Analytical solution for axisymmetric tunnel problems in elastoviscoplastic media

230A The effects of high extraction ratio, pillars aligned at apparent dip, a thrust fault, and a Iocalised orebody roll combined to initiate a rock burst zone in an area of the New Quirke Mine, Ontario, Canada, worked out 2 years previously. Installation of a microseismic monitoring system has resulted in accurate location of seismic events within the array. A microcomputer is used for input/output and data processing, and daily summaries of data can be presented in pictorial form. 846220 Analysis of stoping sequence and support requirements in a high stress environment - ZCCM-Mufulira Division Russell, F M; Armstrong, D R M; Talbot, R In: Rockbursts: Prea~ction and Control (papers to the Symposium, London, 20 October 1983) P161-I73. Publ London: IMM, 1983 For ten years part of the western section of Mufulira was mined without major problems. The area, which was overlain by a river, was mined by post-sandfill stoping methods. In 1973 and 1974 rock bursts occurred. A geotechnical analysis was carried out with the use of a mining simulation program, MSIM3D, which indicated that a change in stoping sequence was required, together with rock support. Stoping was resumed in the area, but in 1977 more rock bursts occurred and a more detailed investigation was initiated. The analyses were again carried out with MSIM3D, with modified input data. The results that were obtained indicated that mining in this area would always be subject to high stress and that subsidence beneath the stream with ingress of water into the workings was not impossible. It was decided to divert the stream and resort to a total extraction method of mining, without post-sandfill and with extensive support ofdevelopment. This has been carried out over the past five years with success, some 6000000t having been extracted with a minimum of rock burst activity. This paper has also been published in IMM Transactions (Sect A), V93+ January 1984. PA I-A9. Tunnels See also: 846264, 846276. 846290. 846291, 846360. 846409 846221 Predicted and measured stresses and displacements around the Darlington Intake Tunnel Lo, K Y; Lukajic, B Can Geotech J V21, N1, Feb 1984. P147-165 The Darlington Intake Tunnel, Lake Ontario, Canada, is Dshaped in section, located in horizontally bedded limestone with variable shaley interbeds. Geotechnical investigations included in situ stress measurements, and laboratory determination of strength and deformation properties and time dependent behaviour. The design of the tunnel included provision for "squeezing ground'. To verify the design approach, field monitoring was carried out during excavation. The results were compared with premonitoring analysis. Post monitoring analysis was also performed using the as-constructed conditions. The performance of the tunnel is in general agreement with both short and long term predictions. 846222 Dynamic response of twin circular tunnels due to incident SH-waves Balendra, T; Thambiratnam, D P; Koh, C G; Lee, S L garttul Engng Struct Dynam V12, N2, March-April 1984. P181-201 A closed form solution is presented for the dynamic response of 2 parallel circular tunnels subjected to SH-waves. It is concluded that: (1) interaction between closely spaced tunnels is

more prominent in softer clay and at a higher frequency, t2) at low frequencies, the shear stress maxima increase as the nondimensional spacing between the tunnels reduces from 3 to 2, and (3) at high frequencies, the influence of scattered waves from the second tunnel on the shear stresses of the first tunnel is significant. 846223 Analytical solution for axisymmetric tunnel problems in elastoviscoplastic media Fritz, P int J Num Anal Meth Geomech I"8. N4. Ju!v-Aug 1984, P325-342 An analytical solution is presented for the time-dependent stresses and displacements in plane strain around a circular hole when it is loaded by an axisymmetric internal and far-field pressure. The material is assumed to be elasto-viscoplastic with dilatant plastic deformations according to a non-associated flow rule. Strain softening is considered by a modified St. Venant slider which is characterized by Mohr-Coulomb yield conditions for both the peak and the residual strengths. Auth. 846224 Strange intrusions clog tank drive New Civ Engr N590, 17 May 1984, P28-29 Unexpected localised intrusions of loose sand and silt from the underlying Reading beds have twice brought tunnelling to a near halt during construction of the North London tank sewers, UK. At Islington, the stiff grey clay suddenly gave way to wet silty clay - this required a switch in construction to a bolted lining. At Highbury Corner. loose dry sand was encountered this drastically cut the rate of progress. 846225 Gallic grouting gets sand taped Winney, M •"~'ew Civ Engr N595.21 June 1984, P18-19 French precision drilling and grouting are being used on the Three Valleys water tunnel, Buckinghamshire. UK, where a second attempt to drive through a vast artesian sand dome intrusion is under way. The sand upthrust was discovered in the line of what was thought to be a straightforward drive through London and Woolwich and Reading clay. The drill logging system is able to provide accurate estimates of ground conditions without continuous sampling. 846226 Tropical shield drive tests tunnellers at the Warangoi hydroelectric scheme Knight. M Tunn Tunnig VI6. N6, June 1984, P45-48 Case study of the construction of the Warangoi hydroelectric scheme, Papua New Guinea. It was anticipated that during driving stresses around the proposed tunnel were likely to exceed the rock strength and that stress slabbing or squeezing could be expected. In addition, clay-bearing rock present contained varying amounts of swelling montmorillonite. The method selected for excavation was a shield-mounted backhoe. A precast concrete segmented lining was installed. 846227 Heave causes headaches during canal tunnel refurbishment McCormack, S Tunn Tunnlg VI6. N6, June 1984, P61-63 Problems which had developed in the Netherton canal tunnel, UK, built in 1858, manifested themselves in 1976. The invert of the tunnel was found to have risen 1.5m. This heave was thought to have been caused primarily by local overstressing of the mud-