4107 OLIVE ST 2018-01-02 MF Import

DAVID L. NELSON AND ASSOCIATES, INC. Consulting Engineering Geology July 13, 1990 Project No. 9490 Page 5 Permanent fill embankments are expected to stand at various slopes depending on the material and compaction effort used. For structural till, t hat is f ill comprised of clean imported or on site soils with a relative compaction in excess of 90% (ASTM D-1557), embankment slopes should be no steeper than 2N:1v, and properly protected from erosion. We do not recommend placing additional fill on the slopes unless the entire embankment is reconstructed as structural fill. Dewatering a Drainage Depending on excavation configuration and ground water conditions at the time of construction, temporary dewatering may be necessary. Typt=ally, cut off drains are used to intercept groundwater before it emerges into the excavation. The cut off drain consists of a trench filled with Pea gravel that intercepts the ground water flow. A perforated pipe is placed near the bottom of the pea gravel and is routed to a suitable discharge point. The actual need and design of the cut off drain should be based on conditions observed in the field at the time of construction. We suggest that a geotechnical consultant be on -site during drain development and construction. Wall and footing drains should be constructed as outlined in the retaining wall section of this report. Erosion potential should be considered moderate to severe for stripped areas with 15% or steeper grades. Erosion potential for areas in which the existing low ground cover is left intact, and surface water is controlled, is expected to be unaffected by the proposed development. Construction phase erosion control could include, but not necessarily be limited to, the use of hay bales, geotextile barriers (silt fences), and controlled surface grading. Roofs and pavements will reduce the surface area available for natural infiltration within the site. This will in turn increase surface runoff. We recommend that roof drains, catch basins or other devices used to collect surface runoff be directed by tight line into the storm drain or other. suitable system. Au:._:: should not be allowed to discharge onto sloping