| The rock mass has defects such as joints,structural planes,and voids that affect the mechanical properties and fracture modes of the rock mass,For example,for a large number of columnar jointed basalt exposed in the construction of hydropower stations,the column contains many hidden fissures that affect the strength and stability of the rock mass.Therefore,the mechanical properties of rock masses not only depend on the rock itself,but also on various defects.At present,there are few studies on the impact of the hidden fissure on the engineering rock mass.Therefore,it is necessary to carry out relevant research to guide the engineering design of water conservancy and hydropower projects and deep rock mass projects.In order to facilitate the study,this paper uses prefabricated hidden fissures to carry out indoor tests,combined with high-speed camera and acoustic emission monitoring methods,using DIC method and acoustic emission parameter analysis method for analysis,and then using PFC2 D program to carry out numerical simulation for verification,in order to further analyze the internal fracture mechanism of rock materials with prefabricated hidden fissures.The main research work and conclusions of the thesis are as follows:(1)The feasibility of making prefabricated hidden fissure-like rock samples is analyzed.The feasibility includes the method of prefabricating hidden fissures,the selection of similar materials,and the production of rock-like specimens.Gypsum and water are selected as similar materials and after many ratio tests,it is finally determined that the ratio of gypsum and water is 3:1.(2)Based on the uniaxial compression laboratory test,the effects of different inclination angles of the hidden cracks on the stress-strain curve,strength and rupture mode are studied,and compared the test results of prefabricated specimens with open cracks,and analyzed the similarities and differences of the effects of hidden cracks and open cracks on the stress-strain curve,peak strength and fracture mode of the specimens.(3)Acquire the acoustic emission signal through the acoustic emission monitoring system and use the acoustic emission parameter analysis method(count,cumulative count and RA-AF)to explore the fracture mechanism of the prefabricated hidden fissure specimen and compare the acoustic emission parameters of the prefabricated specimen with open cracks The similarities and differences between the two rupture mechanisms are analyzed.Prefabricated specimens with open cracks are mainly tensile-shear mixed fracture,while for prefabricated specimens with hidden cracks,tensile fracture is the main type,and shear fracture is supplemented.(4)The parallel bonding joint model in the PFC2 D program was used to construct the model,the smooth joint model was used to simulate the hidden cracks,and the calibration methods and principles of the PFC meso-parameters were discussed.A set of reasonable meso-parameters was obtained by calibrating the data of the complete sample in the laboratory test;and then verified the failure mode and failure mechanism of the rock material with prefabricated hidden fissures. |
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