Discontinuity Orientation Measurement (DOM) drilling system capable of retrieving the reference line-marked core log, which can be used for determining the relative positions and orientations of discontinuity planes along the borehole axis, has been developed. Accuracy of the borehole joints data measured from the reference-lined core and, eventually, the significance and applicability of DOM drilling system for site exploration are verified by comparing with the spatial characteristics of joints investigated by implementing borehole image-taking instruments in the same borehole. Enhancement of boring efficiency has been also confirmed by performing twin drilling operations, one with DOM drilling system and the other with a conventional drilling machine equipped with D-3 core barrel, on two neighbouring sites of 5 m apart.

Ein DOM(Diskontinuitatsorientierungsmessung)-Bohrsystem, das durch Grundlinien markierte Bohrprobelog extrahieren kann und die relativen Lagen und die Orientierungen der sich im Bohrloch verbreitenden Flachen bestimmen kann, ist entwickelt worden. Die Wichtigkeit des DOM-Bohrsystems und dessen Anwendbarkeit auf die Erforschung auf dem Bohrplatz werden dadurch bewiesen, dass man die Genauigkeit der Daten der Bohrlochsspalte, die durch die die Grundlinie zeichnende Bohrprobe gemessen werden, mit dem raumlichen Eigenschaften der Spalte vergleicht, die durch die Bildaufnahme des gleichen Bohrlochs nachgeforscht werden.

Un system de sondage, Discontinuity Orientation Measurement (DOM), capable de recuperer des carottes markes en une ligne de reference a ete develope. Il peux être utilise pour determiner les positions relatives et les orientations des plans de discontinuite le long de l'axe de trou de sonde. Leur signification et applicabilite pour une caracterisation de site est verifiee par une comparaison de la precision des donnees a propos des joints mesures a partir des carottes markes et les caracteristigues spatiales des joints enquêtes par le camera de sondage

Introduction

Comprehensive site characterization of the rock mass is indispensable for the safe design and economic constructions of rock structures. Until recently, in-situ investigation of the spatial characteristics of discontinuities has been carried out by performing geological joint survey on the field rock surface and/or by implementing several types of borehole instruments to acquire the orientations of discontinuity planes along the borehole axis (Haller & Porturas, 1998; Raax, 1997; William et al., 1997; Hornby et al.; 1992, Ze-manek & Caldwell, 1969). More specifically, borehole image- taking apparatus such as Borehole Image Processing System (BIPS), Optical Borehole Image (OBI), and Acoustic Televiewer (ATV) have been used to obtain the image of borehole wall and delineate the types and spatial characteristics of discontinuities crossing the borehole. But, these instruments are very expensive and field implementations for achieving the exploration objectives can only be processed after the completion of drilling operation. Reliance of test results analyzed from the image of borehole wall depends significantly on the borehole conditions and the existence and turbidity of groundwater so that borehole image processing instruments may not be operated in every borehole available for field survey. To avoid these operational restrictions of field instruments and also save the time and expenses for site characterization the use of drilled core.

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