In this paper a contribution for the interpretation of the dilatometer tests (BHD), and assessment of reading errors due to dilatometer displacements during the testing is presented, as well as a new type of flat Jacks to apply in large flat jack tests (LFJ). A new device for applying axial forces to the test core of the STT method for the determination of the complete state of stress, and the interpretation of the biaxial and triaxial tests to obtain the elastic constants are also presented.
dans ce travail on presente une contribution pour l'interpretation des essais au dilatomètre (BHD), et I' evaluation des erreurs de mesure dûs aux deplacements de l'appareil pendant l'execution des essais, ainsi que le nouveau type de verin plat à utiliser dans des essais LFJ. On presente aussi un nouveau système qui permet I'application d'une force axiale à la caroue de sondage qui contient la cellule tridimensionnelle (STT), et l'interpretation des essais biaxiaux et triaxiaux relatifs a ce type d'appareillage.
In diesem Referat wird einen Beitrag zur Interpretation der Dilatometerversuche mit dem BHD geliefert und die Ablesefehler erörtert, die durch Bewegungen, die der Apparat wahrend der Versuchsdurchfuehrung erleidet, verursachten werden. Fernerhin, werden die neuen Geratetypen vorgestellt, die in den Versuchen mit groβflachigen Druckkissen (LFJ) und mit dem tridimensionalen Verformungsmesser (STT) benutzt werden, sowie die Interpretation der zu diesem Meβapparat gehörigen Biaxialversuche.
The construction of large works on rock masses, has involved the thorough study of their mechanical characteristics and their state of stress. The assessment of these characteristics entails the execution of several types of tests, which make it possible to obtain a satisfactory knowledge of the rock mass behaviour, during and after the execution of the projects. Among the relevant mechanical characteristics, it can be pointed out the deformability and the initial state of stress of the rock masses. The deformability may be determined by several methods. Due to their importance, the following are noteworthy: the dilatometer (BHD) and the large flat jack (LFJ), the the former being used along boreholes and the latter on the surface or inside adits. For assessing the complete state of stress in the rock masses several strain cells to be used in boreholes among them the LNEC 3D stress tensor tube (STT) are noteworthy. The Purpose of this paper IS to give some useful indications for the interpretation of such tests, to point out some precautions that should be taken during tests and to present new types of equipment for improving the quality of the testing and the interpretation of the results obtained.
The interpretation of the dilatometer tests is rather difficult, due to the variation in the behaviour of the rock mass during the tests. Thus, if the initial stress (σi) of the rock mass is not null, the application of the pressure (p) at the borehole wall by means of a dilatometer, in a first stage, will decompress the rock mass in a perimetral direction, all the mass being, in this way under compression. With the increase of the pressure, the perimetral stress compressive will decrease until tensile stresses occur. During this second stage there in a change in the lest conditions, deriving from the different behaviour of the rock mass in tension with a tensile zone next to the hole and a compressive zone which is exterior latter. By increasing the pressure, a third stage is obtained.