222 W CASINO RD Geotech Report 2022-10-25

GeoTest Services, Inc. May 3,2019 Mukilteo School District 19-0194 directly over compacted fill soils may be proportioned using a net allowable soil bearing pressure of 1,500 pounds per square foot (psf). The "net allowable bearing pressure" refers to the pressure that can be imposed on the soil at foundation level.This pressure includes all dead loads, live loads,the weight of the footing, and 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 and the foundation option chosen. If foundation Option 1 is chosen and construction is accomplished as recommended and at the maximum allowable soil bearing pressure,GTS estimates the total settlement of building foundations to be less than one inch. Differential settlement between two adjacent load-bearing components supported on competent soil is estimated to be less than one half the total settlement. If Option 2 is selected,total settlement of the building my be on the order of 1 to 2 inches with differential settlement estimated to be half of the total settlement. This can be somewhat mitigated if the building can be releveled after initial construction. Foundation and Site Drainage Positive surface gradients should be provided adjacent to the proposed building to direct surface water away from the building and toward suitable drainage facilities. Roof drainage should not be introduced into the perimeter footing drains but should be separately discharged directly to the stormwater collection system or similar municipality-approved outlet. Pavement and sidewalk areas, if present, should be sloped and drainage gradients should be maintained to carry surface water away from the building towards an approved stormwater collection system. Surface water should not be allowed to pond and soak into the ground surface near buildings or paved areas during or after construction. Construction excavations should be sloped to drain to sumps where water from seepage, rainfall, and runoff can be collected and pumped to a suitable discharge facility. To reduce the potential for groundwater and surface water to seep into interior spaces,GTS recommends that an exterior footing drain system be constructed around the perimeter of new building foundations as shown in the Typical Footing Drain Section (Figure 3) of this report. The drain should consist of a perforated pipe measuring 4 inches in diameter at minimum,surrounded by at least 12 inches of filtering media.The pipe should be sloped to carry water to an approved collection system. The filtering media may consist of open-graded drain rock wrapped in a nonwoven geotextile fabric such as Mirafi 140N(or equivalent)or wrapped with a graded sand and gravel filter. For foundations supporting retaining walls, drainage backfill should be carried up the back of the wall and be at least 12 inches wide. The drainage backfill should extend from the foundation drain to within approximately 1 foot of the finished grade and consist of open-graded drain rock containing less than 3 percent fines by weight passing the U.S. Standard No. 200 sieve (based on a wet sieve analysis of that portion passing the U.S. Standard No. 4 sieve). The invert of the footing drain pipe should be placed at approximately the same elevation as the bottom of the footing or 12 inches below the adjacent floor slab grade, whichever is deeper,so that water will be contained. This process prevents water from seeping through walls or floor slabs. The drain system should include cleanouts to allow for periodic maintenance and inspection. 8