Rotation of principal stress directions in sand under three dimensional stress conditions

342A by underhand longwall cut and fill methods. Estimations are made of rockburst hazards, and predictions considered against field data and real geological setting. 916088 Experimental assessment of static and dynamic properties of a clay deposit Paoliani, P; Di Pasquale, G; Lucarelli, V; Sano, T Soil Dynamics and Liquefaction, Proc 4th International Conference on Soil Dynamics and Earthquake Engineering, Mex&o City, 23-26 October 1989 P61-70. Publ Southampton: Computational Mechanics Publications, 1989 A program of laboratory and field tests to investigate the dynamic behaviour of a soft clay deposit, a possible reactor site in Italy, is described. Static CPTs, vane shear, selfboring pressuremeter, and flat dilatometer tests, plus crosshole, downhole, seismocone, and field seismic dynamic methods were used. Borehole samples were examined in the laboratory. Empirical correlations between measured static and dynamic parameters are explored. 916089 Rotation of principal stress directions in sand under three dimensional stress conditions Gutierrez, M; Ishihara, K; Towhata, I Soil Dynamics and Liquefaction, Proc 4th International Conference on Soil Dynamics and Earthquake Engineering, Mexico City, 23-26 October 1989 P105-115. Publ Southampton: Computational Mechanics Publications, 1989 Many in situ stress paths involve rotation of principal stress directions. Attempts to simulate real conditions for sand in a hollow cylinder apparatus are described. Three types of planar rotation of principal stress were used. Effects of shear stress level, b-value, and type of planar rotation on shear strain and volume strain developed are illustrated. 916090 Behaviour of medium and low plasticity clays under cyclic simple shear conditions Tan, K; Vucetic, M Soil Dynamics and Liquefaction, Proc 4th International Conference on Soil Dynamics and Earthquake Engineering, Mexico City, 23-26 October 1989 P131-141. Publ Southampton: Computational Mechanics Pubfications, 1989 An experimental program involving 7 clays and 20 N G I cyclic undrained direct simple shear tests is described. Constant cyclic shear strain amplitude was maintained in each test. Plasticity index of the clays ranged between 12 and 23, OCR between 1 and 4. Degradation of cyclic stiffness and variation of cyclic pore pressure with number of cycles are correlated with PI and OCR. Results demonstrate that shear strain is the governing loading parameter in cyclic tests and that plasticity strongly influences cyclic behaviour of different clays. This latter parameter can easily and economically be measured for prediction of cyclic load capacity. 916091 Underground excavations in chalk Lake, L M Proc International Chalk Symposium, Brighton, 4-7 September 1989 P461-467. Publ London." Thomas Telford, 1990 A summary of geology, engineering geology, and engineering properties of U K chalks is presented. Discontinuities and their origins, intact and effective strength, influence of flints, time dependency, and permeability are considered. Some major

excavations in chalk are described, tunnclhng above and below water and storage caverns, with constructional problems briefly detailed.

Fracture processes See abo: 916299, 916535 916O92 Time-dependent hydraulic fracturing in potash mines Morgenstern, N R; Sepehr, K lnt J Rock Mech Min Sci V28, N2/3, May 1991, P187-197 A finite element model based on viscoelastic/viscoplastic material behaviour has been used to investigate causes of seismicity and flooding at some Saskatchewan potash mines. Hydraulic fracturing of the brittle Dawson Bay formations above the Prairie Evaporite seam results from mining induced changes to the stress regime. This may be a cause of seismicity. These fractures can form a connecting path with overlying aquifers. Hydraulic fracturing of both the Dawson Bay and underlying evaporite layers is shown to depend on aquifer water pressure, pre-mining stress state, and duration of mining. 916093 Class I vs class II stability: a demonstration of size effect Labuz, J F; Biolzi, L Int J Rock Mech Min Sci V28, N2/3, May 1991, P199-205 An analytical explanation and experimental evidence of the ductile-brittle (class I-class II) transition on the global level for a linearly elastic softening rock is presented. The theory is based on the potential energy of the system, stored per unit volume, converted to fracture energy, dissipated per unit area. This results in a natural size dependency of the load-displacement curve. Tensile fracture in beam elements and shear fracture in compressive elements are analysed using a cohesive zone representation of the fracture. Behaviour is seen to be dependent on geometry and size. 916094 Variability in coaibed-methane well performance: a case study Zuber, M D; Reeves, S R; Jones, A H; Schraufnagel, R A J Pet Techaoi V34, N4, April 1991, P468-475 Three producing wells in the Oak Grove field of Alabama have been studied. Each is examined in terms of geologic setting, stimulation effectiveness, simulator predicted recovery, and observed performance. Effectiveness of the fracturing treatment was markedly affected by local variations in geology and reservoir properties. In situ stress setting, substantially elevated within fault blocks, is the main factor influencing well performance. High stress levels result in low coal permeabilities and high treatment pressure during fracturing, which results in less effective stimulation. 916095 Experience reveals better Bakken stimulation techniques Cramer, B D Oil Gas J 1/89, N17, 29 April 1991, P56-61 Temperature and radioactive tracer logs have been used to map the extent of horizontal fracturing around wells in the Bakker formation, North Dakota. Analysis of bottom hole pressures during and immediately after treatment was used to provide insight into many treatment phenomena. Combinations of fracturing and stimulation treatment, fracturing fluid, and proppant which proved the most effective have been evaluated.

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