Hasan Ghasemzadeh

Forward modeling the magnetic effects of an inferred source is the basis of magnetic anomaly inversion for estimating subsurface magnetization parameters. This study uses numerical least-squares Gauss–Legendre quadrature (GLQ) integration to evaluate the magnetic potential, anomaly, and gradient components of a cylindrical prism element. Relative to previous studies, it quantifies for the first time the magnetic gradient components, enabling their applications in the interpretation of cylindrical bodies. A comparison of this method to other methods of evaluating the vertical component of the magnetic field associated with a full cylinder shows that it has comparable to improved performance in computational accuracy and speed. Based on the developed theory, a conceptual design is presented for an instrument to measure the magnetic gradient effects of subsurface material in the vicinity of a borehole. The significance of this instrument relative to conventional borehole magnetometers is in its ability to determine the azimuthal directions of magnetic sources within the borehole environment.

The numerical investigation in this study focuses on the propagation of hydraulically driven fractures in deformable porous media containing two fluid phases. The fully coupled hydro‐mechanical governing equations are discretized and solved using the extended element‐free Galerkin method. The wetting fluid is injected into the initial crack. The pores are filled with both wetting and non‐wetting fluid phases. Essential boundary conditions are enforced using the penalty method. To model the discontinuities in field variables, the extrinsic enrichment strategy is employed. Ridge and Heaviside enrichment functions are utilized to introduce weak and strong discontinuities, respectively. The nonlinear behavior in front of the crack tip is defined by means of a cohesive crack model. Continuity equations for wetting and non‐wetting fluids through the fracture domain are expressed using Darcy's law and cubic law. The coupling terms of fluids are considered in accordance with their mass transfer among the crack and the surrounding domain, simulating the fluid leak‐off phenomenon and the fluid lag zone. The results demonstrate the success of the proposed numerical framework in simulating the intricate aspects of the hydraulic fracturing process. Sensitivity analysis is performed with varying domain permeabilities and wetting fluid viscosities to elucidate their effects on different aspects of hydraulic fracture.

Pavement design methods based on principles of unsaturated soil mechanics take into account high soil shear strength due to matric suction resulting in more economical design especially in long roads. In this study, the bearing capacity of two-layer unsaturated sand was investigated using both analytical and experimental methods. At first, using the limit equilibrium method an analytical formula was proposed to determine the bearing capacity of two-layer unsaturated sand in which linear suction profile was considered in soil layers. It should be considered that the constant matric suction distribution assumed by the previous researchers does not show the real profile of matric suction within the soil, sometimes resulting in miscalculated unsaturated bearing capacity. Also, the bearing capacity of two-layer unsaturated poorly graded sand was investigated experimentally in different suctions by a special unsaturated chamber apparatus (UCA) designed for this purpose. The results show more than double increase of unsaturated soil bearing capacity with S_r = 25% compared to saturated soil. The formation of failure wedges in all experiments was investigated by image processing. An acceptable agreement was obtained between the theoretical and experimental bearing capacity results.

Untreated surfactant-rich greywater is uncontrollably discharged into the environment in underdeveloped countries and even in some areas of developing countries, which may change soil characteristics. However, there is hardly any research concerning geotechnical behavior of soils contaminated by surfactant. The present study investigates mechanical properties of two types of surfactant-contaminated sandy soils experimentally. Soil samples were collected from Bam County and Shahriar County located in the central parts of Iran. The clean specimens were contaminated by a series of prepared surfactant-rich aqueous solutions containing different amounts of a widely used detergent. The weight ratio of detergent to water was selected equal to 1/20, 1/15, 1/10, and 1/5. Physical characteristics of the contaminant solutions were examined by performing surface tension and viscosity tests. Additionally, geotechnical behavior of the clean and the contaminated samples was investigated through conducting compaction and direct shear tests. Results indicated that the geotechnical properties of the contaminated soils declined by increasing the surfactant concentration in the contaminant. Compared to clean specimens and at the highest contamination level, the optimum water content of both Bam and Shahriar soils reduced from 7.70% and 11.00% to 4.05% and 6.75% as well as the maximum density decreased from 17.87 kN/m³ and 18.52 kN/m³ to 17.37 kN/m³ and 17.88 kN/m³, respectively. Moreover, Bam and Shahriar soils with a maximum degree of contamination showed a reduction in the friction angle from 23.06° and 20.52° to 10.52° and 12.17° as well as a decrease in the formed apparent cohesion of the unsaturated samples by near 56% and 78%, respectively.