Settlement of a shallow foundation is a function of the nature and magnitude of the stress distribution in the underlying soil layer(s) which is transmitted from the load imposed on the foundation by the superstructure. Placing geogrid layers at a shallow depth in soil for reinforcement helps redistribute and reduce the intensity of stress in the soil. Field test results for measuring stress in soil below a circularly loaded area at the top of a soil pad reinforced with multiple layers of geogrid are presented. The tests were conducted on reclaimed land at the proposed lnchon International Airport, South Korea. The stress distribution is a function of the intensity of a load on the foundation, number of geogrid layers used for reinforcement, and thickness of the geogrid-reinforced soil.
During the past twenty years, geogrid and geotextile have been used extensively for soil reinforcement in the construction of retaining wails and slopes of embankments. More recently, results of several laboratory and field studies relating to the ultimate and allowable bearing capacities of shallow foundations supported by geogrid-reinforced soil have been published. Also, in some cases, attempts are now being made to construct shallow foundations on geogrid-reinforced granular soil pads to reduce settlement at allowable loads. In order to estimate the settlement of a shallow foundation, it is necessary to know the distribution of vertical stress transmitted from the foundation to various underlying soil layers. For that purpose, in the case of unreinforced soil, most geotechnical engineers use the solutions derived from Boussinesq's equation (Boussinesq, 1883) for vertical stress caused by a point load applied on the surface of a homogeneous, elastic, and isotropic medium. This is an application of the theory of elasticity. Another empirical stress distribution method commonly used is the so called 2:1 method.