Chryssanthakis, P. (Norwegian Geotechnical Institute) | Westerdahl, H. (Norwegian Geotechnical Institute) | Rose, E. (Norwegian Geotechnical Institute) | Rhett, D. (Phillips Petroleum Company) | Pederson, S. (Phillips Petroleum Company)
Fecker-Rengers-Barton's methods were combined within a computer program, using profiles taken from replicas of a natural joint surfaces digitized at 0.5 mm sampling distance. The program can give the distribution of slope angles integrated over all the profiles. The distribution of maximum angles for various base lengths of asperities and the corresponding dilatancy for these maximum angularities were computed using Rengers equation to obtain its behavior in relation with asperities base length (or shear displacement) under null normal stress. An experimental verification of this analog simulation was performed through a direct shear test program on a well-studied replica of a natural joint under null normal stress (pushtest) for four different shear directions. The dilatancy characteristic results obtained from this testing program compared to those from the analog simulation show a relatively good agreement and permits an evaluation of the directional anisotropy of dilatancy.
The mechanical behavior of jointed rock masses must be predicted on the basis of the joint spatial distribution and the roughness morphology of their surfaces. All experimental findings clearly indicate that the roughness is the dominant factor affecting all aspects of mechanical and coupled behavior of rock joints. Unfortunately, an adequate and unique mathematical representation of roughness has not been realized and remains a great challenge. The current measures of JRC and fractal dimension cannot characterize the joint roughness uniquely and adequately. Unless a major breakthrough in this subject is made, no reliable joint model can be developed (Stephansson & Jing 1995). The usual 2D roughness parameters are insufficient to describe the joint wall surfaces completely. It is now clear that changes in morphology during shear displacement can not be characterized by the only classical statistical parameters, inefficient to explain the stress distribution and mechanical behavior (Riss et al. 1995).
The more important features, characterizing joint roughness during sheafing, are the slope gradient or angularity of asperities, their height distribution and the structures of the morphology over the joint surfaces that control dilatancy and its directional anisotropy which in turn control the joint shear strength, joint stiffness and joint degradation with shear displacement. Promising methods of joint roughness analysis were developed during the last fifteen years, particularly those related to 3D angularity of asperities definition and distribution as well as, the use of geostatistical methods to characterize roughness structures, anisotropies and degradation with shear displacement and even restitute the joint surfaces before and after sheafing (Roko & Daernen 1988, Gentier & Riss 1990, Riss et al. 1995). But even those powerful methods of roughness analysis do not give reliable parameters that can be integrated in a joint stress-dilatancy model satisfactorily. One way to overcome the difficulty, for the moment, is to characterize the dilatancy behavior directly from 2D profiles basic data using the distribution of extreme roughness angles at increasing base length as proposed in the Fecker-Rengers approach.
Senjuntichai, Teerapong (University of Minnesota) | Detournay, Emmanuel (University of Minnesota) | Berchenko, Ilya (University of Minnesota) | Chandler, Neil (Atomic Energy of Canada Limited, Whiteshell Laboratories) | Martino, Jason (Atomic Energy of Canada Limited, Whiteshell Laboratories) | Kozak, Ed (Atomic Energy of Canada Limited, Whiteshell Laboratories)
Cabrera, J. (Institut de Protection et de Surete Nucleaire) | Volant, P. (Institut de Protection et de Surete Nucleaire) | Baker, C. (Applied Seismology Consultants Limited) | Pettitt, W. (Applied Seismology Consultants Limited) | Young, R.P. (Keele University)