الفهرس 
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Abstract
This research investigates the effect of both geotextile and geogrid reinforcement on the behavior of strip footings on sand cushion of varying thickness underlian by weak clay. Footings subjected to concentric and eccectric loads are studied. Experimental and numerical analyses are performed. The experimental study is done by conducting model footing tests, pullout tests and load-extension tests on the reinforcement.
Pullout tests and load controlled-extension tests are performed on the reinforcement to study the soil-reinforcement interaction and the load-elongation propertise of the reinforcement in confinement of soil. One of the important findings of these in-soli tests is that, there is a significant increase in the stiffness and strength of the geotextiles confined with soil compared with that tested in isolation. The stress confinement do not give rise to a reduction in the failure strain when compared to the in-air test. Mathematical hyperbolic model is used to represent the measured load-extension relationship of the geotextile, and their accuracy are discussed. Pullout tests and direct shear tests are performed to measure the soil-reinforcement frictional resistance. Comparison is held between them to show the best test method used to represent the actual behavior in the FEM analyses.
The experimental model footing tests investigate the effect of reinforcement on the load-settlement and load-rotation behavior of the footing. The experimental results for two types of reinforcement in different parameters. These parameters include load eccentricity; thickness of sand cushion; relative density of sand; strength of the underlying clay; width of reinforcement sheet; position of reinforcement layer; number of reinforcement layers and the tensile strength of the reinforcement and aperture size of the geogird. The failure profile and failure mechanism of such reinforced layered soil are also studied. The experimental results shows that for the same tensile strength, the geogrid reforcement is better than geotextile reinforcement . In general, the use of the reinforcement increases the bearing capacity of the footings esprcially with the increase of number of reinforcement layers. The precentage increase in the bearing capacity becomes more pronounced for big load eccentricities and small thicknesses of sand cushion.The optimum position and the optimum width of the reinforcement layer depends on the load eccentricity; relative desity of sand and thickness of sand cushion layer.