The experience is illustrated which has been gathered by the LNEC on carrying out 387 dilatometer tests, contributed by 9 programs spanning a wide range of engineering interests. The examples given point to the reliability of the LNEC dilatometer as an instrument allowing a quality index to be ascribed to rock masses, with an especial significance for their characterization as to deformability.

1 Introduction

The idea of using borehole dilatometers to characterize rock masses for deformability has met with stimulating interest, despite the difficulties which must be overcome to put it into practice. Actually, the main advantage in the use of dilatometers stems from the possibility they afford to appraise rock masses down to considerable depths, even when they are under water.

For some seven years now the Laboratôrio Nacional de Engenharia Civil (LNEC) has been engaged in the development of a dilatometer to operate in rather narrow boreholes, viz. 76 mm in diameter, with a capability to apply high pressures and measure small deformations along four diametral directions. The instrument designed was first described in a paper presented at the 1st Congress of the International Society for Rock Mechanics [1], and has been much improved since. In its present form the LNEC dilatometer, about 1 m long, is suitable for test diameters from 74 to 82 mm and for depths down to 200 m, and is still operative in boreholes holding water. Pressures up to 200 kg/cm2 may be fed to its rubber jacket, whose tops are prevented to extrude by special sleeves. Eight feleers to follow the radial displacement of the bore hole wall are bound to the jacket on generatrices at 45° intervals. The two opposite feelers moving along each direction are centred on cross sections 15 mm apart; the corresponding distance is 40 mm, for two feelers 45° apart. Each feeler is attached to the magnetic core of a displacement transducer with a 4 mm stroke and the accuracy 1 \i. Fig. 1 shows the in-situ operation of a dilatometer.


On décrit l’expérience acquise par le LNEC au cours de 387 essais réalisés avec le dilatomètre et qui faisaient partie de 9 programmes couvrant une vaste gamme d’intérêts dans le domaine du génie civil. Les exemples donnés montrent la fidélité du dilatomètre LNEC en tant qu’instrument permettant d’atribuer in indice de qualité aux massifs rocheux, particulièrement important pour leur caractérisation en ce qui concerne la déformabilité.


Man beschreibt die Erfahrung, die das LNEC aus der Durchführung 387 Dilatometer-Versuchen gewonnen hat. Diese Versuche gehörten zu 9 Programme, die einen grossen Bereich der Ingenieurswesensinteresse umfassten.

Die angegebene Beispiele beweisen die Zuverlässigkeit des LNEC- Dilatometers als ein Instrument, das die Bestimmung einer Qualitätszahl des Gebirgs gestattet, die besondere Bedeutung für die Charakterisierung bezüglich auf die Verformbarkeit hat.

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