| In order to meet the social needs brought by the rapid economic development of our country,large-scale water conservancy projects have been planned,constructed and put into operation.And the stability of high rock slope has become one of the main rock mechanics problems in the construction and operation of these projects.The slope rock mass often breeds geological structural surfaces with discontinuous characteristics,which have an important influence on the deformation and failure characteristics of the slope.Locked section type rock landslide is a common deformation and failure mode of high slope.What's more,there is a relatively good rock bridge locked section in the sliding zone,which controls the stability of rock slope.Therefore,it is of great significance to study the crack initiation and propagation laws of rock bridges in the locked section to reveal the failure mechanism of the high rock slope in the locked section.In this thesis,we generalized the locking section of the slope rock bridge into a rock bridge test piece,used red sandstone as the test material,and utilized high-speed waterjet cutting technology to process cracks to prepare rock bridge specimens with different rock bridge lengths.In addition,we conducted uniaxial compression experiments on these rock bridge specimens,and introduced fractal theory and infrared thermal imaging technology to quantitatively study the characteristics of the whole process of rock bridge failure.The main research work of this thesis can be summarized as follows:(1)According to the stress-time curve characteristics and crack propagation characteristics during the loading process of rock bridge specimens,the failure process can be divided into pore fissure compaction,elastic deformation,unstable fracture development and post-failure stage.In the post-failure stage,the stress-time curve exhibits a significant "back-to-peak rise" characteristic.(2)We used the box dimension method to calculate the fractal dimension of the crack propagation path during the loading of the rock bridge specimen,quantitatively characterized the fracture evolution characteristics of the specimen,and discussed the correlation between the fractal dimension and crack propagation.The study found that thenew cracks generated during the rupture and evolution of rock bridge specimens have morphological self-similarity,that is,fractal characteristics.The fractal dimension gradually increases from the stage of unsteady rupture development,and shows a "catastrophic rise" characteristic after the "post-peak recovery" stage.The data fitting results show that the axial strain and the fractal dimension follow a hyperbolic relationship.When the increment of fractal dimension of the rock bridge specimen reaches 2.56% ? 2.97%,the specimen starts to crack;when 5.14% ? 6.71%,it is in peak stress state;when 14.28% ? 16.74 %,the test piece completely loses its carrying capacity.(3)We combined the infrared thermal imager to define the maximum value(MAXIRT),minimum value(MINIRT),average value(AIRT),coefficient of variation(CVIRT)and skewness coefficient(SIRT)of the infrared radiation temperature field,and quantitatively study the spatial and temporal evolution characteristics of infrared radiation temperature field during loading of rock bridge specimens.It was found that CVIRT and SIRT can better describe the infrared radiation temperature characteristics of rock bridge and show the stage characteristics compared with the three traditional indicators MAXIRT,MINIRT and AIRT,which are closely related to the stress state of rock bridge,the degree of pore compaction and closure,the initiation,propagation and breakthrough of new cracks.At the "post-peak recovery",CVIRT and SIRT both show the precursor characteristics of "abrupt" rise. |
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