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the shear surface should movement occur. Disadvantages of inclinometers include the length of time <br />needed to monitor and they can shear off with sufficient subsurface movement, and might become <br />inoperable after several inches of displacement. <br />These inclinometers are 85 mm (3.34 inches) in diameter. These are the largest diameter <br />inclinometers commonly manufactured and are recommended because they can remain functional <br />with the largest shear displacement compared to smaller diameter casing. <br />Inclinometer casings were installed at least 10 feet into competent bedrock. <br />3.2.3. Piezometers <br />Piezometers were installed in the boreholes described above. At PZ12-03, two (2) piezometers were <br />installed: the upper piezometer is in the colluvium buttress and the lower piezometer is in a coal <br />seam. At PZ12-04, three (3) piezometers were installed: the uppermost piezometer is in refuse, the <br />two lower piezometers are in the colluvium. At PZ12-05, two (2) piezometers were installed: the <br />upper piezometer is in the colluvium buttress and the lower piezometer is in a coal seam. The devices <br />were attached to the inclinometer casing at each inclinometer. The piezometers were finished using <br />the fully -grouted method. <br />These devices are adept at measuring porewater pressures within the slope. High porewater pressures <br />lead to lower shear strengths within the soil and rock, which results in a higher likelihood of slope <br />movement. <br />3.2.4 Monitoring Schedule <br />Monitoring the performance of the RPE East refuse pile is deemed to be important to verify its long- <br />term stability. In-situ measurements relating to deformation and groundwater characteristics can <br />provide useful information as to the refuse pile's performance and give warning of possible <br />problems. <br />As stated in the original permit design in Exhibit 82, instrumentation will be placed in the refuse pile <br />after operations have started and enough material has been placed to reach design capacity grade at <br />each of the instruments shown in the monitoring plan (Exhibit 82, Appendix Q. <br />For deformation monitoring, inclinometers will be placed along the refuse pile centerline within the <br />refuse pile. Additionally, mirrors will be placed on the toe buttress, refuse material, and/or outside <br />the refuse pile footprint. The advantages of mirrors are that they provide much more lateral coverage <br />P:\Mpls\06 CM26\06261003 Haul Road Slide Repair\WorkFiles\Report\MCC_Slump_Repair-Instrumentation-Drain Rev 2012-12-12.docx 15 <br />