4027 4TH ST SE 2018-01-01 MF Import

January 14, 2003 HWA Proiect No. 2002-146-21 generally loosdsoft in consistency and highly susceptible to senlement upon an increase in overburden s�tress. 3.3 SUBSURFACE CONDITIONS 3.3.1 Soils Subsurface conditions encountered consisted of fill overlying alluvium which in tum was over glacial deposits at depth. The boring log in Appendix A provides more detail relative to soil conditions encountered at the boring location. General descripHons of the soil units encountered aze presented below. Fill: Fill soil was encountered to a depth of 23 feet (approx. El. —13 feet) befow the existing ground surface. The fill soils can be sepazated into two distinct layers. 'fhe upper 8 feet is generally clean to silty, gravelly sand with the upper 5 feet of this layer being very dense. This upper sand layer may have been placed as part of past construction at the site or from dredging materinl from the Snohomish River. The lower portion of the fill is generally silt with abundant organics and pieces of wood (cedaz chips). This material may aiso have been dredge material from the Snohomish River from a different area than the sand fill. Alluvium: Below the fill soil, alluvium was encountered to about 95 feet below the existing ground surface (approx. El —85 ft). The alluvium encountered in the explorations can be grouped into 4layers for discussion purposes: Medium dense, upper sand and eravel (Bottom of Layer at EI. —45 ft f)- The upper approximately 32 feet of alluvium encountered in the subsurface exploration consisted of medium dense to dense silty sand. �'ery soft, silt and clay (Bottom of Layer at EI. —82 ft f)- This layer was encountered &om 55 feet below the existing ground to 92 feet below ground. This unit consisted of very soft plastic silt and clay with fine, detrital organics. Very soft, peat (Bottom of Layer at El. —SS ft f) - Below the silt and clay layer, the alluvial deposits consisted of a thin layer of very soft fibrous peat and fine sand. hledium dense, sand (Bottom of Layer at EI. —90ftf) —"Chis layer consisted of inedium dense, fine to medium sand. G(acia! Deposiu: Below the alluvium, glacial outwash was encountered to the depth of our borings (EI. —103.5 ft f). The ouiwash was very dense and consisted of ciean fine to medium sand. This unit was not penetrated by our boring. 2002146 tepon •(nal � S HWA GEOSCIENCES INC. U