This paper presents an experimental study investigating the behaviour of geogrid reinforced sand-clay foundation systems with clay subgrades of different strengths. Model tests were carried out on a circular footing of 150 mm diameter (D) resting on 1 9 1 9 1 m foundation bed having clay subgrades of different undrained shear strengths (c u), ranging from 7 to 60 kPa. Different series of laboratory model tests were performed on homogeneous and layered foundation systems. The layered systems were comprised of dense sand of varying layer thicknesses (H = 0.63-2.19D) overlying the clay subgrades. Pressuresettlement responses obtained indicated that the foundation performances were largely influenced by footing settlement (s/D %), layer thickness (H), and subgrade strengths (c u). The results indicated that the planar geogrid reinforcement, placed at the sand-clay interface, can substantially improve the performance of the foundation beds depending on layer thickness and subgrade strength. A maximum of about 5.6fold improvement in bearing capacity was observed in the study, for very soft clay subgrade of 7 kPa.
Utilization of rubber-sand mixtures as construction materials, such as lightweight filling materials, embankment construction, seismic isolation materials, … etc., provides significant advantages, as scrap tires induce environmental issues. In this study, unconsolidated undrained triaxial tests were performed to examine the shear-strength characteristics of geogrid-reinforced sand-rubber mixtures. The rubber percent (10%, 20%, 30%, 40%, 50% and 60%), the confining pressure of the cell (19.6 kPa, 49 kPa and 98 kPa) and the number of geogrid reinforcements (1 to 4) were varied for investigating the impact of these parameters. The relative density of sand remained constant (80%) during the test. The test results were evaluated in terms of the stress-strain characteristics of rubber-sand mixtures. The test findings demonstrated that by increasing the confining pressure of the cell, the same rubber-sand mixtures with the same relative density and rubber content take more loads. The peak stress of unreinforced rubber-sand mixtures increased with the increasing proportion of rubber content up to 30%, beyond which it decreased as rubber content increased. Maximum peak stress and axial strain have been achieved with 50% of the rubber content and four layers of geogrid reinforcement. The brittleness index of the rubber-sand mixture reduces when geogrid reinforcement is added. The minimum brittleness was found to be 0.042 at 50% rubber content with three layers of geogrid reinforcement. KEYWORDS: Geogrid, Shear strength, Triaxial test, Rubber-sand mixture, Soil reinforcement.
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