7.2. HRSR 08-02-2021 - Laserfiche WebLink

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Preliminary Report of Geotechnical Exploration Main & Gates Redevelopment; Elk River, Minnesota AMERICAN July 9, 2021 ENGINEERING Report No. P-0001445 TESTING, INC. Page 3 of 10 5.2 Subsurface Soils/Geology The site geology consists of fill or topsoil over sandy alluvial soils. Additional information on the soil layers encountered is outlined below. 5.2.1 Fill Fill soils were encountered at the surface of all the soil borings except Boring SB-3. The fill extends to a depth of about 4 to 7 feet below existing grades. The fill soils are primarily silty sands and sands with silt with trace roots and organic fines. Borings SB-2 encountered debris consisting of wood within the fill. These soils are moderately slow draining and susceptible to freeze-thaw movements. Due to the presence of the organic fines and low and variable N-values, we judge that these soils were not placed and compacted for structural support. The existing fill at Borings SB-2 contained pieces of wood. There may be other types of debris present in the fill that were not sampled in our boring. Test pits with a backhoe could further define the amount, type and extent of the debris with environmental sampling performed. Fill that contains debris is considered “Regulated” by the MPCA and requires proper disposal, usually at a designated landfill. Because cutting is anticipated at Borings SB-2 to correct the subgrade soils, environmental pre-qualification of the fill prior to excavation would aid in obtaining representative earthwork bids and help avoid construction delays. 5.2.2 Topsoil Topsoil was encountered at the surface of Boring SB-3. The topsoil extends to depths of about 3 feet beneath existing grade. The topsoil consists primarily of silty sands with organics. These soils are fairly fast draining and moderately susceptible to freeze-thaw movements. Due to the presence of the organic fines, we judge these soils to be slightly compressible under structural loads. 5.2.3 Alluvial Soils Alluvial soils were encountered in all of the soil borings beneath the fill or topsoil. These soils were classified as sands with varying amounts of gravel. These soils had N-values ranging from 2 to 18 blows per foot. The alluvial soils are judged to have moderate strength and moderately low compressibility. They are fast draining and are low to slightly frost susceptible when they are impacted by freezing temperatures. Draft