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C~ <br />9.0 h1INE PLANNING <br />4.1 MINING METHOD <br />The mining method applied in the present CWI mine is <br />room-and-pillar. In this method, rooms and entries are first <br />fully developed in a section from the main entry or main <br />heading; the development advances to the Ear end of the <br />panel. In the second phase, mining retreats back, and the <br />pillars are recovered to the extent that roof conditions <br />permit. This method, frequently applied in the Western <br />United States, results in a high recovery. Under ideal <br />conditions, only pillars between panels are left permanently <br />in place. Final subsidence magnitudes are frequently <br />compared to those resulting from long-wall mining; the <br />timing of the subsidence is different as the final values <br />are reached only during the last phases of mining. <br />koom-and-pillar mining will also be applied within the <br />proposed long-term lease area. <br />9.2 EXISTING !gI[JE <br />• A mine map, dated March 28, 19f33, was made available by <br />CWI for the purpose of the subsidence study. The mine map <br />shows the present development of the mine, zones of total <br />recovery achieved to date, data on the faults that have been <br />encountered during the lifetime of the mine, and additional <br />data such as inflows of water into the mine. <br />As the subsidence problems of the existing mine are not <br />within the scope of the study, the subsidence conditions <br />will be discussed only briefly within this report. The <br />current mining within the existing lease has, however, <br />produced subsidence cracks on the surface. These cracks have <br />been identified within the southwest part of the mine, close <br />to the coal outcrop, and under a relatively low overburden. <br />These cracks were observed approximatel}• between the 1st <br />West and 2nd West panels. These subsidence cracks are the <br />only evidence of subsidence reaching up to the surface in <br />the area. For this reason, they are considered to be very <br />important, and they are described in detail in Section 2. 5. <br />Generally, mining within the existing lease is well <br />advanced. Complete or nearly complete recovery has been <br />achieved mostly ~:ithin the southern part of the mine, while <br />file development of northern panels is proceeding at the <br />~res~nt time. Tn-~ is*_ t:orth plains have been developed close <br /> <br />- 20 - <br />