soil exploration/geoptechinical investigation-2004

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to using interceptor, trenches to lower ground water surfaces under buildings and pavements permanently. If ground water flow-lines approach and meet finished ground surface grades at the project site, adverse ground water seepage may occur at these grades. Interceptor trenches should be considered to eliminate this seepage. We recommend that a geotechnical engineer from our company review and approve any interceptor trenches at the project site. Excavations for foundations, floor slabs, pavements, sewer and utility trenches or other excavations may encounter ground water. The excavation contractor must provide a reliable dewatering method to keep excavations dry when ground water is encountered. If excavations are in poor-draining cohesive soils (silty and clayey) with minor ground water seepage, sumps that are — pumped without interruption can be considered for dewatering. If excavations are anticipated to extend into relatively free-draining granular soil (sandy and gravelly) with significant ground water seepage or inflow, consideration must be given to using well-points to dewater excavations. The contractor must consider the possibility that significant ground water inflow into excavations may occur and provide a reliable dewatering method. SUBSURFACE SOIL IMPACT ON CONSTRUCTION The gravelly fill, topsoil and buried topsoil should be considered unreliable soils beneath the building footprint. Additionally, the Horizon B soil that classifies as CUCH is potentially expansive material, and it too should be considered unreliable soil beneath this footprint. These unreliable soils must be removed beneath the footprint. The gravelly fill can be reused as structural fill, if it -- meets recommendations in the EXCAVATION AND EARTHWORK section of this report for structural fill. The Horizon B and ablation glacial till soils have N values ranging between 3 and 14. This range indicates these soils are not uniform in their material character across the rectangular area of proposed building construction. FOUNDATION SUPPORT — We recommend using a shallow-depth spread footing type foundation to support.the building. We have no information on final bearing grades for the foundation. Therefore, we assume the lowest building floor slab will be at least 4 feet above the maximum anticipated ground water level. As such, we anticipate the foundation bearing grades will lie in Horizon B or ablation glacial till soil. We measured N values in ablation glacial till as low as 3, which indicates this till is not reliable to directly support the building foundation. To attain reliable foundation support„the foundation sub-grade support material must be uniform in - its thickness and material character. The Horizon B and ablation glacial till soils are quite variable in their material characters. Therefore, we recommend correcting existing soils directly beneath foundation bearing grades. The soil correction requires removing at least 2 feet of existing soil beneath foundation bearing grades by over-excavation. The exposed soil along the bottom of over-excavations must be vibro-compacted using several passes of the compactor to increase the density and shearing resistance strength of this exposed soil. This will minimize compressibility of Allied Project 04049 g July 27,2004