2400 33RD ST GEOTECHNICAL INVESTIGATION 2018-01-02 MF Import

SU I30 Mi&010Pita it does not need to be dry, so the designer han the option to not install typical Nall drainage if a differential water head is not likely to occur. However, if there will be. relatively quick drainage from the interior, then drainage is recommended. The system should be fail-safe by either draining by gravity or by having a 'one-way' relief valve in the concrete wal! to allow excess exterior (within the soil) water pressures to drain into the empty basin. The station basement is different since it will be dry on the interior, and exterior wall drainage is recommended. We recommend the installation of 'honeycombed' plastic/non- woven fabric material, installed against the outside of the concrete wall prior to backfilling that prevents infiltration of fines, but allow water to seep down to an exterior footing drain pipe. Such materials are known commercially as Mira -drain or Anke-drain. Manufacturers recommendations should be followed. If a more natural option is preferred, then backfrll the walls and around the footing drain pipe with 18-inch minimum vertical layer of coarse clean sand (ASTM C-33) or WSDOT Gravel Backfill for Drains (WSDOT 9-03.12(4)). 5.7 Pavement Considerations 5.7.1 General Considerations The recommended total thickness of the pavement section will vary depending on the surface loading. In summary, the pavement section consists of the following layers: • A dense running surfrlce of either concrete or asphalt (perhaps CMUs, but if they are to be used, a layer of concrete should be placed underneath). • A leveling coarse/drainage layer. • An improved subgrade layer. • Subgrade. The subgrade preparation (proof rolling, etc.) has been presented in section 5.1.2 and is not discussed further here. The improved subgrade layer is 'structural fill'. It is to be 24 inches thick and placed in a minimum of three (3) lifts. The compaction is to be that of structural GII. As discussed above, this improved subgrade layer is needed to distribute the loading from the heavily loaded vehicles and in the highly traveled areas. The owner has the option to perform this operation over the entire site or just in the areas described above. Our recommendation is to perform the treatment everywhere, so the pavement and the sidewalks, etc. are all founded on similar subgrade. 5.72 Automobile Parking Lot Areas - Asphalt Parking Lot Areas - Asphalt Two sections of asphalt are recommended for automobile parking areas. In the areas where car parking is to occur, the recommended section is 3 inches of class B asphalt over 4 inches of WSDOT Crushed Surfacing - Base Course (9-03.9(3)). This design is based on Guidelines published by the Asphalt Paving Association of Washington, Inc. Geotectulical,'tunnel and Envirorknental Engineers 3080125°Ave NE. Pho (425)969-5779 Iklleme, WA98005 Page 17 Fax (425)961-0677