02-27-2002 Council Agenda - Laserfiche WebLink

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FEB 14 '02 05 :32PM BRAUN INTERTEC P.1124 Drywall Supply, hie. BBXX -02 -01 OA January 29, 2002 Page 7 C.3.a. Drilled Piers. A drilled pier foundation system consists of individual drilled shafts that are filled with concrete, extend through the unsuitable soils and provide support via cnd bearing resistance on the base of the pier and frictional resistance acting oti the sides of the piers. Depending on foundation loads, pier diameters generally range from about 30 to 60 inches. Grade beams spanning from pier to pier are then constructed and used to support the building and floor slabs. Given the soil conditions encountered in the borings, we anticipate that the piers would extend to a depth of 25 feet or more to penetrate the existing till, organic materials and soft lacustrine soils. Piers are generally used where high bearing capacities are needed and the bearing strata is relatively shallow. Because they are large diameter and filled with concrete, they tend to he more expensive than a pile supported foundation system. C.3_b. Piles. Piles consist of driven wood timber, steel pipes or steel H- piles. Pile types and lengths depend on the loads they need to carry. Although the borings performed for this evaluation where not deep enough to provide a pile analysis, we anticipate that either wood piles or steel pipe piles could be used for this project. Although a pile depth analysis would be needed, typical depths for piles generally range from about 40 to 80 feet. After a pile depth analysis has been performed, the number of piles and their configuration would be determined by your structural engineer. C.3.c. Geopiers, From a ground improvement standpoint, the GeopierT'' ground improvement method can also be considered. Geopiers are compacted aggregate columns that, like piles or drilled piers, would support the foundation. Geopiers would allow conventional design and construction techniques to be employed in this case because in the course of creating the compacted aggregate columns, the compressible materials (existing fill, organic and lacustrine soils) would be densified, limiting the extent to which they could settle. Another advantage that Geopiers would have in this case is the fact that they could be terminated at or near the lower boundary of the lacustrine soils, while piles or drilled piers would have to be extended well below the same soils to much greater depths to develop adequate bearing capacity.