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City of Ramsey <br />Project B1705491 <br />August 11, 2017 <br />Page 11 <br />D.2. Utilities <br />D.2.a. Subgrades and Trench Backfill <br />The native and fill soils encountered at likely utility elevations generally appear suitable for pipe and <br />utility structure support and we anticipate that utilities can be installed per manufacturer bedding <br />requirements. However, we encountered some wet, clayey or silty soils in some borings; these soils may <br />have limited stability and not be suitable for backfill or support of utilities if wet. We recommend <br />providing a contingency for further subcutting and soil replacement of utility backfill soils in such soils. <br />In addition, the swamp -deposited clays and silty sands (ST-C6, ST-C11) are not considered suitable <br />backfill materials under any circumstances. These soils should be removed and replaced with suitable <br />grading materials where encountered during excavation. At pipe elevations, we recommend a minimum <br />subcut and replacement with crushed -faced rock that is free of material 1 inch in diameter or smaller. <br />A geotechnical engineer should observe all utility trench excavations and subcuts. <br />D.2.b. Excavation Side Slopes <br />The project area soils appear to meet OSHA Type C requirements in most cases. We recurrrrrlend <br />constructing excavation side slopes to lie back at a horizontal to vertical slope of 1 1/2 to 1 or flatter. In <br />significant depths of organic soils these side slopes may need to be made flatter, or supplemental <br />support may be necessary. <br />All excavations must comply with the requirements of OSHA 29 CFR, Part 1926, Subpart P, "Excavations <br />and Trenches." This document states that excavation safety is the responsibility of the contractor. <br />Reference to these OSHA requirements should be included in the project specifications. <br />Trenches deeper than 20 feet must be designed by a professional engineer. <br />D.2.c. Selection, Placement and Compaction of Backfill <br />We reLurririlerrd backfill placed above and below utilities as shown in Table 6. <br />To achieve compaction over wet or waterbearing subgrades, we recommend the use of sands or gravel <br />with MnDOT aggregate backfill material (Specification 3149.2E). <br />BRAUN <br />!RICER' LC <br />