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' <br /> � UNSUITABLE SOIL Sub rades of <br /> g �eatures such as buildings, pavernents, other structures, <br /> � structurai fill and other important improvements must be prope�ly prepared to support applied loads <br /> from these features. Remove unsuitable soil beneath these features and replace it with structural <br /> backfili up to design subgrades of features. <br /> IUnsuitable soils generally include: soil with excessive moisture; very soft to soft com ressible <br /> P <br /> cohesive soil (clayey and silty); very loose to loose granular soil (sand, gravel, crushed rock); soil <br /> Imixed with debris and rubble; debris and rubble; expansive soil such as CUCH and CH types; <br /> potentially collapsible metastable soil (loess, sand with honeycombed grain structure); natural <br /> I topsoil, buried topsoil or replacement topsoil (all with grass, roots, decaying vegetation, humus and <br /> otherwise undecomposed organic matter with faint to strong odor); organic soil (peat, muck and <br /> OL and OH types with faint to strong odor); uncontrolled and undocumented fill (no compaction <br /> ' control and no placement documentation); other kinds of soil de�ned by the engineer. <br /> STRUCTURAL FILL SUBGRADE The structural fill subgrade should be relatively flat-lying. In <br /> sloping ground, the subgrade should be benched into relatively level steps into the slope. <br /> Subgrades in relatively flat-lying areas (without benching) should provide good bonding between <br /> structural �II and underlying subgrade material. Good bonding minimizes shearing weakness <br /> along the interface between structural fill and underlying subgrade material. Prepare good bonding <br /> by scarifying (removing excessive soil moisture) and recompacting subgrade material to a depth of <br /> at least 12 inches below the subgrade level. Control water content of recompacted material <br /> between plus or minus 2 percent of optimum water content as evaluated by Standard Proctor <br /> method (ASTM: D698). Recompact material according to TABLE C. Subgrade material not <br /> meeting requirements herein must be removed and replaced with structural backfill up to the <br /> designated subgrade level of the structural fill. Where subgrade material is unsuitable because it <br /> has excessive water content, consideration .can be given to aerating it by spreading it out, <br /> scarifying it, or blending it with drier material. Remove all unsuitable material beneath structural fill <br /> and replace it with structural backfill. <br /> CUT AND FILL GRADING TRANSITIONS When cut and fill grading transitions occu� beneath <br /> buildings, roadways, underground pipes or other important structures, the geotechnical engineer <br /> should be contacted to review the transition condition and provide recommendations for special <br /> over-excavation and structural backfill at the transition in the cut portion thereof. Essentially, <br /> uniform and reliable material should be placed completely across the transition zone. This will <br /> minimize differential ground movement, which may otherwise become excessive if dissimilar <br /> materials occur or are placed across the transition zone. <br /> STRUCTURAL FILL Structural fiU can be obtained from onsite, imported, or over-excavated <br /> material. Structural fill must be non-expansive inorganic cohesive material (clayey or silty) or <br /> granular cohesionless material (sandy and gravelly) relatively well graded. Poorly graded gravel <br /> (for example "pea rock") should not be used as structural fill when structural fill thickness exceeds <br /> 2 feet. Cohesive material must have a Liquid Limit less than 45 and a Plasticity Index less than 20. <br /> Allied Projed 05039 8 July 31, 2005 <br />