Failure mechanisms in ultra-close seam mining

! 87A 903451 Cusp catastrophe model for bulk and broken roof collapse Pan Yue; Geng Houcai Proc International Symposium on Modern Mining Technology, Taian, October 1988 P374,384. Publ Taian." Shandong Institute of Mining and Technology, 1988 In underground situations, structures deteriorate gradually until certain conditions are satisfied, when sudden failures occur. A mechanical model of bulk and broken roof collapse is illustrated, and a catastrophe model of the three hinge arch applied. The critical condition for the roof losing its stability and collapsing is determined. An estimate of the released elastic energy is made. The theory is also applied to bulk caving. 903452 Failure mechanisms in ultra-close seam mining Yingxin Zhou; Haycocks, C Rock Mechanics as a Guide for E~fcient Utilization of Natural Resources: Proc 30th U.S. Symposium, Morgantown, 19-22 June 1989 P613-620. Publ Rotterdam: A A Balkema, 1989 In design of separate extraction of close seams, possible failure mechanisms of inner burden must be considered. Loading on the inner burden may be self-loading or external loading by offset upper pillars. Stress analysis was carried out using finite element analysis and low modulus, gravity loaded photo-elastic models, to develop relationships between magnitude of stress fields and failures. Mohr Coulomb failure criteria were used for prediction of shear failure planes. Inner burden thickness and physical characteristics, and degree of pillar offset for both tensile and shear failure were varied. Results show that shear failure of the inner burden is the predominant failure mechanism in close,multiseam mining. 903453 Evaluation of crown pillar rock conditions for remedial capping of highway collapse Carter, T G: Busbridge, J R; Annan, A P; Mackasey, W O; Dixon, D G Proc 15th Canadian Rock Mechanics Symposium, Rock Engineering for Underground Excavations, 3-4 October 1988 P21-30. Publ Toronto: Unirersit)' of Toronto. 1988 Highway collapse resulted from upward migration of a void from the crown area of old silver mine shrinkage stopes through 5m of overburden. Ground penetrating radar and exploration and diamond core drilling were used to map old mine workings and characterise rock mass conditions. Simple parametric analyses of various crown pillar geometries were used to assist evaluation of the areal extent requiring treatment. Reinforced concrete slabs and roller compacted cemented sand fill were applied as remedial measures. 903454 Behaviour of groundwater around a tunnel during excavation in unconsolidated sandstone Akama. Y: Kitamura. T; Kojo, H Proc International Congress on Tunnels and Water, Madrid, 15-18 June 1988 VI. P49-56. Publ Rotterdam: A A Balkema. 1988 Erosion or collapse during construction stages of tunnels in unconsolidated ground can cause serious difficulties. The behaviour of groundwater was studied during the excavation of an inclined shaft and a horizontal tunnel in pliocene unconsolidated sandstone. Deep well dewatering was used. Predicted and observed drawdown are compared, and the location of erosion failure in relation to spring lines and the phreatic surface examined. Water balance in the region and the effect of the construction on it are discussed.

Tunnels See also: 903240

903455 Methane control in tunneling Kissei, F N Tunnlg Teehnoi Newsl N66, Oct 1989, P1-12 Guidelines for preventing methane gas explosions in tunnels, based on extensive experience in coal mines, are presented. Gas problems may be foreseen on the basis of geology or proximity to swampy ground or landfills, and detected using test borings. Typical gas inflow rates and methods for their detection are considered. Ventilation principles for gassy tunnels and degasification via vertical drillholes are described. Monitoring of gas levels and possible causes of failure despite these precautions are finally discussed.

903456 'Gift wrapped' metro is safe from gas and 'quakes Martin, D Tann Tunnlg V21, NiO, Oct 1989, P22-27 The Los Angeles metro will run through geology of granular and fine grained alluvium, and sedimentary rocks of the Fernando and Puente formations, generally of low hardness and weak to moderately strong. Water table is below tunnel depth in most areas. Complications arise because of nearness of the San Andreas fault, methane gas, and remains of oil wells and buried waste. Running tunnels are being excavated by digger shield. A HDPE membrane between primary and final lining prevents gas ingress. The system is designed to resist major damage rather than movement in the event of earthquakes.

903457 Modelling excavation responses in jointed rock Barton, N; Makurat, A Proc NEA Workshop on Excavation Response in Geological Repositories for Radioactive Waste, Winnipeg, 26.28 April 1988 P225-243. Publ France: OECD, 1989 Tunnel excavation in jointed rocks causes complex changes in the rock mass. A constitutive joint model has been developed and incorporated into UDEC to study changes in joint geometry which occur in rock masses surrounding tunnel excavations. Examples of disturbed zone analyses are presented for TBM tunnels in jointed rock and drill and blast tunnels in jointed rock.

903458 Observation of ground movements caused by tunnelling Cording, E J Proc 2nd International Symposium on Field Measurements in Geomechanics, Kobe, 6-9 April 1987 V2, P799-820. Publ Rotterdam: A A Balkema. 1988 Measurement of ground movement is a reliable means of evaluating stability of tunnels in rock or potential damage to structures close to excavations in soil. Cases examined are large chambers in weak tuff subject to stress induced fracturing and shallow chambers in foliated schistose gneiss, tunnels in squeezing ground, and ground movements around tunnels in soils. The compaction grouting technique can be used to control ground movement in the last case.

1990 Pergamon Press plc. Reproduction not permitted