Key Engineering Materials Vol. 857

Abstract: The presence of gypsum in the soil will cause problems if the source of freshwater is available and permeable soil permitting significant movement of water is to take place. The solubility of gypsum by excess water from irrigation or localized leak into the gypseous soil may cause cavity formation. In this research, a model was developed for governing the mass-transport to assess the variation of gypsum content of the soil during dissolution. A general three-dimensional finite element program (PLAXIS tunnel) was selected for the numerical analysis method to generate the solution. Parameters that affect the bearing capacity of a square footing represented by the gypsum content, the cavity volume, and the location of the cavity which represent by three offset distances from the footing center to the cavity center (x, y, and z), where (X) represents the horizontal distance, (Y) represents the vertical (depth) distance, and (Z) represents the diagonal distance. The main results show that the cavity location found to be the most parameter that affects the bearing capacity ratio (BCR). The minimum values are found when the cavity locates at the center of the footing base, and the lowest one (0.211) when the gypsum dissolved equal to 40%, also there is no effect of the cavity location when the ratio of (X/B) and (Z/B) exceed (3.0) for any depth and when the gypsum dissolved less than 10%. For high gypsum dissolution (more than 30%), the dimensionless ratios (X/B), (Z/B), and (Y/B) of the cavity must be more than 5.0.

Abstract: It is widely accepted that soil behavior is complicated taking into account soil anisotropy owing to the fact that this phenomenon arises from oriented soil fabric or structure forged in the deposition stage. In this study, a review of major findings of authors’ previous studies are presented with the main focus on soil anisotropy using extensive experimental results incuding Triaxial (TXT), Simple Shear (SSA), and Hollow Cylinder (HCA) apparatus. Effects of initial anisotropy, fabric evolution, stress path, principal stress rotation and intermediate stress state are evaluated for a crushed silica sand. In addition, the effects of Portland cement content and granulated rubber contents on anisotropic behavior of the sand are investigated. Bender elments are mounted on triaxial specimens both in vertical and horizontal directions to measure the shear wave velocity and hence maximum shear modulus at the end of consolidation as well as during shearing up to large strains at critical state condition, as an index of evaluating the fabric evolution. The effects of principal stress rotation and stress paths reveals the crucial role of soil anisotropy on the behavior of clean sand. However, adding either cement or granulated rubber to the sand has considerably decreased anisotropy.