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~. t` :: <br />• MainCressonSlo eEvaluation AdrianBrown <br />6.2.2 General slope movement monitoring <br />A general slope movement monitoring program has been initiated at the Main Cresson Mine, <br />predominantly on the east wall. The program is being installed incrementally, with a total of 24 movement <br />monitor locations and three base station locations installed to date. Monitor locations are fitted with a <br />reflective prism, attached to the mine wall by a specially designed bracket which allows insertion into a <br />joint, and provides protection to the prism from any falling spall rock8. Data is collected by the CC&V <br />Geological Division staff, under the supervision of the CC&V Survey Section. Data is stored in a Lotus <br />N database which is maintained in the Geological Division at the Main Cresson Mine. <br />The EDM data have been analyzed, and the data and results are presented in Attachment 3. The <br />interpreted results of the movement monitoring on those stations are summarized in Figure 169. This <br />figure shows the current movement rates of the monitor locations at the mine, and is interpreted as <br />followsio: <br />1. Movement of the "Clay" area is expected; the prisms are located on an alluvial material at the crest of <br />the slope in the far-north of the east wall. The movement was reducing over the winter, but may re- <br />activate in the spring. These monitors do not indicate overall wall instability. <br />2. The central portion of the east wall is not moving, due in part to the large bench at the toe of the <br />slope in this location. <br />• 3. The southern portion of the east wall is moving toward the excavation at a rate of up to 0.6 feet per <br />year. This movement is ~ detectable, but not particularly significant; in addition it appears that the <br />movement is associated with the excavation at the toe of the slope, and the rate is reducing. <br />4. The Ada Bell mine area, to the south, is now quiescent, as a result of the excavation having ceased in <br />that area for several years. <br />The movement rates observed to date are low. They are the equivalent of up to 0.02 inches per day, <br />which is considerably below any threshold of concern with respect to movement. This rate of movement <br />can be evaluated based on the following ratesll: <br />a Designed by T.R. Brown, of CC&V. <br />9 The interpretation is that the movement information is presented normalized to the minimum slope distance over the period of record at <br />each location. Typically, the distance between the monitor reduces over time, due to wall movement. <br />10 Note that the vectors shown on Figure 16 point to the measuring point (`Bertha"), as this was the point from which they were <br />measured It is possible that the actual movement maybe somewhat greater in a different direction (in particulaz for location 050-1). <br />it The information presented in this table has been compiled by the author, based on the monitoring of four rock slopes on which <br />• movement lead progressively to failure: Chuquicamata, Chile; Con Imperial Mine, Virginia City, Nevada; Questa Mine, New Mexico; <br />and Twin Buttes Mine, Arizona. Data is generally unpublished. <br />1385D.980612 33 <br />