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Mr. Rick Bloomquist November 26, 1991 Page Two determined by the standard proctor method. In our opinion, proper compaction of a cohesive fill at the proper moisture content at this time of the year may be difficult to achieve. Alternate Two. This alternate would consist of somewhat less extensive excavation of the existing subgrade soils. The alternate would consist of excavation to a depth ranging from about 2' to 3' below planned subgrade. The subcut excavation should then be refilled to grade with a well compacted free-drainin� sand/gravel. In order to discharge water which may collect within the granular soils placed over the less permeable cohesive soils, we recommend that a perforated draintile be installed within the bottom of the granular fill. The draintile should be discharged into the nearby storm sewer system or daylighted to th� adjacent slope, which ever would be acceptable to appropriate authorities. We recommend the bottom of the subcut excavation be sloped to the location of the draintile in order to provide drainage for the entire subgrade area. In our opinion, use of the second alternative would be most preferable and should result in a more stable subgrade which would be less susceptible to moist-volume expansion upon freezing. After our initial site visit, we were informed that Alternate Two as described above would be used to improve the present subgrade stability. On October 25, 1991, we observed the soils in this area at completion of the recommended subcut excavation. At this time, the depth of subcut below planned finished subgrade range frcm 1' to 1.5' in the extreme southeast portion of the slab area, to about 2' in the central portion, and 2.5' to 3' along the western edge and northern portion of the subcut area, just south of the existing storm sewer catch basins. The soils exposed at the completion of this subcut consisted of lean clay, sandy lean clay, silty sand and clayey sand. These soils, were judged to be suitable for placement of the clean granular sand fi11. VVe did recommend to project personnel that the surface of the subcut excavation be recompacted just prior to placement of the sand fill. If we can be of further assistance please contact us. Very truly yours, -� -� � / �.-�-�.��-�,_ �;-�=��4;6--: '; � Gary . Larson Ronald A. Shaffer, P.E. Field Engineer Principal Geotechnical Engineer GAL/RAS/sal AS A MUTUAL PROTECTION TO CLIENTS,THE PUBLIC AND OURSELVES.ALL TWIN CITY TESTING CORPORATION REPORTS ARE SUBMITTED AS THE CONFIDENTIAL PROPERTY OF CLIENTS, AND AUTHORIZATION FOR PUBLICATION OF STATEMENTS,CONCLUSIONS OR EXTRACTIONS FROM OR REGARDING OUR REPORTS IS RESERVED PENDING OUR PRIOR WRITTEN APPROVAL.