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KLE/NFELOER �Bright People.Right Solutions. the perimeter of the structure. Prior to placement of the non-expansive fill, the exposed clay subgrade soil to a minimum depth of 12 inches should be uniformly moisture conditioned to a moisture content ranging from 2 to 4 percentage points above the optimum moisture content and compacted to at least 88 percent relative compaction and not greater than 95 percent relative compaction, unless approved by the geotechnical engineer. The moisture content of the clay should be maintained until placement of the non-expansive fill. A representative from our firm should perform a field check of the soil moisture content and relative compaction prior to placement of the non-expansive fill. 5.6.2.2 Lime Treatment The second option is to improve/stabilize the subgrade conditions by mixing the fill or native clay with lime (lime treatment). This procedure reduces the plasticity/expansion characteristics of the treated clay and has been utilized on other development projects in the site area. Furthermore, the lime provides an added benefit in that it also acts as a cementing agent, increasing the strength and decreasing the flexibility of the subgrade soil. Accordingly, floor slabs supporting concentrated loads exhibit less deflection and tend to perform better overall. During or following rainfall, lime-treated soil also tends to remain reasonably stable, thus providing a firm, accessible working platform for construction. It should be noted that lime increases the pH of the soil and does not promote plant growth. Accordingly, treatment should not be performed in landscape areas or the lime-treated soils should be completely removed and replaced prior to planting. A disadvantage of lime stabilized subgrade beneath building pads is possible disruption during the placement of underground utility lines. If numerous underground lines are placed after treatment, the benefit of lime stabilization is reduced, and the first option (non-expansive fill)would be recommended. As an option, utility trenches excavated through the lime treated pad can be backfilled within the lime treated section with a control density fill or low strength material with a minimum compressive strength of 200 psi. The lime treatment procedure consists of mixing the upper 18 inches of subgrade soils within the proposed floor slab area with high calcium quick lime and compacting the soil as engineered fill to 90 percent relative compaction. The zone of lime-treated soil should extend laterally at least 5 feet beyond the perimeter of the proposed structure. Based on previous lime treatment evaluations in the general project area and laboratory testing done as part of this study, it would be reasonable for estimating purposes to assume an application rate of 4 percent high calcium quick lime by dry weight of soil with a dry unit weight of 115 pcf. 20210067.001A/ST020R111447 Page 21 of 37 May 11, 2020 ©2020 Kleinfelder www.kleinfelder.com