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<br />'-'",.'_'--11'" . <br /> <br />.. <br /> <br />":''''"'''-'-'''' <br /> <br />:;-,.",...l. <br /> <br />," <'-~", ~- . <br /> <br />0019n <br /> <br />. brank:~t drain is encountered. With this modification, the CRB believes that drainage <br />. design for the left abutment trough is adequate. <br /> <br />Question 5: <br /> <br />Is the contractor's proposed method for excavation of gate chamber appropriate? <br /> <br />Response: <br /> <br />The CRB concurs that the presented plan for completing.excavation of the gate chamber <br />is appropriate. Starting excavation on the right side of the chamber, looking downstream, <br />and excavating the crown upward at an approximate slope of 1: 1 with an initial varying <br />excavated width will provide the contractor the capability to safely remove small <br />volumes of material. This procedure will permit the installation of both temporary and <br />permanent rock anchors after partial excavation. Upon completing the initial excavated <br />section and securing the sidewalls and crown, the remaining excavation of the gate <br />chamber can be completed by removing small volumes of rock at anyone time without <br />compromising safety. The proposed blast hole pattern and depth of holes, to "B" line <br />depth will minimize the necessity of removing tights in the crown of the excavation. The <br />CRB is of the opinion that the contractor and Reclamation staff have a good <br />understanding of the complexity and risks involved in completing this excavation and <br />believe the task will be accomplished satisfactorily. <br /> <br />. <br /> <br />Question 6: <br /> <br />Based on the current exposure of the foundation rock, does the Board agree with the <br />planned surface cleanup and treatment of the bedrock as outlined in the specifications <br />(Table 3A, Section 3.1.1)? . <br /> <br />Response: <br /> <br />Yes, with the exception of the Lewis Shale foundation exposed beneath the downstream <br />zone 2 filter blanket. The zone 2 filter blanket and overlying zone 3 blanket are designed <br />to drain any foundation seepage water passing downstream of the grout curtain. The <br />CRB believes that it is important that the joints and fractures in the Lewis Shale be <br />cleaned of any shale powder resulting from dessication or traffic that would tend to clog <br />these features and reduce drainage from the foundation into the fliter blanket. If <br />mechanical excavation and cleaning is found to be inadequate to accomplish the <br />necessary joint cleaning, further methods si.1ch as air jetting and brooming should be <br />used. Clean joints and fractures in contact with zone 2 filter blanket should facilitate <br />rapid dissipation of foundation seepage pressures. <br /> <br />. <br /> <br />-4- <br />