5627 1ST AVE SE 2016-01-01 MF Import

.,., _ Geotechnical Consultation Services Page 6 - 93=l39'7 Hannabrook Rock Wall - Lots 39 through 45 July 26, 1993 A perforated or slotted rigid drain line wkh a minimum diameter of six inches should be installed along the rear edge of the keyway excavation. This drain line should be laid wkh � sufficient gradient to initiate yravity flow to the lowest point in the keyway excavation. Fram this point, the drain line should be connected by means of a tightline to a positive and permanent discharge. We suggest that such a positive and permanent discharge consist of a nearby storm drain catch basin. More specific details regarding this drainage system are presented in the attached ARC Guidelines. Structural Fill: Ideally, but particularly in wet weather,strudural fill should consist of an free- draining, organic-free, granular material with a meximum size of four inches. k should have no more than 85 percent passing the number 4 mesh sieve, and shouid contain no more than 5 percent fines (silt and clay sized particles passing the number 200 mesh sieve). During dry weather and organic-free compactfble material meeting the above maximun si :e criterion is acceptable. Soil Slopes: As mentioned earlier, the area above this proposed rock wall is expected to be sloped. The anticipated post-construction slope gradient is expected to range between about 1.5H:1 V and 2H:1 V, or fiatter. On completion of the const�uction work the exposed slope surface is to be re-vegetated. Precautionary Measures: As indicated above, a protective rock wail is not a retaining wall. It is more'susceptible to damage from exterior causes than, for example, one would expect a reinforced concrete wall to be. Therefore, to achieve a stable and long lasting rock wall structure we recommend that certain practices be totally avoided once the wall is complete. It is critical to the successful completion of this wall that the recommended rock sizes be used as described. The contractor must understand that if the �laced rocks are not of the recommended size it wlll be necesserv to remove a�d reolace them with rocks that meet the reauirements of this letter. We recommend that no excavation be performed within five feet of the top of any rockery. This will help prevent the potential for collapse back into the excavation area of the upper rockery rocks should soil support be removed. More importantly, no excavation work should be conducted within eight feet of the toe of the re-placement rockery. Before performing any excavation in front of any rockery, the depih of the excavation must be checked to see that it does not protrude into the area below an imaginary line drawn at 45 degrees from the bottom exterior edge of the lowest rock. This will help prevent the possibility of undermining any rock and, thus, potentially eliminating some po�tion of the rockery support. Any utility installation must be done before any rockery construction is started. _