Agenda - Council - 10/26/2021 - Laserfiche WebLink

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4.3 Utility Recommendations We anticipate that new utilities will be installed as part of this project. We further anticipate that new utilities will bear at depths about 5 feet below the ground surface. At these depths, we anticipate that the pipes will bear on sandy alluvial soils or compacted engineered fill which in our opinion are suitable for pipe support. We recommend removing all vegetation, topsoil and any soft or otherwise unsuitable soils, if any, beneath utilities prior to placement. We assume that open cut excavation techniques will be used for pipe installation. We further assume that typical excavations depths will be on the order of 5 feet below the ground surface. At typical 1:1 excavation backslopes, the excavation will extend about 5 feet beyond the edge of the excavation. The excavation may extend into/ onto adjacent properties or the adjacent roadways posing a risk of undermining structures on those properties or roadways. In addition, the soils could slough as they are excavated resulting in side slopes flatter than 1:1 further increasing the horizontal limits of the excavation. If site constraints will limit the excavation, trench boxes or temporary shoring may be required. Backfilling We understand that in most cases new pavements will be constructed over the top of the utility trench(s) and that soil excavated for pipe installation will be placed back in the excavations, to the greatest extent possible. We do not recommend re -using topsoil, buried topsoil, organic soils or soils that are black in color for pipe support or for fill or backfill below roadways. It may be possible to re -use these materials in "green areas" such as landscaping berms, if any. We recommend bedding material be thoroughly compacted around the pipes. We recommend trench backfill above the pipes be compacted to a minimum of 95 percent beneath pavements, the exception being within 3 feet of the proposed pavement subgrade, where 100 percent of standard Proctor density is required. In landscaped areas we recommend a minimum compaction of 90 percent. 4.4 Pavement Recommendations The City of Ramsey may have standard plates that dictate bituminous pavement design. If so, we assume the pavements be designed in accordance with the appropriate standard plates. The following paragraphs provide general pavement recommendations in the absence of standard plates. Reconstruction In areas that will be reconstructed we recommend removing all vegetation and topsoil, if any, and all pavements, aggregate base, organic soils and any soft or otherwise unsuitable materials from beneath the pavement subgrade. Prior to placing the aggregate base (Class 5) we recommend compacting the subgrade soils to provide a more uniform surface and to identify soft, weak, loose or unstable areas that may require additional subcuts. Backfill, if needed, to attain pavement subgrade elevation can consist of any mineral soil provided it is free of organic material or other deleterious materials but recommend additional fill, if needed, consist of sandy soils similar to the on -site materials. Granular fill classified as SP or SP-SM should be placed within 65 percent to 105 percent of its optimum moisture content as determined by the standard Proctor. Other fill soils should be placed with moisture contents within a range of 1 percentage point below and 3 percentage points 10