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.
Subsidence: Occurrence, Prediction and Control
1. Natural subsidence and influence of geological processes. 2. Development of concepts and theories of mining subsidence. 3. Mining and ground movement. 4. Methods of predicting mining subsidence. 5. Observed behaviour of mining subsidence. 6. Subsidence prediction by the UK empirical model. 7. Computer based prediction of mining subsidence employing empirical data. 8. Subsidence associated with near-surface tunnels. 9. Subsidence associated with room and pillar mining. 10. Subsidence associated with steeply inclined seams. 11. Subsidence aspects of sloping ground surfaces. 12. Rock-salt and potash mining subsidence aspects. 13. The time factor in mining subsidence. 14. Influence of geological factors on the character of mining subsidence. 15. Subsidence arising from ground-water withdrawal, oil and gas field activities and underground coal gasification. 16. Subsidence aspects of abandoned mine workings. 17. Effects of mining subsidence on surface structures, design considerations and precautionary measures. 18. Ground movement behaviour as indicated by subsidence models. Appendix 1. Mining subsidence and displacement prediction using influence function methods. References. Bibliography. Subject index. Place index. Author index.
Alkali feldspars: ordering rates, phase transformations and behaviour diagrams for igneous rocks
Abstract Homogeneous and heterogeneous phase relationships in the alkali feldspars are reviewed, and behaviour diagrams developed. Al,Si ordering is almost certainly continuous and higher order in both albite and potassium feldspar and has been established reversibly or nearly so down to below 500°C in albite and possibly to ∼ 200°C in potassium feldspar. The degree of order in intermediate albite changes strongly over a range of ∼ 75–150°C depending on pressure, low albite being stable up to about 620–650°C and high albite above about 725°C at low pressure. Symmetry is broken at ∼ 980°C mainly by a cooperative shearing of the whole framework and not by Al,Si ordering alone; there is a thermal crossover near 700°C shearing being dominant above (high albite) and ordering dominant below (intermediate albite). In potassium feldspar symmetry is broken by Al,Si ordering at a temperature of about 500°C The change in degree of order with respect to temperature has been followed easily and reversibly in sanidine from ∼ 1075 to ∼ 550°C and to a lesser extent in microcline from 450 to 200°C. Ordering rates in sanidine down to 500°C and ordering rates in microcline between 450 and 200°C are almost as fast as in albite. Ordering in sanidine at 500°C and below slows and then stops with the development of the tweed orthoclase domain texture. The tweed texture acts as a barrier to further order because the strain energy associated with the (incipient) twin domain texture balances or nearly balances the free energy decrease resulting from ordering. Ordering stops not because of the kinetics of Al,Si diffusion, but because the total driving force is very small or nil. Ordering can readily proceed to completion, with the formation of low microcline, only if the domain-texture barrier is overcome by processes involving fluids or strong external stresses. There is no barrier in albite. The symmetry-breaking process in alkali feldspar changes with composition from mainly shearing in albite to ordering in potassium feldspar. Symmetry is broken equally at a compositional crossover (metastable with respect to exsolution) near Ab80-75 at low pressure and progressively displaced towards Or at higher pressures. Ordering in pure albite occurs by a (nearly) one-step path which progressively becomes two-step with substitution of Or. Diagrams showing the near-equilibrium variation of the order parameters at low pressure with composition and T are given, as well as two extreme phase and behaviour diagrams for complete coherent and complete incoherent (strain-free) relationships. These diagrams can be used to understand feldspar relationships and microtextures in hypersolvus and subsolvus rocks, the occurrence of orthoclase, and of intermediate and low microcline.