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CORNERSTONE C. EARTH GROUP 6.5.1 Scarification and Drying The subgrade may be scarified to a depth of 6 to 12 inches and allowed to dry to near optimum conditions, if sufficient dry weather is anticipated to allow sufficient drying. More than one round of scarification may be needed to break up the soil clods. It has been our experience that disking near-surface soils on a daily basis is more effective than ripping soil with a bulldozer. 6.5.2 Removal and Replacement As an alternative to scarification, the owner/contractor may choose to over-excavate the unstable soils and replace them with dry on-site or import materials. A Cornerstone representative should be present to provide site specific recommendations regarding the appropriate depth of over-excavation, whether a geosynthethic (stabilization fabric or geogrid) is recommended, and what materials are recommended for backfill. For preliminary planning, low to moderately unstable (pumping) soil areas will generally require over-excavation on the order of 6 to 12 inches and may require the use of stabilization fabric or grid (such as Mirafi 600X or Tensar 6X1100 or equivalent). Moderately to severely unstable (pumping) soil areas will generally require over-excavation on the order of 12 to 18 inches and may require the use of one or more layers of stabilization fabric or grid (such as Mirafi 600X or Tensar 6X1200 or equivalent). 6.5.3 Chemical Treatment C Where the unstable area exceeds about 5,000 to 10,000 square feet and/or site winterization is desired, chemical treatment with kiln-dust or cement may be more cost-effective than removal and replacement. Due to the low clay content of the near-surface soils, lime will not likely be an effective soil stabilization option. Recommended chemical treatment depths will range from 12 to 18 inches depending on the magnitude of the instability. For finished street subgrade areas, the depth of utilities should be determined prior to considering this option. 6.6 MATERIAL FOR FILL 6.6.1 Re-Use of On-site Soils On-site soils with an organic content less than 3 percent by weight may be reused as general fill. General fill should not have lumps, clods or cobble pieces larger than 6 inches in diameter; 85 percent of the fill should be smaller than 2'/z inches in diameter. Minor amounts of oversize material (smaller than 12 inches in diameter) may be allowed provided, the oversized pieces are not allowed to nest together, and the compaction method will allow for loosely placed lifts not exceeding 12 inches, such an 815 or REX compactor. 6.6.2 Potential Import Sources Imported soil for use as general fill should be inorganic with a Plasticity Index (PI) of 15 or less. To prevent significant caving during trenching or foundation construction, imported material Ponderosa Active Adult Community Page 14 132-2-1