12728 19TH AVE SE BASE FILE Geotech Report 2025-07-29

' May 28,2007 Proposed Office Building L&A Job No. 7A053 Page 10 Application %of Maximum Dry Density Within building pads of the building lots 95% Roadway/driveway subgrade 95%for top 3 feet and 90%below ' Retaining wall backfill 90% Utility trench backfill 95%for top 4 feet and 90% below STORMWATER DETENTION VAULT An underground concrete detention vault will be constructed under the parking lot to store stormwater collected over impervious surfaces within the subject project site. The location of the detention vault was yet to be finalized while this report was being prepared. It is, however, most likely will be a short distance south or southeast of the office building. Since the site is underlain by very-dense fresh till soils at shallow depth, the vault would be founded on the fresh till soils regardless where it is to be located. We recommend that footing foundations constructed on or into the fresh till soils be used to support the vault and that an allowable soil bearing pressure not to exceed 4,000 psf be used for the design of the detention vault footing foundations. A drain line consisting of perforated, rigid PVC, drain pipe or slotted, corrugated ADS, drain pipe, at least 4 inches in diameter, should be installed at a few inches below bottom of the perimeter footings of the vault walls to intercept and drain away groundwater which may flow towards the vault. The drain lines should have sufficient slope(0.5%minimum)to generate flow by gravity, and water collected in the drain line should be tightlined to discharge into a storm sewer or a suitable stormwater disposal facility. The drain line should be completely embedded in washed gravel wrapped in a layer of non-woven filter fabric, such as 140N by Mirafi Inc. or approved equal. A vertical drainage blanket at least 12 inches thick horizontally, consisting of compacted pea gravel or washed gravel, should be placed against the perimeter vault walls. The remaining backfill should be constructed of structural fill. Alternatively, a vertical drain mat, 111 LIU & ASSOCIATES, INC. I