6301 36TH AVE W 2016-11-01 - Laserfiche WebLink

r June 23,2014 Project No.T-6241 iThe gravity block wall constructed using Ultra-Block units will be adjacent the stormwater pond and will be partially submerged during parts of the year. We have recommend drain rock be installed behind the wall to prevent the backfill material from becoming saturated. The beveled or chamfered block confers will provide weep holes through the wall that will allow the stormwater to pass freely from the front of the wall to the drain rock and then back out into the pond thereby preventing any additional hydrostatic pressure from developing ' behind the wall. Recommended wall construction details for the Ultra-Block walls are shown on attached Figures 7 through 10. Design calculations for all three wall systems are attached in Appendices B, C, and D for building official review. We recommend limiting cut rockeries to a height of ten feet when facing undisturbed dense native soils. Foundation depths should provide for a theoretical 1:1 influence line extending from the footing edge to pass beneath the rockery base. A recommended detail of the rockery is shown on Figure 11. We recommend that all subgrade preparation activities, placement, and compaction of structural fill associated with construction of the walls be completed in accordance with recommendations as outlined in this report. r5.9 Stormwater Detention Facility A stormwater detention pond will be constructed in the north-eastern portion of the development. The proposed pond floor will be 10 to 19 feet below current site grades and formed by a combination of excavation and fill containment berm construction. Our field exploration indicates that the soils in this area consist of medium dense to dense silty sand with gravel overlying dense sand with silt. We would note that our exploration of this area consists of a single test pit excavated approximately 11 feet below current site grades. If the cleaner outwash soils are exposed along the side slopes and floor of the water duality cell, it may be necessary to line the ' cell with less pervious till soils also present at the site to prevent excessive infiltration losses. The need to line the pond should be based on observation of conditions exposed when excavated. ' Fill used to form containment berms for the detention pond should consist of native silty sand with gravel placed and compacted as structural fill. All fill material placed for formation of the containment berm must be placed and compacted structurally as recommended in Section 5.2 of this report. The berm fill should be keyed into the underlying competent native soil a minimum depth of two feet. Interior pond slopes below the stored water level are shown graded at 3:1 with exterior pond slopes graded at 2:1. These slope gradients are appropriated for the pond construction and performance. 5.10 Drainage Surface Final exterior grades should promote free and positive drainage away from the site at all times. Water must not ' be allowed to pond or collect adjacent to foundations or within the immediate building areas. We recommend providing a positive drainage gradient away from the building perimeters. If this gradient cannot be provided, surface water should be collected adjacent to the structures and disposed to appropriate storm facilities. r Page No. 11 1