UC San Diego

Much research has been underway about the mechanism of soil liquefaction and its consequences. In this regard, valuable insights have been gained as to the associated shear and volumetric deformations. During seismic excitation, additional site liquefaction mechanisms are manifested, due to the migration of the pore-fluid towards ground surface. As such, a number of these mechanisms are addressed in this study.Modeling of the potentially large post-liquefaction ground settlement is addressed. The associated formulation is implemented in the widely available OpenSees numerical framework. Salient mechanisms related to site profile stratification are studied. Significance of variability in the post-liquefaction volume change and permeability profile is highlighted, as to the impact on shear deformations, and the potential occurrence of large lateral ground deformations. Related to the above, seams of liquefiable or low shear strength soils are then shown to possibly play an important role in dictating the overall seismic site response outcome. Such strata in a ground profile, might lead to reduced peak ground accelerations at the expense of increased settlements. The interplay between these two aspects is addressed with the aim of striking a balance that results in favorable outcomes for both. In a parametric investigation, consequences for an overlying structure are studied. On this basis, recommendations for potential ground modification to strengthen underlying poor layers are drawn. Specifically, beneficial outcomes might result from an engineered deep relatively thin low strength zone that is left untreated within the implemented ground modification framework. Around the toe zone of a liquefied ground slope for instance, excess pore pressures driven by the relatively high attained values near the crest, might exceed the local effective vertical stress. Intensified de-stabilization might result as a consequence of this process. To this end, an exploratory conceptual experiment is devised and studied. On the basis of the experiment, the results of a simple illustrative numerical study are included. The underlying mechanism is shown to be potentially pertinent to a wide class of practical applications. Further studies are suggested in order to assess the extent of detrimental consequences and potentially needed mitigation strategies. In summary, the main contributions of this study include: i) modeling of the potentially large post liquefaction ground settlements within the framework of the widely available OpenSees numerical framework, ii) highlighting the associated mechanisms for homogeneous as well as stratified ground profile scenarios, iii) exploring the consequences of liquefaction for stratified sites, with emphasis on presence of low strength seams, iv) studying such low strength seam scenarios towards development of beneficial outcomes for overlying structures, in terms of lower accelerations along with tolerable settlements, and v) experimentally exploring the concept of liquefaction-induced high excess pore-pressure driven by geometric ground configurations such as those around slopes, earth retaining structures, and earth dams.