Pseudo-static Slope Stability Analysis Research Articles

Comparison of stability analysis methods for safe design of volcanic rock slope

The performance of the stability chart (SC), limit equilibrium (LE), and finite element (FE) methods for stability analysis of weathered volcanic rock slopes under static and earthquake loads is not fully understood. This research aimed to evaluate the performance of the SC, LE, and FE methods for slope stability analyses by studying a case of a weathered volcanic rock slope at the Leuwikeris Dam diversion tunnel in Indonesia. Site characterisations were carried out to obtain the input parameters for the static and pseudostatic slope stability analyses. The results showed that using various search methods of failure surface and the suggested optimum number of finite elements, multiple non-circular failure surfaces were predicted from the LE and FE methods that were not anticipated in the initial slope design based on the SC method. The location and shape of the failure surfaces from the LE method agreed with those from the FE method. The difference between the Fs values from the static LE analysis and those from the static FE analyses was less than 14%, but the discrepancy increased up to 78% in the pseudostatic analyses. This study highlights the importance of validating the results from one method with the other methods to prevent slope failures.

Pseudo-static slope stability analysis using explainable machine learning techniques

Pseudo-static slope stability analysis using explainable machine learning techniques

Pseudo-static slope stability analysis and numerical settlement assessment of rubble mound breakwater under hydrodynamic conditions

This research focuses on the slope stability analysis of rubble mound breakwaters using the Bishop method, with a specific application to the Chamkhaleh Port in the Caspian Sea region. The study emphasizes the criticality of slope stability in coastal engineering to protect shorelines from erosion and damage caused by waves and currents. The Bishop method is employed in the analysis, allowing a comprehensive assessment of breakwater stability by considering soil properties, slope geometry, and external forces. Sensitivity analysis is conducted to evaluate the impact of various parameters on breakwater stability, enabling optimization of the design and identification of potential failure mechanisms. Additionally, the research addresses numerical settlement analysis using the finite element method. The finite element method proves effective in handling complex geometries and boundary conditions, accurately capturing deformational changes caused by breakwater construction under short-term and long-term conditions. The settlement analysis results indicate acceptable maximum settlements within the project area. To ensure the reliability of the breakwater, geotechnical investigations are conducted to determine the minimum channel slope and allowable distance from the breakwater edge, crucial parameters for achieving acceptable static and pseudo-static safety coefficients. The breakwater's overall stability is assessed, and the factor of safety is quantified to evaluate the probability of slope failure and associated risks. The findings demonstrate the satisfactory stability and settlement performance of the Chamkhaleh breakwater project, affirming its effectiveness in providing coastal protection for the port.

Numerical Analysis of Slope Stability Due to Excavation of Diversion Tunnel at Pamukkulu Dam Site, Indonesia

Located in the Takalar Regency of South Sulawesi Province, the Pamukkulu Dam is planned to use a tunnel type as its diversion structure. One of the critical parts in the tunnel construction is the stability of portal slopes. This research aimed to estimate the effect of tunnel excavation on the stability of the portal inlet and outlet slopes under static and earthquake loads by using the finite element method. The slope stability analyses were carried out under conditions of prior to and after tunnel excavation. The input parameters used were laboratory test results in the forms of index properties and mechanical properties taken from rock core drilling samples, completed with the rock mass quality parameters based on the Geological Strength Index (GSI) classification. The Mohr-Coulomb failure criterion was used to model strength of the soil, while the Generalized Hoek-Brown failure criterion was used to model strength of the rocks. The results of rock cores analysis using the GSI method showed that the inlet tunnel slope consisted of four types of materials, namely residual soil, fair quality of basalt lava, good quality of basalt lava, and very good quality of basalt lava. Meanwhile, the outlet portal slope consisted of three types of materials, namely residual soil, good quality basalt lava, and very good quality basalt lava. The calculated horizontal seismic coefficient for the pseudo-static slope stability analysis was 0.0375. The analysis results of slope stability in the Y1 inlet section had a critical Strength Reduction Factor (SRF) value of 2.35 in a condition prior to the tunnel excavation and a critical SRF value of 2.34 after the tunnel excavation. The Y2 outlet section had a critical SRF value of 13.27 in a condition before tunnel excavation and a critical SRF value of 5.55 after the tunnel excavation. The earthquake load addition at the Y1 inlet section showed a critical SRF value of 2.05, both before and after the tunnel excavation. The Y2 outlet section showed a critical SRF value of 11.49 before the tunnel excavation and a critical SRF value of 5.54 after the tunnel excavation. The numerical analysis results showed that earthquake load reduced critical SRF values of the slopes. At the Y1 inlet section, the tunnel excavation did not have a significant effect on slope stability. It was demonstrated by an extremely small decrease in a critical SRF value of 0.43% for a condition without an earthquake load and an unchanged critical SRF in a condition with an earthquake load. At the Y2 outlet section, the tunnel excavation had a more significant effect on the slope stability. It was exhibited by the decrease in the critical SRF value of 58.18% in a condition without an earthquake load and a decrease in the critical SRF value of 51.78% in a condition with an addition of an earthquake load. However, the analysis of slope stability for both sections showed that all design slopes were above the required allowable safety factor value.

