6.6. SR 08-19-2002 - Laserfiche WebLink

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AET #20-02044 - Page 13 Pavement Sub.ode Preparation We have attached a data sheet entitled "Bimminons Pavement Subgrade Preparation and Design" which presents considerations and recommendations for bituminous subgrade grading work. Refer to this sheet for more complete recommendations for the subgrade preparation work. The primary near surface soils (below the topsoil) consist of alluvial lean clay, silt, silty sand, clayey sand, and sandy lean clay. These soils can become weak and unstable during wet periods or when present near the ground water levels and are frost susceptible. The lean clays and silts are typically poor subgrade soils even when placed at proper water contents and compacted to specified compaction levels. As a minimum, we recommend removing all vegetation, topsoil and swamp deposits. We also recommend the frae alluvial lean clays and silts be removed when present in the top 3' of the subgrade. This excavation should also include ~A:i (H:V) lateral oversizing outside the curb line for lateral support of the fill and pavements. If the excavation terminates at elevations within the top 3' of the subgrade, the bottom of the excavation should be test-rolled to judge the stability of the exposed subgrade. If unstable soils are exposed, they should be subcut and replaced with drier fill; or aerated, dried and recompacted in-place if weather conditions permit. Fill placed in the subgrade areas could be the site sands, sands with silt, clayey sands, or silty sands. All fill placed in the pavement areas should be compacted according to Mn/DOT Specification 2105.3Fl (Specified Density Method). This specification requires the fill placed in the top 3' of the pavement subgrade be compacted to a minimum of 100% of the Standard Proctor Maximum dry density. Any fill placed below the top 3' of the subgrades should be compacted to a minimum of 95 %. The soils should be compacted within the water content requirements of this Mn/DOT specification. We anticipate that mechanical aeration of some of the site soils may be required to satisfy the water content requirements and obtain proper compaction.