence of existing building and deep excavation with the change of distance between them is solved. The grafs of displacement’s dependence several tiers of retaining walls from the distance to an existing building have been presented. According to these data, a plot of the dependence of displacements of separate tiers of retaining walls from the distance to an existing building is constructed. The problem is solved by the finite element method using a nonlinear model of a solid soil environment. The character of the formation of zones of potential slip surface slope is revealed. The dependence of bending moments of the retaining walls from the distance to the existing building is shown. A safe location of an existing building to a deep excavation has been substinated.

Field Testing of Earth Pressures in a Large-scale Natural Loess Slope

An in-situ large-scale earth pressure test was undertaken in a natural loess slope in Lanzhou, China. A 14.5-m-high natural slope was gradually cut into a vertical slope through a series of eight slope cutting work conditions. By pre-installing re-bar meters and cutting slope unloading, the real earth pressure distribution law and potential slip surface development mechanism, along with the variation of the Slope Cutting Depth (SCD), were obtained under the condition that each point in the free surface can move independently and freely. Earth pressure increases slowly at first and then decreases sharply along the Slope Excavating Depth (SED). The increase rate for 9.0 to 10.4 m is 3 to 4 times as much as the former conditions, so the self-stability height of the slope is 9.0 to 10.4 m. The unsaturated natural loess shear outlet of the slope is always located at the H/3 (where H is the natural slope height) position, so the slip surface does not pass through the bottom of the slope. The measured values of unsaturated vertical slope earth pressures are far less than the values calculated by Rankine’s earth pressure theory–especially the size and position of the maximum earth pressure.

Identification of representative slip surfaces for reliability analysis of soil slopes based on shear strength reduction

Although a slope may have numerous potential slip surfaces, its failure probability is often governed by several representative slip surfaces (RSSs). Previous efforts mainly focus on the identification of circular RSSs based on limit equilibrium methods. In this paper, a method is suggested to identify RSSs of arbitrary shape based on the shear strength reduction method. Monte Carlo simulation is used to generate a large number potential slip surfaces. The RSSs are identified through analyzing the failure domains represented by these samples. A kriging-based response surface model is employed to enhance the computational efficiency. These examples shows that the RSSs may not always be circular, and that the suggested method can effectively locate the RSSs without making prior assumptions about the shape of the slip surfaces. For the examples investigated, the system failure probabilities computed based on the shear strength reduction method are comparable to, but not the same as those computed based on the limit equilibrium methods. The suggested method significantly extends our capability for identifying non-circular RSSs and hence probabilistic slope stability analysis involving non-circular slip surfaces.

Shear strength behavior in the interface of contaminated soil with bio-diesel oil and geosynthetics

Abstract This article aims to present the shear strength of soil-geosynthetic interface through laboratory tests. Shear strength of a soil-geosynthetic interface is defined as the primary parameter of slope stability in cases where the potential slip surface runs along a geosynthetic. Besides, palm biodiesel contamination can affect the geotechnical properties of foundation soils. In this study, interface interaction between soil and various geosynthetics, namely A, B, and C was investigated in term of shear strength parameters. The type of palm oil used for contaminating is B20 palm biodiesel ranging from 3% to 10% by the weight of dry sand. The objective of this research is to assess the shear strength parameters at the soil-geosynthetic interface. For this purpose, test specimens of both clean and contaminated sample with different geosynthetics were tested under direct shear test in order to evaluate their shear strength. Results were analyzed based on the behavior of three different geosynthetics as reinforcements and contaminated mining sand. The results of direct shear tests indicate that shear strength varies considerably along the soil-geosynthetic interface. It was found that the shear strength of reinforced sand with geosynthetic C was increased by almost 1.3 times as compared to that of the unreinforced test specimen. A notable discovery is that the reinforced sand with geosynthetic C could improve the shear strength of the soil sample to protect the slopes, particularly shallow foundations on mining sand. However, further laboratory and field investigations are recommended.

