220A UNDERGROUND EXCAVATIONS:SUBSIDENCE

The construction of by-pass road tunnels at Tempere, Fin- land, has involved blasting through fractured rock with a very limited degree of cover (3-10 m). The nature of the granitic rock in the area is described. The equipment used and the steps taken to ensure adequate support of the fra- gile tunnel roofs are also outlined. -D.W.Taylor

Groundwater problems

944403 Construction dewatering in low.permeability soils: some problems and solutions M. Preene & W. Powrie, Proceedings - ICE: Geotechnical Engineering, 107(1), 1994, pp 17-26. Excavations below the natural groundwater level in fine soils are often unstable, but can be stabilized by reducing porewater pressures in the surrounding soil. This paper describes some of the difficulties that may be encountered in the operation of dewatering systems in fine soils, with reference to three case studies. -from Authors

Surface subsidence, caving and rockbursts

isms. Where approprL.ale, brief case studies of the different mechanisms are gxven. Finally, some thoughts are presented concerning support of tunnels subjected to rock- bursting. -Authors

944408 Residual subsidence over abandoned coal mines M. G. Karfakis, in: Comprehensive rock engineering. Vol. 5, ed J.A. Hudson, (Pergamon), 1993, pp 451-476. Residual subsidence may result from roof failure,pillar failure, squeezes and/or punching, or compaction and con- solidation of collapsed zones. The last three of these fac- tors may, depending on mine depth, mined thickness, unsupported roof span, mechanical properties of the under- lying strata and other factors, result m the formation of trough subsidence at the surface. Roof collapses, however, may (depending on factors such as mined thickness, mine depth, bulking and lateral migration of debris) result in chimney subsidence. The following sections examine the mechanisms of residual subsidence, identify the control- ling factors in their development, discuss the different approaches that can be taken to predict, investigate and nutigale residual subsidence, and also present a case study of subsidence abatement projects in Wyoming,

-from Author

944404 Subsidence behavior of the rock structures B.N. Whittaker & D. J. Reddish, in: Comprehensive rock engineering. Vol. 4, ed J.A. Hudson, (Pergamon), 1993, pp 751-780. Subsidence in connection with mining has been carefully monitored and studied in several countries. A vast wealth of information exists on subsidence behavior and engineer- ing principles have been established relating to the predic- tion of subsidence, displacements and surface ground strains. Geological and hydrogeological factors play a major role in connection with the nature and magnitude of subsidence occurrences whether due to natural causes or induced by mining. Consequently, when conducting an assessment of the likely occurrence or predicting the mag- nitude of subsidence using engineering principles and esta- blished subsidence relationships, geology and hydrogeol- ogy require to be taken into account and given al~propriate assessment. -Authors

944405 El p r o g r a m DHH como apoyo a los estudios de subsidencia minera (The DHH programme as an aid to studies of miningsubsidence) J. Gomez de las Heras, A. Ochoa Breton & S. Falcon de Andres, Boletin Geologico y Minero, 104(1), 1993, pp 33-40. In studies of mining subsidence the parameters of the simulation model used must be known to .adapt the theoret- ical basin calculated to that of the real basm subsidence that will occur• Data may be obtained by the installation of topographic stations and measuring their movements. The DHH programme offers the means of con tr01ling this work and enables both horizontal and vertical displacements to be calculated. -A.Scarth

9A.A-~.06 Laboratory experiments: their role in the problem of rock burst prediction V. A. Mansurov, in: Comprehensive rock engineering. Vol. 3, ed J.A. Hudson, (Pergamon), 1993, pp 74"5-771. After a brief introduction, physical and mechanical models of the failure of so!~d~ are discussed in terms of theoretical failme conditions in haterogonous solids, and physical pro- pemes of macrofailure prediction. Rock fail'ux~ laws are p re.se.nted, detailing the influence of microfallure, loading ngumy and volumetric stressed condition on deformation processes. Scale effects and rock failure are discussed and the prediction of rock bursts is presented. -R.Gower

944407 Rockburst mechanisms in tunnels and shafts W.D. Ortlepp & T. R. Stacey, Tunnelling & Underground Space Technology, 9(1), 1994, pp 59-65. Rockburst occurrences in tunnels have been reported from many cou_nmes, and it is apparent that there are dif'rerent concepts of rockbursting.'-l'n this PaPer several dli~r~nt mechanisms of rockburst~g are diJ'tin'guishad, and a - - c ] e~ distinction is drawn between source and damage mechan-

944409 Surface subsidence prediction by nonlinear finite-element analysis Y, Najjar & M. Zaman, Journal of Geotechnical Engineering - ASCE, 119(11), 1993, pp 1790-1804. An improved two-dimensional plane-strain numerical pro- cedure based on the incremental-iterative nonlinear fmile- element method is developed to predict ground subsidence caused by underground mining. The computer code is used to a n ~ ' z e a collapse that occurred in the Blue Goose Lease 1 Mine in northeastern Oklahoma. A parametric study is conducted to investigate the effects of some selected factors on the shape and extent of subsidence pro- fdes. -from Authors

944410 Pseudosinkhole occurrences in Brasilla, Brazil A. F. Mendonca, A. C. B. Fires & J. O. C. Barros, Environmental Geology, 23(1), 1994, pp 36-40. The geological environment in the area consists of low-

rade metamorphic rocks. Over the Precambfian rocks is a teritic layer varying in thickness from centimeters up to

30 m. Erosional problems related to the lateritic terrkins were known prior to the settlement of the city in 1961. During 1986, erosion became a serious threat when several pseudosinkholes occurred in the urban area. Occurrence of ~ seudosinkholes resulted in condemnation of an area of

00 000 m 2 and the demolition of several buildings. Stu- dies have been conducted looking for correlation between pseudosinkhole occurrence and geologic, geomorphic, geotecnmcal, and urban development features, recent results show a much more complex process than previ- ously thought, Field data suggests that termite activity and recharge of the water table by inadequate disvosal of ~sidential sewer systems are directly re|ated to t~e prob- lem. -from Authors

944411 Analysis of residual subsidence movements in the UK coalfields X. L. Yao & D. J. Reddish, Quarterly Journal of Engineering Geology, 27(1), 1994, pp 15-23. The importance of residual subsidence in the study of ground movement due to ~ is discussed and previous research res.ults are briefly revlewed. On the basts of ten cases roves .t.~ated within the UK coalfields, the difference between residual subsidence characteristics along longitu- dinal and transverse lines is studied. A case e ~ l e asso- cia~d with .mining ~ inclined seam is invest~ in detail, showing that different residual subsidence charac- teristics apj~ear due to mining an inclined seam as opposed to a level seam..Addi.tinnall~, a prediction mcklel is presented and applied to determine the duration of residual subsldence. ~ , an empirkal equation, based on data couected within the UK coal lh lds d r ,,.*;,,;,-~,,:. ~.- A,._ U.on of.residual subsidence m put forward with considera- twn ot oom aepth and geological factors. -from Authors