4849 SPIRE LN 2023 Geotech Report 2025-10-15

Proposed Remedial Excavation: 4849 Spire Lane, Everett, WA December 8, 2022 soil be conducted in accordance with the recommendations provided by the environmental consultant. Open Cut Excavations: It is the contractor's responsibility to maintain safe working conditions, including temporary excavation stability. All excavations in excess of 4 feet in depth should be sloped in accordance with Washington Administrative Code (WAC) 296- 155, or be snored. Where space is available, for planning purposes, the excavation may be graded no steeper than 1 H:1 V to remain stable for temporary conditions. Based on our understanding of soil conditions as described above, near vertical excavations will likely remain stable for short periods of time before sloughing occurs, but would not be considered safe for worker entry. If near -vertical cuts are needed to remove environmentally impacted soils adjacent to the building or property lines, sequential slot cut excavations on the order of 4-foot wide can be used to reduce the risk of sloughing provided that they are backfilled within a few hours of excavation, or as directed by a PanGEO representative. Construction equipment and surcharge loads, such as soil stockpiles, should be kept a minimum horizontal distance from the top of an open cut slope a distance equal to one-half the depth of the excavation. Temporaa Excavation Shoring_ If significant sloughing occurs within the vertical cuts, in our opinion it would be feasible to utilize temporary shoring in the form of a trench box and steel plates to mitigate the sloughing of near vertical cuts. Because some of the site soils consist of loose to medium dense granular soils, we anticipate that the trench box will need to be placed in the excavation near the beginning of the excavation sequence, and then pushed down as the excavation proceeds downward. As a minimum, we recommend that the shoring system, if needed, be designed to withstand a lateral earth pressure, expressed as an equivalent fluid pressure, of 40 pounds per cubic foot (pcf). Passive pressure, if needed for design, may be assumed to be 250 pef for the design calculations. If traffic will be located within a horizontal distance equal to the depth of the excavation, we recommend a uniform vertical surface surcharge of 250 psf be used to represent the traffic loading. A higher vertical surface surcharge pressure may need to be considered for construction equipment. For this surcharge, as well as other construction related surcharges that will likely occur adjacent to the shoring system, a coefficient of 0.30 may be used to determine the lateral earth pressures due to surcharge loads on the shoring system. An appropriate safety factor should be included by the shoring designer. 22-389- 4849 spire lane merett—iPt.dou Page 8 PanGEO, Inc.