Failure characteristics of gently inclined shallow landslides in Nanjiang, southwest of China

Large number of rain-induced landslides occurred on 16 September 2011 in Nanjiang, southwest of China. The typical depth of failure surface was from 1 to 5m at the gently inclined interface between the superficial red silty clay and bedrock. In order to explain the failure characteristics of these shallow landslides, we conducted a rainfall infiltration simulation test, calculated rainfall infiltration depth using modified Green-Ampt (G-A) infiltration model as well as considered the atmospheric effects on the slope failures. Results show that the permeability of red clay is extremely low and the rainfall infiltration depth is limited to around 0.5m during a rainstorm. The rainfall infiltration capacity can be enhanced within the depth of atmospheric influence, which is determined as 5.4m in the study area. With the increase of soil depth and the lower degree of weathering, the void ratio and permeability are gradually reduced; thus, the rainfall infiltration continues following a decreasing trend until the bedrock is reached. Within the shallow landslides in the study area, under the condition of rainfall, the slope can keep in a stable state when the depth of wetting front is less than the thickness of soil layer. When the wetting front proceeds to the interface between the silty clay and bedrock, the potential slip surface can develop on such soil-bedrock interface, in relation to the increased pore water pressure and ground water level. Consequently, shallow failures will occur along the soil-bedrock interface in a depth of 1–5m.

Full probabilistic design of slopes in spatially variable soils using simplified reliability analysis method

ABSTRACTA simplified reliability analysis method is proposed for efficient full probabilistic design of soil slopes in spatially variable soils. The soil slope is viewed as a series system comprised of numerous potential slip surfaces and the spatial variability of soil properties is modelled by the spatial averaging technique along potential slip surfaces. The proposed approach not only provides sufficiently accurate reliability estimates of slope stability, but also significantly improves the computational efficiency of soil slope design in comparison with simulation-based full probabilistic design. It is found that the spatial variability has considerable effects on the optimal slope design.

Reliability analysis of slopes in strain-softening soils considering critical slip surfaces

Abstract The paper concerns to the reliability analysis of slopes in strain-softening cohesive soils, using the first order reliability method (FORM). The performance function is based on the Bishop simplified method adapted to take strain-softening into account in terms of the residual factor R F over a potential slip surface, estimated based on a progressive failure model available in the literature. The reliability analysis is carried out on the surface of minimum factor of safety determined using the sequential quadratic programming (SQP). The random shear strength parameters are assumed to follow normal distribution while the residual factor has been considered both as a deterministic parameter and a beta-distributed random variable. The results obtained for an illustrative example shows substantial reduction (21 %) in the value of reliability index when R F is considered as a random variable with an assumed COV of 0.3. Results of FORM-based sensitivity analyses also reveal that R F has the most dominating influence on reliability and thus justifies its inclusion as one of the random variables. A parametric study, varying the assumed correlation coefficient between the random shear strength parameters from 0 to 1, shows that there is a maximum reduction of 16 % in reliability index.

Internal deformation monitoring for centrifuge slope model with embedded FBG arrays

The fiber Bragg grating (FBG) sensing technology was utilized for internal deformation monitoring in a centrifuge test of soil slope. An array of FBG sensors were encapsulated into a sensing fiber with a diameter of 0.9 mm. A pullout test was designed to investigate the frictional behavior between the sensing fiber and soil. It was concluded that, for a certain value of overburden pressure, the fiber strain is equal to the strain of soil as long as the fiber strain is less than its peak value in the pullout test. The sensing fibers were embedded directly into a slope centrifuge model to monitor the internal strain distribution and its variation. It can be found that the horizontal sensors were stretched extremely and the vertical sensors were compressed distinctly near a potential slip surface. Thus, it is possible to evaluate the soil internal deformation as well as the failure of the slope model by using FBG sensing technology. This is verified by a comparison between the results of FBGs and that of a numerical simulation. According to these preliminary results, discussions and recommendations for further research are presented.

