New approaches to the characterization of clay-bearing, densely jointed and weak rock masses

Various classification systems for rock masses have been used in engineerin g applications. However, these systems are not sufficient to classify clay- bearing, densely jointed and weak rock masses. Among the factors that cause this deficiency are the damaging effect of water on rocks, which has not s ufficiently been described in the existing classification systems. This fac tor was allowed for by the inclusion of new parameters in the modified rock mass classification (M-RMR) system developed in recent years. The aim of t his study is to make contributions to the M-RMR classification system and t o overcome the difficulties encountered in the classification procedure. Fo r this purpose, data were collected for rock mass classification from 13 cl ay-bearing, densely jointed and weak rock masses in four regions (Yatagan, Soma, Baskoyak and Guvenc) located in the western and middle parts of Turke y. The discontinuity data were collected by the line-survey technique and e valuated by statistical methods. In addition to the uniaxial compressive st rength test for the determination of the rating for intact rock strength, t he block punch index test was also considered as an alternative parameter, and the slake durability index test and X-ray diffraction analyses were per formed on 104 samples collected from the studied rock masses. Further, the weathering coefficient (W-c) determined by Schmidt hammer was considered as an alternative parameter for the determination of the rating for joint wea thering. As a result of statistical evaluation of data obtained from the fi eld and laboratory studies, it has been concluded that the block punch inde x (BPI) could be used as an alternative parameter for the determination of the rating for intact rock strength in the M-RMR classification system. It was also found that the slake durability index (I-d) determined at the four th cycle would be a more effective approach than the second-cycle index tha t has previously been used to express the unfavourable effect of water on t he rock mass. The propositions made in the present work to contribute to th e M-RMR system were tested in back analyses of three previously failed slop es, and the performance of the system with the newly introduced improvement s appeared to be satisfactory. (C) 2000 Elsevier Science B.V. All rights re served.