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5.0 TENSION MEMBRANE THEORY The tensioned membrane theory was first developed by J. P.Giroud to determine the tensile strength required in a geosynthetic supporting a soil layer over a void. Later Giroud along with Bonparte, Beech and Gross, combined Terzaghi's arching theory with the tension membrane theory and laid the foundation for landfill liner support technology. Essentially, the tension membrane equation enables one to transfer a uniformly distributed normal force into a horizontal reinforcing material that will sag to a given strain limit. The relationship between tension and strain in a liner support design is revealing. As the strain limit is reduced, the required tensile strength increases. As a result, in a strain based design, the factor of safety is applied directly and indirectly to the allowable strain and the required tension respectively. 6.0 SUMMARY OF DESIGN PROCEDURE Combining the work performed at the University of Florida with Terzaghi's original work and the experiments conducted by the Army Corps, one can now correlate the shape of the soil arch to the strength of the soil. This is particularly helpful when there is more than one strata of soil within the arching zone. For landfill liner support applications, one has the ability to calculate the dimensions of the arch within the soil liner system above the geogrid and the dimensions of the arch within the waste above the soil liner system. (See Figure 1). Figure 2 provides the relationship between the width of the yielding zone and the height of the soil arch based on the soil strength parameter. Using this figure one can determine the dimensions of the arch within the soil and waste layers. This will enable one to determine the uniform normal pressure over the yielding area at the base of the liner system. Using Giroud's tension membrane equation one can then calculate the required geogrid tension at the allowable strain limit. Finally, one can select the appropriate geogrid. A step by step procedure along with a design example follows. (4)