Investigation of Stability of a Slope Subjected to Water Table and Seismic Load

The stability of the slopes is the major concern in the field of Geotechnical Engineering. Usually three methods of analysis have been proposed for the evaluation of slopes response under seismic loads. These three methods are Pseudo-static method, Newmark’s displacement method and Dynamic finite element analysis method. In Pseudo-static method the earthquake’s inertial forces are simulated by the inclusion of static horizontal seismic acceleration co-efficient (kh) and vertical seismic acceleration co-efficient (kv) in limit equilibrium analysis. It is one of the most dangerous conditions of natural slope when it experiences a seismic vibration the countervailing water pressure has disappeared, it causes a danger to the slope. In this work, by applying the Morgenstern-Price presented by the computer program SLOPE/W was applied to define the potential slip surface and calculate the factor of safety of the defined slope for the maximum horizontal seismic acceleration co-efficient (kh). Calculation of relative lateral displacement of the slope surface and deformed shape of the defined slope due to the effects of horizontal seismic acceleration were done with the help of QUAKE/W software analysis. It was founded that the stability of the defined slope rapidly decreased.

Stability estimation of slopes having their slip surface determined by means of the STAB-3D method based on sliding body equilibrium analysis

Most of the three-dimensional analyses of landslides are based on simple 2D methods analysing chosen characteristic flat sections of the analysed sliding body. Assumptions of the method of flat limit equilibrium analysis for a spatial solution have been elaborated. This is a combination of 2D analysis of flat sectional views and 3D analysis of the landslide’s sliding body, which disregards any stress that does not affect equilibrium. It is assumed, however, to apply only when dealing with structural slope failure (i.e. when the soil layers have the predisposition to shape the determined slip surface with a consistent decrease and explicit slide direction). This can also apply when examining the stability of a scarp or slope for the layered soil of potential slip surfaces and slide direction to be defined. The basic assumptions, equilibrium equations, and practical usage of the method have been described for an exemplary landslide. This method allows one to define in a straightforward manner the stability of slopes, to plan a way of preventing potential landslides, and to control those that have already arisen.

Risk assessment of slope failure considering multiple slip surfaces

For a slope with a large number of potential slip surfaces, the consequence of slope failure along different slip surfaces could be quite different. When the soil parameters are uncertain, the location of the slip surface with minimum factor of safety is also uncertain, making the consequence of slope failure also uncertain. The traditional equation for risk assessment may only be suitable for slope failure along a given slip surface, but may not be directly applicable to slope failure with a large number of potential slip surfaces. In this study, a new equation is suggested for risk assessment of slope failure considering the system failure probability. A response surface method is used to enhance the computational efficiency. Three slopes are studied to illustrate the proposed method. It is found that the consequence of slope failure is an important weighting factor in the risk assessment of slope failure. A slip surface with a larger failure probability but small consequence may be associated with a smaller risk. Hence, the most probable failure surface may not always be the slip surface with the largest risk. For the three examples studied in this paper, the risk of slope failure are all governed by the representative slip surfaces. Therefore, the risk of slope failure can then be assessed in a simplified manner by taking into account only the representative slip surfaces. Both the reliability method and empirical method can be used for representative slip surfaces identification.

Kinematical Limit Analysis for a Slope Reinforced with One Row of Stabilizing Piles

Stabilizing piles are commonly used to improve slope stability. The load that a pile should sustain and the associated slip surface under a prescribed factor of safety are two critical design parameters in practice. Based on the kinematically admissible failure mechanism, a limit analysis approach is introduced, which considers two potential slip surfaces that individually lie in the upslope and downslope of the piles. The explicit formulas for the upslope thrust force and downslope resistance on a pile are derived, which enables the calculation of the maximum load on a pile and the corresponding critical slip surfaces using a computer program. The maximum load and critical slip surfaces under a design factor of safety are mainly affected by soil properties and five other parameters: location of the pile row, dip angle of the slope face, action point and dip angle of the force, and improvement coefficient of the slope stability. The relevant quantitative calculation can be performed using the proposed method. Moreover, the possible failure with the upslope soil surpassing the pile top under a specified design factor of safety is significantly illustrated in the paper, which is helpful in the rational determination of the location of the pile row.

