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Hennepin Parks ' <br /> Project BABX-91-589 <br /> December 19, 1991 <br /> Page 6 , <br /> ' <br /> . P v m n , <br /> C 5 a e e ts <br /> C.S.a Subgrade Preparation: Because of the potential for high groundwater to be , <br /> � encountered during the parking lot construetion, we recommend one of two altematives be <br /> used. ' <br /> • Alternative 1 - If groundwater is not encountered, we recommend the topsoil be <br /> removed from the parking and drive areas. The depth of topsoil ranges from 1 1/2 to ' <br /> 3 feet. After removing the topsoil, the underlying soil should generally be silty sand <br /> or silty clayey sand. These subgrade soils should be scarified if the areas are cut to ' <br /> grade and then compacted to a minimum of 95 percent of the modified Proctor <br /> density. Where fill is required, we recommend it consist of a debris-free mineral soil. ' <br /> The moisture content of the fill should be within three percentage points of optimum <br /> moisture. If placed within 3 feet of final grade, we recommend it be compacted to a <br /> minimum of 95 peccent of the modified Proctor density. We recommend fill placed , <br /> more than 3 feet below tinished grade be compacted to a minimum of 90 percent of <br /> the Proctor density. <br /> ' <br /> • Alternative 2 - If groundwater is high, we recommend removing only the su�cial <br /> vegetation and leaving the remaining topsoil layer. We recommend the upper 6 inches ' <br /> of the resulting subgrade be scarified and surface compacted. Where fill is required, <br /> we recommend it be placed and compacted as discussed above. If there are areas , <br /> which cannot be compacted, we recommend the unstable materials be subexcavated <br /> down to stable soil and be replaced by materials which can be compacted. <br /> , <br /> You indicated to us that the current plans call for the use of on-site soils where fill is <br /> required. Therefore, the fill materials used in the parking lot will likely be similar to those ' <br /> encountered in the borings. These soils will be a mixture of silty sand, silty clayey sand and <br /> sandy lean clay. Laboratory tests to determine a representative R-value of these soils were not <br /> . included in our scope of services. Because of the variability of these soils, we have assumed , <br /> an R-value in the range of 10 to 20 for our design. <br /> , <br /> , <br /> ' <br />