Strength Characteristics Of Sinian Dengying Formation In Bedding Shear Zone Of Daguangbao Landslide

The strength of cataclastic rock masses is generally low in geological engineering,which caused by early tectonization,weathering,erosion and so on.Cataclastic rock masses are common in many large engineering projects and it seriously influences the safety of the project construction,such as high dams,military works,slopes etc.There exposed a bedding shear zone in the south side of the landslide and the rock masses are seriously broken,in addition,the Daguangbao landslide have occurred due to the presence of cataclastic rock masses,so Daguangbao landslide has received much research attention.Based on previous research and filed investigation,a series of mechanical tests including uniaxial compression testing,point-load testing,and wave velocity testing were carried out in the laboratory to study the mechanical strength and deformation of the cataclastic rock mass in Daguangbao landslide.A new method for obtaining the mechanical parameters of a rock mass is proposed based on the improved Hoek–Brown criterion.What's more,in this study borehole shear testing was carried out in the bedding shear zone in the field to compare with the Hoek–Brown criterion and the improved method.To summarize,the results as follows:Borehole shear tests were performed to obtain the stress–strain curve.The deformation curve can be divided into four regions: microscopic fracture closure,followed by elastic deformation,then development of microfractures,and finally fracture coalescence.The shear strength parameters in the bedding shear zone of cohesive C were 205.7 to 398.7 kPa and the internal friction angle was between 25.4° and 26.4°.Analyzing the problems and shortcomings in the field experiment,repeated crackles caused the test data to be less,it is verified that the Phicometre in situ borehole test instrument is only suitable for strong weathered rock and soil.This paper mainly focuses on improvement of the geological strength index GSI and the rock mass disturbance coefficient D.The structure plane surface grade SCR,the structure plane condition factor Jc,the rock mass basic quality index BQ,and the rock mass structure grade SR are considered.With this method,the GSI value is a set of possible numbers within given intervals rather than a constant value.The error will greatly decrease and the improved method is more reasonable than Hoek–Brown rock-mass strength criterion.The improved methods compared with the E.Hoek method,Yan method and Xia method.The strength parameters of rock mass predicted in four adit in dam site of hydropower station.Finally,the results are compared with field experiments,the results show that the improved method is more accurate and realistic,compared with the method of internal cohesion,the method is closer to the large shear test in the field,and the other methods of the internal friction angle are close to the large shear test.According to the filed investigantion,the characteristics of joint occurrences,roughness,aperture,filler,spacing,trace length,and weathering/erosion were examined.Uniaxial compression tests,point-load tests,and wave velocity tests were successfully conducted.The parameters obtained from those laboratory tests were incorporated into the improved Hoek–Brown formulas used to calculate the physical and mechanical parameters.The values of these parameters were as follows: cohesive form 0.435–0.66 MPa,internal friction angle 18.35°–24.95°,deformation modulus 1.9–3.1 GPa,and tensile strength 0.014–0.29 MPa.Comparing with the Hoek–Brown criterion,the results from the improved method are smaller and are closer to the values measured in borehole shear testing.It is found that there is a big difference between the two methods in the upper limit of the minimum principal stress,which results in the deviation of the results.But the results of the improved method are closer to the field test,Further reduce the deviation between the two methods,the empirical method is closer to reality.