3620 36TH PL NE 2018-01-02 MF Import

the contractors' equipment once overlain by structural fill. Once necessary cuts area made to achieve grade the geotextile may be placed directly on the native ground surface. The geotextile should be placed such that there are no folds or wrinkles and the material is pulled taut. Adjacent geotextile panels should be overlapped a minimum of 2 feet. The first loose lift of fill placed over the geotextile should be 12 inches thick and spread uniformly with a dozer. Equipment should not be routed directly on the geotextile or when there is less that 12 inches of cover. In addition, rubber -tired equipment should not be allowed over the geotextile unless there is at least 18 inches of cover. Due to the anticipated soft ground conditions the geotextile may be damaged without adequate protection during construction. In our opinion, it is not necessary or recommended to placed quarry spalls or other granular materials directly on the exposed native subgrade and compact the materials into the subgrade to achieve adequate support prior to placing the geotextile. 4.2.5 Structural Fill Materials Materials placed as fill to raise site grades in the vicinity of proposed structures, roadways or other improvements or placed as base course below building slabs and pavements are classified as structural fill for the purpose of this report. Structural fill material quality varies depending upon its use as described below: • Structural fill placed to raise site grades should meet the criteria for common borrow, WSDOT Standard Specification 9-03.14(P. 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 as described in Section 9-03.14(1) with the exception that the percent passing the U.S. No. 200 Sieve should be less than 5 percent. Common borrow should not be planned as structural fill during the wet season, as compaction can be very difficult if not impossible to achieve. Admixtures may be needed to improve the workability of the soils, and once in place, common borrow would still be very susceptible to disturbance from construction traffic during the wet season. • Structural fill placed as crushed surfacing base course below pavements should meet WSDOT Standard Specification 9-03.9(3) for Base Course. • Structural fill placed as capillary break material below slabs -on -grade should consist of 1'/.-inch minus crushed rock with negligible sand or fines. • Consideration should be given to using the modified gravel borrow described above for use as the preload material for compost system Nos. 1 and 2, Once the preload is complete this material can be used elsewhere on the site as structural fill even during periods of wet weather. This material may also be rolled to preload compost system No. 3 prior to spreading it out for reuse under planned pavement areas or to raise site grades. 4.2.6 On -site Soils The on -site native soils consist of silt, organic silt :,;,Al.,;Ity sands for the most part, with the silty soils near the ground surface in most areas. These soils contain a high percentage of fines, are typically wet, and are highly sensitive to small changes in moisture content. They are also highly susceptible to disturbance from construction traffic. In their existing condition and once disturbed, they will be all but 1 lU G e o E n 9 i n e e r s 11 File No. 10625-001.02/123003