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Subsurface Soil Investigation Letter 10-25-2014Interstate Geotechnicai Engineering, Inc Patrick 3 Hines, PE 8167 100'h st s Cottage Grove MN 55016 (612) 414 -5770 25 October 2014 Mr James Rudos 14846 Timber Hill Road Minnetonka MN 55345 Re: Subsurface Soil Investigation Proposed Single Family Residence W of 2061 W 65th St, Chanhassen, Minn In accordance with your authorization, I have completed the above referenced investigation to determine site suitability for the proposed construction. A summary of my findings together with boring logs and my conclusions and recommendations are presented in the enclosed report. I found, as you already have been briefed, more than usual problems with the site. There is a total of 5'/4'& 61/4' at the locations of Boring 1 & Probe 1A, respectively, of unsuitable soil in the form of topsoil fill, general and varying till, and buried original humus. Below at first is a low sand content lean clay, generally dark in color, saturated, very soft to soft (w/ depth). It is "normally consolidated" (consolidated enough to only support its own weight, not additional weight of fill soils or structures above). The overburdening fill has not been inplace long enough to force further consolidation. The moisture content test in this material indicated nearly 42 %, high for a lean clay. This material extends only from 53/4 to 7' in Boring 1, but from 61/4' to 83/2 in Probe IA. The first 9" of this material in Probe lA is very soft and is a borderline marl material. All of the aforementioned materials are unsuitable for structure support should be removed. I do acknowledge that excavators are often reluctant to excavate further once the buried organic soil is cleared, so understandings should be inplace at the time of gathering bids. Base soil below at first is a lean clay, a little sandy, dark gray, saturated, rather soft to medium. It has inclusions of a poorly graded (biased finer grained) sand with a few fines, also dark gray, saturated, loose to firm. Deepest soil, commencing at 1 Pin Boring 1, is a lean clay, rather sandy, dark gray, low gravel content, medium. Theses materials are glacial till. The sand inclusions in the upper portion are glacial outwash. All of these base mineral soils are suitable for residential construction, with conditions. Refusal to auger advancement was not encountered by boring termination depth of 23', indicating lack of bedrock to this level. Very importantly, groundwater was found in the main Boring at 1.8' (elev 961/4±). It is aquifer groundwater, but marginally so. It appears to be contained primarily in the sand inclusions at 7' +. But it also is coming from the upper soft and very soft clay, possibly from Mr James Rudos 25 October 2014 Page 2 the lower organic soil. Proper construction on the site (removing the softer lean clay, promoting good site drainage) will mitigate some of this. Thus, water found presently can be regarded as a maximum level. Slab grade of the proposed residence should be set in accordance with City requirements utilizing this level. I recommend complete removal_ of all unsuitable soil which is likely to be the fill and buried organic soil as encountered plus the overly soft clay found in both the boring and probe. While this amounts only to another 11/4 in the vicinity of Boring 1, it is another 2'+ in the vicinity of Probe 1A. As indicated, excavators may be reluctant to excavate below organic soil level, but it is necessary (see longer discussion in the report). It is so important that full time inspection of the excavation by a soils engineer may be necessary. Of course, other zones of unsuitable soil not represented by the boring and probe could still be encountered due to the nature of small volume random sampling. Any other depths or zones of unsuitable soil should be removed as well. You could lower footings somewhat so that you have to provide less oversizing and not stray onto the neighbor's property. But footings here should not be lowered so much as to rest directly upon the suitable base soil as it is only marginally suitable. You need a little fill (2' is recommended) to spread footing loads out with depth. Footings maybe generally designed allowing the usual 2000 psf foundation bearing capacity, which will likely result in normal strip or pad footings. Special attention is again drawn to the advisory that excavations be examined by the Soils Engineer to verify soil boring results and to document adequacy of site preparation. Again this is very important as how much softivery soft clay must be removed will require a high degree of field judgment. Fill, as used, should be tested for compaction adequacy. Soil correction should not be abated below slabs in any manner (ie, do not let the excavator try to "trench around" slab areas). Thank you for the opportunity to have been of service. If you have any questions on this, or if I can be of assistance in any additional capacity, do not hesitate to contact me at your convenience. Sincerely, INTERSTATE GEOTECHNICAL ENGINEERING, Inc atrick J Hines, President enclosures pH/SC