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page 4 <br />• (B) Description of h4easures Taken to Prevent Subsidence- <br />Caused Damage to the State Highway and to the Intake <br />Shaft - Damage from subsidence will be prevented tlrr•ough <br />the use of a substantial barrier pillar between retreat <br />mining and the state highway and a barrier pillar <br />betvreen retreat mining and the intake sheft. Oesigrr <br />GT this barrier pillar is based open subsidence studies <br />done in the mine area ?ntitled: "Borne Engineering <br />Geoleaic factors Ccn±rolling Coal Mine Subsidence In <br />Utah and Colorado" published by tire IJnited States geologic <br />Survey, Professional Faper -969, ~,~ritten by °ichard Ounrud. <br />The basis for the calculations ar•e found on page 19 of <br />this report and applied to the 6 Lert mining unit located <br />in 3rd South, Somerset mine: <br />"Although only t~rro benchmarks are located <br />above the 6 Left rriinin, unit, periodic mea- <br />surements yielded rather precise subsidence <br />profiles and limit angles, particularly for <br />pror"files 4, 5, and 6 (figure 16). The limit <br />anole, measured with respect to tire horizontal, <br />is 69° to 70° in weak overburden that thickens <br />from 600 to 900 feet (123 to 274 n~eters) over <br />about 400 feet (122 meters) of horizontal dis- <br />tance. The limit angle may be less steep for <br />flat-lying surfaces and similar strata. The <br />• configuration of profile 7, 3, 9, and 10 sug- <br />gests that the limit angle steepens r'rom 76° <br />