NUMERICAL EVALUATION OF TUNNEL PORTAL SLOPE STABILITY AT BAGONG DAM SITE, EAST JAVA, INDONESIA

Geometries of excavated tunnel portal slopes at Bagong Dam site was initially designed without taking into account earthquake load. The excavated slope designs also assumed the rocks consisting the slopes were homogenous. The purpose of this research was to evaluate stability of the excavated tunnel inlet and outlet slopes at the Bagong Dam site under static and earthquake loads using finite element method. Stability of the natural slopes was also analyzed for comparison. The numerical static and pseudostatic analyses of slope stability were carried out using RS2 software (Rocscience, Inc.). Input data used in the numerical analyses were obtained from engineering geological mapping, rock core analyses, and laboratory tests. Seismic coefficient applied in the pseudostatic slope stability analyses was determined following guideline described in Indonesian National Standard. The engineering geological mapping and evaluation of rock cores indicated that the inlet tunnel slope consisted of four types of materials, namely residual soil, poor quality of volcanic breccia, very poor quality of volcanic breccia, and good quality of volcanic breccia. The outlet portal slope consisted of six types of materials, namely residual soil, very poor quality of limestone, poor quality of limestone, very poor quality of volcanic breccia, poor quality breccia, and good quality breccia. Based on the secondary elastic wave velocity (Vs) values, the rock masses in the research area were classified as hard rock (SA). Seismic analyses based on the earthquake hazard source map with 10% probability of exceedance in 50 years provided by the National Earthquake Center (2017) indicated that the PGA and the corresponding amplification factor FPGA in the research area were 0.3 and 0.8, respectively. The calculated seismic coefficient for the pseudostatic slope stability analyses was 0.12. The numerical analysis results showed that, in general, earthquake load reduced critical Strength Reduction Factor (SRF) values of the slopes. However, the natural and excavated tunnel portal slopes were relatively stable under static and earthquake loads. The natural slope at the tunnel inlet with a 40° inclination had critical SRF value of 4.0, while that of at the tunnel outlet with a 51° inclination had critical SRF value of 2.6. Under static load, the excavated slopes at the tunnel inlet and outlet having a 45° inclination had critical SRF values of 2.4 and 5.0, respectively. Under earthquake load, the excavated slopes at the tunnel inlet and outlet had critical SRF values of 2.3 and 3.5, respectively.

