Aurelian C. Trandafir

Reduction of Lateral Earth Forces Acting on Rigid Nonyielding Retaining Walls by EPS Geofoam Inclusions

Expanded polystyrene (EPS) geofoam panels of low stiffness installed vertically against the rigid nonyielding retaining structure provide additional deformations in the backfill. This behavior will lead to the mobilization of a greater portion of the soil strength, thus decreasing the lateral earth thrust acting on the rigid retaining wall. This study addresses the effect of geofoam compressible inclusion on lateral earth thrust acting on a rigid nonyielding retaining wall by small-scale model tests and numerical analyses. The finite-element code used in the numerical modeling is validated against the stress measurements on a 0.7-m-high wall model. Significant reduction is observed in the lateral earth pressures attributable to deformations concentrated at the lower half of retained soil mass. The effects of compressible inclusion thickness, relative stiffness of the EPS geofoam, and strength parameters of the backfill on lateral earth thrust acting on rigid nonyielding walls are investigated by a series ...

Stiffness Degradation and Yielding of EPS Geofoam under Cyclic Loading

This paper summarizes major findings from a laboratory study based on stress-controlled cyclic uniaxial compression tests with initial deviator stress conducted on expanded polystyrene (EPS) geofoam. The experiments involved nonelasticized EPS cylinders of various densities subjected to various static deviator stresses and cyclic loading conditions to provide a detailed description of the geofoam cyclic stress-strain response in the viscoelastic and visco-elasto-plastic domains. Experimental results characterizing the viscoelastic behavior were compiled into a normalized Young’s modulus and damping ratio versus cyclic axial strain amplitude relationships. A unified formulation that can be used to determine the normalized modulus degradation curve for a given static deviator stress level and geofoam density (within 15–25u2009u2009kg/m3 ) was developed. Examination of the yielding behavior of EPS geofoam under cyclic loading revealed a nonlinear increase in the accumulated plastic axial strain with the increasing n...

Finite-element Analysis of Lateral Pressures on Rigid Non-yielding Retaining Walls with EPS Geofoam Inclusion

An elasto-plastic constitutive model for expanded polystyrene (EPS) geofoam was employed with a finite-element analysis addressing the lateral pressures on a rigid non-yielding retaining wall with geofoam inclusion. Experimental results from laboratory uniaxial and triaxial compression tests were used to derive the parameters of the elasto-plastic constitutive models for the geofoam inclusion and the backfill soil used in the finite-element investigation. The numerical study revealed that for the analyzed EPS density, specific combinations of geofoam panel thickness and retaining wall height may induce plastic strains in the geofoam. The results were compiled into design charts providing the distribution of lateral pressures on the wall and the geofoam isolation efficiency as a function of EPS panel thickness and wall height.

Risk Assessment of Slope Instability Related Geohazards

The paramount importance of slope instability hazards assessment and management is by and large recognized. The general mechanisms of slope instability processes are now fairly well understood but there remains the problem of establishing the risks to lives and property. This is being tackled by relating the local ground conditions to the regional geological surveys and integrating this with site-specific information to produce a hazard potential estimate.

Insights into Effectiveness of Simplified Seismic Displacement Procedures to Evaluate Earthquake Behavior of a Deepwater Slope

This paper employs numerical modeling to investigate the ability of simplified procedures based on sliding block methodology to provide a reasonable characterization of the seismic displacements of a deepwater slope. Earthquake-induced permanent shear displacements obtained from dynamic finite-element analyses of a deepwater slope subjected to various input base excitations are presented and compared with the seismic displacements predicted by two relatively recent simplified procedures available in the literature. The numerical outcomes indicate that the simplified procedures may be overly conservative in evaluating the earthquake-induced permanent shear displacements along the sliding surface of deepwater slopes. Based on the limited displacement data set developed under the present study, correlations aiming at improving the predictive capability of the selected simplified procedures in respect to evaluation of seismic performance of deepwater slopes are provided.

Geomechanics of a snowmelt-induced slope failure in glacial till

An integrated approach involving field, laboratory and numerical investigations was undertaken to study the progressive deformation mechanism of a slope in glacial till above the Town of Alta, Utah that experienced catastrophic failure due to rapid snowmelt in June 2010. Detailed geometry of the slope surface and of the exposed sliding surface obtained from global positioning system surveying together with strength and stress–strain parameters derived from laboratory triaxial tests on undisturbed samples of glacial till collected from the landslide site were employed with finite-element modeling to examine the effects of an increase in snowmelt-induced perched water table on the yielding behavior of the slope prior to catastrophic failure. The numerical results indicate gradual development of a plastic yield zone along the sliding surface with progressive rise in the perched water table above the toe of the slide mass, which was spreading out throughout the slide mass at the stage corresponding to the onset of catastrophic slope failure. The evolution of the slope safety factor obtained from limit-equilibrium stability analyses in relation to the development of the finite-element computed yield zone along the sliding surface is also discussed.

Numerical Insights into Mechanisms of Earthquake-Induced Catastrophic Landslides on Gentle Slopes in Liquefiable Soils

Catastrophic landslides characterized by large and extremely rapid movements are among the most destructive phenomena associated with failure of slopes during earthquakes. An understanding of the mechanism involved in the occurrence of catastrophic slope failures is of major importance in the process of developing effective mitigation strategies against such geohazards. This paper employs numerical analysis to illustrate two major concepts addressing the geomechanics of catastrophic landslides on gentle slopes in liquefiable soils due to earthquakes. For slope angles less than 20o but greater than about 10o, results from laboratory geotechnical research indicate that the mechanism controlling the high mobility of the slide mass after failure appears to be the gradual loss in shear strength with progressive shear displacement, culminating in ultimate steady state strengths smaller than the static (gravitational) driving shear stress. Numerical results from a dynamic sliding block analysis addressing the seismic performance of a well-documented earthquake-induced catastrophic landslide in Japan are used to illustrate this failure mechanism. Slopes characterized by very mild gradients approaching horizontal ground conditions may experience large landslide movements due to earthquake-induced ground liquefaction as a result of void redistribution and formation of water films in liquefied deposits with continuous low permeability interlayers. A numerical example employing a finite-element scheme for transient seepage coupled with changes in volumetric strains due to excess pore pressure dissipation is used to illustrate the evolution of the water film developed beneath a low permeability interlayer in a liquefied sand deposit.

Reduction of Lateral Earth Forces on Yielding Flexible Retaining Walls by EPS Geofoam Inclusions

In the light of recent research showing that expanded polystyrene (EPS) geofoam inclusions possess the ability to reduce lateral earth forces on rigid nonyielding retaining walls, this study investigates the potential application of geofoam as a compressible inclusion behind yielding flexible retaining walls. In this context, results of static physical tests on a 0.7m high cantilever retaining wall with dry cohesionless backfill were addressed. In the physical modeling study, wall deflections and lateral earth pressures were monitored to investigate the effect of EPS geofoam inclusion on the behavior of cantilever wall models. It was found that an increase in wall flexibility resulted in a decrease in the load reduction efficiency of the geofoam inclusion since the active stress conditions may already be achieved in the retained soil mass due to lateral wall deflections. However, the geofoam inclusion still provides an additional reduction of lateral force and flexural deflections of the cantilevered flexible walls due to the arching effect induced in the retained soil mass by the lateral compression of the geofoam panel occurring predominately in the lower mid-height of the wall stem.