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Hennepin Pazks ' Project BABX-91-589 December 19, 1991 ' Page 4 , • . . . � C. Preliminary Analysis and Recommendations C.1 Proposed Construction , We understand the proposed construction w�ill�consist of a one-story visitors center as well as paved parking and drive areas. At this time, the type of construction, floor grade and building i loads are unknown. For this report, we have assumed column loads to be less than 50 kips and wall loads to be less than 3 kips per lineal foot. We have also assumed a floor grade of , 942.0 feet. Once actual loads and floor gr.ades have been finalued, a review of this report should be made by us to determine if the recommendations contained herein need to be revised. , C.2 Building Pad Preparation � We recommend the topsoil and the upper clay layer be removed from within the building area. The estimated excavation depth at each boring location is about 2 feet. Variations will likely occur between the borings which will not be evident until the excavation is underway. ' If areas of the building require fill below proposed footing grades, we recommend the excavation of topsoil be oversized to provide lateral stability to the fill. The bottom of the , excavation should be oversized 1 foot beyond the outside edge of the footings for each foot of depth below the bottom of the footing (a 1:1 slope). . . ' We recommend the bottom of the excavation be observed by our soils engineer or an assistant to evaluate the completeness of the topsoil removal and the suitability of the soils left inplace. ' This must be done prior to the placement of filt. In the area of Boring ST-7, we recommend the loose silty sand be surface compacted to , increase its inplace relative density. Given the soil's classification and moisture content, there is, however, a small risk the surface compaction will result in the sands becoming unstable. If , this occurs, a limited subcut of the silty sand may be needed. With suitable soils exposed, we recommend the bottom of the excavation be surface , compacted by several passes of a lazge drum, self-propelled compactor. This will further densify the upper natural sands. The excavation can then be backfille� with controlle� fill ' using loose lifts not exceeding 12 inches and compacted by a large drum, self-propelled compactor. The moisture content of the fill should be within three percentage points of ' �