Hazard Assessment of Bedrock Discontinuities Using Integration of Structural Data and Geotechnical Characterization: A Case Study from the Northern Galala Plateau, Egypt

Discontinuities represent a significant role in the deformation of foundation bedrocks and the stability of many slopes. Moreover, assessing and analyzing the different slope failures through fieldwork and laboratory tests of the intact rock mass is important to determine discontinuities' geometrical and geo-engineering parameters. The Northern Galala Plateau is considered a typical case study of instability problems due to excessive bedrock discontinuities. The present study deals with the mapping and assessment of bedrock (Paleozoic sandstones) discontinuities using structural mapping/analysis and geotechnical qualifications as an integrative approach. The study was started by collecting structural data, joint surveying and delineating fault zones as well as highly fractured zones. In addition, the geotechnical qualifications and stability of slopes were assessed using kinematic analysis and Rock Mass Rating (RMR) of discontinuity sets at the lower slope. Quantitative descriptions and statistical distribution of fractures at the study site were well defined. The kinematic analysis of sandstone bedrock masses revealed wedge and/or toppling failures which are controlled by uncomplimentary discontinuities. As a result, RMR values suggested the majority of foundation bedrock is classified as good rock II category, whereas RMR for the fault zone is classified as fair rock III category. Furthermore, discontinuities could not necessarily lead to instability problems during and after construction. The present study highlights the influence of integration between both structural and geotechnical techniques for suitability assessment in development processes which in turn could provide important keys for decision-makers.