Safety Factor Of Slope Research Articles

Seismic stability analysis of two-stage slopes reinforced with one row of piles

Seismic stability of a two-stage soil slope reinforced by one row of piles is analyzed using the upper bound theorem combined with pseudo-static method considering the pile axial force. For a specified safety factor of the piled slope, explicit expression of the required pile shear resistance is derived, in which the effect of axial force of the piles on the potential slide mass omitted in most of previous studies is reasonably introduced. Analysis results of examples show that the pile shear resistance and potential slip surface by the proposed method are in good agreement with those by numerical simulation. The pile reinforcement effect on the slope is operational under smaller seismic conditions, whereas it is limited and not significant with the increase of the seismic excitations. The pile shear resistance and range of the critical slide mass increase with the horizontal seismic acceleration coefficient. Compared with the existing results omitting the pile axial force, more conservative upper bound solutions of the pile shear resistance are obtained by the proposed method, especially under higher design safety factor and seismic loads. Widening the bench and constructing the pile row near the slope crest are conducive to practicably optimize the reinforcement effect on the two-stage slope under seismic excitations.

Application of Harmony Search Algorithm to Slope Stability Analysis

Slope stability analysis is undoubtedly one of the most complex problems in geotechnical engineering and its study plays a paramount role in mitigating the risk associated with the occurrence of a landslide. This problem is commonly tackled by using limit equilibrium methods or advanced numerical techniques to assess the slope safety factor or, sometimes, even the displacement field of the slope. In this study, as an alternative approach, an attempt to assess the stability condition of homogeneous slopes was made using a machine learning (ML) technique. Specifically, a meta-heuristic algorithm (Harmony Search (HS) algorithm) and K-means algorithm were employed to perform a clustering analysis by considering two different classes, depending on whether a slope was unstable or stable. To achieve the purpose of this study, a database made up of 19 case studies with 6 model inputs including unit weight, intercept cohesion, angle of shearing resistance, slope angle, slope height and pore pressure ratio and one output (i.e., the slope safety factor) was established. Referring to this database, 17 out of 19 slopes were categorized correctly. Moreover, the obtained results showed that, referring to the considered database, the intercept cohesion was the most significant parameter in defining the class of each slope, whereas the unit weight had the smallest influence. Finally, the obtained results showed that the Harmony Search algorithm is an efficient approach for training K-means algorithms.

The effect of flood on slope stability along downstream riverbank of MuaraBangkahulu River, Bengkulu City, Indonesia

The flood which occurred due to the rainfall intensity in Bengkulu City of Indonesia could inundate the downstream area of MuaraBangkahulu River, especially TanjungAgung Sub-District. In 2019, a huge flood had occurred in Bengkulu City and triggered the environmental effect to riverbank in TanjungAgung. This environmental effect is a massive slope failure on downstream riverbank in TanjungAgung. This study is therefore conducted to analyze the slope stability in the area during the normal and the critical conditions. A slope stability analysis using finite element method is performed. First, the maximum discharge of MuaraBangkahulu River is estimated. Furthermore, slope stability analyses are conducted by considering the normal condition and the increase of river water level due to the maximum discharge (the critical condition). Mapping of factor of safety for riverbank slope and soil deformation is conducted. The results showed that slope along downstream riverbank of MuaraBangkahulu could undergo slope failure under both normal and critical condition. The results also showed that the factor of safety decreases due to the increase of river water level. The results of this study could be used by local government to consider slope countermeasure in the study area

Freeze-Thaw Effects on Stability of Open Pit Slope in High-Altitude and Cold Regions

The cycle of the freeze-thaw action must be taken into account in the stability analysis of an open pit slope in the high-altitude and cold regions, because the natural process of freeze-thaw poses a significant effect on mechanical properties of the rock mass. To achieve this purpose, a linear relationship between the geological strength index (GSI) and the Tianshan slope rock mass rating (TSMR) system is established considering the effect of the freeze-thaw action by introducing a freeze-thaw correction coefficient δ. The GSI value is modified for rock mass in high-altitude and cold regions. The improved Hoek-Brown criterion considers the influences of the freeze-thaw action and steep and gentle slopes. The research outcome is applied in the No. 4 minefield open pit coal mine in the Muli mining area. Numerical calculations are performed by inputting rock mass mechanical parameters obtained in traditional and modified criterions, to discuss the influences of the freeze-thaw action on the stabilities of both the present mining slope and the final slope at the end of the designed mining. The results show that the safety factors of the original slope are 2.33 and 1.67, respectively, while after the modification, they are 2.14 and 1.61, respectively. In terms of the No. 4 minefield open pit coal mine, the slope stability meets the design requirement, although taking the freeze-thaw cycle into account.

