Slope Stability Evaluation Research Articles

Stability evaluation of the high fill deposit slope subjected to rainfall considering water deterioration

Stability evaluation of the high fill deposit slope subjected to rainfall considering water deterioration

Numerical study on spatial distribution of blast-induced damage zone in open-pit slope

The excavation damage zone in rock slopes after drill-and-blast operations is of great significance for assessing the slope stability and design of open pit mines. The traditional method simplifies, the spatial distribution of the damage zone in a slope following blasting is as a single radius distributed, which leads to an inaccurate evaluation of slope stability. Herein, a model coupling the tensile damage and the Drucker-Prager yield criteria is established to investigate the spatial distribution characteristics of blast-induced damage zone in the final wall of an open-pit. Explosive explosion is converted to an equivalent pressure time history acting on the blasthole wall and the extension of the damage observed in the field test is reproduced successfully by numerical simulation. The proposed model is verified on the basis of the site-monitored data from the Wushan Copper mine, a large-scale open-pit mine in Inner Mongolia, China. The results show that the damage decreases with increasing depth, exhibiting a nonlinear distribution behind the slope face. The maximum depth and scopes of horizontal and vertical damage occur at the slope crest. The proposed model is compared with five widely used damage models and proves to be more capable of representing the spatial distribution of the damage zone observed in the site test. Finally, the formation mechanism of the maximum damage depth along the crest is also revealed.

Establishment of Readily Mathematical Formulation for the Evaluation of Slope Stability in Earth-Fill Dams

Establishment of Readily Mathematical Formulation for the Evaluation of Slope Stability in Earth-Fill Dams

Numerical Evaluation of Slope Stability based on Temporal Variation of Hydraulic Conductivity

Slope failure is a common phenomenon all over the world on both man-made and natural slopes. Prolonged rainfall is one of the climatic factors which is largely responsible for slope failure. During heavy and prolonged rainfall, a part of the rainwater infiltrates through the soil and seeps into the slope. The infiltrated water lowers the matric suction and increases the porewater pressure. Eventually, the generated porewater pressure decreases the strength of the soil which results in slope failures. To evaluate the effect of rainwater seepage on slope stability, it is necessary to investigate the hydraulic conductivity of the slope soil. The objective of this study is to evaluate the effect of hydraulic conductivity on slope failure mechanisms. A finite element analysis of slope stability was conducted using Geo-Studio software. A numerical model was developed and calibrated with field monitoring data. The field monitoring data included the observation of hydraulic conductivity using a Guelph Permeameter. Afterward, the temporal variation of rainfall and hydraulic conductivity was incorporated into the SEEP/W program and the consequent changes in slope stability were evaluated in SLOPE/W. From the numerical analysis, with the identical strength parameters of the soil, different factors of safety were observed when the slope sections retain different hydraulic properties. Based on the numerical analysis, it was observed that hydraulic conductivity greater than 4×10-6 cm/s leads to slope failure. Periodic monitoring of hydraulic conductivity in the field may provide deep insight into rainfall-induced slope failures.

The importance of unsaturated soil properties in the development of slope susceptibility map for Old Alluvium in Singapore

Slope failures caused by rainfall are a regular occurrence in residual soils. As a result of climate change, increased precipitation is anticipated; preventing slope failures due to rain is therefore essential. One typical technique for pinpointing regions at risk for slope failures is the use of a “slope susceptibility map.” Because the groundwater table is usually deep, many slopes in residual soil are typically unsaturated. Soil-water characteristic curve, permeability function, and unsaturated shear strength are the essential unsaturated soil parameters that should be factored into the creation of a slope susceptibility map. This research involved the Old Alluvium region in Singapore as a case study. Transient rainfall infiltration and grid-based regional slope stability (TRIGRS) model was used to establish pore-water pressure distributions over this region. Scoops3D was utilized to include the pore-water pressures calculated by TRIGRS for evaluating slope stability in three dimensions. To assess the reliability of the developed slope susceptibility map, two-dimensional (2-D) numerical analyses were performed on a subset of historically unstable residual soil slopes at the Bidadari site. Minimum safety factors determined via numerical analyses of the slopes under study agreed well with those determined via the slope susceptibility map.

