07-27-1994 Council Agenda - Laserfiche WebLink

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Page Three Organic layers were encountered below the fill at three locations. About a 4" layer of somewhat consolidated peat was encountered below the fly ash fill at test pit 1. About 2' of soft peat was encountered below the fly ash at test pit 2. At test pit 4, a 1' thick layer of firm organic clay was encountered below the silty sand fill. The test pit logs indicate that the native, undisturbed mineral soils at the site consisted either of soft gray lean clay, gray silty sand or gray sandy silt soils. First encounter with these mineral soils was at depths ranging from 4.5' to 10' below the surface. These soils were typically found to be wet. The test pits were not left open to allow the groundwater level to stabilize, but it did appear that the static groundwater level would be above the elevation of the mineral clay and sand soils, as was suggested by the previous geotechnical report. ENGINEERING REVIEW Discussion - As indicated in a previous section, conventional earthwork activities which would limit differential and total settlements to normal values would include total removal of existing fly ash or other fill layers along with any organic layers below the fill, to expose undisturbed natural soils such as gray lean clays and gray silty sands. Also, we understand that this type of earthwork program would be cost prohibitive for the type of structure proposed. Rather, we understand the cost factor would require construction of the proposed steel building upon the existing fill at the site. In our opinion, based on our experience in similar situations, it is often feasible to construct light structures on existing fill systems. This is particularly feasible in cases where the structure is more tolerant of differential and total settlements than a normal building. In our opinion, it would be feasible to construct a steel building upon the existing fill, after removal of peat soils. However, due to the uncertainties involved in the existing fill system strength, we strongly recommend that only a all -steel building be considered, and that masonry wall construction not be considered for this structure. This is due to the tighter settlement tolerances required for proper performance of masonry buildings. Based on our observations during the test pit program, it appeared that the firmness of the majority of the fly ash fill and underlying sand fill was satisfactory. This, combined with the general lack of organic layers beneath the majority of the fill, appeared to indicate that the fill material was placed in a somewhat controlled manner. However, we have no documentation, Page 53