2017-02-21_REVISION - M1988112 (3)

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hand pressure. Due to the weak matrix structure, the conglomerate was broken into constituents of gravel, sand, silt, and clay during drilling. • CONGLOMERATE: Conglomerate was encountered below the weathered conglomerate and extended to the termination depth of the soil borings. The transition from weathered to unweathered conglomerate was identified by the friability of the retrieved rock pieces, slight change in matrix coloration, the degree of difficulty excavating test pits, and a change in drive sample blow counts. Although intact core pieces were occasional retrieved in the CME continuous core barrel in well -cemented layers of rock, the conglomerate was typically broken up by the augers into constituents of gravel, sand, silt, and clay during drilling. 2.2.3 Laboratory Testing Representative samples of soil and rock materials were collected during the field investigation and select samples were submitted to a geotechnical laboratory for analyses. Laboratory testing included measurement of water content, dry density, standard Proctor compaction, Atterberg limits, grain size distribution, specific gravity, direct shear, point load, soil resistivity and conductivity, sulfate, and pH. Full laboratory test reports are included Appendix A. In summary, the alluvial overburden and weathered conglomerate materials are characterized as broadly graded, granular soils that classify as silty to clayey SAND with gravel (SC or SM, with gravel, in accordance with the Unified Soil Classification System). The fines fraction (particles smaller than a No. 200 sieve) of samples tested ranged from 14 to 18 percent by weight. Fines were either non -plastic or exhibited low plasticity, with plasticity indexes on the order of 9 to 11 percent. The gravel fraction (particles retained on a No. 4 sieve) for the two alluvium samples tested was less than 20 percent, while the weathered conglomerate samples contained higher gravel -size fraction of 27 to 30 percent by weight. The broadly -graded, excavated native materials should be readily compactable in embankment and backfill zones. Two standard Proctor compaction tests were completed, one on a bulk sample of the alluvium and one on weathered conglomerate. The results were similar, with maximum dry densities (pcf)/optimum moisture content (%) of 127.7/9 and 130.9/7.5, respectively. Shear strength tests were conducted on remolded samples of the overburden and weathered conglomerate materials compacted in the laboratory to densities on the order of 95% of maximum dry density at moisture contents near optimum. These strength test results were used to estimate soil bearing capacity and shear strength of the structure foundation and in cut and fill slopes constructed in these materials. Intact core samples of the conglomerate bedrock generally were not able to be obtained by the drilling and sampling methods that were used. The bedrock was broken up by the drilling action into its constituent gravel, sand and fines fractions. A few intact, well -cemented pieces of the conglomerate were subjected to point load tests to estimate the unconfined compressive strength of the more highly -cemented pieces of conglomerate in the rock mass. The compressive strengths ranging from 70 to 1740 psi, indicate the intact rock mass is characterized as weak to San Luis Project - South Diversion Ditch Drop Structure - Final Design Report 6