Dynamic growth of slip surfaces in catastrophic landslides.

This work considers a landslide caused by the shear band that emerges along the potential slip (rupture) surface. The material above the band slides downwards, causing the band to grow along the slope. This growth may first be stable (progressive), but eventually becomes dynamic (catastrophic). The landslide body acquires a finite velocity before it separates from the substrata. The corresponding initial-boundary value problem for a dynamic shear band is formulated within the framework of Palmer & Rice's (Proc. R. Soc. Lond. A 332, 527–548. (doi:10.1098/rspa.1973.0040)) approach, which is generalized to the dynamic case. We obtain the exact, closed-form solution for the band velocity and slip rate. This solution assesses when the slope fails owing to a limiting condition near the propagating tip of the shear band. Our results are applicable to both submarine and subaerial landslides of this type. It appears that neglecting dynamic (inertia) effects can lead to a significant underestimation of the slide size, and that the volumes of catastrophic slides can exceed the volumes of progressive slides by nearly a factor of 2. As examples, we consider the Gaviota and Humboldt slides offshore of California, and discuss landslides in normally consolidated sediments and sensitive clays. In particular, it is conceivable that Humboldt slide is unfinished and may still displace a large volume of sediments, which could generate a considerable tsunami. We show that in the case of submarine slides, the effect of water resistance on the shear band dynamics may frequently be limited during the slope failure stage. For a varying slope angle, we formulate a condition of slide cessation.

Modified Limiting Equilibrium Method for Stability Analysis of Stratified Rock Slopes

The stratified rock of Jurassic strata is widely distributed in Three Gorges Reservoir Region. The limit equilibrium method is generally utilized in the stability analysis of rock slope with single failure plane. However, the stratified rock slope cannot be accurately estimated by this method because of different bedding planes and their variable shear strength parameters. Based on the idealized model of rock slope with bedding planes, a modified limiting equilibrium method is presented to determine the potential sliding surface and the factor of safety for the stratified rock slope. In this method, the S-curve model is established to define the spatial variations of the shear strength parameterscand φof bedding plane and the tensile strength of rock mass. This method was applied in the stability evaluation of typical stratified rock slope in Three Gorges Reservoir Region, China. The result shows that the factor of safety of the case study is 0.973, the critical sliding surface for the potential slip surface appears at bedding plane C, and the tension-controlled failure occurs at 10.5 m to the slope face.

Efficient and consistent reliability analysis of soil slope stability using both limit equilibrium analysis and finite element analysis

Limit equilibrium methods (LEMs) and finite element methods (FEMs) of slope stability analysis can be used in computer-based probabilistic simulation approaches (e.g., direct Monte Carlo Simulation (MCS) and Subset Simulation (SS)) to evaluate the slope failure probability (Pf). For a given slope problem, the computational effort for the LEM is generally much less than that required for the FEM, but the FEM tends to give a more realistic prediction of slope failure mechanism and its associated factor of safety. To make use of the advantages of both the LEM (e.g., computationally more efficient) and FEM (e.g., theoretically more realistic and rigorous in terms of slope failure mechanisms), a new probabilistic simulation method is developed in the paper. The proposed approach combines both a simple LEM (i.e., Ordinary Method of Slices considering a limited number of potential slip surfaces) and FEM with the response conditioning method to efficiently calculate Pf of slope stability and to give an estimate of Pf consistent with that obtained from directly performing MCS and SS based on the FEM. It is illustrated through two soil slope examples. Results show that the proposed approach calculates the Pf properly at small probability levels (e.g., Pf < 0.001). More importantly, it significantly reduces the number of finite element analyses needed in the calculation, and therefore improves the computational efficiency at small probability levels that are of great interest in slope design practice. In addition, the proposed approach opens up the possibility that makes use of the information obtained using a simple model (e.g., LEM) to guide the reliability analysis based on a relatively sophisticated model (e.g., FEM).

