8407 BROADWAY SECURE SPACE STORAGE Geotech Report 2025-04-24

Zi pperGeo Broadway Everett Expansion Project No. 2601.01 Geoprofessional Consultants July 7, 2022 Shallow Foundation Depth and Width For frost protection, we recommend the bottom of all exterior footings bear at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings should bear at least 12 inches below the surrounding slab surface level. We recommend that all continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively. Resistance to Lateral Loads Resistance to lateral loads can be achieved through passive earth pressures on the face of embedded foundation elements and base friction. For conventional shallow footings located outside of the existing stormwater vault area, we recommend using an ultimate base friction coefficient and passive earth resistance values of 0.5 and 450 pcf equivalent fluid pressure, respectively. We recommend that passive resistance be neglected in the upper 18 inches of embedment. The above values do not include safety factors.Appropriate safety factors or resistance factors should be used for design. Note the above value for friction coefficient assumes concrete cast against soil. If option B above is used,the project structural engineer should determine the friction coefficient for concrete cast against CDF or lean concrete. For conventional shallow footings located inside the stormwater vault area,the value of available passive resistance will depend on the distance between the face of footing and face of vault,and depth of footing. In order to rely on passive earth pressures and for those pressures not to impose load on the existing stormwater vault, the full passive earth pressure failure surface must be uninterrupted between the face of footing and the stormwater vault wall. The passive earth pressure failure surface can be assumed to be a line extending upwards from the bottom edge of the footing at an angle of about 28 degrees. A graphical depiction of this limiting criteria is provided in Figure 2. If the full passive earth pressure failure surface cannot be developed, passive earth pressures should be ignored. Due to their small diameter,the lateral capacity of vertical pin piles should be ignored.Alternatively, piles battered up to 15 degrees could be considered to reduce overall lateral loads. We recommend battered piles be used in combination with vertical piles. The lateral capacity of battered piles should be taken as the horizontal component of the unfactored axial pile load (not the horizontal component of the axial compressive capacity) provided that the resisting force acts in the opposite direction of lateral loads. Any remaining lateral load may be resisted by passive earth pressures on the face of foundation elements embedded at least 1.5 feet below finished grade. Base friction for pile-supported foundations should be neglected. On-Grade Concrete Slabs Subgrade Preparation Slab subgrades should be prepared in accordance with the Site Preparation section of this report. Prior to placement of slab reinforcement or form work, slab subgrades should be compacted to a firm and unyielding condition and to at least 95 percent of the modified proctor (ASTM D1557) maximum dry density. 14