Effect of Bedding Orientation and Spatial Variability of Stratification Shear Strength on Stability of Transversely Isotropic Rock Slope

The spatial variability of soil properties is inherent. A series of direct shear tests were carried out on strongly weathered slates samples with weak bedding planes, the result of which indicates the existence of variability of shear strength parameters. Based on the testing results, several numerical simulations of slopes were conducted considering such a variability of shear strength. The results had shown that the weak bedding planes affect the shape of sliding arc as well as the factor of safety of slopes. As the dip angle of bedding planes increases, the shape of the sliding surface changes from circular to a mixed form of circular and planner. When incorporating the spatial variability of weak planes’ shear strength into the stability analysis, the safety factors of slopes would reduce, in which the sliding arc exhibited a sliding band comprising multiple sets of sliding arcs.

STUDY ON RHEOLOGICAL CONSTITUTIVE MODEL OF CILILIN VOLCANIC CLAY, INDONESIA IN RELATION TO LONG-TERM SLOPE STABILITY

: Ground movements do not remain constant over time but it is a time-dependent phenomenon in the form of long-term deformations due to in-situ stresses acting all the time on the slope body. Therefore, the time-dependent behavior of soil mass is an important factor that influences long-term slope stability. To understand the long-term slope stability, research on soil rheological characteristics is required so that the time-dependent soil strength reduction can be known. The result of the research will be very useful for the policymaker in disaster mitigation and regional planning. To determine the rheological characteristics of Cililin Volcanic Clay, a laboratory shear creep test was carried out on soil samples taken from the Cililin area, West Java, Indonesia, which is well known as landslide-prone areas. Fifteen undisturbed soil samples were prepared for laboratory shear creep tests. The level of shear stress applied to the shear creep test is 50% - 95% of the peak strength. Then, the soil rheology constitutive models were established which are used to understand the creep behavior of the soil, determine the soil long-term strength, estimate the reduction of soil parameters as a function of time and calculate long-term slope stability. The result shows that the long-term strength of soil is reduced 48.80% from its peak strength after 16 years. The cohesion and internal friction angle reduced from 44.72 kPa and 30.34o become 21.82 kPa and 15.94o, respectively, and the slope safety factor is reduced from 2.16 to 1.04. Rheological modeling also shows that slope stability is a function of time.

Study of PLSR-BP model for stability assessment of loess slope based on particle swarm optimization

The assessment of loess slope stability is a highly complex nonlinear problem. There are many factors that influence the stability of loess slopes. Some of them have the characteristic of uncertainty. Meanwhile, the relationship between different factors may be complicated. The existence of multiple correlation will affect the objectivity of stability analysis and prevent the model from making correct judgments. In this paper, the main factors affecting the stability of loess slopes are analyzed by means of the partial least-squares regression (PLSR). After that, two new synthesis variables with better interpretation to the dependent variables are extracted. By this way, the multicollinearity among variables is overcome preferably. Moreover, the BP neural network is further used to determine the nonlinear relationship between the new components and the slope safety factor. Then, a new improved BP model based on the partial least-squares regression, which is initialized by the particle swarm optimization (PSO) algorithm, is developed, i.e., the PLSR-BP model. The network with global convergence capability is simplified and more efficient. The test results of the model show satisfactory precision, which indicates that the model is feasible and effective for stability evaluation of loess slopes.

Novel Model for Limit-Equilibrium Analysis of Slope Stability with a Nonlinear Strength Criterion

Slope stability has always been a concern of the geotechnical engineering community, and geotechnical scholars have continued to explore the reasonable failure mechanism of slopes and make the theoretical models of slope stability more reliable. This work established a novel model for limit-equilibrium (LE) analysis of slope stability with a nonlinear strength criterion. In this theoretical model, the thrust line of interslice force and corresponding increment are reasonably simplified. Then, the formula of normal stress on slip surface is derived by assuming the increment of normal interslice force. Meanwhile, strength reduction technology is applied to reduce the shear strength of the geotechnical body on the slip surface with slope factor of safety (FOS) to obtain shear stress on the slip surface. Thereafter, mechanical equilibrium conditions satisfied by the whole slope sliding body and newly introduced equation about increments of interslice force are used to solve LE stability of the slope. For stability analysis of a slope with a nonlinear strength criterion via a simple and feasible calculation process, an iterative loop solution strategy is adopted in the analysis. After comparison and analysis of several slope examples, the feasibility and rationality of the present method are verified. Moreover, the present method has high efficiency in terms of calculation speed.

