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JO& <br />MP ENGINEERING <br />Pipe Bedding <br />Pipe zone bedding material should consist of crushed, processed, or naturally occurring granular material, <br />free of organic matter and other deleterious material, and should meet the gradation requirements of <br />Gravel Backf ill for Pipe Zone Bedding per Section 9-03.12(3) of the 2021 WSDOT Standard Specifications. <br />Trench Backfill and Compaction <br />Trench backfill material should meet the material and compaction requirements as described in Section <br />4.9 of this report. <br />4.9 STRUCTURAL FILL <br />The term "structural fill" refers to any materials placed under foundations, slab -on -grade floors, <br />sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations <br />concerning structural fill are presented in the following paragraphs. <br />A/Intcrinlc <br />Typical structural fill materials include gravel, crushed rock, quarry spalls, CDF, LMC, well -graded <br />mixtures of sand and gravel (commonly called "gravel borrow" or "pit -run"), and miscellaneous mixtures <br />of silt, sand, and gravel. Soils used for structural fill should not contain any organic matter or debris, or <br />any individual particles greater than approximately 6 inches in diameter. <br />Fill Placement <br />Generally, quarry spalls, CDF, and LMC do not require special placement and compaction procedures. In <br />contrast, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts <br />not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a <br />mechanical vibratory compactor. <br />Compaction Criteria <br />Using the Modified Proctor test (ASTM D1557) as a standard, we recommend structural fill be used for <br />various on -site applications and compacted to the following minimum densities: <br />MP ENGINEERING, PLLC MPGEOTECH.COM 15 <br />