Seismic earth pressures on rigid and flexible retaining walls

While limiting-equilibrium Mononobe–Okabe type solutions are still widely used in designing rigid gravity and flexible cantilever retaining walls against earthquakes, elasticity-based solutions have been given a new impetus following the analytical work of Veletsos and Younan [23]. The present paper develops a more general finite-element method of solution, the results of which are shown to be in agreement with the available analytical results for the distribution of dynamic earth pressures on rigid and flexible walls. The method is then employed to further investigate parametrically the effects of flexural wall rigidity and the rocking base compliance. Both homogeneous and inhomogeneous retained soil is considered, while a second soil layer is introduced as the foundation of the retaining system. The results confirm the approximate convergence between Mononobe–Okabe and elasticity-based solutions for structurally or rotationally flexible walls. At the same time they show the beneficial effect of soil inhomogeneity and that wave propagation in the underlying foundation layer may have an effect that cannot be simply accounted for with an appropriate rocking spring at the base.     

A Potential Mitigation Measure for the Seismic Distress of the Circuit Wall at the Acropolis of Athens

Geotechnical and Geological Engineering - The seismic design of new retaining structures is usually performed following modern seismic norms. Nonetheless, there are various monumental retaining...     

Analytical evaluation of the dynamic distress of rigid fixed-base retaining systems

The current study proposes an analytical closed-form solution for the dynamic distress of rigid fixed-base retaining systems aiming at evaluating the main assumptions and limitations of the pertinent available elasticity-based methods. The new solution is actually an extension of the well-known model of Wood and is capable of evaluating the dynamic distress of either a single or a pair of rigid fixed-base walls interacting with each other, in the case of harmonic base loading. Wall distress is mainly evaluated in terms of dynamic earth pressures, shear forces and bending moments, while the original concept of a “distress spectrum” is introduced as a potential new tool for the seismic design of retaining structures. Distress and wall deformation are interrelated in a number of three-dimensional graphs, where dynamic interaction phenomena are evident. Finally, given the rigorous nature of the new solution, its results verify qualitatively and quantitatively the negligible amplitude of the computational errors of the approximate elasticity-based solutions proposed in the literature.     

Topography and Soil Effects in the MS 5.9 Parnitha (Athens) Earthquake: The Case of Adámes

Large concentration of damage to residential and industrial buildings occurred in regions near the banks of the Kifisos river canyon during the 7-September-1999 Parnitha (Athens) Earthquake. One such region, which experienced unexpectedly heavy damage, was the small community of Adámes, which borders the canyon near its deepest point. To explore whether in addition to structural factors the particular topographic relief and/or the actual soil profile contributed to the observed concentration and non-uniform distribution of damage within a 300 m zone from the edge of the canyon cliff, wave propagation analyses are conducted in one and two dimensions. Finite-element and spectral-element formulations are used to this end. To avoid spurious wave reflections at the artificial boundaries, ourtwo-dimensional (2-D) finite-element analyses utilize Bielak's Effective Seismic Excitation method. Soil layering and stiffnesses are determined from 10 SPT-boreholes and 4 crosshole tests. Ricker wavelets and six realistic accelerograms are used as excitation; two of the latter are selected from the literature and four are obtained on the basis of the four strongest motions of the earthquake, recorded in central Athens.The results show that the 2-D topography effects are substantial only within 50 meters from the canyon ridge. These effects materialize only in the presence of the relatively soft soil layers that exist in the profile at a shallow depth. The so-called Topographic Aggravation Factor (TAF), defined as the 2-D over 1-D Fourier spectral ratio, varies around 1.4 over a broad frequency band which covers the significant excitation frequencies. At the location of four collapsed buildings, about 250 m from the edge, 2-D (topography) effects are negligible, but the specific soil profiles amplify one-dimensionally all six ground base excitations to spectral acceleration levels that correlate well with the observed intensity of damage, at least in a qualitative sense.     

Seismic behaviour of flexible retaining systems subjected to short-duration moderately strong excitation

Using finite-element modelling, this paper explores the magnitude and distribution of dynamic earth pressures on several types of flexible retaining systems: L-shaped reinforced-concrete walls, piled walls with horizontal or with strongly inclined anchors, and reinforced-soil walls. The utilized base excitation is typical of earthquake motions of either high or moderately low dominant frequencies having a peak ground acceleration (PGA) of 0.40 g and relatively short duration. Linear as well as non-linear (Mohr–Coulomb) soil behaviour is investigated, under dry conditions. The results show that, as the degree of realism in the analysis increases, we can explain the frequently observed satisfactory performance of such retaining systems during strong seismic shaking.     

Effects of local site conditions on the seismic response of municipal solid waste landfills

Over the last decade, the seismic response of landfills made of municipal solid waste has drawn attention mainly due to the environmental and public-health issues that could be raised in the event of a failure. Nevertheless, there are several associated technical issues that have not been adequately investigated. One of these is the impact of local site conditions on the earthquake-induced accelerations and, thereby, on the seismic design of a landfill. This study presents the results of a parametric numerical simulation that has been performed in order to examine the effects of local site conditions on the dynamic response of a typical landfill. Emphasis is given on the special characteristics of ground motion, while the material nonlinearity of both soil and waste is taken into account by an equivalent-linear procedure. Results indicate that local site conditions may play a significant role in the seismic response of a landfill. However, this role cannot be judged a priori as beneficial or detrimental, as it depends not only on soil conditions and seismic excitation, but also on the material and geometric characteristics of the landfill.