DRAFT <br />and protected with vegetation to reduce the risk of surface erosion due to rainfall. Final <br />grading across the site should provide for positive drainage of surface water away from <br />exposed slopes to reduce the potential for erosion. All fill slopes should be overbuilt then <br />trimmed back to desired grades using hydraulic excavators equipped with smooth-edged <br />buckets to remove any soft or loose materials from the slope surfaces and reduce the risk <br />of surficial sloughing or slumping of the slopes. <br />5.2.4 Structural Fill <br />We anticipate the use of structural fill for the project will primarily include overall site <br />grading and backfilling of temporary excavations for foundations and utilities. We <br />recommend all structural fill consist of granular material such as sand, sandy gravel, or <br />crushed rock with a maximum size of about 2 inches and not more than about 5% passing <br />the No. 200 sieve (washed analysis). Granular fill should be placed in lifts and compacted <br />with vibratory equipment to at least 95% of the maximum dry density determined in <br />accordance with ASTM International (ASTM) D698, and the relative compaction of the fill <br />should be evaluated based on field-density testing. Appropriate lift thicknesses during <br />placement will depend on the type of compaction equipment used. For example, if hand- <br />operated, impact- or vibratory-plate equipment is used, lift thicknesses should be limited <br />to about 6 inches. If smooth-drum vibratory rollers or heavy vibratory-plates are used, lift <br />thicknesses up to about 12 inches are appropriate. If backhoe- or excavator-mounted <br />vibratory plates are used, lift thicknesses up to 2 feet may be acceptable. <br />In our opinion, the gravel and cobbles at the site are likely suitable for reuse as structural <br />fill, provided they are relatively well graded and do not contain excessive amounts of silt <br />and material larger than about 4 inches. However, it should be noted that field-density <br />testing of the gravel and cobbles will generally not be possible due to the relatively large <br />size of the material, and the relative compaction of the fill will need to be evaluated based <br />on visual observations during placement and performance testing using proof rolling with <br />loaded dump trucks or other heavy equipment. In this regard, it should be understood <br />that use of the on-site gravel and cobbles as structural fill will require additional <br />observation and oversight by a GRI representative during construction, and use of the <br />gravel and cobbles may not be practical in smaller fill areas or areas of limited access. All <br />on-site materials to be used as structural fill should be reviewed by a GRI representative. <br />All utility trench excavations located within the limits of new facilities, hardscape areas, or <br />other improved areas should be backfilled with granular structural fill following the <br />recommendations provided above. The use of backhoe- or excavator-mounted vibratory- <br />plate compactors or "hoe-packs" is usually most efficient for compacting trench backfill; <br />however, impact-plate compactors or "jumping jacks" are commonly used in shallow <br />trenches. Particular care should be given when operating hoe-packs to prevent damage <br />GRI #6497-A - 2.MO Indoor Football Practice Facility Page 9 <br />August 26, 2021 <br />