| In recent years,the hydropower,transportation and mining projects develop rapidly in China,and a lot of rock slopes under complex conditions are encountered in these projects.Therefore,the rock mechanics are increasingly important for the evaluation and prevention of rock slope engineering.The bedded rocks are the most common rock types for constituting the rock slopes,and they are usually cut into complex geo-masses by the bedding planes and structural flaws.Since the bedding planes form in the diagenesis and the structural flaws are triggered by the tectogenesis,they play distinct roles in the deformation of the bedded rocks and slopes.Up to date,although plenty of researches have been conducted on the bedded rocks and slopes,some critical issues still remain to be solved.These issues include:the co-effects of the bedding plane and structural flaw on rock rupture and mechanical behavior,the strength criterion of the bedded rock with anisotropy incorporated,the failure types of the bedded rock slopes and the relative fracture evolution,the local failure probability of the bedded slopes,etc.In the current dissertation,we conduct a comprehensive study on these issues by using the methods of laboratory experiments,analytical calculation and geological analysis.The main contents and results of the study are as follows:The fracture evolution and mechanical behavior of the bedded rock containing a structural flaw are investigated.We have developed the method,technique and procedure for manufacturing artificial bedded rocks.A series of bedded specimens with different bedding and flaw inclinations are prepared for uniaxial compression tests.The stress-strain data and fracturing images are both recorded in the testing process for investigating the fracture evolution.The results are as follows:?1?Four stress-strain curve types,nine crack types and five failure modes are observed from the recorded data.The mechanical parameter,crack types and failure mode are highly correlated with bedding and flaw inclinations.?2?The bedding inclination exerts little effect on the elasticity modulus but great effect on the uniaxial compression strength and the axial strain at the peak stress.Both of the latter two present a decrease-increase trend with bedding inclination.As the flaw inclination changes from-90 to 90°,both of the uniaxial compression strength and elasticity modulus show a decrease-increase trend,and the axial strain at the peak stress decrease progressively.?3?The effect of bedding inclination on fracture distribution:by increasing the bedding inclination,the crack initiating from the flaw tends to propagate along the bedding plane,and even results in sliding failure along the whole bedding plane;as the bedding inclination increases to90°,the bedding splitting fracture is the main crack type.The effect of flaw inclination on fracture distribution:the bedding sliding fracture is the main crack type in the specimens containing pro-dip flaws,but multiple tensile cracks initiate in the specimens containing anti-dip flaws in addition to bedding sliding fractures.Besides,the accumulative length of the bedding fractures is positively related to the bedding inclination,but shows weak relationship with the flaw inclination.?4?The effect of bedding inclination on failure mode:with the increase of bedding inclination,the failure mode transfers from purely tensile failure to mixed tensile-shear failure,and ultimately to splitting failure.The effect of flaw inclination on failure mode:the specimen containing pro-dip flaw fails as the bedding shear nature,but the specimen containing anti-dip flaw fails as mixed tensile-shear nature.The facture evolution and mechanical behavior of the bedded rock containing parallel structural flaws are investigated by uniaxial compression tests.?1?The results are as follows:three stress-strain curve types,five crack combination types and eight crack coalescence types are observed from the tests,and they are all dependent on the bedding angle,bridging angle and flaw inclination.?2?The stress-strain curve transforms from the gradual-decline type to the sharp-drop type with the increase of the bedding angle.The brittle failure is more possible to occur in the specimen with positive bridging angle than that with other bridging angles.?3?The effect of bedding angle on mechanical parameters:by increasing the bedding angle,the uniaxial compressive strength shows a decrease-increase trend,the elasticity modulus respectively shows an increase-decrease trend and an increase trend when the bridging angle is less and greater than 0°,and the coalescences stress ratio shows an increase-decrease trend.The effect of bridging angle on mechanical parameters:by increasing the bridging angle,the uniaxial compressive strength remains steady,the elasticity modulus respectively decreases for shallow bedding plane and increases for steep bedding plane,the coalescence stress ratio respectively shows a decrease-increase trend for pro-dip flaw and an increase-decrease trend for anti-dip flaw.The effect of flaw inclination on mechanical parameters:as compared to anti-dip flaws,the specimens containing pro-dip flaws has larger uniaxial compressive strengths,low-variety elasticity modulus and similar