Pseudo-static Stability Analysis Research Articles

Estimating sliding displacement of slopes induced by earthquake sequences based on the finite element method

After shocks trigger or worsen landslides by exacerbating damage to slopes. In this study, slope sliding displacements induced by seismic sequences were calculated. The combined effects of mainshocks and aftershocks on slope sliding were examined in this study using 273 ground motion records from real seismic sequences. A three-layer clayey slope was modeled in OpenSees. The ground motions were input for dynamic analysis to calculate the corresponding sliding displacements. More than 20% of the seismic sequences caused slope instability. The Arias intensity (Ia) of the mainshock had the strongest correlation with sliding displacements. The strength reduction technique was used for the pseudo-static stability analysis of the slope whose yield acceleration (ky ) value was 0.23g. The Newmark method computed smaller displacements compared to the finite element method which calculated the dynamic behavior of the slope more accurately when Ts/Tm > 0.1. The Ia of the mainshock was the optimal parameter. An empirical model based on finite element numerical analysis was proposed for predicting slope sliding displacements induced by seismic sequences. The predictive model, unlike the traditional rigid sliding block method, prevented some unrealistic assumptions. The proposed model was more conservative than numerical algorithm-based predictive models that compute only the mainshock effect.

Pseudo-static stability analysis of a laterally confined dip slope investigated by dynamic centrifugal models

Pseudo-static stability analysis of a laterally confined dip slope investigated by dynamic centrifugal models

Static and pseudo-static stability analysis of right earthen embankment of nagarjuna sagar dam by geostudio

To ensure the safety of the dam, stability assessment of the dam is necessary. The objective is to perform slope stability analysis for upstream, downstream and seepage analysis during steady state, transient seepage conditions and to know about the displacement occurred at history nodes by the application of pseudo-static ground motion. The present work deals with the behavior of the Right earthen embankment of Nagarjuna Sagar which is in earthquake prone area of Zone-II (as per IS 1893-2002). Stability parameters slope, seepage and earthquake analyzed by SLOPE/W, SEEP/W, QUAKE/W tools in GeoStudio 2022 (finite element modeling based software). The model with full reservoir level is first analyzed by SEEP/W to find piezometric line which is basis to perform SLOPE/W for finding slope stability. Later an earthquake motion of 0.1 peak ground acceleration is subjected to it by using QUAKE/W. It is concluded from results, that obtained factor of safety lie within safety limits and seepage loss observed during the design life of 100 years is 562290 m3, 3431117 m3 for steady state and rapid drawdown.

Stability Charts for Pseudostatic Stability Analysis of Rock Slopes Using the Nonlinear Hoek–Brown Strength Reduction Technique

This paper presents a set of stability charts for the stability assessment of rock slopes that satisfy the Hoek–Brown (HB) criterion under various seismic loading conditions. The nonlinear Hoek–Brown strength reduction technique is used to conduct pseudostatic stability analysis of rock slopes subjected to horizontal seismic excitation. Based on an extensive parametric study, first, a set of stability charts with a slope angle of β = 45° under static and pseudostatic conditions are proposed by using ABAQUS 6.10 software. Second, the slope angle weighting factor (fβ) and the seismic weighting factor (fkh) are adopted to characterize the influence of slope angle (β) and horizontal seismic acceleration coefficient (kh) on the rock slope stability. Finally, the reliability of the proposed charts was validated by three typical examples and two case studies, and the results show that the values of the factor of safety (FOS) obtained from the proposed charts are consistent with the values from other methods. The proposed charts provide an efficient and convenient way to determine the FOS of rock slopes directly from the rock mass properties (γ and σci), the HB parameters (mi and GSI), the slope geometry (H and β), and the horizontal seismic coefficients (kh).

Pseudo-static stability analysis of wedges based on the nonlinear Barton-Bandis failure criterion

This paper investigates the stability of a three-dimensional (3D) wedge under the pseudo-static action of an earthquake based on the nonlinear Barton-Bandis (B-B) failure criterion. The influences of the mechanical parameters of the discontinuity surface, the geometric parameters of the wedge and the pseudo-static parameters of the earthquake on the stability of the wedge are analyzed, as well as the sensitivity of these parameters. Moreover, a stereographic projection is used to evaluate the influence of pseudo-static direction on instability mode. The parametric analyses show that the stability coefficient and the instability mode of the wedge depend on the mechanical parameter of the rock mass, the geometric form of the wedge and the pseudo-static state of the earthquake. The friction angle of the rock φb, the roughness coefficient of the structure surface JRC and the two angles related to strikes of the joints θ1 and θ2 are sensitive to stability. Furthermore, the sensitivity of wedge height h, the compressive strength of the rock at the fracture surface JCS and the slope angle α to the stability are insignificant.

