Soil structure interaction for shrink-swell soils a new design procedure for foundation slabs on shrink-swell soils

摘要

Problems associated with shrink-swell soils are well known geotechnical problems thathave been studied and researched by many geotechnical researchers for many decades.Potentially shrink-swell soils can be found almost anywhere in the world especially inthe semi-arid regions of the tropical and temperate climate. Foundation slabs on grade onshrink-swell soils are one of the most efficient and inexpensive solutions for this kind ofproblematic soil. It is commonly used in residential foundations or any light weightstructure on shrink-swell soils.Many design methods have been established for this specific problem such asBuilding Research Advisory Board (BRAB), Wire Reinforcement Institute (WRI), Post-Tensioning Institute (PTI), and Australian Standards (AS 2870) design methods. Thisresearch investigates most of these methods, and then, proposes a moisture diffusion soilvolume change model, a soil-weather interaction model, and a soil-structure interactionmodel.The proposed moisture diffusion soil volume change model starts with proposing anew laboratory test to determine the coefficient of unsaturated diffusivity for intact soils.Then, it introduces the development of a cracked soil diffusion factor, provides a chartfor it, and explains a large scale laboratory test that verifies the proposed moisturediffusion soil volume change model.The proposed soil-weather interaction model uses the FAO 56-PM method tosimulate a weightless cover performance for six cities in the US that suffer significantly from shallow foundation problems on shrink-swell soils due to seasonal weathervariations. These simulations provide more accurate weather site-specific parameterssuch as the range of surface suction variations. The proposed weather-site specificparameters will be input parameters to the soil structure models.The proposed soil-structure interaction model uses Mitchell (1979) equations formoisture diffusion under covered soil to develop a new closed form solution for the soilmound shape under the foundation slab. Then, it presents a parametric study by carryingout several 2D finite elements plane strain simulations for plates resting on a semiinfiniteelastic continuum and resting on different soil mounds. The parametric studyoutcomes are then presented in design charts that end with a new design procedure forfoundation slabs on shrink-swell soils.Finally, based on the developed weather-soil-structure interaction models, thisresearch details two procedures of a proposed new design method for foundation slabson grade on shrink-swell soils: a suction based design procedure and a water contentbased design procedure.