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<br />sand, and silty sand. Alluvial soils have been deposited above the till. Some mixed till soils <br />and topsoil also appear above the Till, very likely as fill. Normally, a glacial till can provide <br />adequate support for an elevated tank of this size. That is, Till can normally provide a <br />bearing capacity of 3,000 psf with a total settlement of 1" and a differential settlement of <br />approximately Y2". These are acceptable soil properties for an elevated water tank <br />foundation. However, based on the laboratory consolidation testing that was done on the <br />standard penetration boring test samples, the data suggests that this particular (glacial) Till <br />has been significantly over-consolidated by the glaciers as they retreated. Based on the <br />laboratory testing, the total settlement was judged to be on the order of 5". Also based on <br />this testing, the differential settlement was anticipated to be on the order of 2 Yz". The <br />differential settlement value is completely unacceptable for an elevated water tower. <br />Beneath the (glacial) Till, the deep boring encountered Dolostone, which appears to be part <br />of the Shakopee formation. The Dolostone was somewhat weathered and could be a gravity <br />deposited rock, but bedrock maps published by the Minnesota Geological Survey indicate <br />that contact with bedrock should be in the vicinity of the depth that the boring indicated. <br /> <br />--, <br />, \ <br /> <br />Because the standard penetration borings forced us to conclude that we had unacceptable <br />settlement values, the use of one day's work of an electric cone penatrometer (CPT) was <br />authorized. This allowed the data to include six additional tests to a depth of approximately <br />45 feet. The goal of the CPT use was to quantify the apparent uniformity of the soft soil in <br />the hope of reducing both the total settlement prediction and more importantly the <br />differential settlement prediction. The results of the CPT testing did, in fact, show that the <br />glacial till at the anticipated foundation depth was in fact very uniform. However, it also <br />verified that it was significantly over consolidated. The total settlement prediction was <br />reduced from 5" to only 4" and the differential settlement prediction was reduced from 2 Y2" <br />to approximately I". Unfortunately, even I" of differential settlement is more than the <br />elevated tank manufacturers will allow. <br /> <br />-' <br /> <br />Therefore, it does not appear possible to support the elevated tank on a spread footing <br />foundation. It is recommended that the tank be supported on a deep foundation, or more <br />specifically an end bearing pile foundation. This site is conducive to a reasonable length pile <br /> <br />Water Tower Feasibility Report <br /> <br />15 <br />