Pseudo-static Analysis of Reinforced Soil Wall Based on Pasternak Model

One of the major reasons for the popularity of reinforced soil structures is their ability to perform better under seismic loading conditions. This could be attributed to the conservatism associated with the design procedure that considers only the axial direction of the pullout force rather than an appropriate seismic design. The kinematics of failure, however, suggests that the direction of the pullout force is not axial, and it is inclined to the horizontal direction. This paper presents the pseudo-static stability analysis of a reinforced soil wall considering the obliquity of the pullout force, where the backfill soil is idealized as a two-parameter Pasternak model. The effect of various controlling parameters such as horizontal seismic coefficient, material properties of the backfill and the wall geometry on the pullout response is also studied under the seismic loading conditions. The results are compared with the conventional methods of analysis. The comparisons show that the present analysis removes the extra degree of conservatism prevailing in the conventional methods and thus gives a better estimation of the pullout capacity. A typical design of reinforced soil wall is also shown to demonstrate that the present analysis can be easily integrated with the existing methods.

Stability Charts for Pseudostatic Stability Analysis of 3D Homogeneous Soil Slopes Using Strength Reduction Finite Element Method

This paper uses the modified strength reduction finite element method to propose stability charts for pseudostatic stability analysis of three‐dimensional (3D) homogeneous soil slopes subjected to seismic excitation. These charts are developed in a wide range of input parameters for purely cohesive slopes and cohesive‐frictional slopes, respectively. Effect of the horizontal seismic load is approximately considered using the quasistatic approach. The stability charts allow to determine the factor of safety without any iterative procedure and identify the corresponding critical slope failure mechanism. A slope example is employed to illustrate the application and reliability of these stability charts.

Framework to assess pseudo-static approach for seismic stability of clayey slopes

Approaches commonly used to assess the seismic stability of slopes range from the relatively simple pseudo-static method to more complicated nonlinear numerical methods, e.g., finite element (FE) and finite difference (FD). The pseudo-static method, in particular, is widely used in practice as it is inexpensive and substantially less time consuming compared to the much more rigorous numerical methods. However, the pseudo-static method is widely criticized because it does not take into account the effects of the earthquake on the shear strength of the slope material nor the seismic response of the slope. Hence, some researchers recommend its use only in slopes composed of cohesive materials that do not develop significant pore pressures or that lose less than about 15% of their peak shear strength during earthquake shaking. However, the use of the pseudo-static method in these soils is also problematic as clayey slopes generally fail in pseudo-static stability analyses (i.e., factors of safety are less than 1) and the failure surface is completely predominated by the thickness of the clayey layer in the slope or foundation. The reliability of the pseudo-static method in natural clayey slopes is examined here based on rigorous numerical simulations with FLAC. The numerical results are compared and verified using available static and dynamic 1g laboratory tests. This article then addresses some of the crude assumptions of the pseudo-static method and provides practical suggestions to be applied to refine the outcomes of pseudo-static analyses not only in terms of the computed safety factors, but also in the prediction of the failure surface through the consideration of additional aspects of the dynamic responses of the clayey slopes.

Determination of the safety factor of the slope in homogenous low-height earth dams using pseudo-static stability analysis

Determination of the safety factor of the slope in homogenous low-height earth dams using pseudo-static stability analysis

Pseudo-static stability analysis of rock slopes reinforced by passive bolts using the generalized Hoek–Brown criterion

The stability analysis of passive bolt-reinforced rock slopes under seismic loads is investigated within the framework of the kinematic approach of limit analysis theory. A pseudo-static method is adopted to account for the inertial forces induced in the rock mass by seismic events. The strength properties of the rock material are described by a modified Hoek–Brown strength criterion, whereas the passive bolts are modeled as bar-like inclusions that exhibit only resistance to tensile-compressive forces. Taking advantage of the ability to compute closed-form expressions for the support functions associated with the modified Hoek–Brown strength criterion, a rotational failure mechanism is implemented to derive rigorous lower bound estimates for the amount of reinforcement strength to prevent slope failure. The approach is then applied to investigating the effects of relevant geometry, strength and loading parameters in light of a preliminary parametric study. The accuracy of the approach is assessed by comparison of the lower bound estimates with finite element limit analysis solutions, thus emphasizing the ability of the approach to properly predict the stability conditions and to capture the essential features of deformation localization pattern. Finally, the extension of the approach to account for slipping at the interface between reinforcements and surrounding rock mass is outlined.

