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4. ENGINEERING ANALYSIS AND RECOMMENDATIONS 4.1 Discussion Fills No information was provided to us regarding density tests or placement observations for the existing fills placed at the boring locations. However, the fills encountered in our borings did not contain organics and have been inplace for a long period of time. Therefore, it is our opinion that these fills are suitable for continuing support of the pavement section. Organics In contrast to the other borings, PB -13 encountered swamp deposits consisting of peat and organic clay. The swamp deposits were encountered from about the 5 to 20 foot depths. Organic soils and vegetated root zones are not suitable for direct support of the roadway. Where they are greater than 4 feet below the top of subgrade in existing roadways, they are generally acceptable to leave inplace provided that new construction does not include raising grade outside the existing embankment. In road widening areas, added fill can initiate settlement. This settlement is oftentimes greater than that experienced in the adjacent existing embankment. Given this differential settlement, a longitudinal crack will appear between the existing roadway and the widened roadway. The organic soils would not be suitable to support new underground utilities and would require excavation and replacement. If vertical elevations of the roadway are raised in areas containing organics, new settlements can occur, and we recommend the organics be completely excavated. Organic soils should also be removed where the roadway will be widened. Lake Deposits The sands with silt, silty sands, and silty sands with clay encountered in the borings are generally capable of supporting the roadway and underground utilities. General It is our opinion that groundwater could be encountered by excavations at this site and could affect construction of underground utilities. Generally, the soils in the upper 4 feet of the subgrade influence pavement performance the most. The soils within the pavement subgrade consist of organic soils, clays and silts, which are frost susceptible soils. Consideration should be given to partially subcutting these soils and replacing with a non -frost susceptible granular fill to reduce the potential frost heave below the pavement section. 4.2 Pavement Areas Table 3 below presents the existing roadway pavement section and subgrade profiles. Table 3: Roadway Soil Boring Profiles Geotechnical Report Oneka Lake Boulevard and Harrow Avenue Improvements Hugo, Minnesota WSB Project No. 010893-000 Page 6 Bituminous Aggregate Boring No. Asphalt Base Subgrade Soils Thickness Thickness (Upper 4 feet) inches inches PB -1 4 10 Fill (Sand with Silt), Silty Sand PB -2 4 12 Fill (Silty Sand), Silty Sand P13-3 4 10 Silty Sand P13-4 4 11 Fill (Sand with Silt), Silty Sand Geotechnical Report Oneka Lake Boulevard and Harrow Avenue Improvements Hugo, Minnesota WSB Project No. 010893-000 Page 6