10632 7TH AVE SE Geotech Report 2025-07-28

I June 6 2008 Serenity Meadows �i L&A Job No. 8A017 Page 15 I prepared as described in the SITE PREPARATION AND GENERAL EARTHWORK section of this report Prior to placing road base material,the subgrade soils should be compacted to a non- yielding state with a vibratory roller compactor and proof-rolled with a piece of heavy construction equipment, such as a fully-loaded dump truck. Any areas with excessive flexing or pumping should be over-excavated and re-compacted or replaced with a structural fill or crushed rock placed and compacted in accordance with the recommendations provided in the STRUCTURAL FILL section of this report. We recommend that a 6-inch-thick minimum, compacted, crushed rock base (CRB), consisting I' of 7/8-inch-minus crushed rock, be used for the roadway. Such crushed rock base may be replaced with a 2-to-3-inch layer of leveling course constructed of compacted 7/8-inch crushed rock if the roadways are to be based on cuts into undisturbed, dense to very-dense,fresh,advance outwash and, or till soils. The crushed rock or subgrade base should be overlain with a 3-inch asphalt treated base (ATB) topped by a 2-inch-thick Class B asphalt concrete (AC) surficial course. DRAINAGE CONTROL Rain Gardens Storm runoff captured over impervious surfaces of the proposed development of the site,such as a driveways and roadways,will be disposed onsite through a series of rain gardens roofs and paved y y � in accordance with a minimum impact design(MID) method. A typical section of rain garden is shown on Plate 8. The rain gardens will be interconnected with an under drain consisting of a PVC drain line buried in a gravel-filled trench. The rain gardens will consist of excavated ponds lined with a 18 to 24 inch thick layer of compost amended soil mix. The sections of this PVC drain line under the rain gardens will be slotted to allow water to flow from the under drain;line into the rain gardens. Stormwater to be discharged into the under drain line is to be routed into sediment control structures/oil-water separators. Water stored in the rain gardens would then LIU & ASSOCIATES, INC.