Ergün Tuncay

Comparison of stresses obtained from Acoustic Emission and Compact Conical-Ended Borehole Overcoring techniques and an evaluation of the Kaiser Effect level

The purpose of the study was to compare stress values obtained from Acoustic Emission and Compact Conical-Ended Borehole Overcoring stress measurement techniques applied at an underground limestone mine in Japan, and to investigate the effect of rock anisotropy and confining pressure on the Kaiser Effect level which has been used to determine in situ stresses by the Acoustic Emission technique. Initially, Acoustic Emission tests were carried out on limestone cores extracted from horizontal boreholes in a pillar and hanging wall in the underground mine. The stress values obtained were two or three times greater than those obtained by the Compact Conical-Ended Borehole Overcoring method. In the second stage, the anisotropy of a granite block was determined by P-wave measurements. Core specimens extracted from two different directions were pre-loaded under axisymetric triaxial conditions by applying a series of differential stresses. The cores were then re-loaded under uniaxial conditions and the Kaiser Effect levels were determined. It was concluded that both the anisotropy and confining pressure have an important influence on the Kaiser Effect level.RésuméLe but de l’étude était de comparer les valeurs de contraintes obtenues à partir de la technique de mesure par Emission acoustique (AE) et une technique de Sur-carottage (CCBO), mises en œuvre dans une mine souterraine de calcaire au Japon. De plus, les effets de l’anisotropie de la roche et de la pression de confinement sur l’effet Kaiser défini dans les techniques d’émission acoustique ont été étudiés. Initialement les essais d’émission acoustique ont été réalisés sur des carottes de calcaire issues de forages horizontaux réalisés dans un pilier et une couche de toit de la mine souterraine. Les valeurs de contraintes obtenues étaient deux ou trois fois plus grandes que celles obtenues par la méthode de sur-carottage. Dans une deuxième étape, l’anisotropie d’un bloc de granite a été déterminée par des mesures de vitesses d’ondes P. Des échantillons carottés suivant deux directions différentes furent pré-chargés sous conditions triaxiales symétriques en appliquant différents niveaux de contraintes. Les échantillons furent re-chargés sous conditions uni-axiales et les valeurs d’effet Kaiser déterminées. On a conclu que l’anisotropie et la pression de confinement avaient tous deux une influence importante sur les valeurs d’effet Kaiser.

Assessments on slope instabilities triggered by engineering excavations near a small settlement (Turkey)

In this study, the mechanisms of slope instabilities triggered by engineering excavations at location of a planned tunnel portal in the northwest region of Turkey were assessed, and stability of the current slopes which has impacts on safety of a settlement (village) and agricultural fields was investigated. In the first stage of the study, in order to identify the geological units and structural properties of the sedimentary rocks in the area, to clarify the mechanisms of instabilities and to characterize discontinuity and rock mass properties field works were conducted. In this content, geotechnical boreholes, geophysical explorations between the boreholes, line surveys to explore discontinuity properties, preparation of slope profiles using topographical techniques and sampling of rock blocks and discontinuity planes were performed. In the second stage, laboratory tests were carried out on the samples to determine the geomechnical properties of the slope forming materials and discontinuities. Then, back analyses of the instabilities were made to assess the responsible shear strength parameters of the geological units during failures by considering laboratory shear test results too. Based on the backanalyses of the failures, the strength properties of the slope debris were estimated, and it has been clarified that the residual shear strength properties are the factors controlling slip mechanism along the beddings. Following the stability analyses, it is understood that a further instability along the mass or bedding planes in the failed and redesigned area are not expected, if the current slope geometry is not changed. However, safety factor calculated for the slope in the debris is 1.1 which is well below the recommended value in the literature. The minimum safety factor for currently stable slopes which were cut at the eastern part of the failed area is 1.22 which is also less than that suggested in literature. Some remedial measures such as mini-pile or slope flattening are suggested after analyses to increase the factor of safety for this part below the settlement.

Assessment of the Mechanism of a Slope Failure in a Hydroelectric Power Plant Site

In this study, the mechanism of a slope instability, which occurred in the area of a stream type hydroelectric power plant and threatened its loading pool and power house, and triggering factors were investigated and the applicability of some remedial measures were assessed. An assessment of the geological and engineering data from the study site indicated that the instability has developed in a certain part of the slope cut along the bedding plane in a sedimentary sequence, where the dip directions of the slope and bedding planes coincide. The back-analysis of the instability proved that the residual shear strength of the bedding planes was a critical factor. A series of analysis conducted along different slope profiles indicated that the most critical mode of failure and colluvial deposits are not anticipated. Some remedial measures such as slope flattening, the use of rock bolts and slope rotation were also assessed based on preliminary analyses.