Slurry and EPB shields

159A and apparent strength enhancement recorded at the walls of model wellbores. An important ramification of the theory is the prediction of a failure pattern in which fractures parallel to the borehole wall may initiate some distance inside the surrounding rock. Auth.

lining-rock interaction methods using models of linear-viscoelastic, linear-elastic linear viscous, and linear elastic non-linear viscous rock behaviour. Calculations of lining pressures show that the former tends to underestimate compared with the latter. Auth.

893424 Mechanical stability of the linkage in deep underground coal gasification (In French) Schmitt, N; Nguyen Minh, D Proe 6tk International Conference on Rock Mechanics,

893428 Design and construction of a shallow tunnel with large span in an urban area Wittke, W

Montreal, 30 Aug-lO Sept 1987 V2, P1223-1226. Publ Rotterdam: A A Balkema, 1987 The linkage tunnel in underground coal gasification must withstand high temperatures (800-1000 deg K) and pressures. The mechanical stability of such a tunnel has been examined using small scale model tests. Mechanical properties of the coal, a non-swelling anthracite, were first measured. Convergence curves were determined under simulated in situ conditions. Results were analysed and a stability criterion proposed. 893425 Seismic activity in a flooded Saskatchewan potash mine Gendzwill, O J; Prugger, A F Proc 2nd International Symposium of Rockbursts and

Seismicity in Mines, Minneapolis, 8-10 June 1988 PI39-148. Publ Minneapolis: Unirersity of Minnesota, 1988 Usually failure in potash mines is due to stress changes associated with subsidence over mined out areas. Failure in a Saskatchewan potash mine which intersected an aquifer, which led to seepage, is described. Initially inflow was controlled by grouting and roof support, but eventually the mine was closed. Soon after, a series of microseismie events occurred, culminating in a magnitude 2.7 earthquake and aftershocks. The events occurred close to the location of water inflow in the mine. A proposed sequence of events is presented. Inflow causes undercutting of pillars and cavern formation, the mine fills with water, hydrostatic pressure is restored, earthquakes occur and, following failure, a stable arch forms.

Int J Min Geol Engng V6. N2, July 1988, P127-146 Construction of a tunnel with a wide span through alternating layers of sandstone and claystone overlain by 2.4m of sandy loam is described. Site investigation included pressuremeter and Lugeon tests in test pits and boreholes, leading to evaluation of discontinuities and joint orientation. The tunnel was constructed using the New Austrian Tunnelling Method, and a 10m reinforced concrete pillar was constructed in an exploratory tunnel in the centre of the 2 tunnel tubes. Stability analysis using the finite element method revealed that the resulting stress distribution showed that the rock mass above the tunnel forms an arch and takes part in stress redistribution around the opening. 893429 Comparison of rock mass disturbance in TBM and drill and blast drivages at the Donkin Mine, Nova Scotia Aston, T R C; Gilby, J L; Yuen, C M K

lnt l Min Geol Engng V6. N2, July 1988, P147-162 Two tunnels were driven through sandstone, one by TBM, the other by drill and blast. A variety of methods were used to assess rock mass disturbance: borehole dilatometer to measure in situ rock modulus, seismic reflection surveys of tunnel sidewalls, laboratory tests on core samples, and in situ gas permeability testing. This showed the borehole dilatometer gave the most realistic evaluation of actual deformation characteristics and TBM excavation caused less damage than drill and blast. The zone of rock mass disturbance compares favourably with numerical and field values from US nuclear waste disposal research.

Tunnels See also: 893207 893426 Influence of engineering geology and rock mechanics in tunnelling Muller, L

lnt Assoc Engng Geol Bull N38, Oct 1988, P5-13 Geological conditions dominate tunnelling, being unaffected by theoretical or economic considerations. They act in a manner predetermined by their nature, yet influenced by the way rock is treated in excavation and support. Factors affecting stand-up times and problems in evaluating these times, and difficulties in interpreting geotechnical data are considered. Contracting and costing complications are discussed. Finally, general advice to the practising engineer on the approach to tunnelling in rock is presented. 893427 Design of tunnel linings in a creeping rock Ladanyi, B; Gill, D E

lnt J Min Geol Engng V6, N2, July 1988, P113-126 The effect of longterm rock deformation on lining pressure is considered using different concepts of rock behaviour. These include the conventional characteristic-line or convergenceconfinement method, modified to allow for rock ageing, and

893430 Soft ground NATM tunnel designs for the Washington, D. C. Metro lrshad, M; Heflin, L H Tunnlg Underground Space Technoi I/3, N4, 1988, P385-392

NATM was used in extension sections of the metro in preference to shield tunnelling or cut and cover. Ground conditions were primarily sands, gravel, and plastic clay with sand lenses. Dewatering was carried out to improve stability, with grouting where necessary. Tunnel design, initial and final linings, excavation sequence, initial support for running tunnels, and shaft and station construction are described. NATM advantages were lower surface settlement, better waterproofing, capital and construction cost savings, and rapid construction. 893431 Slurry and EPB shields Pearse, G

World Tunnlg VI, N4, Dec 1988, P304-315 Problems arising when tunnelling in soft ground are briefly stated, and how shield tunnelling machines overcome them is examined. The various types of shield available, slurry shield, hydroshield, thixshield, earth pressure balance shield, mechanical earth pressure balance shield, and universal shield, are described and particular characteristics noted. Manufacturers are listed.

1989 Pergamon Press pie. Reproduction not permitted RMMS 26-3 .~---P