This study presents results of an experimental study of the micromechanical proppant behavior during settling in both narrow smooth and rough fractures. This fundamental analysis seeks to better understand dynamics of particle interactions in a dense phase slurry on a small particle size scale, representing proppant settling in narrow hydraulic fractures. Particle Image Velocimetry (PIV) is used for analysis of velocities of individual particle and group particles and their relative paths, collisions and agglomerating in viscous Newtonian fluid. The displacement vectors show the movements of group of particles and global velocity trends of the observed area. The results from this experimental study indicate dependency of settling velocity on particle size and shape, as well as the dependency of different size of particle or agglomerate particles. The measured results, including vertical velocities and displacement vectors of singular particle and agglomerated particles, were compared with previously published theoretical and empirical relationships. It can be seen that forming of proppant agglomerates during settling, caused by frequent particle-particle and particle-wall collisions and interactions, changes the overall settling velocities predicted by the previous experiments in larger slots. The slurry settling velocity depends on the relationship between settlement, proppant concentration and occurrence of proppant agglomeration. This study also compares the different agglomerations in different fluid. This study presents the influence of proppant concentration and proppant agglomeration. The effect of wall can also been found when the concentration and agglomeration is high. In order to better understanding proppant settling in hydraulic fracture where mostly rough, the proppant settling in narrow slot with adding rough surface is also analyzed. By comparing experimental results of proppant settling in narrow slot with both smooth surface and rough surface, it can be found that the rough surface can diminish average settling velocity. The decreasing of proppant concentration and agglomeration is also found in this study.

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.