Application of photogrammetry and in-situ test technology in the stability evaluation of gangue dump slope

Application of photogrammetry and in-situ test technology in the stability evaluation of gangue dump slope

Evaluation of Slope Stability at Interface using Thin Soil Material Model in Finite Element Software

Cases of landslides on clay shale slopes have been an intriguing study in Indonesia. Most of the slopes failed due to the weathering of the clay shale rock. As studies focused on the properties of clay shale, several FEM analyses indicated a unique translational type of failure between the interface of clay shale and its overburden. However, the modeling of the interface in a case study was still limited. This study aims to evaluate a landslide using a thin-soil interface model using FEM software. The model used two conditions, extreme groundwater level conditions. There were several iterations of the shear strength parameters of the interface layer conducted. Results indicated that the thin-soil interface could portray the interface condition at the landslide. Compared to laboratory interface results, the interface would fail at a high degree of saturation due to water infiltration at the surface. Also, granular overburden with high permeability had a higher chance of failure than cohesive overburden. From the results, this study opened the path to incorporating the interface layer in clay shale slope analysis. However, further studies are needed using the thin-soil interface model in other clay shale landslide cases to synthesize its repeatability.

Kinematic and Slope Mass Rating Application for Rock Slope Stability Evaluation Along Shanadar-Goratu Road in the Gali-Ashkafte Valley, Erbil, NE-Iraq

A Study of rock slope stability along the Shanadar-Goratu main road, which is located near Mergasur town, northeast of Erbil city, is very necessary because many many slope failures take place every year, especially in the wet season. It is the main road between Erbil city and many towns and villages in the Mergasur district. For the current research, eight (8) rock-cut slope stations have been selected for 4.5 kms along the road from Shanadar to Goratu, based on differences in discontinuity pattern, slope geometry, and failure types. Field data has been assessed by the kinematic method, through DIPS v7.0 software, and by slope mass rating classification system, through SMRTool - v205 software. Kinematic analysis from DIPS v7.0 software showed that three types of failures (planar, wedge and toppling failures) may occur, and the largest susceptible rock masses to failure are of slope stations no. 1,5 and 8. In the worst conditions, the discrete-SMR and continuous-SMR pointed out that slope stations no. 1, 5 and 7 are completely unstable (class V – very bad slopes) with a failure possibility of 90%, while slope stations no. 2, 3 and 4 are unstable (class IV – bad slope) with failure possibility of 60%. However, slope stations no. 6 and 8 are partially stable (class III – normal slope face) with failure possibility of 40%, with an exception for slope station no.6 which is unstable (class IV – bad slope face) from continuous-SMR.

Impact of longwall mining on slope stability – A case study

Abstract In recent decades, many open pit (OP) mines have either already made the decision or are at the planning stage to change their mining activity from OP to underground (UG) to remain competitive. Technically, before the OP ends its operation, both OP and UG mining will have to be operated simultaneously for a certain period of time. It is well known that UG operation causes subsidence, discontinuous deformations, and changes in hydrogeological conditions. In case of UG operation located below the OP mine, slope deformation can be expected as a result of subsidence induced by UG exploitation. This paper presents a numerical analysis of slope stability under the influence of the longwall mining operation at the Cao Son OP mine in Vietnam. All calculation variants were performed using the Finite Difference Method code, FLAC. In order to evaluate slope stability of the OP slope, various geometry configurations showing advances of both OP and UG extractions were examined. Based on the outcomes, assessments on OP slope are presented, and then, practical actions regarding the location and direction of UG extraction are recommended, with an aim to minimize the impact of underground mining on OP slope.

Analysis of Rainfall Infiltration and Improvement of the Analytical Solution of Safety Factors on Unsaturated Inner Dump Slopes: A Case Study

