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<br />. <br /> <br />. <br /> <br />. <br /> <br />001941 <br /> <br />4 <br /> <br />. <br />eRB Recommendation No.5: <br /> <br />There are some very large grout takes being experienced in the Lewis Shale at considerable <br />depth beneath the valley floor. The CRB recommends that criteria be provided to the grout <br />inspectors with regard to initiation of grout thickening to a more stable grout mix soon after it <br />becomes obvious that a hole has very little tendency to be tightening under the thin initial mix. <br />This thickening should continue at intervals until a mix is obtained which will result in reaching <br />tight refusal. <br /> <br />The CRB believes that a grout curtain also serves the purpose of exploration of foundation <br />conditions. Where large grout takes occur, we recommend that investigations be undertaken to <br />try and identify the cause of the large injection of grout. This should lead to a foundation <br />interpretation, which may facilitate improved treatment and allow a determination as to whether <br />or not the feature or features have any implications, which need further remediation. As the <br />geologic interpretation progresses, it may be necessary to do further subsurface investigations by <br />taking appropriately located and oriented core borings. In this event, the investigations would <br />likely need to include both vertical and inclined borings. Specialty tools, such as triple tube core <br />barrels, straddle packer pressure tests, and Acoustical Televiewer CATV) bore hole surveys may <br />be needed to supply sufficient data for the interpretation. The data obtained must be carefully <br />interpreted to identify and evaluate the geologic conditions causing the large grout takes. The <br />CRB would like the opportunity to review and discuss this interpretation with Reclamation as <br />soon as practical after it is completed. <br /> <br />Reclamation response: <br /> <br />Reclamation concurs in this recommendation. Decision Memorandum No. DEC-RB- <br />8311-19, enclosed here as Appendix E, discussed Reclamation's investigation and <br />analysis program that has been completed. As documented in the Decision <br />Memorandum, Reclamation believes that: <br /> <br />· The high grout takes and difficulty in closure were due to grout pressures <br />exceeding the insitu stress in some zones within the Lewis Shale. This resulted in <br />the grout pressures causing some minor compression of these zones by the grout <br />and increasing the grout takes. <br />· There were no anomalous joints or other discontinuities encountered, as exhibited <br />in the cores, that indicates that there was a systemic system of <br />joints/discontinuities that were oriented unfavorably to the orientation of the grout <br />holes. <br /> <br />Reclamation concludes that the constructed grout curtain will serve its intended purp08e <br />without further modification. <br />