Pseudo-static slope stability analysis around the landslide at railway tunnel, South Sumatera, Indonesia

On January 23rd 2016 there was a landslide in the Lahat-Lubuk Linggau railway, right at the mouth of the railway tunnel in Lahat Regency. About 5 meters thick of soil covered the railway, causing the railway to be stopped for several days. Since the tunnel was built in 1928 until landslides occur in 2016 which means it has been 88 years. The landslide can be caused by several factors, these factors are slope geometry, physical and mechanical characteristics of rocks or soil, geological structure, hydrology and hydrogeology, and external forces such as ground vibration due to railway traffic and earthquake. The results of research on the main causes of landslides in the mouth of the railway tunnel include relatively steep morphological influences, degradation of rock strength due to weathering, dip rock structure in the direction of slope, and ground vibration due to earthquakes. Based on field observations, the slope next to the case study area of the landslide is also unstable. Therefore, it is necessary to analyze the slope stability in the area that has the potential to landslide, using a pseudo-static slope stability analysis on the consideration of the effect of ground vibration due to earthquakes is quite significant to slope stability. The results of the pseudo-static slope stability analysis is showing out that the factor of safety is around 1.22-1.16 with a seismic coefficient of 0.10-0.125 g. To anticipate future landslide we suggest to be conducted studies on slope stabilization methods including building retaining walls, drainage channels and shotcrete walls.

Ön Yüzü Geomembran Kaplı Yüksek Bir KayaDolgu Barajın Deprem ve Geomembranda Yırtık Olması Durumunda Performansının Değerlendirilmesi

This paper presents stability and seepage evaluation of a high rockfill dam with a geomembrane seepage barrier by considering scenarios of a possible occurrence of a large earthquake due to the active faults in the region and also a seepage flow in the dam due to a possible rupture of the geomembrane liner. For this purpose, finite element transient seepage and pseudo static slope stability analyses were both carried out together to assess the critical potential failure surfaces and safety factors of the rockfill slopes. Therefore, pore water pressures on the failure surfaces were first calculated using the time varying (transient) numerical seepage analyses method which is essentially important to determine the time dependent variations of seepage paths and water pressures within the rockfill as well. In the analyses, it was determined that the most critical slope failure case is when a geomembrane liner tears at the time of the highest reservoir water elevation since the hydraulic head is maximum and causes the largest seepage pressure in the rockfill there. Analyses showed that if a strong earthquake struck the region, both the upstream and downstream slopes are safe with sufficiently high safety factors. In addition, in case of a possible tear and leakage on the geomembrane liner, the dam will also withstand well with 2.25 horizontal to 1 vertical slopes. However, it is recommended that constructing a downstream toe drain or a relief well will provide an additional safety measure against any heave occurrence or instability of the rockfill since the embankment and bedrock foundation are pervious causing high seepage pressures at the downstream toe of the dam.

A simplified approach for studying the influence of vertical accelerations on seismic response of slopes

ABSTRACTA simplified approach is presented for estimating permanent displacements in slopes as a result of both vertical and horizontal seismic accelerations. A study of 52 earthquake records showed that the time difference between maximum horizontal and vertical accelerations varied between 0 and 10.3 s. The approach is illustrated for an earth dam embankment by analysing the effects of five of the above earthquake records. The approach combines a pseudo-static slope stability analysis for estimation of the critical (or yield) horizontal-vertical acceleration combinations, and a Newmark type displacement analysis. Guidelines are presented for conservative choice of soil strength parameters of saturated clays for use in the stability analysis. While permanent displacements of up to 40 cm were predicted without considering the vertical acceleration component, no additional displacement above 3.5 cm resulted when this component was included. The predicted additional displacement was consistently less than 10%, and in 50% of the analyses, vertical acceleration led to smaller predicted displacements. The simple approach may be applied in analysis for any slope using real earthquake records. Using existing, empirical expressions for permanent displacement, based only on horizontal accelerations, the effect of the vertical accelerations may be conservatively estimated by increasing the displacement by 10%.

A comparative study of pseudo-static slope stability analysis using different design codes

Many researchers have developed new calculation methods to analyze seismic slope stability problems, but the conventional pseudo-static method is still widely used in engineering design due to its simplicity. Based on the Technical Code for Building Slope Engineering (GB 50330—2013) of China and the Guidelines for Evaluating and Mitigating Seismic Hazards in California (SP117), a comparative study on the pseudo-static method was performed. The results indicate that the largest difference between these two design codes lies in determination of the seismic equivalence reduction factor (feq). The GB 50330—2013 code specifies a single value for feq of 0.25. In SP117, numerous factors, such as magnitude and distance, are considered in determining feq. Two case studies show that the types of slope stability status evaluated by SP117 are in agreement with those evaluated by the seismic time-history stability analysis and Newmark displacement analysis. The factors of safety evaluated by SP117 can be used in practice for safe design. However, the factors of safety evaluated by GB 50330—2013 are risky for slope seismic design.

