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- . . . . . - - - - -. -' . . --:•:.ter_,��:�« Fi�esentation and Discus on of Rc�cult�t In a contour plot, a contour line represents the same elevation along a line. A closed contour therefore indicates either.a depression or a mound. The presence of closed contours representing a deep depression is an unacceptable condition in the design of a liner system. The deformed surface elevations in each grid point are calculated by the computer Program. The deformed surface contours on the 7 percent sloping surface are then plotted for each case, as shown on Figures EX—1 - EX 4. Where the thickness-of the soil/waste layer is 1.8 in (6 feet), as shown on Figure EX 1, the presence of the void will date a depression 9 cm (0.3 feet) deep. This depression could trap and accumulate liquids, hindering•the free flow of leachate towards a collection point. When the thickness of the soil/waste layer above the void is increased to-2.25 in (7.5 feet), the depression is reduced to less than 3 cm (0.1 foot), as shown on Figure EX 2.- With a 2.7 in (9 foot) thick soil/waste-layer over the void, the depression disappears. The disturbance in the liner surface deerreases as the depth to the void increases, as seen when the thickness of the soil/waste layer is increased to 3.6 m (12 feet) figure EX 3 and 13X_4). To evaluate the potential for gradereversal, a characteristic curve of required soil/waste thicknesses (T) over a 0-9 in (3 feet) wide by 0.9 m (3 feet) deep by 1.8 m (6 feet) long void versus liner surface grades (a) is illustrated on Figure 3. s.0 . a 4.0 0 C 0 2: v 3.0 �O o �O v 00. 2_ 0 0-0'� � O . Cr Ct: N 1.0 0 0.0 0 5 10 15 20 25 30 35 40 Con#oinmenf Liner Grade (degree) Figure 3 Required controlled fill thickness to prevent grade reversal (T) versus containment liner grade (a) on. 0.9m x 0.9m x 1.8m (3'x3'x6') void Geosyndxtics'93-vancouver,Canada- 1505