Rainfall infiltration is one of the main triggers of inner dump slope failure in the process of mining coal. Changes in water content throughout the process of rainfall infiltration have rarely been studied. The reductions in soil strength due to water migration have seldomly been considered in the existing analytical solution of the safety factor (F.S) for unsaturated inner dump slopes in an open-pit mine. In this work, a new mechanical model was developed by improving the conventional analytical solutions of F.S for unsaturated inner dump slopes to accommodate water-induced degradation in the mechanical strength of waste material. Parameter analysis was carried out via a case study of the Shengli #1 open-pit coalmine. The results showed that the wetting front depth increased with increasing rainfall time, and the increasing rate was constant during the non-compressive infiltration stage, while it decreased gradually in the compressive infiltration stage. The F.S of the transition layer decreased at first and then increased with increasing infiltration depth. By considering the water migration in the inner dump slope, the calculation result of F.S by the analytical solution in the paper can more precisely represent the in situ conditions. It was larger than that of the saturated strength, but smaller than that of the natural strength. The position of the minimum F.S did not alter in the wetting front, but was close to the position of the wetting front. The depth of the potential slip surface can be calculated by the converse solution of the analytical equation when F.S = 1 for rainfall infiltration, and the most dangerous slope surface can be determined. The depth (hmin) of the potential slip surface increases with increasing wetting front (hf) by a linear function, and increases with increasing depth ratios of the saturation layer (λ). The depth ratio (i) of the minimum F.S increases with increasing λ by an exponential function. The improved analytical solution can be used to evaluate the potential sliding surface under rainfall conditions, which is helpful for evaluating slope stability and analyzing dangerous surfaces under rainfall conditions and providing guidance for reinforcement schemes.

Active fault investigation and slope stability evaluation for Aso Bridge in Japan

The Aso Bridge in Japan is located near the Futagawa Fault, which is considered to be the epicentre fault of the Kumamoto earthquake. This paper presents the technical findings obtained through the investigation and design of the Aso Ohashi Bridge replacement project after the Kumamoto earthquake, including (a) extraction of active fault zones, (b) evaluation of fault activity found on the cut slope and (c) stability evaluation of the excavated surface behind the bridge piers considering the mechanical properties of the columnar joints.

Slope Stability Analysis Method of Unsaturated Soil Slopes Considering Pore Gas Pressure Caused by Rainfall Infiltration

The variation of pore gas pressure caused by rainfall infiltration is an important factor that leads to slope failures. The purpose of this study is to propose a new slope stability analysis method that considers pore gas pressure and examines the effect of airflow on slope stability by using a numerical method. A water-air two-phase flow analysis was conducted to investigate the distribution of pore air pressure, pore water pressure, and water saturation triggered by rainfall infiltration. Then the variation of the load resulting from pore gas pressure was incorporated into the slope stability analysis method based on the unsaturated soil shear strength theory and the residual thrust method to simulate the influence of airflow on the Tanjiahe landslide in China. In order to study the infiltration behavior with respect to initial saturation, water and gas flow analyses were performed considering various initial states of saturation under similar settings. Results showed that the pore gas pressure between the slope surface and the slip band clearly varied and that it decreased during the process from the slide bed to the deep direction. Then, the pore water pressure formed in the saturated zone was transferred by the airflow to the slope toe. As a result, because the pore gas pressure gradient increased the thrust of the slide mass, the safety factor decreased over time. Moreover, in the first step, the magnitude of infiltration decreased with an increase in initial saturation, while when the magnitude dropped to the minimum value, it then went up with an increase in initial saturation. The maximum value was usually reached at a saturation degree of 0% or 100%. When evaluating slope stability, the safety factor obtained by the slope stability analysis method that considered the water-gas coupling effect was much lower than when it was not considered during the process of a similar seepage. The impact on the slope failure was significant and may provide a practical reference for hazard assessments to control rainfall-induced landslides.

GIS and geomorphological mapping applied to landslide inventory and susceptibility mapping in the El Estado River basin, Pico de Ori-zaba, Mexico

With the purpose of strengthening the knowledge and prevention of landslide disasters, this work develops a methodology that integrates geomorphological mapping with the elaboration of landslide susceptibility maps using geographic information systems (GIS) and the multiple logistic regression method (MLR). In Mexico, some isolated works have been carried out with GIS to evaluate slope stability. However, to date, no practical and standardized method has been developed to integrate geomorphological maps with landslide inventories using GIS. This paper shows the analysis carried out to develop a multitemporal landslide inventory together with the morphometric analysis and mapping technique for the El Estado River basin where, selected as the study area, is located on the southwestern slope of the Citlaltepetl or Pico de Orizaba volcano. The geological and geomorphological factors in combination with the high seasonal precipitation, the high degree of weathering and the steep slopes predispose its surfaces to landslides. To assess landslide susceptibility, a landslide inventory map was prepared using aerial photographs, followed by geomorphometric mapping (altimetry, slopes and geomorphology) and field work. With this information, landslide susceptibility was modeled using multiple logistic regression (MLR) within a GIS platform and the landslide susceptibility map was obtained.

