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'CON V In a contour plot; elevation alonga contour line represents the a line. A closed contour therefore indicates either.a depression or a mound The presence of elo contours representing a deep depression is an unacceptable condition ie. the design of a liners stem. The deformed surface elevations in each grid point ane calculated by the computer Program- The deformed surface contours on the 7 percent sloping surface are then plotted For each case, as shown Oil Figures EX I - EX 4. Where the this ess-of the SOR/waste layer is 1.8 m (6 feet), as shown on Figure- the presence of the voidwill create a depression 9 em ({3.3 feet) deep. This depression could t Ftrap and accumulate liquids, hinderi-ng-the f= flow of leachate towards a collection point. When the thicknim of the soil/waste layer above the void is increased to-2.25 m .5 t feet), the depression is uced to less than 3 cm (0.1 foot)., as shown on Figure EX 2, With a 2.7 m (9 foot) thick so /waste layer over the void, the depression disappears. The disturbance in the liner surface decr tases as the depth to the void increases, as seen when the thickness of the so"/waste layer is i creased to 3.6 m (12 feet) (Figure EX 3 and EX 4). To evaluate the potential for grade reversal, a characteristic curve of required soil/waste thicknesses (T7 over a 0 9 m (3 feet) wide by 0.9 m (3 feet) deep by 1.8 in (6 feet) long void versus liner surface grad (a) is illustrated on Figure 3. 5.0 E H 4.0 0 Y7 N N C) C O U s 3.0 c ,0. U ~ 00 O. 2.0 0- O v � o 1.0 --. 0�--�'�__ o 0.0 ' 0 5 10" 15 a'20 25 30 35 40 Contoinm.ent Liner Grade (degree) Figure 3 Required con olled U thickness to prevent grade reversal (T) versus containment liner grade (a) on 0.9m x 0.9m x 1.8m (3'x3'x6') void Gcosynttrbcs'93-Vancouvcr�Canada-1305