1800 41ST ST 2023-06-23 - Laserfiche WebLink

Mr. Bill Helsley December 17,2015 I Discussion and Recommendations I The granular fill material observed below the organic surface layer was noted to be relatively compact and dense and in our opinion, would be suitable for support of the pavement structure. To prepare the pavement subgrade all vegetation, organic surface soils, and other deleterious material should be stripped and removed from below the pavement areas. Surface stripping depths of approximately three to ten inches should be expected to remove the organic surface soils. Once stripped cut and fill operations required to establish the design subgrade I elevations can be initiated. All exposed subgrade surfaces should be observed by a representative of Terra Associates to verify soil conditions are as expected and suitable for support of new fill or the pavement section. The subgrade should be proofrolled using heavy rubber-tired equipment to determine if any isolated soft and I yielding areas are present. If excessively yielding areas are observed, and they cannot be stabilized in place by compaction, the affected soils should be excavated and removed to firm hearing and grade restored with new structural fill. If the depth of excavation to remove unstable soils is excessive, the use of geotextile fabrics, such I as Mirafi 500X, or an equivalent fabric, can be used in conjunction with clean granular structural fill. Our experience has shown that, in general, a minimum of 18 inches of a clean, granular structural fill placed and compacted over the geotextile fabric should establish a stable bearing surface. ISome of the existing fill soils encountered at the site contain a sufficient amount of soil fines that will make them difficult to compact as structural fill when too wet or too dry. The ability to grade and compact these soils will depend on their moisture content and the prevailing weather conditions at the time of construction. When wet soils are encountered, the contractor will need to dry the soils by aeration during dry weather conditions. Alternatively, the use of an additive such as Portland cement or lime to stabilize the soil moisture can be Iconsidered. If the soil is amended, additional Best Management Practices (BMPs) addressing the potential for elevated pH levels will need to be included in the Storm Water Pollution Prevention Program (SWPPP) prepared Iwith the Temporary Erosion and Sedimentation Control(TESC)plan. If grading activities are planned during the wet winter months, or if they are initiated during the summer and I extend into fall and winter, the owner should be prepared to import wet weather structural fill. For this purpose, we recommend importing a granular soil that meets the following grading requirements: U.S.Sieve Size Percent Passing 6 inches 100 No.4 75 maximum I No. 200 5 maximum* * Based on the 3/4-inch fraction. I Prior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural fill. I The subgrade fills should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soil's maximum dry density, as determined by American Society for Testing and Materials (ASTM)Test Designation D-1 557 (Modified Proctor). The moisture content of the soil at the time of compaction should be within minus one to plus three percent of its optimum,as determined by this ASTM standard. Project No.T-7332 IPage No.2 1