student and faculty conducting research

PhD Students and Post-Doctoral Researchers

Randa Khaleel Asmar

  • Advisor:
      • Prof. Youssef Hashash
  • Departments:
    • Civil and Environmental Engineering
  • Areas of Expertise:
      • Geotechnical Engineering

  • Thesis Title:
  • Thesis abstract:
      • Solving complex boundary value problems in geotechnical engineering requires a soil constitutive model that reliably captures the soil behavior under general loading conditions. Laboratory testing has greatly contributed to the development of constitutive models that reflect soil nonlinear and anisotropic behavior. Available laboratory testing devices are designed to generate uniform stress and strain states within a tested specimen and therefore provide information on material behavior within a narrow range of stress￿strain paths and do not cover the loading conditions which occur in field problems. The process of development of material constitutive models remains lengthy and requires numerous tests to cover a broad range of loading paths. This limited information generally results in a constitutive model that may not be justifiable to represent loading conditions that differ substantially from the ones in laboratory tests. A new laboratory testing device that can generate more generalized states of stress in the soil specimen is introduced. Self-learning simulations (SelfSim) inverse analysis computational engine is integrated with the newly developed device. The new device inherits essential features of the standard triaxial test, including specimen preparation, device set-up, consolidation and shearing procedures as well as instrumentation. Additional lateral displacement restraint clamps are introduced to generate 3D shearing conditions within the tested specimen. The testing setup also includes a close-range photogrammetry system to accurately measure the 3-D deformations of the specimen. Using two high resolution digital cameras mounted in front of the cell, the system is able to capture the specimen￿s deformed shapes synchronously with measurements of loads, axial displacement, and pore pressures/volume change during the shearing process. These measurements provide input required for SelfSim learning to extract induced stress-strain behavior of the tested specimen. SelfSim is employed to interpret Ottawa sand shear behavior. The tested sand specimens cover three different relative densities, and were tested under three different confining pressures in both the traditional triaxial device and the modified device. SelfSim analysis extracts stress strain behavior from within each specimen using load and displacement measurements. A soil-specific material constitutive model can be generated from this information. The constitutive model can then be directly used within a numerical analysis (e.g., finite element (FE) method) of a geotechnical problem.
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