4849 SPIRE LN 2023 Geotech Report 2025-10-15

Proposed Remedial Excavation: 4849 Spire Lane, Everett, WA December 8, 2022 not become evident until construction. If variations do appear, PanGEO should be requested to reevaluate the recommendations in this report and to modify or verify them in writing prior to proceeding with earthwork and construction. GROUNDWATER Groundwater was not encountered in our test pit progressed up to 12 feet below existing grade at the time of our test pit exploration on September 28, 2022. In addition, no groundwater was noted up to 35 feet below existing grade in the direct push probes progressed on March 22, 2022. It should be noted that groundwater levels may vary depending on the season, local subsurface conditions, and other factors. In general, the water level is the highest and the seepage rate in the greatest during the winter and early spring (typically October through May). GEOTECHNICAL RECOMMENDATIONS Several different excavation alternatives were considered to protect the existing structure from potential damage during the excavation activities. One option is to utilize a temporary shoring system, such as a solider pile wall, to provide stability to the walls of the remedial excavation. Alternately, we understand the preferred option, which is anticipated to be the most cost-effective, is to underpin the foundation of the existing residence adjacent to the proposed excavation with small diameter driven pipe piles to mitigate the potential adverse effects the excavation adjacent to the house could have on the foundation. Once the existing foundation is underpinned, the soils can be excavated out adjacent to the foundation. However, because we anticipate the upper 4 feet of soil to consist of loose to medium dense poorly graded to well graded sand, some sloughing of the near -vertical excavation could occur, which could result in the loss of soil below the footings or floor slab of the building. To reduce the potential of significant sloughing, the excavation could be performed in narrow slot cuts, on the order of 4 feet wide, or narrower, perpendicular to the building footing, and immediately backfilled with controlled density fill (CDF). UNDERPINNING EXISTING FOUNDATION — DRIVEN PIPE PILES (PIN PILES) To provide support for the existing structure during the planned remedial excavation, which will occur directly adjacent to the south wall of the existing residence, we recommend 22-389 4849 spire lane evere1 _rpt.docx Page 5 PanGEO, Inc.