Performance-Based Probabilistic Seismic Slope Displacement Procedure

Engineers often use simplified seismic slope displacement procedures to evaluate the seismic performance of earth structures and natural slopes. Current state of practice procedures typically separate the estimation of the ground motion intensity measure ( IM) from the estimate of seismic displacement ( D), given the selected IM hazard level. Thus D is estimated based on a single IM value. A straightforward performance-based seismic slope assessment procedure is proposed, which considers the full range of potential IM values to estimate seismic slope displacements directly related to a hazard level. Seismic performance is assessed through either a Newmark-type seismic displacement estimate or a calibrated seismic coefficient that can be used in pseudostatic slope stability analyses. The procedures were developed for a wide range of earth systems for shallow crustal earthquakes and subduction zone earthquakes. Currently employed simplified slope displacement procedures do not provide consistent assessments of the actual seismic slope displacement hazard. The proposed procedures can be readily used in practice to perform rigorous performance-based seismic slope displacement hazard assessments.

Estimation of seismic slope displacements in North Anatolian Fault Zone, Karamürsel (Kocaeli,Turkey)

The seismic stability of slopes and earthquake induced displacements should be evaluated with particular emphasis on earthquake records with site specific geological and geotechnical setting. The right lateral strike slip North Anatolian Fault (NAF) caused considerable damage on environment and residential areas of northern Turkey during the devastating 17.08.1999 Marmara and 12.11.Duzce earthquakes. Several mass movements have occurred around Karamursel, Oluklu, Ihsaniye, Hayriye and Yalakdere towns of Kocaeli within weathered/completely weathered Upper Cretaceous aged flysch, Eocene aged flysch and Pliocene soil deposits. A total of 38 instabilities were encountered and classified during the field studies. Geotechnical data were compiled from previous work and trial pits. Pseudostatic slope stability analysis were conducted along the identical slopes selected from the geological units. Peak ground acceleration values were picked up from stations, located around the study area. The static factor of safety values were calculated for slopes for each lithological unit. The critical acceleration values to cause seismic displacement were extracted from pseudostatic analyses. Variation of seismic displacements based on different amplitudes of a single scenario earthquake was calculated by double integration. Earthquake triggered seismic displacements could reach up to 46 cm based on the such scenario earthquake record of Marmara earthquake. Failed slopes and quiescent slopes might be triggered by an earthquake. This must be considered during land use planning for any single residence or agricultural purposes.

Investigation of the failure mechanism and stabilization of a landslide in weathered tuffite, Giresun, northeastern Turkey

This study investigates the causes and failure mechanism of the Aksu landslide that occurred during the construction of the Giresun–Espiye road between KM: 1 + 030–1 + 170 in northern Turkey and recommends proper stabilization techniques. For the purpose of investigating the causes and mechanism of this slope failure, engineering geological mapping, geotechnical investigation and rock mass characterization were performed. From top to bottom, weathered tuffite, tuffite, flysch, and dacitic tuffite were the major units in the study area. The disturbance of the slope by the excavations performed at the toe of the slope (i.e., due to the foundation excavation for the Tunel restaurant building and for the road cut) led to a “translational slide”. The “translational slide” occurred in completely weathered tuffite due to the disturbance of the stability of the slope by the excavations performed at the toe of the slope, particularly for the foundation excavation of the Tunel restaurant building and for the road cut along the Giresun–Espiye road. The rise in the groundwater level was also another important factor that has contributed to the occurrence of the landslide. After establishing the geometry of the landslide in detail, the shear strength parameters of the failure surface were determined by the back analysis method. Sensitivity analyses were performed and landslide failure mechanisms were modeled to quantify the contributing factors that have caused the formation of the Aksu landslide. The influence of an earthquake was investigated through pseudostatic slope stability analysis. Toe buttressing, ground water drainage, and surface water drainage alternatives were considered for stabilizing the slope.

