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•� ..c.,�.�µn.n�.gm.a'.� ^��.�qt.e.. ..... _ _ ".?n .. .. x�,rE'r.+2^,,di»'�� .n Presentation and Dim sign.of Results- 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. i Where the thickness of the soil/waste layer is 1.8 m (6 feet), as shown on Figure EX_1, the presence of the void will create a depression 9 em (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 m (9 foot) thick soil/waste layer over the void, the depression disappears. The disturbance in the liner surface decreases 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 EX-4). To evaluate the potential for grade reversal, a characteristic curve of required soil/waste thicknesses (T) over a 0.9 m (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. 5.0 E 4.0 O � N N � O � 3.0 0 o 1-- `00 U 0.0, C1 N 2 O� L O 0 -__ ''---_0- � 1 o 1 .0 0 0.0 0 5 10 15 20 25 30 35 40 Containment 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 Geosynaxtics'93-Vancouver,Canada- 1505