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KLEINFELDER . of engineered till is recommended .letting may be performed on trench backfill placed outside the structural areas provided sufficient time is set aside to allow consolidation to occur Field density tests should be performed to document the recommended fill compaction These tests however often indicate relative compaction less than 90 percent In lieu of compaction tests we suggest that the adequacy of the ietting be evaluated on a performance basis gddanonal Considerations Based on our findings, the average moisture content of the subgrade soils was well above the optimum moisture content This condition, if encountered during earthwork, could delay grading by causing an unstable backfill condition Typical remedial measures include spreading, discing, and aerating the soils during dry weather, mixing the soil with dryer materials, removing and replacing the soils with an approved fill material, or mixing the soil with an approved hydrating agent, such as a lime or cement product Our firm should be consulted prior to implementing any remedial measure to observe the unstable backfill condition (if encountered) and provide specific recommendations 5.4 Pipeline Settlement We anticipate the proposed pipeline excavations will be backfilled to their onginal grade (i e , street grade), and the pipeline and compacted backfll will exert no significant additional load on the underlying undisturbed soils Therefore, theoretically, elastic deformation (i e , • recompression) of the foundation materials induced by backfill placement and compaction should occur quickly upon load application The maximum recompression of trench or pit bottoms should be less than one inch and should occur upon backfilling From a practical viewpoint the total amount of pipeline settlement will depend on the condition of the foundation materials Therefore, it is necessary that stable trench bottoms are maintained during construction Water leaking from pipes and joints can increase the effective unit weight of the foundation and backfill soils, inducing long-term settlement of the pipeline and adjacent ground surface In addition, dispersion and piping of silts and sands into open joints from surface infiltration could produce loss of ground, voids, and subsidence of the ground surface Therefore, the pipeline should be designed, constructed, and maintained as water tight Backfill placed within trench and pit excavations will compress or settle due to its own weight and possibly traffic vibrations Accordingly care should be taken when placing, moisture conditioning, and compacting backfill materials Estimates of backfill settlement range from 0 2 to 0 4 percent of the backfill depth Where trenches and jacking pits are backfilled with granular sands most of if not all this settlement should occur curing or immediately following compaction Where clays are used for backfill settlement will occur more slowly • 13629 GO1i2002R369 -�orll 19 2002 D 2002 Klemfelaer inc Pace l l of 16