The use of a fabric as a separating layer between a soft subgrade and granular fill, for access roads, working platforms, vehicle standing areas, etc., was one of the first uses of geotextiles in ground engineering and is probably still commercially the most important. Al-though there have been many studies of such a form of construction (e.g. see Ruddock 1977 and several papers to the International Conference on Soil Reinforcement, Paris, 1979) design methods are still largely empirical and it is often difficult to calculate the balance of costs and benefits of using fabrics in this way. A research programme has been started at Oxford University to investigate the problem by means of model tests and computer analyses. The study is mainly concerned with the reinforcing effect of the material, rather than its performance as a filter, particularly in view of the recent introduction of high-strength, high-modulus mesh or grid structures for soil reinforcement.
As a preliminary stage a series of simple two-dimensional tests have been performed at approximately 1/l0th scale. Granular fill, with or without reinforcement, was spread over a soft subgrade, represented by foam rubber, and deflections due to a surface strip loading determined. Several different reinforcing materials were used, including smooth sheet material as well as various mesh or grid structures, and the effects of varying fill particle size, fill thickness, reinforcement stiffness and subgrade stiffness investigated. It is appreciated that foam rubber is not an accurate substitute for soft clay, and the tests deliberately