1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC Geotech Report 2022-10-25

Permanent Slopes We recommend that permanent cut and fill slopes be constructed no steeper than 2H:1V. To achieve uniform compaction, we recommend that fill slopes be overbuilt slightly and subsequently cut back to expose properly compacted fill. To reduce erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of grading. Until the vegetation is established,some sloughing and raveling of the slopes should be expected. This may require localized repairs and reseeding.Temporary covering,such as clear heavy plastic sheeting, jute fabric, loose straw or excelsior matting should be used to protect the slopes during periods of rainfall. Pavement Recommendations Subgrade Preparation We recommend that the subgrade soils in new pavement areas be prepared and evaluated as described above in the "Earthwork and Structural Fill"section of this report. If the pavement subgrade is adequately prepared in accordance with our recommendations, a California Bearing Ratio (CBR) value of 12 to 15 is appropriate for pavement design purposes. Prior to placing new fills, pavement base course materials or gravel below pavements, subgrade areas should be proof-rolled to locate any soft or pumping soils. Proof-rolling can be completed using heavy tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed, they should be removed and replaced with structural fill. New Hot Mix Asphalt Pavements In automobile parking areas,we recommend a minimum pavement section consisting of 2 inches of HMA, Class l inch, PG 58-22 over 4 inches of crushed surfacing base course. In drive areas or areas of truck traffic, the minimum pavement section should consist of at least 3 inches of HMA over a minimum of 6 inches of crushed surfacing base course.The HMA should meet the requirements in Section 9-02 of the WSDOT Standard Specifications. The crushed surfacing base course should meet the requirements of Section 9-03.9(3) of the WSDOT Standard Specifications. The crushed surfacing base course should be compacted to at least 95 percent of the MDD prior to HMA placement. Asphalt-Treated Base Recommendations Asphalt-treated base(ATB)may be used to support temporary construction traffic and then be incorporated into the final pavement design. At the completion of construction, the ATB would be overlain with HMA to provide the final pavement sections. If ATB is used,we recommend substituting 1 inch of ATB for 2 inches of base course material. For full-depth ATB replacement, this results in pavement sections of 2 inches of HMA over 2 inches of ATB in automobile parking areas, and 3 inches of HMA over 3 inches ATB in truck traffic areas. The above recommendations for ATB use are based on our experience. Depending on the frequency of construction traffic on the above pavement sections, it should be expected that some localized areas of the ATB will need to be repaired and/or replaced prior to placing the HMA. GEOENGINEERS_Os April 22,2016 Page 12 Fl;eNo 1Oi3 710-01