54 MINING CONDITIONS UNDER CITY OF SC KANTON, DA.
TESTS OF ROOF-SUPPORTING DEVICES.
COMPRESSIVE STRENGTH OF ANTHRACITE.
In 1903 an exhaustive series of tests was conducted under the direction of a committee of the Scranton Engineers’ Club for the purpose of determining the compressive strength of anthracite coal. The report of this committee on tests is printed in an appendix (see p. 77) to this report. The results, however, may be summed up briefly in the statement that a pressure of 216 tons per square foot will cause the average ordinary mine pillar to begin cracking, and a pressure about twice as great (432 tons per square foot) will crush it to powder.
This general statement, however, does not apply equally to all coal beds, for the tests prove a great variation in strength, even between different parts of the same bed. In some instances the weight required to crack the pillars was as low as 30 tons per square foot.
TESTS AT LEHIGH UNIVERSITY.
In order to test the value of the several artificial devices for supporting the roof of a coal mine, as well as to search out an inexpensive combination of materials which might be more cheaply installed and withal more permanent and efficient, and better adapted to certain localities than some of those mentioned, we prosecuted a series of tests at the Fritz engineering laboratory at Lehigh University, South Bethlehem, Pa., the results of which are also given in an appendix (see p. 83) to this report. A tabulated summary of the results follows, and from it mining engineers may readily compute the supporting value of any particular construction.