Slope failures in residential land on valley fills in Yamamoto town

As a result of the 2011 off the Pacific Coast of Tohoku Earthquake, five slope failures occurred in a residential area on artificial valley fills in Taiyo New Town, Yamamoto, Miyagi Prefecture. The site was constructed by leveling a hilly area and using the cut materials as fill for the valleys to provide foundation ground for houses. The fill material was sandy and was derived from the weathering of tuffaceous sandstone which had formed the natural ground. Each of the five slope failures was observed to have occurred either at the edge of the artificial valley fills or within the embankment sections that had been widened for road construction. Laboratory tests show that the fill, which had a fines content of Fc=20%, had a very low liquefaction resistance, which further decreased with the application of initial shear stress. A pseudo-static slope stability analysis, using conventional strength parameters, could not explain the slope failure at one of the sites that failed, but it could explain the slope failure when the dynamic strength was used to represent the soil strength at the slip surface. Thus, the slope failures in Taiyo New Town, at least at the one site analyzed in this study, could be attributed to the liquefaction of the fill material induced by the intense shaking.

Cyclic shear behavior and seismic response of partially saturated slopes

In order to quantitatively investigate the effects of degree of saturation on the cyclic shear characteristics and seismic response of sloping grounds, undrained cyclic triaxial tests and online pseudo-dynamic response tests were conducted on decomposed granite (Masado) soil samples. Online testing is a method of feeding soil response characteristics directly from soil samples into a modeling algorithm. In the both series of tests, soil specimens prepared under different degrees of saturation and subjected to various initial shear stresses were tested. The results obtained from the tests quantitatively confirmed the notion that unsaturated soils do not undergo large strength decrease as fully saturated ones do. The initial static shear stress and applied dynamic stress define the mode of failure of the soil. Higher saturation ratio and/or steeper slopes lead to lower cyclic resistance and larger deformation. The experimental results obtained were then used in conjunction with pseudo-static slope stability analysis and modified Newmark sliding block model to estimate the deformation of embankments which were under different degrees of saturation. The example calculations clearly showed the effect of saturation on the magnitude of seismic-induced displacements of embankments.

A grade-3 method of zonation for seismic slope stability: An Italian case study

This paper presents a seismic microzonation study performed in an area of the Northern Apennines (Italy) in order to reduce the level of risk from landslide hazard, to support decisions in urban planning and to provide useful information for building design. The area in question measures about 2.6km2 and is characterised by considerable landslide susceptibility also in non seismic conditions as evidenced by a number of surveys carried out over the past years. The slope deposit, lying over a marley-arenaceous formation, shows a variable thickness from a few metres to 30m and consists of fine silty-clay, clay-sandy and silty-sandy soil in a variable amount. Quiescent and active landslide areas with ground movements involving the shallowest layers of the soil deposit have been detected.Given the relatively high seismicity of the region, the aim of this study is to describe the principles and criteria adopted in a seismic risk analysis conducted over a limited area in order to carry out a very high and detailed level of zonation for ground motion and slope stability (i.e., Grade 3 according to the definition in the Manual for Zonation on Seismic Geotechnical Hazards). For this purpose, reliable expected earthquakes were assumed and in-depth geologic, geomorphologic, geotechnical and geophysical analyses were carried out to define a subsoil model for performing numerical analyses of local seismic response and slope stability in both non-seismic and seismic conditions. The proposed methodology consists of the following three steps: (i) identification of a number of seismic inputs for the numerical analyses; (ii) implementation of numerical analyses to evaluate the amplification of ground shaking and to assess potential for slope failure; (iii) mapping of homogeneous areas with respect to expected site amplifications and landslide risk. The study allowed the mapping of four zones which are expected to be homogeneous in terms of both amplification factor of seismic motion (FA) and safety factor against landslide (FS). Quiescent and active landslide zones were thus identified with greater accuracy together with the most probable sliding surfaces. For this purpose, a 1-D numerical code was adopted for seismic response analyses and limit equilibrium methods were implemented and numerically solved in static and pseudo-static slope stability analyses.

