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- 17 - <br />I, at the mine bench and various ground water conditions. As a <br />result of these analyses, several conclusions and recommen- <br />dations could be made: <br />i. 1. The stability of the natural slope is very marginal <br />~! because of the steep slope gradient, if saturated conditions <br />~: are assumed; it is very probable that any excavation or fill <br />placement would result in a slope failure if performed during <br />a wet season and without appropriate drainage. <br />2. An effective underground drainage system should be <br />designed and constructed to prevent the saturation of the sur- <br />ficial layer of soil above and below the retaining structures. <br />This drainage system should provide for the long-term stab- <br />ility of the road. <br />3. It is not possible to recoa~end the details of the <br />• drainage extent for 211 possible combinations of road cuts and <br />fills; for the expected heights of the walls, a minimum depth of <br />10 feet below the natural surface appears to be sufficient <br />according to our analyses. Deeper drainage might be necessary <br />for road sections where the walls are higher than 10 feet; in <br />such a case, criteria, as presented for the mine bench portal <br />cuts, should be applied. A drainage system will be required <br />below the retaining walls that support the fills if a potential <br />! for the saturation of the soil below the foundation exists. It <br />i <br />appears that stable conditions can be achieved if saturation of <br />a layer about 10 feet thick is prevented. <br />~ 4. It cannot be estimated whether the recommended drainage <br />systems should be installed prior to or during the construction; <br />this will depend largely on ground water conditions at the time <br />of construction. It is very probable that, if ground water is <br />intersected by an excavation a slide might develop immediately; <br />• on the other hand, an excavation in soils above the ground <br /> <br />