Laboratory model tests for determination of the ultimate bearing capacity of a surface strip foundation supported by a stronger sand layer of limited thickness underlain by a saturated weaker clay layer with and without geogrid reinforcement at the sand-clay interface has been presented. Based on the model test results, the critical values of the thickness of sand layer-to-foundation width ratio, and width of the geogrid layer-to-foundation width ratio for derivation of the maximum benefit from the reinforcement has been presented. An approximate theory has also been developed to estimate the bearing capacity ratio of the foundation on layered soil with geogrid reinforcement.; Laboratory tests have also been conducted to evaluate the magnitude of the permanent settlement of a surface strip foundation subjected to an allowable static load superimposed by a cyclic load of low frequency. The critical number of load cycles required for the development of the maximum permanent settlement due to a cyclic load has been determined to be about 2 {dollar}times{dollar} 10{dollar}sp5{dollar} to 3 {dollar}times{dollar} 10{dollar}sp5{dollar}. This critical value is independent of the magnitude of the static load intensity and the peak dynamic load intensity.; The effect of the presence of a continuous void of square cross section in the clay layer on the ultimate bearing capacity of a strip foundation has been investigated. The critical depth below the foundation, and the critical lateral distance from the foundation at which the void will have no effect on the bearing capacity has been established.
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