On the Concept of two Preferred Planes and Its Analysis Methods

The deformation and failure of the rock slopes usually occur along the discontinuities that exist in the rocks. It is of extreme importance to analyse the occurrence, characteristics and cooperation with each other of these discontinuities.From the information that we know it is recognized that there exist various research models or ways:1. Simple modelFrom discontinuities to structural weakness plane.2. E. Hoek's modelFrom discontinuities through centre of pole concentration to preferred plane.There is no doubt that E. Hoek's model is of great value.According to these models, through the studies of rock slopes, such as Fuxikou of Hunan province,Qixiashan of Jiangsu etc. A new model has been gained from which we can explained as follows:From discontinuities to preferred plane:（statistical preferred plane Geo-preferred plane） True preferred planeTwo preferred planes are to be considered when analysing the stability. From thestudies of these two surfaces as the sum the true preferred plane is determined at last.The programme for engineering-geological investigation of geo-preferred plane is: a. Analysis of regional structural line;b. Research local compress fault;c. Measure three element of fault;d. Dividing faults into old, new and active;e. Seat for geo-preferred planes.The programme investigation of statistical preferred plane is;1. Space detail line survey;2. Pole equilibrium stereo-projection;3. Contour diagram;4. Find out pole concentrations;5. Seat for statistical preferred planes.Practice has shown that if we take the analysis methods mentioned in this paper, it will be effective and helpful to our work.