Laserfiche WebLink
HR Green, Inc. <br />Project B2204225 <br />October 3, 2022 <br />Page 8 <br /> <br /> <br />C.2. Site Grading and Subgrade Preparation <br /> <br />C.2.a. Removals <br />We recommend removing unsuitable soils consisting of topsoil, soils containing more than 5 percent <br />organic material, vegetation, existing structures, pavements, and aggregate base from the proposed trail <br />area, within 2 feet of the proposed trail embankments and its associated oversize areas. Based on the <br />borings, typical soil correction depths along most of the proposed trail alignment will be about 1 to <br />2 feet. We also recommend having a geotechnical engineer, or an engineering technician working under <br />the direction of a geotechnical engineer (geotechnical representative), evaluate the suitability of exposed <br />subgrade soils prior to backfilling and/or test rolling. <br /> <br />C.2.b. Excavation Oversizing <br />When removing unsuitable materials below structures or pavements, we recommend the excavation <br />extend outward and downward at a slope of 1H:1V (horizontal:vertical) or flatter. <br /> <br />C.2.c. Excavated Slopes <br />Based on the borings, we anticipate on-site soils in excavations will consist of clayey sand or sandy lean <br />clay fill. These soils are typically considered Type B Soil under OSHA (Occupational Safety and Health <br />Administration) guidelines. OSHA guidelines indicate unsupported excavations in Type B soils should have <br />a gradient no steeper than 1H:1V. Slopes constructed in this manner may still exhibit surface sloughing. <br />OSHA requires an engineer to evaluate slopes or excavations over 20 feet in depth. <br /> <br />An OSHA-approved qualified person should review the soil classification in the field. Excavations must <br />comply with the requirements of OSHA 29 CFR, Part 1926, Subpart P, “Excavations and Trenches.” This <br />document states excavation safety is the responsibility of the contractor. The project specifications <br />should reference these OSHA requirements. <br /> <br />C.2.d. Pavement Subgrade Preparation <br />We recommend the following steps for pavement subgrade preparation, understanding the <br />reconstruction will generally match existing grades. Note that project planning may need to require <br />additional subcuts to limit frost heave or remove and replace unsuitable soils. <br /> <br />1. Once the removals are performed as recommended in Section C.2.a, have a geotechnical <br />representative observe the excavated subgrade to evaluate if additional subgrade <br />improvements are necessary. <br /> <br />41