Stability charts for pseudo-static slope stability analysis

Most design manuals and codes recommend a simple pseudo-static approach for analysis of slope stability under seismic conditions. Exceptions to this recommendation include problems involving liquefaction, soils exhibiting significant strength loss under cyclic loading, and exceptionally large earthquakes. These unusual situations are not considered in the present work. Conventional applications of the pseudo-static approach are based on slice methods which involve various kinematic and static assumptions. The present work is based on a variational formulation of limiting equilibrium and a strength reduction procedure. The advantage of these formulations is that they do not involve kinematic and/or static assumptions. The main purpose of the present work is to present a design chart for pseudo-static analysis of homogeneous slopes applicable over a wide range of input parameters. Such charts are useful for preliminary design, and allow the designer to assess the effects of various parameters on stability “at a glance”.

Assessment of Seismic Slope Stability Using GIS Modeling

In recent years there has been a growing interest in developing GIS based models for mapping and identification of seismically-induced landslide hazards. A review of assumptions in the relationships and the data typically used in GIS seismic slope stability models, shows that there are three components which are commonly used together: pseudo-static slope stability analysis, attenuation of ground shaking models, and Newmark's displacement method (Newmark 1965). These relationships are typically combined in a raster or vector data model to produce a map of seismically-induced landslide displacements. To produce a map of ground displacement, a digital coverage of the geology and a high resolution DEM are needed at the very least. Additional data layers such as shear strength parameters and soil depth can be estimated from the geology and they can add to the sophistication and accuracy of the model. A case study was developed which combines the components of site and slope response in a vector data model and the results show that qualitatively acceptable results can be readily obtained. However, the model falls short of capturing the overall performance of any particular slope and at best it only provides a mean estimate of the potential seismically induced slope displacement. Thus, more sophisticated methods of slope and site response will have to be implemented in this platform to increase the robustness of the model. In particular, the resolution and quality of input data sets will have to be improved and rigorous probabilistic procedures will have to be implemented, so that the error bounds and the magnitude and the source of errors can be fully quantified.

Back Analysis Technique for Slope Stabilization Works of Embankment Landslide Due to Foundation Instability

ABSTRACT This paper deals with the overall stability of an embankment foundation failure that lies at km 40 + 700 of the new Irbid-Amman Highway in Jordan. Slope stability back analysis was carried out for the slope to assess the conditions at time of failure, and estimate most representative shear strength parameters of foundation materials. Slope stability analysis was also carried out for proposed remedies. Probabilistic seismic hazard analysis was carried out for the landslide site. Peak Ground Acceleration (PGA) value of 0.2 g was estimated for design. This corresponds to a 90% probability of non-exceedence in a 50 year design life of the highway. Pseudo-static slope stability analysis was also carried out. The study concluded that the landslide movement occurred within the foundation colluvium material. It resulted primarily from the excessive load of the embankment and excess piezometric pressures generated within the slope. The most feasible remedial measure to stabilize the landslide area was removal of existing failed embankment down to the top of sandstone layer, and reconstruction (using imported free-drainage rockfill) of a split level embankment together with the construction of surface and subsurface drainage system. These measures were successfully implemented in the field.

Damage at Sürgü Dam during May 5, 1986, Malatya, Turkey, Earthquake

On May 5, 1986, an earthquake of magnitude about 6 struck South Anatolia, creating widespread damage at rural structures and causing extensive longitudinal cracks at the crest of Sürgü Dam. In this paper general information about the earthquake is given and the results of block-mass and circular arch types of pseudo-static slope stability analyses are presented. It has been concluded that the critical acceleration levels obtained from the analyses are under the expected acceleration levels at the dam's body during the earthquake. Probabilistic findings based upon seismicity observed in the last century indicate that substantially higher level of ground shaking may occur at the dam site. Such occurrences are considered to cause hazardous damage to the dam.