Borehole imaging characteristics and quality evaluation methods of clastic rock slope in Three Gorges Reservoir area

The lithology of the strata in the Three Gorges Reservoir area is complex, and there is significant difference in the occurrence environment of the rock mass. There are many factors that affect the quality of the rock mass. Under the periodic hydraulic action, the clastic rock bank slope rock mass has formed a unique structural feature, which is unfavorable to the long-term safety and stability of the bank slope. Based on the survey and statistics of the characteristics of clastic rocks in the reservoir area, a large number of in-situ borehole tests were carried out, the typical borehole imaging characteristics of clastic rock of bank slope in the reservoir area were classified and summarized, and the block size and fracture characteristics of borehole cores of rock masses with different fracture characteristics were analyzed in detail. Based on the corresponding relationship between core fracture characteristics and borehole imaging fracture characteristics, the rock mass quality evaluation index RQ is established, and its applicability is verified by comparing with the traditional RQD and acoustic testing results. The research results show that the borehole imaging characteristics affecting the rock mass quality of the clastic rock reservoir bank in the Three Gorges reservoir area mainly include four structural types: sedimentary layered structure, soft filling structure, primary fracture zone and borehole axial fracture cutting. RQ takes into account the different structural types to divide the length zones of blocks, and quantifies the contribution of rock mass ratio in different regions to the rock mass quality evaluation value. Based on the internal structural characteristics of rock mass, the rock mass quality of clastic rock bank slope can be evaluated more objectively, avoiding the error introduced by mechanical damage during drilling and coring. The research results are helpful to analyze the quality distribution characteristics of clastic rock bank slope rock mass in the Three Gorges Reservoir area, and provide a theoretical method and technical idea for quantitative description of rock mass quality evolution.