2410 RAILWAY AVE Geotech Report 2023-04-06

Penske Truck Leasing-Proposed Service Facility,2410 Railway Ave, Everett,WA Mar.8,2019/Rev.Feb. 25,2020 Geotechnical Engineering Report P1493-T18 Subgrade Compaction: Exposed subgrades should be compacted to a firm,unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet- !" weather filling are presented subsequently. Regardless of soil type, all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Specifically, building pad fill soil should be compacted to a uniform density of at least 95 percent ' (based on ASTM:D-1557). Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • Existing Fill/Alluvial Soils: Underlying the existing vegetation and gravel/quarry spall base material, we encounteredgranular alluvial soils comprised of fine to P P coarse sand with some to trace silt and gravel,plus abundant organics,hog fuel,and timber to a depth of around 25 feet. This material would not be suitable for reuse as structural fill due to its high relative organics content. • Organic-Rich Silt: Interbedded with the alluvial sand throughout much of site is a silt unit comprised of mostly fines and a varying organics content, including hog fuel and burnt wood. Due to the fact that these soils are highly moisture sensitive, ' contain organic material,and are generally in an over-saturated condition,we do not recommend the re-use of this soil group as structural fill. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to reduce long-term raveling,sloughing,and erosion. We generally recommend that no permanent slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 21/2H:1V) would further ' reduce long-term erosion and facilitate revegetation. Slope Protection: We recommend that a permanent berm, swale,or curb be constructed along the topedge of allpermanent slopes to intercept surface flow. Also, a hardyvegetative groundcover g P g should be established as soon as feasible, to further protect the slopes from runoff water erosion. ' Alternatively,permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4_2 Preloading We recommend that the proposed building area be preloaded to preinduce a major portion of the settlement that would otherwise occur when building loads are applied. ' Preload Thickness: Based on the assumed building loads, and additional load to the soil after the existing grade has been raised, we recommend a minimum preload thickness of 5 feet should be placed. Migizi Group, Inc. Page 9 of 17