Evaluation of Slope Stability within the Influence of Mining Based on Combined Weighting and Finite Cloud Model

Coal mining under slopes often leads to slope instability, resulting in substantial economic losses and human casualties. Therefore, constructing a scientific and practical slope stability evaluation model for slope disaster prevention and control is of great significance. In this study, seven evaluation indexes were selected, and their influence mechanisms were analyzed to establish a system of evaluation indexes for the stability of mining slopes in Xing County, Shanxi Province, China. A new evaluation model for the stability of mining slopes was established based on the interval analytic hierarchy process (IAHP) to determine the subjective weights of the indexes and the improved CRITIC method to determine the objective weights of the indexes, which circumvented the limitations of subjective or objective weights by combining the minimum discriminating information. The model was applied to the mining slopes in Xing County, Shanxi Province, and the results showed that slopes A, C, D and E were in an unstable state, slope B was in an understable state after mining. Finally, the accuracy of the evaluation results was verified through field surveys. The model has engineering application value in predicting the stability of mining slopes and can provide theoretical suggestions for later slope management to ensure the safe production of coal mines.

Application of information gain in the selection of factors for regional slope stability evaluation

Application of information gain in the selection of factors for regional slope stability evaluation

Probabilistic Risk Assessment of Soil Slope Stability Subjected to Water Drawdown by Finite Element Limit Analysis

This study investigates the probabilistic stability of embankment slopes subjected to water level drawdown using the random field finite element method (RFEM) with strength reduction technology. The shear strength of soil properties was controlled by cohesion and internal friction angle for the slope shear failure. The cohesion and internal friction angle were modeled by a random field following the log-normal distribution. The factor of safety (FOS) for the embankment slope with random soil is calculated by strength reduction technology. During the numerical simulation, the limit analysis upper bound and lower bound method are applied to the finite element method, respectively, to obtain the upper bound and lower bound value of the FOS. Seepage action is also considered during the water drawdown by setting five different water levels (WLs). A total of 1000 Monte Carlo simulations are performed for each work condition, resulting in histograms of the FOSs. The results show that the FOSs obtained by the random field model are all lower than those by the deterministic method. Even if the FOSs obtained by the two methods are close, there still exists the possibility of slope failure. Compared to the deterministic results, the RFEM method is more reasonable for evaluating slope stability.

Computer-Aided Slope Stability Analysis of a Landslide—A Case Study of Jhika Gali Landslide in Pakistan

The present research study has been undertaken to carry out slope stability evaluation of the Jhika Gali landslide in Pakistan using GeoStudio. For this purpose, the site geometry of the existing slope adjacent to the slided one was measured and samples were collected from the site. The in-situ moisture content was 14% and dry unit weight was 18.63 kN/m3. Unconfined compression tests and unconsolidated-undrained (UU) triaxial tests were performed on samples reconstituted at in-situ dry unit weight, standard Proctor and modified Proctor maximum dry unit weights. The test results show that the shear strength and deformation parameters, i.e., undrained shear strength, angle of internal friction and deformation modulus decreased from 200 kPa to 90 kPa, 23° to 12° and 51 MPa to 32 MPa, respectively, with an increase in the percentage of saturation from 35% to 95% at a specific dry unit weight. The slope was also modeled in GeoStudio for limit equilibrium analysis, and slope stability analysis was performed using the values of undrained shear strength and the angle of internal friction as determined in the laboratory at varying degrees of saturation. The limit equilibrium analysis showed that the factor of safety reduces from 1.854 to 0.866 as the saturation of material increases from 35% to 95%. The results also suggest that, as the percentage of saturation increases above 85%, the soil loses its shear strength significantly and gains in bulk unit weight, so at this stage the material starts sliding. Additionally, slope stability analysis was carried out by changing the slope geometry in three different ways, i.e., by reducing the height of the slope, adding a counterweight at the toe of the slope and by making benches on the slope. The results of GeoStudio analysis showed that the slope will be stable even above 85% degree of saturation.

