Experimental Research On Three-Dimensional Joint Morphology Quantification And Shear Strength Property Of Tensile Hard Rock Joints With And Without Cement Grouting

Natural rock mass is consists of rock blocks and discontinuities such as joint, fetures et al, these discontinuities have greatly weakened rock mass. Tensile hard rock joint is commonly encountered in large hydropower projects, this type of joints mainly appeared in hard rock, it is produced during tectonic movements, tension toppling and excavation unloading. Since shear strength of this type of joint is low, it greatly weakend hard rock and resulting in stability problem of rock structure. Therefore, tensile hard rock joints are taken as the main object of this study. Three-dimensional morphology quantification and shear strength property of this type of joints with and without cement grouting are researched by test and theoretical analysis in this paper.The main contents are as follows:(1) Research on three-dimensional joint morphology quantification.Tensile rock joint specimens are prepared by splitting method, laser scanning is used to study joint morphology characterisitcs, and a new three-dimensional roughness index is established based on statistical and fractal method. The new index has clear physical meaning, it has the advantage of being able to quantify main characteristics of joint morphology and being independent of measuring scale. Besides, different orders of joint roughness have also been considered, and it can be convenient used because of its easing requirements on morphology measuring scale.(2) Experimental research on shear strength property of tensile hard rock jointsShear strength and dilation property, morphology damage, and their evolution during cyclic shearing of tensile hard rock joints are researched by test. Test results shows that, shear strength of this type of joint is high, but it decreses rapidly after peak value as shear displacement increses; dalition effect is obviously observed during shearing and dalition displacement is large; morphology damage during shearing mainly occurs in the earea where local undulating angle is big; shear strength decreses during cyclic shearing as shear time increses, meanwhile the morphology damage increses.(3) Research on peark shear strength model of tensile hard rock jointsOn the basis of test results and theoretical analysis, a new three-dimensional peak shear strength model is established based on the new roughness index, and it is verified by test results. The new peak shear strength model has clear definition and is easy to use. It has the advantage of being able to describe anisotropy of peak shear strength, and caiculating result has high accuracy even when mearsuring seal is enlarged.(4) Experimental research on shear strength property of cement grouted tensile hard rock jointsCement grouted joint specimens are parepared, and its shear strength and dalition property, damage modes, and joint grouting mechanism are researched by test. Test results shows that, cement grouted joints has high shear strength, but it decresed sharply after peak value and residual shear strength is low; dilation effect is obviously observed but dilation displacement is small; shear damage mostly occurs on interface of joint wall and cement stone, but cement stone will be shredded when normal stress is high and cement filling percentage is small; in terms if grouting mechanism, cement grouting has added bond strength for joint interface but wekened joint contact condition.(5) Reserch on peak shear strength model of cement grouted tensile hard rock jointsOn the basis of test results and theoretical analysis, peak shear strength model of cement grouted tensile hard rock joints is established, and it is verified by test results. The peak shear strength model has clear physical meaning, it has the advantage of being able to describe anisotropy of peak shear strength, and it also welly reflects the influence of bond strength, cement filling percentage and strength ratio of joint wall-cement stone to peak shear strength of cement grouted tensile hard rock joints.(6) Experimental research on long term shear property of cement grouted tensile hard rock jointsCreep property and long term shear strength of cement grouted tensile hard rock joints are researched by test, and revised transition creep method to determin long term shear strength is established. Creep test results shows that, shear creep displacement is obviously observed during shear, only attenuation creep occurs when shear stress is low, but both attenuation creep and second period creep occurs when shear stress is high, accelerated creep has not observed during shear; long term shear strength dertermined by revised transition creep method is very close to that determined by method reconmmoned by speciofication, but the new method has the advantage of more convenient to use and has higher accuracy; the ratio of long term shear strength to peak shear strength of cement grouted hard rock joint is about 50% under experimental condition of this study.