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Mr. Sam Roberto <br />Project BBXX- 01 -119A <br />May 24, 2001 <br />Page 6 <br />D.1.c. Dewatering <br />We recommend dewatering excavations to the extent possible. In our opinion, conditions appear <br />favorable for using sumps and pumps. To facilitate the dewatering process, and provide a stable <br />platform on which to place excavation backfill, consideration should be given to lining the <br />excavation bottoms with a stabilizing aggregate meeting the gradation requirements of Mn/DOT <br />Specification 31492H, Coarse Filter Aggregate. <br />D.l.d. Selecting Replacement Backfill and Additional Required Fill <br />We recommend that the first two feet of backfill placed over the excavation bottoms in this case <br />consist of coarse, free - draining sand having less than 50 percent of the particles by weight <br />passing a 40 sieve, and less than 5 percent passing a 200 sieve (roughly equivalent to Mn /DOT <br />Specification 3149.2J, Fine Filter Aggregate). We recommend placing this material in a single <br />lift, and compacting it statically (without vibration). <br />Subsequent backfill may consist of suitable deposits of existing fill (free of debris or organic <br />material), or imported soils. Though imported material may consist of silty sand, clayey sand, <br />sandy lean clay or lean clay having a plastic index of 15 or less, poorly graded sand or poorly <br />graded sand with silt will be more easily spread and compacted. <br />D.l.e. Placement and Compaction of Bad/fill and Fill <br />After spreading the initial 2 -foot lift of coarse, free - draining sand, we recommend spreading <br />subsequent backfill in 4- to 8 -inch lifts, depending on the composition of the material and the <br />type of compactor used. We recommend compacting all backfill to at least 95 percent of its <br />maximum dry density, determined according to American Society for Testing and Materials <br />(ASTM) Test Method D 698 (standard Proctor). <br />D.2. Spread Footing Foundations <br />