3-D CRITICAL SLIP SURFACE BASED ON ARTIFICIAL INTELLIGENT

The problem of slope stability is an important issue for human and structural safety. To prevent landslides, the stability analysis of the three-dimensional (3D) slope is essential, but the most important and difficult problem is how to determine the 3D critical slip surface with the minimum safety factor in the earth slope. The critical slip surface of two-dimensional 2D soil slope stability was calculated by several researchers using optimization techniques. The Grey Wolf optimization technique (GWO) was applied to evaluate the critical slip surface (CSS) of soil slopes. This is one of the optimization techniques used to solve several engineering problems to determine the critical slip surface and the corresponding 3D soil slope safety factor. As the fundamental particle, a general rotating spherical shape was introduced for 3D slope stability research. The results showed the efficiency and effectiveness of GWO in evaluating the (CSS) of 3D soil slope compared with other optimization methods, as the safety factor is lower than the other results, and the failure form is much more close to the natural slope shape. By using GWO the critical slip surface of a slope can be located in a larger scope and more rapidly than the previously presented methods.

Stability Analysis of Slope Considering the Energy Evolution of Locked Segment

Researches on the energy evolution of the key blocks is helpful to reveal the failure process of locked-segment type slope, whose stability is governed by the locked segment along the potential slip surface. In order to study the failure mechanism of the locked segment in the process of slope progressive failure due to strength attenuation, a series of stability analysis on the numerical models of locked-segment type slope were implemented to record the relationship curve between energy and strength reduction coefficient. Then, according to the variation law and characteristic of energy evolution, the failure process of the locked segment was divided into four stages: elastic stage, initial damage stage, extensive damage stage and failure stage. And the reduction coefficient corresponding to the peak of the energy evolution curve was employed to achieve landslide warning. In addition, the method to determine the safety factor of locked-segment type slope was given, and its reliability was verified by comparing with other traditional methods. Finally, the formula for calculating the initial sliding velocity was presented based on the residual strain energy which is defined as the elastic strain energy of the locked segment when the slope is unstable.

INTEGRATED SLOPE STABILITY ANALYSIS (SSA) WITH TRANSIENT GROUNDWATER FINITE ELEMENT METHOD FOR EMBANKMENT ANALYSIS

The content of level has a big enough role in the value of the physical characteristic and the mechanical of material. The behavior of water in these materials needs to be analyzed first in order to support the slope stability analysis. Modeling of water behavior in materials in the construction of Tailing Storage Facilities (TSF) will be integrated in the slope stability analysis. This study aims to provide an explanation about the analysis of the Fishing Storage Facilities (TSF) which integrates transient groundwater analysis using the finite element method in supporting the stability analysis of the embankment of Tailing Storage Facilities (TSF). The variables that are used in the analysis, they are the parameters of physical properties and mechanic material for embankment and permeability parameters in analyzing groundwater. The analysis method for geotechnical and geohydrology modeling uses the finite element method. The results of analysis showed that groundwater behavior in the embankment material can be known in detail so that it can be integrated with stability analysis. It can be seen that there is a decrease in the value of the slope safety factor using the Integrated Slope Stability Analysis method compared to the conventional method. Adding an impermeable layer using a thickness of 5 m of clay material and a thickness of 20-30 m to support the retaining wall/foot is the criterion of optimal stability. The required lining material thickness (D) can be expressed by the following drawdown percentage equation function: reduction percentage = (1-0.8661D (-0.031)) * 100%.

Study of the influence of suction profile seasonal variations in the global sliding safety factor of a granite residual soil slope

Study of the influence of suction profile seasonal variations in the global sliding safety factor of a granite residual soil slope

Investigation of rock slope stability using a 3D nonlinear strength-reduction numerical manifold method

Due to rock masses' nonlinear failure property, it is inappropriate to investigate the stability of rock slopes using the traditional SRM (strength reduction method) which is based on the linear MC (Mohr-Coulomb) failure criterion. To conduct 3D analysis (three dimensional) of rock slopes, we propose a 3D-NSRNMM (3D nonlinear strength reduction numerical manifold method) that is based on the nonlinear GHB (Generalized Hoek-Brown) failure criterion. To effectively implement the proposed 3D-NSRNMM, two methods are adopted to convert the GHB parameters into the average and instantaneous equivalent MC parameters. With the proposed 3D-NSRNMM, the influences of different types of equivalent MC parameters, and boundary conditions on rock slopes' stability are investigated. The numerical results assessed from the proposed 3D-NSRNMM indicate that: 1) boundary conditions will significantly influence the safety factor and failure mode of a rock slope obtained from 3D analysis; 2) the safety factor from two-dimensional analysis is more conservative compared with 3D analysis; 3) Furthermore, safety factors based on the instantaneous equivalent MC parameters are very close to those based on the average equivalent MC parameters, but 3D rock slopes' failure modes based on the two different types of equivalent MC parameters are a little different from each other.

