Opening of Quotes - Laurel Woods Drainage Improvements Proj No. 121-007 - Selge Construction Co., Inc.

Home Browse Search

Weaver Consultants Group 5 4 DESIGN RECOMMENDATIONS 4.1 Basis Our recommendations for the proposed storm sewer are based on data presented in this report, which includes four test borings along the proposed alignment. Subsurface variations can exist at a site which may not be indicated by such a dispersed and limited boring program, particularly given the presence of existing below-grade utilities and expected associated fill soil. If such variations or unexpected conditions are encountered during construction, or if the project information discussed herein is incorrect or changed, we should be informed immediately since the validity of our recommendations may be affected. 4.2 Storm Sewer Recommendations Prior to excavating trenches for piping in those areas where cut-and-cover techniques will be used, we recommend that all underground utilities within the project limits be relocated or temporarily removed where necessary. Following relocation/removal of utilities, excavation for the piping may then proceed. Based on our observations of the subsurface conditions, we anticipate that excavations for the system will typically expose very loose to medium dense granular-type soils. Considering the granular nature of the soils, it is our opinion that the excavated granular soils may be re-used as backfill. Granular soils (i.e., soils containing less than 12 percent fines) which meet the requirements discussed in Section 5.3 are considered conducive for pipe support and fill placement. To reduce the risk of settlement of the backfill, we recommend that the bedding material and soils used for structural backfill surrounding the pipe be mechanically compacted to a minimum of 95 percent of the standard Proctor density (ASTM D 698). Where the storm sewer is beneath roadways, we recommend the fill be compacted to 98 percent of Standard Proctor density. Additionally, periodic field density tests performed by WCG are recommended during fill placement to determine the adequacy of compactive effort. Considering we anticipate that granular-type soil will be encountered at the pipe inverts, a separate bedding material may not be required. The borings did note the occasional presence of cobbles near the probable sewer depths. Cobbles should be relocated away from the installed sewer as to not create hard points on the pipe. Granular backfill placed around the pipe in uniform layers, not exceeding 6 in. in loose lift thickness, is recommended. We also recommend that the backfill be placed and hand compacted in layers simultaneously on each side of the pipe. In our opinion, compaction equipment should operate parallel to the axis of the pipe and over-compaction may cause movement of the pipe prior to being seated. Therefore, caution should be exercised during this initial phase of pipe placement. Note that the pipe manufacturer may provide backfill requirements/procedures pertaining to their particular pipe. If this is the case, then the manufacturer's specifications should be adopted.