Using a sonic technique to estimate in situ stresses

187A Several phenomena were identified such as lump softening (loss of suction) on resaturation, and the lack of any effect of water salinity. There is a need for rational field guidelines for compaction to minimize post-reclamation subsidence. 856153 Feasibility studies on the prediction of rockbursts at Western Deep Levels Van Zyl Brink, A; Mountfort. P I Proc 1st International Congress on Rockbursts and Seismicity in Mines, Johannesburg, Sept 1982 P317-325. Publ Johannesburg. S A I M M , 1984 Research has been carried out since 1977 at the Western Deep Levels gold mine, South Africa, into the use of microseismic events to predict major seismic action. Analysis of pre-recorded microseismic events after large events have occurred has suggested prediction is possible. A description is given of the monitoring system now being installed, with which it is hoped to make real time predictions. 856154 Seismological network of the South African Geological Survey Fernandez, L M: McDonald, A J Proc 1st International Congress on Rockbursts and Seismicity in Mines, Johannesburg, Sept 1982 P333-335. Publ Johannesburg. S A I M M , 1984 The SAGS has seventeen stations which monitor regional and distant natural seismic events, as well as artificial events including rock burst and nuclear explosions. Recent work includes improving the network's coverage of seismicity in mining areas and establishing an accelerometer network to monitor ground accelerations in mining related seismic events. 856155 Influence of stabilizing pillars on seismicity and rockburst at ERPM Deliac, E P: Gay, N C Proc 1st International Congress on Rockbursts and Seismicity in Mines, Johannesburg, Sept 1982 P257-263. Publ Johannesburg. S A I M M , 1984 Seismic records obtained over a 5 month period at the East Rand Proprietary Mines, South Africa, are analysed to evaluate the influences of stabilising pillars, geology and mining activity. Seismicity and the release of seismic energy follow the active faces closely and are also associated with north-south running dykes. Stabilising pillars are not associated with significant seismic energy release. Of the rock bursts identified, only 2 of 24 occurred in the region protected by stabilising pillars. Rock burst occurrence does not appear to depend upon seismic event magnitude, but damage from rock burst apparently increased with event magnitude. 856156 Precursors to rock failure observed in laboratory experiments Walsh, J B Proc 1st International Congress on Rockbursts and Seismicity in Mines, Johannesburg, Sept 1982 P269-275. Publ Johannesburg. S A I M M , 1984 Physical properties of rock change as stress approaches fracture strength. Changes are related to lengthening of existing microcracks and opening of new ones. There is an increase in volume, dilatancy, due to lateral expansion. Laboratory experimental results are reviewed and the changes with approaching fracture of seismic velocities, acoustic emission, seismic attenuation, electrical resistivity, permeability and deformation are examined. The mechanics of the process involved are emphasised. 66 refs.

856157 Seismic observations during test drilling and destressing operations in German coal mines Will, M Proc 1st International Congress on Rockbursts and Seismicity in Mines, Johannesburg, Sept 1982 P231-234. Puhl Johannesburg: S A I M M , 1984 There are regulations concerning outburst prevention for German coal mines. Test drilling is the main tool for detecting dangerous stress concentrations and destress drilling the main remedial measure. The amount of coal drilled per metre and seam reactions (bursts, audible cracks) are noted. The use of seismic observations to obtain an objectively valid scale for seam reactions is considered. 856158 Using a sonic technique to estimate in situ stresses Mao, N; Sweeney, J: Hanson, J; Costantino, M In: Rock Mechanics in Productivity and Protection (paper to the 25th Symposium on Rock Mechanics, Evanston, Illinois, 25-27 June 1984) P167-175. Publ New York: AIME. 1984 The development and laboratory testing of equipment to estimate in situ stress by measuring stress-induced sonic velocity anisotropy is described. 856159 Comparison of frictional material models with respect to shear band initiation Molenkamp, F Geotechnique V35, ]72, June 1985, P127-143 The existing elasto-plastic models of geomaterials have been developed on the basis of experiments in which uniform straining was attempted. The shear bands observed in experiments have been described directly without direct relation to the elasto-plastic models. However. shear band initiation can be considered as an instability of plastic flow: consequently the material behaviour under uniform deformation and the occurrence of a shear band can be considered as coupled phenomena. The coupling relations are elaborated and applied in the calculation of shear band initiation for a range of popular constitutive models of materials like drained clay, sand. concrete and rock. It is found that amongst the popular elasto-plastic models large variations in the predicted slope of the shear band and the predicted instant of initiation occur. Auth. 856160 Low gradient permeability measurements in a triaxial system Olsen, H W; Nichols, R W; Rice, T L Geotechnique V35, N2, June 1985, P145-157 The equipment and procedures for permeability measurement with the flow-pump method in a conventional triaxial apparatus are described and results of experimental measurements on sand, sandy silt and silty clay presented. This method is compared with constant head and falling head methods and found to have the following advantages: (l) permeability can be measured more quickly and at smaller gradients; (2) direct flow rate measurements and associated errors are avoided: (3) errors from the small intercept in the flow rate-hydraulic conductivity relationship and from seepage induced permeability can be minimised. 856161 Stress-strain-strain rate relation for the compressibility of sensitive natural clay Leroueil, S; Kabbaj, M; Tavenas, F Bouchard. R Geotechnique V35, N2, June 1985, P159-180