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

1 ' ■ Structural fill placed immediately outside below -grade walls (drainage zone) should consist of washed gravel in conformance Section 9-03.12(4) of the 2018 WSDOT Standard Specifications, as shown on ' Figure 4. ■ Structural fill placed as crushed surfacing base course (CSBC) below pavements should conform to Section 9 03.9(3) of the 2018 WSDOT Standard Specifications. ■ Structural fill placed as capillary break below slabs should consist of 1-inch minus clean crushed gravel with negligible sand or silt in conformance with Section 9-03.1(4)C, grading No. 67 of the 2018 WSDOT ' Standard Specifications. 4.5.5.2. Reuse of On -site Soils ' Based on the samples collected from our explorations, the moisture content of the fill and the native glacial till is typically near the optimum moisture content for compaction. However, the soils are very moisture sensitive and can be difficult to compact during periods of wet weather or if impacted by groundwater seepage. Therefore, we recommend that they be used as Common Borrow only during periods of extended dry weather. Soils with high fines content, such as silt, clay and glaciolacustrine deposits will not be suitable for reuse as structural fill and should be exported from the site or used in landscape areas if encountered ' during construction. 4.5.5.3. Reuse of Existing Asphalt and Concrete Rubble Existing asphalt pavement, base course, and portland cement concrete (PCC) rubble may be reused as structural fill if properly crushed during demolition. Recycled asphalt pavement should not be used as structural fill under building footprints or in landscape areas. PCC rubble and base course materials may ' be reused as structural fill throughout the project except in landscape areas. For use as structural fill, the asphalt and concrete rubble should be crushed or otherwise ground up and should meet the gradation requirements for gravel borrow as described in Section 9-03.14(1) of the 2018 WSDOT Standard ' Specifications. If recycled asphalt and/or concrete will be used under pavement areas, we recommend that it meet the gradation requirements for CSBC as described in Section 9-03.9(3) of the 2018 WSDOT Standard Specifications. 4.5.6. Fill Placement and Compaction Criteria Structural fill should be mechanically compacted to a firm, non -yielding condition. Structural fill should be placed in loose lifts not exceeding 12 inches in thickness if using heavy compactors and 6 inches if using hand operated compaction equipment. The actual lift thickness will be dependent on the structural fill material used and the type and size of compaction equipment. Each lift should be moisture conditioned to within 2 percent of the optimum moisture content and compacted to the specified density before placing subsequent lifts. Compaction of all structural fill at the site should be in accordance with the ASTM D 1557 (modified proctor) test method. Structural fill should be compacted to the following criteria: 1. Structural fill placed below floor slabs and foundations, and against foundations, should be compacted to at least 95 percent of the MDD. 2_ Structural fill placed behind below -grade walls should be compacted to between 90 to 92 percent of the MDD. Care should be taken when compacting fill near the face of below -grade walls to avoid over -compaction and, hence overstressing the walls. Hand operated compactors should be used within 5 feet behind the wall. Wall backfill placed within building footprints, but under a second -floor level should be compacted to between 90 to 92 percent of the MDD within 5 feet of the walls and to at least ' GMENGINEERS� October30,2019 Page14 File No. 21288-002-00