Unconventional pseudostatic stability analysis of the Diezma landslide (Granada, Spain) based on a high-resolution engineering-geological model

A novel unconventional pseudostatic analysis is proposed here to infer on the sensitivity of a landslide to earthquakes characterized by different physical properties. Several sine waves with different amplitudes, frequencies and phases were applied to the landslide mass assuming limit equilibrium conditions. The unconventional approach was used for the Diezma landslide case study. The landslide is located 25km from the city of Granada (Spain). Although the slope had repeatedly suffered small-scale stability problems since the construction of the A-92 highway, a larger failure occurred on 18 March 2001 and damaged the highway between kilometers 272.6 and 272.8. The landslide had an estimated volume of 1.2Mm3 and involved a disordered deposit of silt and clay with heterometric blocks within the Numidoide Formation, which outcrops along the contact between the Maláguide and Dorsal domains of the Betic Cordillera mountain range. Despite the 18 million Euros spent since 1999 on geotechnical investigations and stabilization solutions, the numerous reactivations that occurred through 2010 and 2013 demonstrate the persistent activity of the landslide.The geometry of the large slope failure corresponding to the first activation of the Diezma landslide was used to back-analyze the stability of the slope based on a high-resolution engineering-geological model. The model was developed from the analysis of numerous borehole logs as well as from geophysical investigations consisting of seismic noise measurements.The results demonstrate that the safety factor (SF) of the Diezma landslide varies significantly for frequencies less than 1Hz; moreover, unstable conditions are reached at frequency values between 0.5 and 1Hz for water pressure distributions corresponding to Bishop factors (ru) between 0 and 0.36. To estimate the co-seismic displacements, the geometrical and mechanical properties of the landslide mass were used to derive its characteristic periods for thickness (Ts) and length (Tl), which were compared with the characteristic period of the earthquake (Tm). The results indicate that the maximum expected co-seismic displacements are up to 2m for an earthquake with a Tm value close to 1s and an Arias Intensity on the order of 1m/s.

Slope stability assessment of a re-activated landslide on the Artvin-Savsat junction of a provincial road in Meydancik, Turkey

The purpose of this study is to determine the most suitable remediation techniques for an active landslide area in Turkey, using a geological engineering assessment of a re-activated landslide that occurred during the construction of the Artvin-Savsat Junction on the Meydancik Provincial Road, at Km: 12 + 200. For this, the geotechnical parameters of the mobilized geological material—which is colluvium along the sliding surface—were determined by back analyses of the landslide at three geological sections. The landslide was then modeled along the most representative section of the study area by considering its mechanism, the parameters determined from the geotechnical investigations, the size of the landslide, and the location of the slip circle. In addition, pseudo-static stability analyses were performed comprising the earthquake potential of the site. The most suitable slope remediation technique was decided using the surface and subsurface conditions. The shear strength parameters were specified as c = 0 kPa and ϕ = 10° for the landslide material and pre-stressed anchoring was considered as a remediation method.

Vertical acceleration response of horizontally excited reinforced walls

ABSTRACT: An understanding of the vertical acceleration response of geosynthetic-reinforced slopes subjected to horizontal input ground excitations is essential to robust seismic design. A series of stepwise intensified shaking tests was performed using simple sinusoidal waves with various horizontal peak ground accelerations (HPGA = 0.2–1.0g where g = gravitational acceleration) and wave frequencies (f = 3, 6 and 15 Hz) to investigate vertical acceleration responses at the crest of a reinforced model slope subjected to horizontal input ground excitations. Vertical accelerations at the edge of the slope crest (av1) occurred under relatively small HPGA associated with a negligibly small displacement of the slope. A large vertical acceleration of the unreinforced zone (av2) occurred under relatively large HPGA associated with a large displacement of the slope. Measured horizontal peak acceleration (ahp) against vertical peak acceleration (avp) at the crest of the slope indicate that values of avp under a specific HPGA increase with increasing input wave frequency. At the verge of the ultimate displacement state, values of avp at the crest of the unreinforced zone were consistently greater than those for the crest of the reinforced zone, suggesting that a downward slump of the failure wedge behind the reinforced zone occurred at the ultimate displacement state of the slope. Pseudo-static stability analyses were performed for the tested slopes based on the observed range of vertical-to-horizontal acceleration ratio (λ) at the crest of slopes loaded with f = 3 and 6 Hz. It was shown that the influence of λ on the critical seismic coefficient (khc) of the slope increases with increasing reinforcement force. Values of khc decreased by 8–30% when λ increased from 0 to +1.5, indicating that a vertical acceleration induced by the slump of the soil mass plays a role in destabilising the slope and/or in increasing the plastic displacement of the slope.

