A critical evaluation is made of the dynamic pressures and the associated forces induced by ground shaking on a rigid, straight, vertical wall retaining a semi-infinite, uniform viscoelastic layer of constant thickness. The effects of both harmonic and earthquake-induced excitations are examined. Simple approximate expressions for the responses of the system are developed, and comprehensive numerical data are presented which elucidate the effects and relative importance of the various parameters involved. These solutions are then compared with those obtained by use of a simple model proposed previously by Scott, and the accuracy of this model is assessed. Finally, two versions of an alternative model are proposed which better approximate the action of the system. In the first, the properties of the model are defined by frequency-dependent parameters, whereas in the second, which is particularly helpful in analyses of transient response, they are represented by frequency-independent, constant parameters.

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Dynamic soil pressures on rigid vertical walls

A critical evaluation is made of the response to horizontal ground shaking of flexible cantilever retaining walls that are elastically constrained against rotation at their base. The retained medium is idealized as a uniform, linear, viscoelastic stratum of constant thickness and semi-infinite extent in the horizontal direction. The parameters varied include the flexibilities of the wall and its base, the properties of the retained medium, and the characteristics of the ground motion. In addition to long-period, effectively static excitations, both harmonic base motions and an actual earthquake record are considered. The response quantities examined include the displacements of the wall relative to the moving base, the wall pressures, and the associated shears and bending moments. The method of analysis used is described only briefly, emphasis being placed on the presentation and interpretation of the comprehensive numerical solutions. It is shown that, for realistic wall flexibilities, the maximum wall f...

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Dynamic response of cantilever retaining walls

Seismic Soil Pressure for Building Walls-An Updated Approach

The evolution of the methodology for the evaluation of seismic earth pressures on retaining structures and basement walls is reviewed together with observations of field performance. The case history data and data from recent experimental work are used to show that the currently used methods are quite conservative and lead to excessively conservative designs in regions where design PGA exceeds 0.4g. Specifically, the experimental data from seismic centrifuge tests shows that the seismic earth pressure distribution for moderate size retaining structures, on the order of 6-7 m high, is triangular, increasing with depth. Moreover, there is no significant increase in seismic earth pressure between unbraced and braced structures with fixed base, while the loads on free standing cantilever structures are substantially lower owing to their ability to translate and rotate. The significance of the observed seismic earth pressure distributions is that the dynamic force can be applied at 1/3H, as is done for static loading, which substantially decreases the design level seismic moments on the structures.

Seismically Induced Lateral Earth Pressures on Retaining Structures and Basement Walls

Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep-excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading. For instance, no significant damage or failures of retaining structures occurred in the recent Wenchuan earthquake in China (2008) or in the subduction earthquakes in Chile (2010) and Japan (2011). To develop a better understanding of the distribution and magnitude of the seismic earth pressures on cantilever retaining structures, a series of centrifuge experiments were performed on model retaining and basement structures with medium dense cohesionless backfill. This paper provides a general overview of the research program and its results. Two sets of centrifuge-scale experiments were carried out on the centrifuge at the Center for Geotechnical Modeling at UC Davis. Three different types of prototype retaining structure were modele...

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Seismic Earth Pressures on Retaining Structures and Basement Walls in Cohesionless Soils

Based on the behavior of backfill soil, the state of knowledge reflects three design approaches: elastic solutions, elasto-plastic solutions and fully plastic (static) solutions. The major differences in the fully plastic solutions utilizing Mononobe-Okabe's approach have been with the application point of the resultant force. Plastic solutions do not consider soil-structure interaction effects and are based on rigid body motions. Elastic dynamic solutions are proposed that provide guidelines to estimate backfill pressures for small lateral displacements. Solutions are also provided to estimate dynamic pore-water pressures. The study of these papers indicates that there is a general lack of a comprehensive treatment of the subject and there is a need for further investigations in the following areas for the dynamic case: passive soil pressures; elasto-plastic backfill soil models; soil-structure interaction effects; mixed soils; surcharge effects; and wall stability for combined bearing, sliding, and overturning.

Hagop N. Nazarian

Papers

Earthquake-Induced Lateral Soil Pressures on Structures