Soil stability under earthquakes: a sensitivity analysis

The slope stability behaviour of cohesive and cohesionless soil slopes was evaluated under earthquakes with different frequencies and amplitudes (0.01 to 1.0 g). The study focused on the computation of slope instability thresholds at different slope heights (5, 10 and 15 m) and inclinations. This parametric analysis was performed with a nonlinear finite element method (FEM) in plane strain using the Mohr Coulomb constitutive model and accounting for stiffness and strength increase with depth. The steepest slope for each soil type was defined as the slope at its marginal stability with a safety factor under static conditions between 1.01-1.06. All the acceleration histories were sinusoidal functions at frequencies of 1, 2 and 4 Hz. The amplitude of these accelerations was gradually increased until the point they initiated instabilities in the slopes. These accelerations were denoted by critical peak accelerations (PGAc). This study demonstrates that lower peak accelerations (PGA) are needed to trigger instabilities at steeper slopes. Also, the highest frequency used in this parametric study (4 Hz) has higher PGAc, and in most cases the lowest frequency (1 Hz), which is close to the natural frequencies of the site (0.6 to 1 Hz) experience the lowest PGAc. The strength of the materials also governs the sliding thresholds, being higher for the stronger ones

Role of numerical model and parameter variability on seismic response of slopes: the case of Las Colinas landslide

This paper presents the results of a sensitivity analysis on the influence of the strength, stiffness and damping parameters of the soil on the seismic response of a real slope. The analyses have been performed for the Las Colinas slope (El Salvador) using the finite element code PLAXIS and the data available in the literature. Las Colinas landslide was a destructive event which was triggered by the El Salvador earthquake on 13 January 2001. During this event, 183˙500 m3 of volcanic deposit slid and struck the houses on the foothill, killing 500 people. In this study a sensitivity analysis was performed to highlight the influence of the parameter uncertainties on the seismic response of the slope. The sensitivity analyses on the stiffness and strength parameters of the soil were performed by using their low, best and high estimates, using reported data and empirical equations. The sensitivity studies on the damping factor showed an unexpectedly large influence on the results. For a better understanding of this issue, the role of damping in each layer on the total response was examined separately. In addition, the effects of mesh and model sizes, as well as performance of different boundary conditions were investigated. The results show that, while a suitable numerical tool is in general capable of predicting and simulating the seismic response and failure of a complex slope, it is essential to undertake a careful evaluation of the mechanical parameters and modelling features. The results also show that for a realistic assessment of the uncertainties of the response it is important to identify the parameters that have the largest influence on the total response

Identification of effective properties of the railway substructure in the low-frequency range using a heavy oscillating unit on the track

As the demand for predictions of train-induced vibrations is increasing, it is essential that adequate parameters of the railway structure are given as input in the predictions. Gathering this information can be quite time-consuming and costly, especially when predictions are required for the low-frequency emission. This article presents a procedure for deriving the effective properties of the foundation under the sleepers of a railway track from measurements taken with a heavy oscillating unit on the track. The unit consists of two masses inside a modified freight car that exert a dynamic force in the range 3–30 Hz on one of the two axles. The ratio of force applied on the axle over the resulting response measured with an accelerometer is studied. The foundation of the sleepers is modelled using a frequency-dependent complex-valued dynamic stiffness.Design and ConstructionCivil Engineering and Geoscience