Two aspects of seismically-induced liquefaction are discussed which are of vital engineering significance: the triggering condition and the consequences of liquefaction. The triggering condition is examined with respect to liquefaction analysis, note being taken of the onset condition which is governed by cyclic strength. Consequences of liquefaction are discussed with respect to post-seismic stability analysis, in which the residual strength plays a major role. Procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced, and the applicability of this method for estimating associated ground settlements is discussed. The evaluation of residual strength requires a better understanding of undrained sand behaviour. Results of extensive laboratory rests on Japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better. The results of laboratory tests on silty sands are examined in the same way. AH the results are...

Liquefaction and flow failure during earthquakes.

A simple stress-ratio controlled, critical state compatible, sand plasticity model is presented, first in the triaxial and then in generalized stress space. The model builds upon previous work of the writers, albeit the presentation here is made with extreme simplicity in mind, and three novel aspects are introduced. The first is a fabric-dilatancy related quantity, scalar valued in the triaxial and tensor valued in generalized stress space, which is instrumental in modeling macroscopically the effect of fabric changes during the dilatant phase of deformation on the subsequent contractant response upon load increment reversals, and the ensuing realistic simulation of the sand behavior under undrained cyclic loading. The second aspect is the dependence of the plastic strain rate direction on a modified Lode angle in the multiaxial generalization, a feature necessary to produce realistic stress-strain simulations in nontriaxial conditions. The third aspect is a very systematic connection between the simple triaxial and the general multiaxial formulation, in order to use correctly the model parameters of the former in the implementation of the latter. The simulative ability of the model is illustrated by comparison with data over a very wide range of pressures and densities.

Simple plasticity sand model accounting for fabric change effects

Regression models for estimating coseismic landslide displacement

A simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake-induced deviatoric deformations is presented. It utilizes a nonlinear fully coupled stick-slip sliding block model to capture the dynamic performance of an earth dam, natural slope, compacted earth fill, or municipal solid-waste landfill. The primary source of uncertainty in assessing the likely performance of an earth/waste system during an earthquake is the input ground motion. Hence, a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements. A seismic displacement model is developed that captures the primary influence of the system’s yield coefficient ( ky ) , its initial fundamental period ( Ts ) , and the ground motion’s spectral acceleration at a degraded period equal to 1.5 Ts . The model separates the probability of “zero” displacement (i.e., ⩽1 cm ) occurring from the distribution of “nonzero” displacement, so that very low values of calculated...

Simplified Procedure for Estimating Earthquake-Induced Deviatoric Slope Displacements

The factors to be considered in the earthquake-resistant design of dams are discussed and defensive measures which may be taken to mitigate the effects of these factors are summarized. Available information concerning the field performance of dams during earthquakes is reviewed and conclusions are drawn concerning the potential for earthquake-induced sliding for different types of construction materials and earthquake shaking intensities. Finally, available methods for evaluating the stability and deformations of the slopes of a dam due to earthquake shaking are reviewed and their applicability illustrated. Conclusions are drawn concerning the significance of the type of soil used for construction and the possibility of delayed failure, after the earthquake ground motions have stopped, due to pore water pressure re-distribution within an embankment. Suggestions are made concerning the appropriate role of analytical procedures in the overall assessment of the seismic stability of dams in relation to the un...

Considerations in the earthquake-resistant design of earth and rockfill dams

The method uses the concept of yield acceleration but is based on the evaluation of the dynamic response of the embankment rather than a rigid body behavior. The yield accelerations, for a potential sliding mass, is estimated on the basis of the static undrained shear strength (with some reduction due to effects of cycling) using pseudostatic methods of stability analysis. The permanent deformations are estimated by numerical double integration of the time history of induced accelerations for various depths of the potential sliding mass. Design curves are presented that were developed on the basis of finite element response computations of embankments subjected to base accelerations representing earthquakes of magnitudes ranging between 6-4 and 8-2. The simplified procedure is illustrated by an example computation. The permanent deformations are estimated for a 135-ft (40-m) high sandy clay embankment that was shaken by a magnitude 8-2 earthquake and the results are compared with the observed field behavior.

Simplified procedure for estimating dam and embankment earthquake-induced deformations

The method uses the concept of yield acceleration but is based on the evaluation of the dynamic response of the embankment rather than a rigid body behavior. The yield accelerations, for a potential sliding mass, is estimated on the basis of the static undrained shear strength (with some reduction due to effects of cycling) using pseudostatic methods of stability analysis. The permanent deformations are estimated by numerical double integration of the time history of induced accelerations for various depths of the potential sliding mass. Design curves are presented that were developed on the basis of finite element response computations of embankments subjected to base accelerations representing earthquakes of magnitudes ranging between 6-½ and 8-¼. The simplified procedure is illustrated by an example computation. The permanent deformations are estimated for a 135-ft (40-m) high sandy clay embankment that was shaken by a magnitude 8-¼ earthquake and the results are compared with the observed field behavior.

The effort to model sand behavior within the framework of critical-state soil mechanics would benefit from a state variable that relates the current void ratio and mean pressure of the soil to its ...

State Pressure Index for Modeling Sand Behavior

Closure to “Simplified Procedure for Estimating Dam and Embankment Earthquake-Induced Deformations”

Particular emphasis is given to dam performance in six major earthquakes—San Francisco (1906); Ojika, Japan (1939); Fallon, Nevada (1954); Kern County, California (1952); Tokachi-Oki, Japan (1967); and San Fernando, California (1971). An attempt is made to determine relationships between embankment characteristics and observed performance. It is concluded that (1)Hydraulic fill dams on stable foundations can safely withstand accelerations up to about 0.2g from Magnitude 6.5 earthquakes; (2)virtually any well-built dam can withstand moderately strong shaking up to about 0.2g or more with no detrimental effects; (3)dams built of clay soils seem to be able to withstand extremely strong shaking from large magnitude earthquakes without significant damage; (4)dams may fail up to 24 hrs after being shaken by an earthquake probably due to cracking leading to piping and erosion; and (5)primary concern should be given to dams constructed of saturated sandy soils or on sand foundation materials. Prototype performance is cited as a basis for these conclusions.

Faiz I. Makdisi

Papers

Simplified procedure for estimating dam and embankment earthquake-induced deformations

Simplified procedure for estimating dam and embankment earthquake-induced deformations

State Pressure Index for Modeling Sand Behavior

Closure to “Simplified Procedure for Estimating Dam and Embankment Earthquake-Induced Deformations”

Performance of earth dams during earthquakes