Quality Evaluation And Stability Analysis Of Clastic Bank Slope Rock Mass In The Three Gorges Reservoir Area Based On In-situ Drilling Test

Clastic rocks have a wide distribution,complex slope structure and diverse lithology,and exhibit different forms of rock deterioration after being affected by reservoir water and weathering.Compared with carbonate rocks,clastic rocks are more obviously affected by reservoir water and weathering,and the quality of rock mass is reduced more rapidly.The Three Gorges reservoir area in Hubei has a wide distribution of clastic rocks and a large number of developed geological hazards.It is important to analyze the stability of the rock mass of the shore slope through the evaluation of the rock mass of the shore slope for the safety of the residents in the reservoir area,the safety of shipping and the operation of the reservoir.This paper analyzes the characteristics of the borehole images of clastic rock slopes in the Three Gorges reservoir area based on the borehole image test,and proposes a rock quality evaluation method based on the borehole longitudinal wave velocity and the borehole images,and further analyzes the stability of the rock slopes by combining the laminar fracture production and the reservoir bank structure revealed by the borehole images.The main research contents and conclusions of this paper are as follows:(1)The characteristics of borehole images of clastic reservoir bank rock masses in the Three Gorges reservoir area in Hubei are analyzed,and the rock mass image characteristics are divided into four categories: first,sedimentary layering type,where the two types of lithologies have obvious sedimentary interfacing;second,soft filling type,where the nature of the filling layer differs greatly from the adjacent rock masses,and the filling is formed by fracture water transport,deposition to fill or the rock masses on both sides of the fractures are dislodged to form the filling;third,fracture zone type,where the fractures are densely developed and The rock integrity on both sides is good,the fracture spacing of the fracture zone is small,and the thin laminated rock between some fractures is cut by longitudinal fractures,showing a fractured shape;fourth is axial fracture cutting type,the intersection angle between drilling direction and fractures is small or nearly parallel,and the extension range of fractures in the hole is long.(2)A rock integrity evaluation method(RQ method)is proposed based on the correspondence between fracture characteristics of cores and fracture characteristics of borehole images.The applicability of the index was verified by comparing with the results of conventional RQD and acoustic testing.The method can accurately locate the sedimentary layered structure,weak filling structure and fracture zone structure of the rock mass more precisely,and quantitatively describe the influence of different interval lengths on the integrity of the rock mass.(3)By analyzing the relationship between geological strength index(GSI)and RMR89,the relationship between rock integrity,nodal conditions and scoring values in the GSI chart was derived.The quantitative evaluation method of GSI based on borehole test results was constructed by quantifying rock integrity with RQ and introducing rock longitudinal wave velocity to quantify rock weathering degree parameter Rw.The method uses RQ values to reflect the internal block characteristics of the rock mass and longitudinal wave velocity to reflect the physical and mechanical properties of the rock mass,and achieves quality evaluation over the full length of the borehole through the complementary advantages of the two borehole testing techniques.Finally,the feasibility of the method was verified through the comparison of multiple methods.(4)Two bank slopes with different structures in Shazhenxi Town Sewage Treatment Plant and Hejiawan were selected,and the quality of the bank rock mass was evaluated by using the GSI quantitative evaluation method through the actual measured data of the boreholes,and the influence on the stability of the bank was analyzed by the deflating projection method to infer the range of the potential sliding surface of the bank by combining the nodal fracture production revealed by the borehole images.The results show that the rock quality of the bank of Shazhenxi Town sewage treatment plant varies greatly,and the unstable conditions exist in the range of11.5～13.7m in QGZK3 borehole,which is located in the 1.5～2.2m thick rock fragmentation zone,and the sliding may occur along this fragmentation zone;the rock quality of the bank of Hejiawan gradually becomes better with the increase of borehole depth,and the potential sliding surface of the bank slope may develop in GZK9 borehole The potential sliding surface of the bank slope may be developed near the location of GZK9 borehole 16.2～17.5m and GZK10 borehole 12.4～13.2m.