Three-dimensional upper-bound analysis of rock slopes subjected to seepage forces based on Hoek-Brown failure criterion

Three-dimensional upper-bound analysis of rock slopes subjected to seepage flows is a classical problem in geotechnical engineering. However, it is difficult to obtain a rigorous upper-bound solution of the safety factor of slopes when seepage flows are involved. In order to address this problem, the three-dimensional (3D) hydraulic head distributions inside a slope under steady state hydraulic conditions are solved numerically. The obtained numerical hydraulic head distributions are further employed to compute the seepage forces applying to the 3D discretized rotational failure mechanism to assess the stability of a rock slope. The Hoek-Brown yield criterion is employed to characterize the failure of rock masses. The generalized tangential technique is employed to formulate the problem as a classical optimization problem. The particle swarm optimization algorithm combined with the Nelder-Mead simplex algorithm is used to search for the best solutions of slope safety factor. The proposed approach is validated by comparing with 2D plane strain analysis results in the literature. Parametric analysis shows that the safety factor increases as mi or GSI increases, but decreases with the increase of the slope angle β and B/H. It is also found that the 3D influence is significant for B/H smaller than 10, beyond which it becomes negligible. The computational results in the form of design tables are presented for practical use in rock engineering.

Practical reliability analysis for earthquake-induced 3D landslide using stochastic response surface method

This study investigates the effect of spatial variability on the stability of a real 3D slope subjected to earthquakes by conventional Monte Carlo simulation (MCS) and a stochastic response surface method. The stochastic response surface method used in this study (VRSRSM) was combined with a variance reduction method due to spatial averaging of soil parameters in slope failure to reduce a large computational load due to the realization of spatially correlated input parameters in three-dimensional space. In order to verify the applicability of the stochastic response surface method with a variance reduction method for 3D slope reliability, the safety factor for a simple 3D slope under non-seismic and seismic conditions was analyzed by MCS and VRSRSM. The VRSRSM was applied to risk evaluation of deep-seated landslides caused by the 2016 Kumamoto earthquake along with backcalculation of strength parameters based on the slope failure geometry and field investigation.

Factors Affecting Slope Instability of the Nhan Co Alumina Red Mud Basin and Economical, Environmentally Friendly Soil Stabilization

Since 2017, there have been recurring landslides in the red mud basins of the Nhan Co alumina factory, Dak Nong Province, Vietnam, during the rainy seasons. Changes in physical and mechanical soil parameters due to rain water infiltration and the formation of tension cracks have been considered as the main causes of slope instability. The soil cohesion and angle of internal friction decreased nearly thrice and twice, respectively, as the soil became saturated. An economical and environmentally friendly reinforcement using bamboo stem piles in combination with slope regrading is suitable for the site conditions. With a light slope regrading, a bamboo stem pile spacing of 5.3 m ensures that the slope factor of safety (FS) is 1.30, which satisfies the requirements specified by the national technical regulations. The results are helpful and serve as practical fundamentals for a comprehensive control of slope stability of the red mud basins in the Nhan Co alumina factory to avoid possible catastrophic destruction of the local ecology by the spreading of an extremely high pH fluid and mud from the red mud basins due to the landslides into the red mud basins.

Slope stability assessment and landslide vulnerability mapping of the Institut Teknologi Kalimantan area

Slope stability analysis was carried out in the Institut Teknologi Kalimantan which is an area with educational facilities that have a high risk of soil movement. The research area consists of slopes that often reported landslides, especially during the rains time. Evaluation is carried out to the important factors that affect slope stability such as slope geometry consist of 23 zones, soil parameters consist of 7 drilling holes, and past landslide occurrence. Slope stability was evaluated using back analysis based on soil parameters under critical conditions and field investigation and slope geometry using SLOPE/W software to obtain the safety factor (SF) of a certain slope. Landslide vulnerability maps are created based on the risk and potential landslide or landslide occurrence. Based on the results of the stability analysis, there are 6 zones with unstable conditions and a high potential for landslides and 4 zones in critical conditions with moderate landslide potential. The modeling also shows that in the same soil parameter value with a steep slope, the value of the safety factor is getting smaller. This means that the potential for soil movement is greater. Besides, the loading at the top of the slope also causes a reduced safety factor.

