11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

If the subgrade deteriorates during proof-rolling or compaction, it may become necessary to modify the proof-rolling or compaction criteria or methods. Backfill in old utility trenches or previously placed to construct the existing road prism that exhibit surface settlement or pavement distress should be tested and recompacted if necessary.Where new fill is required, the uppermost 2 feet supporting all new structures, sidewalks, slabs and new pavement should be compacted to at least 95 percent of the MDD estimated in general accordance with ASTM D 1557. Material below this level should be compacted to at least 90 percent of the MDD. Structural Fill Materials Materials used to construct roadways, placed to support retaining structures or foundations, or placed behind retaining structures is classified as structural fill for the purpose of this report.Structural fill material quality varies depending upon its use, as described below: 1. As a minimum,structural fill placed to construct embankments and roadways,to backfill utility trenches and to support foundations should meet the criteria for common borrow,WSDOT 9-03.14(3).Common borrow will be suitable for use as structural fill during dry weather conditions only. If structural fill is placed during wet weather,the structural fill should consist of gravel borrow,WSDOT 9-03.14(1). 2. Structural backfill for walls should meet the criteria for gravel backfill for walls,WSDOT 9-03.12(2). 3. Structural fill placed to surround collector pipe (drain rock)should meet the criteria for gravel backfill for drains,WSDOT 9-03.12(4). 4. Structural fill placed as crushed surfacing base course below pavements should conform to WSDOT 9-03.9(3). On-site Soils The soils observed in the explorations generally contain a high percentage of fines (silt and clay) and are moisture-sensitive.Some of the on-site soils may meet the criteria for common borrow and may be suitable for use during dry weather construction only, provided the soil has a moisture content near optimum. Fine-grained soils(silt and clay),or existing fill with wood or other debris do not meet the criteria for common borrow and should not be used. Peat and organic silt soils are unsuitable for use as structural fill. 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 1 foot in thickness. Each lift should be conditioned to the proper moisture content and compacted to the specified density before placing subsequent lifts. Structural fill should be compacted to the following criteria: 1. Structural fill placed behind retaining walls should be compacted to at least 90 percent of the MDD in general accordance with ASTM D 1557. Care should be taken when compacting fill near the face of retaining walls to avoid overcompaction and hence overstressing the walls. 2. Structural fill in embankment and new pavement areas, including utility trench backfill, should be compacted to 90 percent of the MDD (ASTM D 1557), except that the upper 2 feet of fill below final subgrade should be compacted to 95 percent of the MDD(ASTM D 1557). GEOENGINEERS_O April 14,2017 Page 22 File No.2095-032-00