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<br />. . . <br /> <br />l..'... <br />001945 <br /> <br />"-"".;' <br /> <br />. . . <br /> <br />-,.., <br /> <br />. RESPONSE TO QUESTIONS <br />Question 1: <br /> <br />Regarding the zone 4 material placed in the dam so far is the excavation, placement, <br />compaction, and resultant in-place densities obtained acceptable given the strength and <br />drainage design requirements for this material? <br /> <br />Response: <br /> <br />. <br /> <br />A substantial quantity of zone 4 material was placed on the lower left abutment within <br />the shell upstream of the core to provide support to the area where the shallow rock slides <br />occurred. This material was placed in 30-inch layers and compacted in accordance "vith <br />specification requirements, 4 passes of a 10-ton vibratory smooth-drum roller. The <br />physical properties of the in-place material were tested in the field and in the laboratory. <br />Materials from the upper layers in BAB with somewhat more .fines (10 to 13% .minus <br />#200) and from lower layers in BAB with somewhat less fines (6 to 8% minus #200) <br />were sampled and tested. Sand content varied from 22 to 40%, gravel and cobble sizes <br />varied from 50 to about 70%. In-place dry densities of the compacted material varied <br />from 125 to 143 pcf with relative density 67 to over 100% (average 88%). The 6-foot <br />ring density test, performed May 18, yielded a dry density of 140 pef, relative density <br />84%. In the opinion of the CRE, the excavation, placement, compaction and in-place <br />density of the material are satisfactory. <br /> <br />The CRE was able to. view the side-walls of three trenches excavated through the zone 4 <br />material and the excavation for the ring density test. The matrix of the zone 4 material <br />appeared to be filled with sand and fine gravel sizes, although small voids are present <br />because of the segregation that takes place during placement. One of the trenches was <br />partially filled with water to test the ability of the fill to drain. A drawdown rate of 0.8 ft <br />drop in 15 minutes was measured. This indicates that the material will readily drain, but, <br />because of the sandy matrix, the material is not as free-draining as a compacted coarse <br />rockfill. The eRE is satisfied with the drainage characteristics of the zone 4 material. <br /> <br />Question 2: <br /> <br />Are the plans to deal with nested cobbles in the zones 4 and 4B adjacent to zones 1,2, 2A <br />and 3 sufficient? <br /> <br />Response: <br /> <br />. <br /> <br />Zone 4B is similar to zone 4 except that the oversize rock cobbles (plus 7 inch) are being <br />removed at the BAB processing plant. In an effort to gain insight concerning the CRE <br />response to the above question, two of the above mentioned trenches were excavated into <br />zone 4 material at the contact with the rock abutment. Nested cobbles were seen at some <br />locations on the zone 4 surface at the contact with the abutment, but this appeared to be a <br />surface condition that extended only one or two cobbles deep. Below the surface at the <br /> <br />-2- <br />