2401 TAYLOR DR Geotech Report 2022-10-25

2401 Taylor Drive Geotechnical Engineering Study Everett, Washington Liquefaction Liquefaction is the process of loose, saturated sand losing its internal shear strength when subjected to cyclic loading, as may occur during an earthquake. Due to the strength and silt content of the underlying native sediments and lack of a shallow groundwater table at the site, the potential for liquefaction to occur is low, in our opinion. Ground Motion It is our opinion that earthquake damage to the proposed structures, when founded on suitable bearing strata in accordance with the recommendations contained herein, will likely be caused by the intensity and acceleration associated with the event. Structural design for the project should follow 2015 IBC standards. The 2015 IBC defines Site Classification by reference to Table 20.3.-1 of the American Society of Civil Engineers publication ASCE 7,the current version of which is ASCE 7-10. In our opinion the subsurface conditions at the site are consistent with a Site Classification of"C" as defined in the referenced documents. Erosion Hazards and Mitigations The steep slope at the very north end of the subject property is classified as a High Erosion Hazard Area as defined in EMC Title 19, Chapter 19.37.080(a)(3) while the flatter southern part of the site is classified as a low erosion hazard area. The following discussion addresses potential erosion hazards that could develop during construction. The most effective erosion control measure is the maintenance of adequate ground cover. Maintaining cover measures atop disturbed ground provides the greatest reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October 1 through March 31), exposed soil should not remain uncovered for more than 2 days unless it is actively being worked. Ground-cover measures can include erosion control matting, plastic sheeting, straw mulch, crushed rock or recycled concrete, or mature hydroseed. Some fine-grained surface soils are the result of natural weathering processes that have broken down parent materials into their mineral components. These mineral components can have an inherent electrical charge. Electrically charged mineral fines attract oppositely charged particles and can combine (flocculate) to form larger particles that will settle out of suspension. The sediments produced during the recent glaciation of Puget Sound are, however, most commonly the suspended soils that are carried by site storm water. The fine-grained fraction of the glacially derived soil is referred to as "rock flour," which is primarily a silt-sized particle with no electrical charge. These particles, once suspended in water, may have settling times in periods of months. Therefore, the flow length within a temporary sediment control trap or pond has virtually no effect on the water quality of the discharge, since silt will not settle out of suspension in the time November 6, 2019 SONDERGARRD GEOSCIENCES, PLLC 4