coalescence stress ratios.?4?Crack distribution:By increasing the bedding angle,the main crack types transform as follows:ordinary tensile crack,tensile crack containing bedding sliding portions,bedding sliding fracture and bedding splitting fracture.The en-echelon crack is more possible to initiate in the specimens with positive bridging angle than those with negative bridging angle.The step-form crack is more likely to occur in the specimens containing pro-dip flaws than those containing anti-dip flaws.?5?Crack coalescence:By increasing bridging angle,more bedding fracture portions initiate within the ordinary cracks.By increasing bridging angle,coalescence transforms from indirect to direct categories.The direct coalesce are more likely to occur in the specimens containing anti-dip flaws than those containing pro-dip flaws.The bedded rock is examined to confirm to parabola strength criterion.The parabola strength criterion for bedded rocks is proposed by introducing two anisotropic mechanical parameters(i.e.,k?and?c?)into that for homogeneous rocks.The proposed criterion incorporates both the influence of inclination of the bedding plane on rock strength,and the strength characteristics under high stress state.The shape of the parabola strength criterion envelope is controlled by k?,while?c?affects only the strength level.The results verified by 466 experimental data indicate that:?1?The parabola strength criterion gives results that are in high agreement with the experimental results,and shows less error than the McLamore-Gray criterion and Tien-Kuo criterion.?2?The prediction errors of parabola strength criterion for the data measured under high confinement are lower than that under low confinement,and higher for sliding failure along the bedding plane than non-sliding failure.?3?The prediction is effective even though the experimental data used for prediction is reduced,which indicates the reliability of the parabola strength criterion under the condition of limited experimental data.The failure modes for bedded rock slopes are summarized,and the evolution of fractures in bedded rock slopes containing joints is analyzed.The bedding planes dominate the failure of the bedded rock slope,meanwhile the joints and free surface have influence on the failure.According to the inclination of the bedding plane,the bedded rock slopes are classified into five categories,which respectively corresponds to the failure mode of horizontal slopes:?creep-tension failure?,bedded slopes?including planar failure,step-wise failure,sliding-collapse failure,wedge slip failure and deflecting sliding failure?,vertical slopes?including toppling failure and collapse failure?,steep anti-inclined slopes?including flexural toppling failure,blocky toppling failure,and blocky-flexural toppling failure?,and flat anti-inclined slopes?tension-shear composite failure?.Under the long-term effect of gravity,bedded rock slopes tend to fail by deep sliding or toppling,which is characterized by multi-scale failure behaviors:at the scale of local rock mass,visco-plastic creep deformation occurs associated with gradual expanding of tensile fractures and shear bands that has a time effect;at the scale of the holistic rock slope,the material structure,topography,morphology,etc.change gradually,and where is close to the earth surface and high localization of stress occurs has the significant changes.The uniaxial compressive tests on bedded rocks containing joints the can reveal the evolutionary process of fractures in bedded rock slopes.The calculation model for flexural toppling failure probability of anti-dip slopes is established,which consists of four steps,namely:establish the geomechanical model of the anti-dip slope,and randomly generate the physical and mechanical parameters confirming to the statistical distributions;determine the boundaries of the toppling area and sliding area;calculate the stability of each rock column from the slope toe to slope crest;obtain the local failure probability of the slope by iterative calculation.The calculation model can be applied to the analysis of the local failure probability of anti-inclined slopes under complex conditions.The study results show that:?1?The local failure probability decreases with the increase of the frictional angle of the rock,rock tensile strength or the frictional angle of the bedding plane,but increases versus the increasing gravity.The place of the rock column with the maximum failure probability changes with the change of gravity and tensile strength,but less affected by the frictional angles of the rock or the bedding plane.?2?The variations of gravity,the frictional angle of the rock,rock tensile strength,and the frictional angle of the bedding plane show influence on the calculation result in an ascending sequence,in which the frictional angle of the bedding plane has the most significant impact among the other three factors.?3?With the increase of the inclination of the bedding plane,the maximum failure probability rises and then declines.With the increase of the dip angle or height of the slope,or decrease of the dip angle the slope crest,the maximum failure probability exhibits gradual increase. |
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