1033 51ST PL SW Geotech Report 2022-10-28

• Foundation drains should be used to mitigate the buildup of hydrostatic pressure, prevent flooding of the bottom story, provide freeze/thaw protection, and prevent heaving. We recommend the grading of yards, surrounding pavement, and the overall site drainage be comprehensively managed to prevent draining water toward the structures. Footing drains should consist of a filter fabric-wrapped, drain rock-filled trench that extends at least 12 inches below the lowest adjacent grade(i.e., slab subgrade elevation). A perforated pipe should be placed at the base to collect water that gathers in the drain rock. Discharge for the footing drains should not be tied directly into the stormwater drainage system, unless mechanisms are installed to prevent backflow. 8.3 EXCAVATIONS 8.3.1 General Excavations will be.required for the installation of new footings, utilities,and other earthwork. Conventional earthmoving equipment in proper working condition should be capable of making the necessary excavations. Glacial till underlies the site. Glacial till in the project area is known to contain boulders and glacial erratic rocks, which can require over-excavation and associated backfilling. 8.3.2 Utility Trench Excavation Trench cuts should generally stand near vertical to a depth of approximately 4 feet In the fill, provided groundwater seepage is not observed in the sidewalls. If seepage is encountered that undermines the stability of the trench, the sidewalls should be flattened or shored. Contractors working at the site should be aware that some caving in the upper 4 feet of trenches could occur, especially if debris or loose fill is encountered. Groundwater was'not noted during our explorations. Dewatering of utility trenches for the project will not likely be required. If groundwater is encountered, it would likely consist of perched groundwater within a sandy zone of the glacial till material during the wet season. If this occurs,dewatering of utility trenches could be accomplished using a standard sump pump. While we have described one approach to trench excavation, it is the contractor's responsibility to select the excavation and dewatering methods, monitor the trench excavations for safety, and provide any shoring required to protect personnel and adjacent improvements. All trench excavations-should be in accordance with applicable.OSHA,.and state regulations. 8.3.3 Trench Backfill Material Pipe bedding should be placed and compacted in accordance with City standard drawings using crushed surface base course in accordance with WSS 9-03.9(3)-Crushed Surfacing. Overlying'trench°backfill material should be placed and compacted in accordance with City standard drawings using native material or imported gravel borrow per WSS 9-03.14(1) -Gravel Borrow. In our opinion,It will not be necessary to use imported gravel borrow if the native soil can be adequately moisture conditioned and compacted. G EODESIGN`z 10 NWHome-1-01:101618