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

Zi pperGeo Broadway Everett Expansion Project No. 2601.01 Geoprofessional Consultants July 7, 2022 We recommend that all permanent cut or fill slopes be designed at a 2H:1V (Horizontal:Vertical) inclination or flatter. All permanent cut and fill slopes should be adequately protected from erosion both temporarily and permanently. Construction Dewatering Groundwater was not encountered at the time of the explorations as discussed previously. If groundwater is encountered, excavations that extend below the groundwater table may require dewatering. The contractor should be responsible for dewatering means and methods. If dewatering is necessary, the contractor should address the potential impacts and risks associated with dewatering such as dewatering- induced settlement. Building Foundation Recommendations Based on soil conditions encountered in our borings, it appears that supporting the proposed building on conventional shallow footings is feasible. However, support characteristics of in situ site soils appears to be marginal, and some footing subgrade remedial work is recommended to limit post construction settlements. Additionally, a significant portion of the south building line is located in close proximity to the existing stormwater detention vault, and we understand the vault wall was not designed to accommodate building footing surcharge loads. As such, new building footings located in close proximity to the vault wall will need to be designed such that they do not surcharge the vault wall. Geotechnical recommendations for building foundations are provided below. Building Foundations/Stormwater Vault Interaction In order to prevent building foundations from imposing surcharge loads on the existing stormwater vault wall, footing bearing stresses should be transferred to a sufficient depth below the ground surface such that the vertical stress increase zone below footings does not intercept the vault wall. The vertical stress increase zone below building foundations can be represented by extending a line down from the edge of the footing closest to the vault at a 1H:2V(horizontal:vertical)angle. Achieving this bearing stress transfer could be completed in a number of ways including the following: A. Place the bottom of footings at a sufficient depth below the ground surface such that the stress increase zone below the footings does not intercept the vault wall. B. Place the bottom of footings at typical depths below the ground surface for frost protection and transfer bearing stresses to an adequate depth using controlled low-strength materials such as CDF or lean concrete. This option would require over-excavation of soils below footings to a sufficient depth and backfilling with CDF or lean concrete. CDF or lean concrete should have a minimum compressive strength of 300 psi at 28 days. C. Place the bottom of footings at typical depths below the ground surface for frost protection and transferring bearing stresses to an adequate depth using deep foundations such as pin piles. Graphical depictions of the above options are shown on the attached Figure 2. 11