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<br />. <br /> <br />. <br /> <br />.' <br /> <br />..,_,0"';;; <br /> <br />. ~ ", 'I' <br /> <br />. <br /> <br />0J191f6 <br /> <br />till! abutment contact, the sand and fine gravel matrix generally filled the voids of the fill <br />within the entire layer thickness. <br /> <br />The CRE is of the opinion that both zones 4 and 4B (with plus 7-inch cobbles excluded) <br />placed against wnes 1, 2, 2A and 3 will result in a satisfactory contact. Placement <br />techniques should be developed to avoid nested cobbles, as much as practicable, at the <br />layer surface at the contact. Based on our inspection of the test trenches, the CRE does <br />not anticipate the need to provide any special measures, such as the raking of rock <br />cobbles from the surface at the contact. <br /> <br />Question 3: <br /> <br />The shallow rock slides that occurred on the upstream left abutment slopes appeared to be <br />caused by combination of geometry, weak shear planes, and destabilization by <br />excavation. Reclamation's assessment, by data review and analysis, is that there are no <br />significant impacts to the overall embankment stability represented by conditions that <br />caused these slides. Do you agree? <br /> <br />Response: <br /> <br />The CRE agrees with Reclamation's assessment that there are no significant impacts to <br />the overall embankment stability. Back calculation of the shear strength on the sliding <br />surface (bedding planes in the Lewis Shale) yielded a friction angle of about 150 and no <br />cohesion. Data from borings and laboratory testing and using the Rock Mass Rating <br />system indicates high cross-bedding shear strength within intact rock. A series of <br />stability analyses of the dam simulating the condition at the end of construction were <br />performed. Potential failure surfaces. were oriented upstream. Calculated factors of <br />safety exceeded 4.0 when using the low bedding shear strength and the high cross <br />bedding shear strength. <br /> <br />The CRE recommends several further stability analyses with the full reservoir and with <br />potential failure surfaces oriented downstream following bedding below the core and <br />crossing bedding below the downstream shell. These additional analyses are <br />recommended to complete the analysis of darri stability. <br /> <br />Question 4: <br /> <br />Is the drainage design for the left abutment trough adequate? <br /> <br />Response: <br /> <br />Reclamation's plan for providing drainage of the deep trough on the downstream left <br />abutment is to excavate an open cut channel through the barrier that divides the trough <br />and stream channel. The excavated channel would have an invert elevation to match the <br />downstream end of the trough and an invert slope equal to or greater than the trough <br />slope. To insure drainage, the trough and open cut channel would be backfilled with a <br />10- foot depth of zone 3 material that extends the drain downstream until the zone 3 <br /> <br />-3- <br />