Simplified approach for locating the critical probabilistic slip surface in limit equilibrium analysis

Abstract. This paper aims to develop a rapid and practical procedure that can locate the slip surface for a slope with the minimum reliability index for limit equilibrium analysis at the minimum expense of time. The comparative study on the reliability indices from different sample numbers using the Monte Carlo simulation method has demonstrated that the results from a large enough sample number are related to those from a small sample number with high correlation indices. This observation has been tested for many homogeneous and heterogeneous slopes under various conditions in parametric studies. Based on this observation, the reliability index for a potential slip surface can be calculated with a small sample number, and the search for the minimum reliability index and the slip surface can be determined by a heuristic optimization algorithm. Based on the comparisons between the critical deterministic and probabilistic slip surfaces for many different cases, the use of the proposed fast method in locating the critical probabilistic slip surface is found to perform well, which is suitable for normal routine analysis and design works.

Three-dimensional rock slope stability analysis considering the surface load distribution

Previous studies on slope stability mainly focused on conditions under gravity load in which the slope tends to slide down along the potential slip surface. However, the existence of a horizontal load on the slope surface can restrain the slope-slipping trend and improve the stability of the slope, similar to the effect of a retaining wall. The slope failure mode can be altered by a sufficiently large horizontal surface load. In this case, the slope stability problem will be converted to a rock foundation stability problem. However, the reciprocal transformation of slope stability and rock foundation stability has been rarely studied. This study considers the Ice and Snow World project in Changsha, China, as the engineering background. This project is located at an abandoned mine pit, the structural load of which mainly acts on the top of the pit. To study the three-dimensional (3D) slope stability under the slope surface load, a 3D slope model is established using the numerical commercial code. The mechanical parameters of the rock mass, as well as the value and the distribution areas of the surface load, are changed to identify the corresponding safety factor of rock mass, deformation and failure mode.

Ground Penetrating Radar Investigations of Landslides: A Case Study in a Landslide in Radziszów

Abstract The article presents the results of research of the activated landslide in Radziszów in 2010. The study focused on the evaluation of engineering geology conditions, preceded by geophysical surveys. It mainly focused on the GPR method using the IDS georadar equipped with antennas in the frequency range of 100 MHz. Antenna selection was based on archival research which showed that the depth of occurrence of clays, where the roof can be a potential slip surface, ranges between 3-10 m below the surface. GPR method applied allowed the course of the potential slip surface to be determined and the results obtained significantly correlated with the results of engineering geology tests carried out.

Real-time Remote Monitoring System Based on the Large Deformation Cable with Constant Resistance for Landslide Disaster and Its Application

It is meaningful for researching on monitoring and forecasting technology of slope stability to prevent landslide disasters, especially in the water system fields. Based on the mechanical principle of interaction among sliding mass, sliding bed and monitoring cable, a new type of energy absorbing cable (called Large Deformation Cable with Constant Resistance) which can have 2000mm deformation with constant pull load of 850kN is developed. The mechanical principle of relative movement between sliding mass and sliding bed is proposed, and the multi-factor monitoring is transformed into single landslide mechanical monitoring. The relationship between sliding force of slope and pretightening force of monitoring cable is set up. According to the physical model experiment of landslide, the sliding force at the potential slip surface will change continually before the landslide. When the sliding force is greater than the shear resistance at the potential slip surface, the landslide will take place, which means the variation of sliding force at the potential slip surface will be ahead of displacement on the ground of slope. Consequently, monitoring the variation of sliding force at the potential slip surface is better than that of the displacement. Based on above principle and experiment, the system of real-time remote monitoring and forecasting for landslide disasters based on the large deformation cable with constant resistance is developed, which can realize the real-time remote monitoring warning of sliding force. Several landslides have been successfully predicted.