Stability Evaluation of Medium Soft Soil Pile Slope Based on Limit Equilibrium Method and Finite Element Method

The stability of an open-pit slope is an extremely important factor related to the safe production of an open-pit mine. It is the first safety technical problem encountered and should be solved in the process of mine design and production. By the means of an engineering geology and hydrogeological investigation of the waste dump area of the Nayuan open-pit coal mine and numerical simulation research, this paper analyzes and studies the slope stability of the stope and waste dump of the Nayuan open-pit coal mine in detail and puts forward measures such as slope prevention and automatic monitoring to achieve the goal of protecting the slope of the stope and waste dump and the surrounding environment. The main research results are as follows: (1) The geotechnical physical and mechanical indexes of stope and waste dump are collected and analyzed, and the geotechnical mechanical indexes in this report were determined, which basically meet the requirements of slope stability analysis. (2) The limit equilibrium method and finite element method were used to analyze and evaluate the current slope stability of the Nayuan open-pit coal mine. It was concluded that the foundation of the waste dump is basically stable, and the potential landslide modes of the slope are arc-shaped sliding surface and arc-shaped straight-line sliding surface. The numerical simulation and checking results showed that the current stope and waste dump slope are stable. (3) According to the analysis and evaluation results of slope stability, feasible slope prevention measures are put forward. The research results are of great significance to the safety of important facilities in open-pit mines and provide a basis for the design and safety implementation of open-pit slope engineering.

Effect of spatial variability on stability and failure mechanisms of 3D slope using random limit equilibrium method

It is well known that soils are prone to spatial non-uniformity, which affects evaluations of slope stability and failure mechanisms. This paper presents a probabilistic slope stability evaluation, considering the 3D spatial variation in the soil properties, by the random limit equilibrium method (RLEM). Specifically, 3D random fields of cohesion c, friction angle ϕ, and soil unit weight γ are generated using a fast Fourier transform. The RLEM is applied to evaluate the effects of the 3D spatial variability of the soil properties on slope stability and failure mechanisms. A Monte Carlo simulation is used to interpret the slope reliability and variation in slope failure dimension. Based on the critical slip surface passing different portions of a slope (slope base, inclined face, and crest), four main failure mechanisms (two base failures and two face failures), and one additional failure mechanism (toe failure), are identified for spatially variable slopes, and the corresponding distributions of the stability number (Ns) and sliding volume (V) are investigated in detail. The results show that the large variation in the soil properties induces changes in the failure mechanisms, and a threshold of c-ϕ values is found for a shift from base failure to toe failure. Lastly, associated sensitivity studies are performed to explore the effects of the uncertainties of the input parameters on the uncertainty of the output. The results estimated by partial Spearman correlation coefficients show that cohesion has the greatest influence on the stability number, and that a positive influence of the unit weight, contributing to slope stability, is found for a base failure mechanism.

Устойчивость откоса грунтовой плотины при сработке водохранилища

Introduction. One of the possible factors acting on the stability of the slopes of an earth dam is the change of water levels in the reservoir or the downstream reservoir. A hazardous event can be a rapid drawdown of the reservoir due to, for example, an emergency or a technological necessity. Examples of collapse of ground dam slopes caused by changes in water level in the reservoir are given, as well as the results of estimation of the effect of reservoir drawdown on the stability of the upstream slope. A homogeneous enclosing dam made of loam on a non-rock base with a height of 29 m and upper and lower slopes of 1:3.5 was considered. The research was conducted for two cases of drawdown: slow drawdown with the rate of vertical water level decrease v = 0.25 m/day and fast (emergency) drawdown with the rate of v = 4.4 m/day. Materials and methods. Calculations of filtration of soil dam for steady and unsteady modes and assessment of stability of the dam slope are carried out by numerical method of finite elements using PLAXIS software package. The research statement and theoretical foundations, laid in calculations of filtration and stability of slopes are given. Results. Researches have shown that at decrease in a water level of a reservoir with the big speed the danger of infringement of stability of a slope increases. Conclusions. According to the practice of designing, the evaluation of change in the upper slope stability coefficient of the uniform ground protecting dike taking into account decrease of the water level in the reservoir taking into account filtration forces of unsteady filtration has been carried out. Variants with different rates of drawdown are considered. It is established that at high rates of drawdown the coefficient of slope stability decreases. The obtained results testify to necessity of taking into account filtration forces of unsteady filtration in evaluation of slope stability when designing homogeneous dams made of low-permeable soils.