Dislocation creep regimes in quartz aggregates

286A 925101 Influence of rift in granite and stress conditions on hydraulic fracturing Choi, S O; Synn, J H; Lee. H K Proc 7th I S R M International Congress on Rock Mechanics, Aachen, 16-20 September 1991 V1. P441-445. Publ Rotterdam: A A Balkema, 1991 Hydraulic fracturing experiments were carried out on 150mrn cube specimens of granite with a 10mm diameter central hole in order to study effects of rift (direction of easiest splitting) and stress conditions on the fracture patterns obtained. Minor horizontal stress was 20MPa while major horizontal stress was 40-100MPa and aligned parallel to or perpendicular to rift. AE activities were monitored and mapped to indicate fracture propagation. Tensile strengths calculated from these experiments and fracture toughnesses from 3 point bending tests both showed a variation of about 10%, according to fracture direction to rift. 925102 New method for hydraulic fracturing and evaluation of fractures Hibino, S; Kaieda, H; Hori, Y Proc 7th I S R M International Congress on Rock Mechanics, Aachen, 16-20 September 1991 VI, P501-504. Publ Rotterdam: A A Balkema. 1991 A method for hydraulic fracturing of Hot Dry Rock is presented, which can produce multiple fractures in a well without the use of open hole packers. It has been demonstrated at a site in Akila, Japan, where fractures were produced at 3 different depths in a 400m deep well. Casing pipes are set in the well and back grouted. The pipe is reamed at the desired depth of fracture, the well pressurised, and a sand barite plug used to prevent water loss to existing fractures. Effectiveness was determined by acoustic emission, BHTV, and mise-a-lamasse measurements. 925103 Geotechnical characterization of a thermally cracked marble Klimis, N Proc 7th I S R M International Congress on Rock Mechanics, Aachen, 16-20 September 1991 V1, P539-544. Publ Rotterdam: A A Balkema. 1991 The evolution and characterisation of microcracks in Carrera Marble as a result of thermal cycling have been studied by several methods: the continuity index, based on P wave velocity properties; the quality index, based on P wave attenuation properties; and examination of mechanical properties and scanning electron micrographs. The theoretical basis of the methods is outlined. The choice of a monomineralic rock was to simplify analysis. Experimental results and theory are compared. Promising information on the geometry of the evolving crack field is obtained. 925104 Filled 'subsidence' cracks is San Luis Canal excavations, California, U.S.A. Prokopovich, N P Proe 4th International Conference on Land Subsidence, Houston, 12-17 May 1991 ['379-386. Publ I A H S Press." Wallingford, 1991 About 9000 nearly vertical cracks, 20-40mm wide with mostly vertically laminated clay filling, were found in Holocene-Pleistocene alluvium during excavations for a canal. The crack frequency ranged from less than 10 to over 850/kin. Two zones of hydrocompaction due to groundwater overdraft, with up to 5m of settlement and l-2m wide cracks, were also found. The

most numerous filled cracks are probably related to tension failures. These clay filled cracks interrupt lateral migration of groundwater and interfere with drainage. 925105 Stability of a geothermal reservoir crack connecting with a horizontal natural fracture in the earth's crust Hayashi, K; Sayama, T; Abe, H Proc International Conference on Mechanics o f Jointed and Faulted Rock, Vienna, 18-20 April 1990 P659-666. Publ Rotterdam: A A Balkema, 1990 Using linear fracture mechanics, the behaviour of a fluid filled reservoir crack connected to a natural horizontal fracture in the earth's crust is analysed. The effects of stress contrast across the horizontal fracture, fracture toughness contrast, elastic properties contrast, of friction on the norrnalised fluid pressure at the point of intersection, and of fluid leakage are discussed. The stress contrast across the horizontal fracture is shown to be the main factor governing the reservoir system behaviour. Inferences to stability of the reservoir system are discussed.

Time dependent behaviour See also." 925425 925106 Pore pressure response due to penetration through layered media Elsworth, D lnt J Num Anal Meth Geomech V16, NI. Jan 1992, P45-64 As an analogue to penetration in a layer of finite thickness, a solution is developed for a point dislocation traversing a slab of saturated porous material under set upper and lower hydraulic boundary conditions. Pressure response is conditioned by geometric parameters and dimensionless values of penetration rate, time since penetration initiation, and time since penetration cessation. Parameter determination is problematical and possibly non-unique. Relevance to interpretation of piezocone data is discussed in detail. 925107 Dislocation creep regimes in quartz aggregates Hirth, G; Tullis, J 1 Struct Geoi VI4, N2, 1992, P145-159 High temperature triaxial creep tests were carried out on Heavitree and Black Hills quartzites and a fine grained novaculite. TEM and optical microscopy were used to examine the microstructures characteristic of the three regimes of dislocation creep which occur, dependent on relative rates of dislocation production, dislocation climb, and grain boundary migration. Within each regime the microstructure is related to the mechanism of dynamic recrystallisation in operation. Processes which control which regime is dominant, and how these are affected by changes in temperature, strain rate, and presence of water are discussed. Interpretation of microstructures of naturally deformed rocks is considered. 925108 Effect of porosity on the strength of quartz aggregates experimentally deformed in the dislocation creep regime Hirth, G; Tullis, J Tectonophysics V200, NI/3, Dec 1991, P97-110 Quartz aggregates with porosities from below 1% to about 8% were deformed in the dislocation creep regime. Significant but transient strengthening results from the presence of porosity. High densities of tangled dislocations develop around the

1992 Pergamon Press Ltd. Reproduction not permitted