Powerhouse cavern stress analysis at consecutive excavation stages

262A strata, computational methods, and failure mechanisms in the bedded rocks with high horizontal in situ stress are described. Rockbolt design procedures for the Bondi pumping chamber and the Sydney Ocean Outfall Tunnels are illustrated. 924439 Appropriate support selection Tarkoy, P J Tuan Tuanlg I,'23, NIO, Oct 1991, P42-45 Selection of support impacts directly on cost, safety, and rate of progress of tunnelling projects. Selection on the basis of ground classification schemes, generally at the design stage but sometimes at the heading, is becoming common. Empirical, observational, or measurement-based approaches may be used. Three case histories are presented which illustrate the criteria used in support selection and highlight their shortcomings. A list of questions to be posed when selecting support is presented. 92A.AA.~ Difficult rock comminution and associated geological conditions Tarkoy, P J; Marconi, M Proc Tunnelling '91, London, 14-18 April 1991 P195-207. Publ London: Elsevier, 1991 Conditions are encountered in many types of project which cannot by attributed to factors measurable by classical methods and are not easily discerned or predicted in conventional exploration or testing prior to tender. The Field Penetration Index (gross normal cutter force in kg/penetration in mm per revolution) is defined as an effective index of energy expended in tunnel boring or drilling. This correlates well with total hardness in 'normal' conditions, but not when problems occur. Many case studies are described and typical geological features leading to problems in batholithic and metamorphic rocks identified. These are not easily detectable. The value of extensive site characterisation before tender is indicated. 924441 Zurichberg railroad tunnel Chavan, F; Ritz, W; Windier, H J; Yanagisawa, S Proc 1989 Rapid Excavation and Tunnelling Conference, Los Angeles, 11-14 June 1989 P663-677. Publ Littleton: SME, 1989 The twin track, 11.52m diameter, 4.3kin long rail tunnel in Switzerland runs through the Zurichberg, comprised of Sussewassermolasse covered by a thin morainic layer. The formation is finely bedded sandstone, siltstone, and marl, with compressive strength 10-100MPa. Poor cementation and presence of expansive clay minerals in the marl lead to potentially squeezing conditions. A shielded TBM was used for the drive, with a 25cm thick precast concrete lining installed from the shield tail. Average rates of nearly 12m/day were achieved in two nine hour shifts. Final lining is 28cm of in situ concrete. 924442 Freudenstein tunnel. Tunnel construction in swelling rocks Prommersberger, G; Kuhnhenn, K Proc 1989 Rapid Excavation and Tanneih'ng Conference, Los Angeles, 11-14 June 1989 P678-700. Publ Littleton: SME, 1989 Most swelling rock in Germany belongs to the Keuper formation, layered claystone/siltstone/marl/dolomite, with intercalations of gypsum and anhydrite which can lead to squeezing conditions. Possible remedial and preventative measures

against squeezing are discussed. The construction of the 6.9kin long Freudenstein tunnel through gypsum Keuper is described. Grouting was used to minimise water problems, but it was also necessary to place a compressible layer beneath the tunnel bottom to absorb swelling strain of the rock.

Stresses around underground openings See also: 924100, 924103, 924166 924443 Consideration of the lateral forces generated by powered supports Smart, B G D; Olden, P W H; Metcalfe, K Min Engr VI51, N364, Jan 1992, P189-196 Lateral movement between mine roof and floor has been measured less frequently than vertical movement, but is of similar magnitude and thus important from the strata control point of view. Field data indicate that the orientation of major horizontal stress and the face may influence relative lateral movement. A numerical model incorporating the mechanics of the support is used in modelling the phenomenon. For a 2-1eg support, active lateral force developed on the roof is primarily dependent on operating height and floor stiffness. The benefits of applying high lateral force are examined for cases of strong roof with dominant parting plane and well defined breaks (advantageous) and of weak roof with dominant parting plane near the working horizon (detrimental). 92AAAA Soil-reinforcement interaction under a joint of buried conduit Sohn, J; Lee, W J; Lee, B S Proc 4th International Conference on Geotextiles, Geomembranes and Related Products, The Hague, 28 May-I June 1990 V2, P839-844. Publ Rotterdam: A A Balkema, 1990 Differential settlement, which can arise from many causes, leads to many problems with buried pipes. Finite element analysis is presented for the case of a pipe with flexible joints, installed on a layer of reinforced earth, and subject to differential settlement resulting from uniform surface loading of a localized area. Deformation mode and stress variations are examined and the effectiveness of reinforcement evaluated with respect to placement length and depth of the reinforced layer. 924445 Powerhouse cavern stress analysis at consecutive excavation stages Kalkani, E C Proc I S R M International Symposium on Static and Dynamic Considerations in Rock Engineering, Swaziland, 10-12 September 1990 P157-164. Publ Rotterdam: ,4 A Balkema, 1990 The state of stress around the powerhouse cavern of the Pigae hydropower project in Greece has been analysed using a modification of the finite element code SAP-IV. The rock mass, interbedded sandstone and siltstone, is considered as isotropic and homogeneous for the analysis. Stress and displacement distributions are evaluated for five consecutive construction stages. Sidewall displacement and extent of tensile areas in the sidewalls are illustrated as the excavation proceeds from top to bottom.

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