soil exploration/geoptechinical investigation-2004

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The underlying sub-grade that supports structural till must be properly prepared, to eliminate a surface of weakness lying along the interface between structural fill and underlying sub-grade - material. This prepared underlying sub-grade must be at least 12 inches thick. Water content of this sub-grade must be controlled within plus or minus 2 percent of the optimum water content, as evaluated by Standard Proctor method (ASTM: D698). Percent compaction of the sub-grade must be according to TABLE C. Sub-grade material not meeting these recommendations must be removed and replaced with structural backfill meeting requirements. Consideration can be given to _ correcting the existing sub-grade material by removing (over-excavation) at:least 12 inches of this material, adjusting its water content to optimum value, and rbackfilling this over-excavation using reworked sub-grade material meeting requirements of structural backfill. Where removed material - is wet of optimum water content, consideration can be given to aerating this material, by spreading it, spreading and scarifying it, or blending it with drier material. Structural fill can be obtained from onsite, imported or over-excavated material. Structural fill must be non-expansive inorganic cohesive (lean clay) material or cohesionless (sand and gravel) material and not silt. Cohesive material must have a Liquid Limit less than 45 .and a Plasticity Index less than 20. Cohesive structural fill and structural fill with over 20 percent fines passing #200 sieve must be placed in lifts compacted to a thickness of 6 to 8 inches using a sheepsfoot or pneumatic tire roiler.making at least 4 to 6 passes. Cohesionless structural fill must be placed in lifts compacted to a thickness.of 10 to.12 inches using smooth drum vibro-rollers making at least 4 _ to 6 passes. Use a power tamper, rammer or vibro-plate compactor on fill in confined areas. In these areas loose lifts should be up to 4 inches thick with the compactor making at least 4 to 6 passes. Water content of structural fill must be controlled and maintained between 2 percent dry — and 1 percent wet of the optimum water content as evaluated by Standard Proctor method (ASTM: D698). Percent compaction, of structural fill must be according to TABLE C. We recommend thoroughly mixing structural fill before compaction to distribute moisture uniformly. For fill that is wet of optimum, consideration can be given to aerating this material, by spreading it, spreading and scarifying it, or blending it with drier material. We recommend that excavation and earthwork construction be periodically monitored, to evaluate compliance with the recommendations in this report section. The monitoring should be made by a — qualified soils engineering technician from our company under supervision by the Professional Engineer. Consideration should be given to providing drainage ditches to prevent surface water run-off from wetting, accumulating and standing in open excavations. Vertical cuts and excavations should not be considered stable in any case. All excavations should _ be sloped back, shored or shielded to protect workers. Trenching and excavation activities must conform to federal, state and local regulations at a minimum. The gravelly fill, topsoil, buried topsoil, Horizion B soil, and ablation glacial till encountered in the borings generally classify as — Type C soil. This classification is according to OSHA construction standards for excavations. Maximum allowable slopes for shallow excavations in Type C soil is 1.5:1 (hodzontal:vertical), Allied Project 04049 11 July 27, 2004