A study on geotechnical characterization and stability of downstream slope of a tailings dam to improve its storage capacity (Turkey)

Tailings, waste products of the ore-dressing processes, are usually stored in a slurry form and pumped into sedimentation pond which is surrounded by natural heights and/or artificial walls. The database of International Commission of Large Dams and United Nations Environment Programme showed that several hundreds of tailings dam have failed since 1910. One of the reasons of these failures is slope instability. Construction of mine tailings dams in Turkey has started to increase, particularly in the recent decade. This paper focuses the study undertaken to assess the geotechnical characteristics and stability of downstream slope of a tailings dam at a copper-zinc mine in the Black Sea Region of Turkey. At the mine site there are two tailings dams located at two different elevations. The upper dam was completely filled and is out of service. Increasing amount of tailings filling the pond of the lower dam resulted in a limited storage, and therefore, it has been decided that heightening of the dam about 7 m to improve its storage facility would be necessary. For the purpose, a series of investigations in the vicinity of the tailings dam and some geomechanical laboratory tests were carried in conjunction with the use of empirical methods to determine mechanical properties of the current dam material, tailings and the rockfill material that will be used for heightening of the dam. The results of the static and pseudo-static stability analyses based on the methods of limit equilibrium and numerical modelling indicated that circular and non-circular failures are the most critical modes of failure for the dam and safety factor gradually decreases when the tailings rise up to a specific elevation in the pond. However, the ranges of the calculated safety factors from both methods are considerably similar and suitable for heightening of the dam by 7 m in terms of stability. The results suggest that any instability is not expected under both static and dynamic conditions after the current height of the tailings dam is increased by 7 m, if the slope geometry considered in the analyses is not changed and the tailings in the pond do not rise up to an elevation of about 475 m. In addition, magnitude of permanent settlement of the dam due to a probable earthquake was also assessed using two empirical methods and the results from both methods showed similar amount of settlements which were in tolerable limits.

Soil slopes under combined horizontal and vertical seismic accelerations

Conventional methods of designing earth structures are based on pseudo-static stability analysis employing a horizontal seismic coefficient. This paper discusses the stability and permanent displacement of a slope subject to combined horizontal and vertical accelerations. A log-spiral failure mechanism is used. It is shown that seismic force has a significant effect on stability and permanent displacement of slopes. The parametric study reveals that vertical acceleration may play an important role on stability and permanent displacement if the corresponding horizontal acceleration is large. © 1997 John Wiley & Sons Ltd.

Mitigative Design for Colluvial Slope Instability, Wadi Es-Sir Sewage Treatment Plant, Jordan

Lagoons were constructed within colluvial deposits in an area of 140,000 m2 as part of Wadi Es-Sir Sewage Treatment Plant Project in Jordan. The site has been excavated into steps and risers to construct the lagoons. A major noncircular slope failure occurred in October 1993 on the upper slope of the middle lagoon, resulting in an interruption of construction. Field and laboratory investigations were conducted to identify various geomorphologic zones, stratigraphy and geotechnical properties of all materials encountered at the site. Slope stability back analysis of failed slope was carried out using the 2-D limiting equilibrium Simplified Janbu method. Also, stability analysis was carried out for existing and improved conditions for all lagoons. Dry, partially saturated and fully saturated conditions were considered in the analysis. Pseudostatic stability analysis of the slopes was carried out considering a horizontal bedrock Peak Ground Acceleration (PGA) value of 0.2 g, evaluated at the site using a line source probabilistic seismic hazard assessment model incorporated in the computer program FRISK (McGuire, 1978). The study showed that the failure occurred through colluvial material due to the removal of a large amount of such materials near the toe of the slope during construction of the lagoon. The location of the slip surface was between 8 to 12 m in depth. Effective residual shear strength parameters along the failure plane were found to be: angle of friction (ϕ′) = 17°, and cohesion (c′) = 0.05 kg/cm2. Stability conditions for slopes at all lagoon sites were found to be unacceptable. Recommended measures to stabilize the slopes include replacing (partially or fully) the existing colluvial materials with free-drained rockfill to reach acceptable factors of safety under design conditions. These measures were implemented at the site.