Shallow strip foundation on geogrid-reinforced clay under static and cyclic loading

The use of geosynthetics in the design and construction of earth-supported and earth-retaining structures has increased greatly during the past decade. Reinforcement is the primary function of geogrid. Geogrids are now extensively used for reinforcement of backfill of retaining walls, and stabilization of slopes. It appears however that they can also be used to reinforce the soil supporting shallow foundations to increase the ultimate and allowable bearing capacities.; This study has primarily been directed to evaluate the beneficial effects of geogrid reinforcement in saturated and near-saturated clays on the ultimate bearing capacity of a strip foundation. Laboratory model test results for the ultimate bearing capacity of strip surface foundation supported by a saturated clay layer reinforced by layers of geogrid are presented. Laboratory tests were conducted to determine the critical nondimensional values for the depth and width of the geogrid reinforcement layers, and also the location of the first layer of geogrid with respect to the bottom of the foundation to mobilize the maximum possible bearing capacity ratio. Based on the laboratory model tests the optimum size of geogrid layers and maximum depth of reinforcement to mobilize maximum bearing capacity ratio has been determined. Bearing capacity ratios at various levels of settlement are discussed. Based on the experimental results presented in these tests, a semi-empirical relationship has been developed to estimate the ultimate bearing capacity of a strip foundation supported by geogrid-reinforced saturated clay.; The laboratory model study has been further extended to evaluate the permanent settlement of a strip foundation supported reinforced-clay subjected to a combination of static and cyclic loading. For a given combination of the intensity of static and cyclic loads, the progress of permanent foundation settlement with the number of load cycles were monitored and described in detail. Based on the test results presented in cyclic load tests, a semi-empirical relationship has been presented to estimate the permanent settlement due to cyclic loading only.; The results of the present tests indicate that the use of geogrid reinforcement in clay subgrades helps improve their bearing capacity performance significantly.