2710 14TH ST BLDG A Geotech Report 2023-12-29

We recommend PCC pavements incorporate construction joints and/or crack control joints spaced maximum distances of 12 feet apart, center -to -center, in both the longitudinal and transverse directions. Crack control joints may be created by placing an insert or groove into the fresh concrete surface during finishing, or by sawcutting the concrete after it has initially set-up. We recommend the depth of the crack control joints be approximately one-fourth the thickness of the concrete; or about 1.5 inches deep for the recommended concrete thickness of 6 inches. We also recommend the crack control joints be sealed with an appropriate sealant to help restrict water infiltration into the joints. 4.6.4. Asphalt -Treated Base If pavements are constructed during the wet seasons, consideration may be given to covering the areas to be paved with ATB for protection. Light -duty pavement areas should be surfaced with at least 3 inches of ATB, and heavy-duty pavement areas should be surfaced with at least 6 inches of ATB. Prior to placement of the final pavement sections, we recommend the ATB surface be evaluated and areas of ATB pavement failure be removed and the subgrade repaired. If ATB is used and is serviceable when final pavements are constructed, the CSBC can be eliminated, and the design PCC or asphalt concrete pavement thickness can be placed directly over the ATB. The contractor may need to increase the thickness of these recommended ATB sections based on planned heavy equipment and construction traffic loading. 4.7. Drainage Considerations The contractor should anticipate shallow perched groundwater conditions may develop and seepage may enter excavations depending on the time of year construction takes place, especially in the spring and winter months. However, we expect this seepage water can be handled by digging interceptor trenches in the excavations and pumping from sumps. The seepage water if not intercepted and removed from the excavations will make it difficult to place and compact structural fill and may destabilize cut slopes. All paved and landscaped areas should be graded so surface drainage is directed away from the buildings to appropriate catch basins. Water collected in roof downspout lines must not discharge into or be routed to the perforated pipes intended for footing or wall drainage. 4.8. Infiltration Considerations Sieve analyses were performed on selected soil samples collected from the test pits that were completed as part of this study. The soil samples typically consisted of fill, native weathered or relatively unweathered glacial soils. Design infiltration rates for glacially consolidated deposits based on grain size analyses are not recommended by the Washington State Department of Ecology Storm Water Management Manual (2014). Based on our analysis, it is our opinion that the on -site native glacial soils have a very low infiltration capacity. The majority of the soils across the site are composed of glacially consolidated, dense glacial till and stiff to hard glaciolacustrine deposits with a relatively high fines content, which limits the infiltration capacity. The results of the sieve analyses indicated that the fines content (material passing the U.S. No. 200 sieve) typically ranges from about 36 to 98 percent. Due to the density of the native glacial soils and relatively high fines content, infiltration should be assumed to be very low when designing infiltration 7 L GEOENGINEERS� October30, 2019 Page 19 File No. 21288-002-00 1� L