917 112TH ST SE Geotech Report 2022-10-25

Habitat for Humanity of Snot- T sh County ES-5168 April 26, 2017 Page 11 Stormwater Vault Design We understand a stormwater vault will be constructed near the northern portion of the site. Vault foundations should be supported on,competent native soil or crushed rock placed atop competent native soil. Final stormwater vault designs must incorporate adequate buffer space from,property boundaries such that temporary excavations to construct the vault structure can be successfully completed. Perimeter drains should be installed around the vault and conveyed to an approved discharge point. The presence of perched groundwater seepage should be anticipated during excavation activities for the vault. The following parameters can be used for stormwater vault design: • Allowable soil bearing capacity (dense native soil) 5,000 psf • Active earth pressure (unrestrained) 35 pcf • Active earth pressure (unrestrained, hydrostatic) 80 pcf • At-rest earth pressure (restrained) 50 pcf • At-rest earth pressure (restrained, hydrostatic) 100 pcf • Coefficient of friction 0.40 • Passive earth pressure 350 pcf • Seismic surcharge 6H* *Where H equals the retained height Vault retaining walls should be backfilled with a minimum of 18 inches of free-draining material or suitable sheet drainage that extends along the height of the walls. The upper one foot of the wall backfill can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall and connected to an approved discharge location. If the elevation of the vault bottom is such that gravity flow to an outlet is not possible, the portion of the vault below the drain should be designed to include hydrostatic pressure. Design values accounting for hydrostatic pressure are included above. ESNW should observe grading operations for the vault and the subgrade conditions prior to concrete forming and pouring to confirm conditions are as anticipated, and to provide supplemental recommendations as necessary. Additionally, ESNW should be contacted to review final vault designs to confirm that appropriate geotechnical parameters have been incorporated. Earth Solutions NW,LLC