The data processing method and the practical method to measure surface topography of rock structure faces by segment in field are studied in this paper. The surface topography of a great deal of rock structure faces are measured at the dam site of the Three Gorges Project on the Yangtze River in China. The fuzzy synthetic judgement to topographic characteristics of rock structure faces is made with three topography parameters. Various types of rock structure faces at the project are graded in terms of the indices of synthetic judgement. Based on the topography measurement results and the information of in-situ shear tests, the relationship between indices for synthetic judgement and friction coefficients of rock structure faces is set up, which in turn leads to the evaluation of their friction coefficients by the indices of synthetic judgement of various types of rock structure faces.
The deformation and failure of rock masses are controlled by mechanical behaviour of rock structure faces, and the surface topography of rock structure faces is one of the most primary influencing factors of their mechanical behaviours. The root of mean square of surface slope i is used by Patton to describe this influence (Patton, 1966). Barton put forward ten typical profiles of rock joints in order to explain rough degree of surface of rock structure faces and joint roughness coefficient (JRC) to describe the effects of surface topography on their mechanical behaviours(Barton,1976). Swan measured surface topography of rock structure faces and calculated their topography parameters that is used for predicting their shear behaviours(Swan,1985).' Sun chose three of many parameters of surface topography to grade rock structure faces and predicted their friction coefficient(Sun, 1991). In this paper the theory and method to measure surface topography of rock structure faces in field are studied. According to the information of in-situ shear tests, the field rock structure faces are graded by fuzzy synthetic judgement method and the evaluating values of friction coefficients of various kinds and grades structure faces are obtained.
The method of profile line measurement is one of basic methods to measure surface topography of rock structure faces. Because surface topography of field rock structure faces usually stretch long while the measurement range of profilometers is limited, surface topography can be measured only by segment. When the parameters of surface topography are calculated, all measurement data must be based on the same reference line, which is not easy to be ensured in segment measurement of profile line. As the reference line of every segment can be defined arbitrarily and the dip angle of reference line relative to horizontal plan can be measured, the included angle between reference lines of any two segments can also be determined. On the other hand, the terminal point of former segment is the starting point of next segment. Site relationship of data points in every segment can be determined completely. So the data points of various segments.
