902 PINE ST NORTH SOUND BEHAVIORAL HEALTH TREATMENT CENTER Geotech Report 2022-10-25

GeoTest Services, Inc. November 16,2018 North Puget Sound Behavioral Health—Treatment Center Addition Job No. 18-0770 Allowable Bearing Capacity Assuming the above foundation support criteria are satisfied, continuous or isolated spread footings founded directly on firm and unyielding unweathered native glacial till (very dense, grey or brown, gravelly sand), may be proportioned using a maximum net allowable soil bearing pressure of up to 4,000 pounds per square foot (psf). The designer may incorporate the use of weathered glacial till or structural fill proportioned using a maximum net allowable bearing pressure of up to 2,500 psf. At most locations explored, dense to very dense unweathered native soils were intersected at 1 to 2 feet BGS. The B-4 drilling location did not intersect dense or greater conditions until about 5 feet BGS due to the overlying fill soil encountered. The term "net allowable bearing pressure" refers to the pressure that can be imposed on the soil at foundation level resulting from the total of all dead plus live loads, exclusive of the weight of the footing or any backfill placed above the footing.The net allowable bearing pressure may be increased by one-third for transient wind or seismic loads. Foundation Settlement Settlement of shallow foundations depends on foundation size and bearing pressure, as well as the strength and compressibility characteristics of the underlying soil. Assuming construction is accomplished as previously recommended and for the maximum allowable soil bearing pressure recommended above, we estimate the total settlement of building foundations should be less than about 1 inch and differential settlement between two adjacent load-bearing components supported on competent soil should be less than about one half the total settlement. The soil response to applied stresses caused by building and other loads is expected to be predominantly elastic in nature, with most of the settlement occurring during construction as loads are applied. Considerations For new construction adjacent to or connecting to an existing building, we recommend that no surcharge be placed on the existing structure's foundation elements. New foundation elements should be designed to be at the same grade or at a lower grade than the existing foundation to prevent a surcharge situation to develop. If concern for the zone of influence between the existing and planned foundations develop during project design, we recommend lowering the bearing capacity as addressed above or matching the bearing capacity of the previously constructed foundation. Concrete Slab-on-Grade Conventional slab-on-grade floor construction is considered feasible for the site. Floor slabs may be supported on properly prepared native subgrade or on structural fill placed over properly prepared native soil. Existing fill below parking areas appears to be suitable to remain as slab support, based on our limited explorations. New floor slabs should not be founded on topsoil, organic fill, or loose/soft fill or native soils. Prior to placement of capillary break material in the upper slab area, the prepared slab subgrade should be proof-rolled as recommended in the Site Preparation and Earthwork section of this report. We recommend that interior concrete slab-on-grade floors be underlain by a minimum of 6 inches of compacted, clean, crushed free-draining gravel with less than 3 percent Page 9of17