25 E BEECH ST 2017-01-13 - Laserfiche WebLink

� Geotechnical Engineering Study Regarding: Underpinning of 25 E Beech St, Everett Introduction � In the course of our investigation, we performed soil sampling to a depth of 4' with a 3" hand auger at which point the boring was terminated due to obstructions, presumably large gravels. Due to the presence of charcoal to a depth of 3' in the location of the boring, we concluded that soils were disturbed within the past 200 years due to construction, clearing, or logging to this depth. This may have contributed to settlement. We also observed that footings were constructed within a few inches of grade which may also have contributed to settlement. 25 E Beech St, Everett Geologic Setting According to the Washington State Department of Natural Resources, the site sits at 500ft elevation atop Quaternary age Vashon till. These sediments were deposited during the Vashon Stade of the Fraser Glaciation and include clays, silts, sands, pebbles, cobbles, and boulders with occasional stratified lenses. This till ranges from compact to locally cemented, creating hardpan in some regions. The Department of Natural Resources classifies the liquefaction susceptibility at this site to be 'very low,' and categorizes it into seismic site class C with a design category of D1. Risks While every effort has been made to define and quantify geologic risl< to this site, unknowns may exist beyond the reasonable scope of investigation. Portions of the footings outside of the proposal we reviewed may experience settlement in the future and may require work at that time. Load calculations are based upon 2000 psi compressive strength standard concrete, construction defects or internal stresses may result in cracks forming or expanding during driving or lifting. Recommendations We recommend that the proposed underpinning proceed using 2" diameter driven pin piles and Grip-Tite retrofit brackets. We recommend that piles be driven using a 160 pneumatic hammer until rejection. Rejection is defined as less than 1" driven in 3 minutes of continuous driving.