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August 28, 1991 BALBI&CHANG ASSOCIATES <br /> File No. 1525-69 <br /> and contractors that specialized in such a field. For shoring design, we recommend the <br /> following typical soil parameters: (a) Moist Unit Weight = 125 pcf, (b) Cohesion = 1,000 <br /> psf. <br /> H. Pavement Subgrade Preparation <br /> Laboratory testing on a bulk soil sample collected from the project site had resulted a <br /> Resistance Value (R-value) of 5. If the entire project site is treated with lime, the <br /> characteristics of subgrade soils will change substantially. In order to take advantage of lime <br /> treatment, the R-value of the near surface soil should be at 50 or higher after lime treatment. <br /> We recommend that the R-value of 50 be.used as the criteria to determine the optimum <br /> amount of lime mixed into the soil. The depth of lime treatment should extend to at least 12 <br /> inch below the finished soil subgrade. Additional R-value test should be conducted after lime <br /> treatment is completed in order to verify the final subgrade conditions. The following <br /> recommendations are essential to the satisfactory performance of asphalt pavement and should <br /> be incorporated in the project plans and specifications. <br /> a. All trench excavation should be properly backfilled and compacted as previously <br /> specified in the "Trench Excavation and Backfill" section of this report. <br /> b. All pavement subgrade soils should be prepared in accordance with recommendations <br /> contained in the "Site Preparation and Grading" section of this report and are stable <br /> and non-pumping at the time the base rock is placed. <br /> C. An adequate drainage system should be provided to prevent both surface water and <br /> subsurface seepage from saturating subgrade soils and aggregate base. This is <br /> especially important where pavement abuts landscaped areas. <br /> d. The aggregate base material of the"pavement section should be compacted to 95 <br /> percent of the relative compaction and meet the requirements of Caltrans Standard <br /> Specifications for Class 2 Aggregate Base. Aggregate subbase material, if used in <br /> pavement section, should also be compacted to 95 percent and meet the requirements <br /> of Caltrans Standard -Specification for Class 2 Aggregate Subbase. <br /> I <br /> Pate 14 of 17 <br />