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Adritiona~~ calculations show that the factor of safety is actually highest <br />at the narrowest widths. This is because the overburden is lessening, so <br />less support is required in this area. For that reason, CWI proposes an <br />adequate outcrop barrier of 5U ft. outhy the burnline where no pillar <br />• extraction will take place. Here again, this is conservative because indi- <br />cations show that there is unaltered coal past the so-called burnline. <br />The burnline location is difficult to anticipate. CWI proposes rooming of <br />entries to the burnline to note location, to collect data, and to set 50 ft. <br />limits of no pillar extraction. CWI currently develops in this manner to <br />locate projected faults and we have experienced no operational problems. <br />See drawings attached which show burnline determination and subsequent out- <br />crop barrier design. <br />Monitoring: <br />CWI acknowledges that theoretical calculations must be substantiated with <br />site specific information. This is especially true in nonhomogeneous <br />stratas. With Lhat in mind, CWI will monitor coal strength properties in <br />the next areas to be mined around the outcrop. These areas are designated <br />8N-2E and 8N-lE. Those sections are shown on Map 2-4 and are colored yel- <br />low, indicating mining in 1981. <br />Coal properties to be evaluated will be uniaxial and triaxial compressive <br />tests, and also use of point load testing to correlate the relationship <br />between compressive strength and point load tests. This will assist in <br />quicker coal strength results for site specific conditions. <br />The mining Conditions such as roof, rib, floor, groundwater, etc., will be <br />documented. This conditions information, coal strength properties, and the <br />surface monitoring for subsidence features as described in Section 2.05.6 <br />will be included in the "Annual Subsidence and Hydrology Report" and sub- <br />mitted to the Division. <br />Procedure to Change Design: <br />If the above monitoring indicates problems between theoretical outcrop bar- <br />rier pillar size and actual requirements, or abrupt chanyes in strength <br />parameters, CWI will propose new outcrop barrier pillars for Division <br />approval. <br />u <br />