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' - 17 - I ~. ' I I i i, at the mine bench and various ground water conditions. As a i ~' result of these analyses, several conclusions and recommen- ' ~ dations could be made: I ~ 1. The stability of the natural slope is very marginal ~I because of the steep slope gradient, if saturated conditions i are assumed; it is very probable that any excavation or fill ' ~ placement would result in a slope failure if performed during ' a wet season and without appropriate drainage. ~ t ~ 2. An effective underground drainage system should be ' designed and constructed to prevent the saturation of the sur- fi i l l i b d f c a ayer o so ove an l a below the retaining structures. This drainage system should provide for the long-term stab- , ~ ility of the road. ' 3. It is not possible to recommend the details of the drainage extent for all possible combinations of road cuts and fills; for the expected heights of the walls, a minimum depth of ' 10 feet below the natural surface appears to be sufficient ' ! according to our analyses. Deeper drainage might be necessary f d h or roa sections w ere the walls are higher than 10 feet; in such a case, criteria, as presented for the mine bench portal ~ cuts, should be applied. A drainage system will be required below the retaining walls that support the fills if a potential ' ~ for the saturation of the soil below the foundation exists. It j appears that stable conditions can be achieved if saturation of ' i a layer about 10 feet thick is prevented. 4. It cannot be estimated whether the recommended drainage systems should be installed prior to or during the construction; this will depend largely on ground water conditions at the time ' ~ of construction. It is very probable that, i£ ground water is intersected by an excavation a slide might develop immediately; on the other hand, an excavation in soils above the ground ~,~~..A.,..~.r