Assessing the soil moisture effects of planted vegetation on slope stability in shallow landslide-prone areas

Soil moisture plays an important factor to impact runoff and the slope stability, but how vegetation affects the soil moisture variability of slope stability is poorly understood. In order to compare the stability of different shrub slopes under the effect of soil moisture, four types of shrubs (Periploca sepium, Lespedeza bicolor, Ziziphus jujuba, and Punica granatum) are selected for ecological restoration in shallow landslide-prone areas, and the effects of rhizosphere soil moisture and plant roots on the slope stability are studied. Trace infiltration is applied in order to study plant roots and soil moisture impact. The shear strength of the roots slope soil under different moisture content is determined by laboratory shear strength test. The slope safety factor of different shrubs is obtained by FLAC 3D (Fast Lagrangian Analysis of Continua 3D) simulation. Among the four shrubs, thick roots show the greatest improvement to soil porosity, and fine and medium roots could provide more preferential flow channels for water infiltration. The soil moisture content significantly increases after planting Lespedeza bicolor. At 10% soil moisture content, the P. sepium slope safety factor is highest in four shrubs (1.39). When the soil moisture content reaches 30%, the safety factor value of the L. bicolor slope reaches the maximum, and the safety factor value of L. bicolor decreased by 25.6%. The results show that even during the wettest condition of the soil (saturated soil moisture content 30%), the mechanical reinforcement form the L. bicolor root maintains some degree of stability. Shrubs have a good effect on enhancing the stability of slopes, especially in areas prone to shallow landslides.

Elastoplastic-damage-seepage coupling model and numerical algorithm for rock slope stability evaluation

The stability of slope under complex geological conditions is one of the essential issues in geotechnical engineering. The mechanical damage caused by external force load and the hydraulic property of rock have both significant influences on slope stability. However, the two factors and the coupling process between them are not considered in the traditional slope safety calculation method. Firstly, in this paper, an elastoplastic-damage-seepage coupling model is established based on the modified Mohr-Coulomb (M-C) criterion. This model takes into account the weakening effect of damage on the strength of rock mass. Further, according to the Biot's theory and the evolution equation of permeability coefficient, a complete hydraulic-mechanics (HM) coupling model is established. Secondly, the fully implicit backward Euler algorithm and "strict-cornered" algorithm are used to integrate the stress precisely. The complete coupling analysis of HM is implemented by the step-by-step iterative method. By combining the centrifugal loading method (CLM) with the FEM program, the factor of slope safety (FOS) under the coupling influence of damage-seepage can be solved. The calculation results showed that, compared with the traditional rounded M-C model, the results obtained by the "strict-cornered" algorithm method in this paper are closer to the theoretical solution. The solution process is robust with a global second-order convergence rate. After considering the effects of damage and seepage, the FOS is obviously reduced. Finally, the model is applied to the stability evaluation of an actual engineering. The variation rules of pore water pressure, displacement field, damage zone and FOS are calculated under different head heights. The model built in this paper considers the coupling characteristics of rock seepage-stress-damage well. The proposed numerical algorithm ensures the accuracy and rationality of the calculation results which provides a theoretical foundation for engineering application.

Investigation of Failed Slopes Based on a New Method of Back Analysis in Rock Masses: A Case Study

Small variation in shear strength parameters results in remarkable changes in the safety factor (SF) of a rock slope. In this regard, rock mass strength of a failed slope can be estimated with reasonable accuracy using back analysis approach. The conventional back analysis (BA) procedure is based on trial and error approach on the mb and s parameters of Hoek–Brown failure criterion in conjunction with the Geological Strength Index (GSI) classification system. A new BA procedure presented in this paper, a functional relationship, that indicted all possible combinations of mb and s constants, was derived using stability analysis of a slope assuming that the SF of the slope is equal to unity. Then, another relationship is established between mb and s based on the magnitude of GSI. Intersection of the two relationships when plotting on a graph, defines a unique value for mb and s. Finally, effect of the constant a in the generalized Hoek–Brown failure criterion on the GSI value obtained from the method BA is discussed and its effect is considered in the BA approach. The most advantage of the proposed method is that a reliable GSI is obtained in a relatively short time. For better explanation of the new BA procedure, this method is used for the back analysis of a failed slope along the national railway of Iran. Comparing results obtained from the new BA approach and the traditional back analysis method well-specified which the new proposed BA approach increases the accuracy of parameter estimation.