THE SITING OF A PRISON COMPLEX ABOVE AN ABANDONED UNDERGROUND COAL MINEl by
-. This roper discusses in *M tie process undetien to mitigate the effects of any fiture mine subsidence on prison structures proposed above old abandoned underground workings. The site for a proposed prison complex purchased by the State of Indiana was located in west-central Indiana and was undermined by an old abandoned room and pillar mine. The original plan for construcdon cmsisted of one phase. Based on a study of the mine map and subsurface verification of the extent of mining it was determined that all prison buildings and important structures could be placed above solid coal to the north. One masonry building, however, was located within the potential draw zone of mine works which still contained significant mine voids. Based on empirical data the subsidence potential was estimated and the building waa accordingly designed to be mine subsidence mktant It was decided that a phase two prison complex should be constructed adjacent to and just south of the Phase I complex. This complex would be directly above the underground workings. The first stage of design was to minimim subsidence potential by positioning the exposure of significant structures to the subjacent mining assuming the mine map was sufficiently accurate. Subsequently, an extensive subsurface investigation program was then undertaken to: 1. ascertain whether or not mine areas where buildings would be located were already collapsed and thus only nominal, if any, subsidence could occur in the fhture; and 2. ver@ the presence of solid coal areas within the mine as indicated on the mine map. Based on all the site information gathered subsidence pmfilea were developedfkoman empirical data base of subsidence events in the Illinois Coal Basin. As a result of this work many structures on the site required no or nominal subsidence considerations. For others that could be potentially affected by future subsidence movement, however, preliminary subsidence resistant designs were completed using the expected level of potential subsidence movement. The estimated costs to make each of these structure subsidence resistant waa significant. Mine backfilling measures were taken at these structure locations.
REMOTE SENSING OF ABANDONED MINE WORKS USING DOWNHOLE RADIO IMAGING TECHNIQUES
Because of the potential for surface subsidence, electromagnetic radio imaging method or RIM was employed to identify old (prior to 1928), mine workings in a 300-foot deep by approximately 5-foot thick coal seam below a proposed construction site near Carlisle, Indiana. Cross-borehole RIM delineated the worked regions in the coal seam between pairs of boreholes using distinct variations in the measured signal strength (i.e., attenuation) of continuous radio waves transmitted at three different frequencies (422.5, 532.5, and 612.5 kHz). At the Carlisle site, 33 holes spaced 113 feet to 293 feet apart were drilled within an approximately 900,000 square-foot area. The holes were specifically positioned to calibrate signal attenuation for worked and unworked sections of the seam and then to verify the original mine workings map. Of the 43 pairs of holes measured, 36 clearly showed the presence or absence of mining using single-frequency data. In the remaining 7 cases, multiple-frequency data provided clear answers. In 3 areas, mine workings were detected that were not indicated on the original map.
The crystal structure of stilpnomelane. Part II. The full cell
Summary The structural formula of stilpnomelane averaged from 37 representative literature analyses and based on the determined structure is (Ca,Na,K)4(Ti0·1Al2·3Fe35·5Mn0·8Mg9·3)[Si63Al9](O,OH)216·nH2O. Ferrostilpnomelanes have up to 12 R 3+ cations in the octahedral sheet, ferristilpnomelanes commonly have between 24 and 30 R 3+ cations, rarely up to 37. The two groups can be distinguished by accurate X-ray powder diffraction, ferrostilpnomelanes having d 001 less and a greater than have ferristilpnomelanes. The unit cell is triclinic, a = b∼21·8 Å, γ = 120°, d 001∼12·2 Å, P . Hexagonal groups or ‘islands’ of 24 silicon-oxygen tetrahedra co-ordinate to the octahedral sheet, the centres of the ‘islands’ are displaced by 5a/12, 8b/12 on either side of the octahedral sheet as a result of warping of this sheet to permit articulation with the smaller tetrahedral sheet. The 24-tetrahedra ‘islands’ are linked laterally by 6-member rings of inverted tetrahedra, which in turn link at their apices to like rings connecting the next sheet of ‘islands’. Thus a single tetrahedral layer is 4 tetrahedra thick and has symmetry 6/m. The 6-member rings of tetrahedra act as hinges permitting up to 0·5 Å extension or contraction of the tetrahedral sheet to accommodate variations in the octahedral sheet dimensions with varying R 2+/R 3+ ratio.