| Rock masses containing joints and fissures are a complex type of media commonly existed in rock engineering in cold regions such as dam foundations,slopes,tunnels and underground caverns.Because of repeated freezing and thawing,it will result in the damage,strength deterioration and continuously increasing deformation in the rock masses,which will further affect the stability during excavation and operation.With the massive rise of engineering construction in the cold regions,especially the increasing freeze-thaw(F-T)geotechnical problems along the upcoming construction of the Sichuan-Tibet Railway need to be solved.F-T cycling induced damage is currently a prominent problem in cold region engineering.Previous studies have mostly been on rock specimens containing straight or plane flaws,and it is common in nature for rocks with arc-shaped joints to be found,therefore its damage and strength deterioration mechanism under F-T cycling conditions need to be further investigated.Based on the above issues,we select the sandstone-like specimens with arc-shaped flaws as the research object and adopts the research methods combining laboratory tests and discrete element method(DEM)to explore the mechanical properties,damage characteristics and failure mechanism of the rock-like specimens subjected to F-T cycles and uniaxial compressive loading.The following works have been conducted and some findings have been concluded:(1)A newly developed highly brittle cement mortar is developed as a type of rock-like material.We adjust the chord length l corresponding to the arc-shaped flaw,the values of the central angle a and the inclination angle ? to prefabricate rock-like specimens with different arc-shaped flaws.After 28 d of constant temperature maintenance,F-T cycling tests,uniaxial compressive tests and scanning electron microscopy tests are carried out on different groups of specimens.Stress-strain curves and relevant physico-mechanical parameters of the specimens are obtained.The variation regularity of F-T coefficient and modulus of elasticity has been analyzed.Subsequently,we have summerized the F-T damage characteristics and failure mechanism of rock-like specimens containing arc-shaped flaws.Moreover,the microscopic electron microscopic images of particles on the damage surface of the specimens and the macroscopic crack extension patterns of the specimens after uniaxial compression damage,combined with the scanning electron microscope test,have been used to analyse the evolutionary processes of the emergence,extension and interaction of microcracks and the mechanical damage evolution mechanism in rock specimens containing arc-shaped flaws.(2)To further investigate the mechanical properties of ice filled jointed rock masses in cold region engineering,ice-filled flaw specimens are produced by immersion freezing of the specimen,a comparative analysis of the similarities and differences between rock-like specimens without and with filled ice in uniaxial compression tests,in terms of both mechanical properties and damage modes,and the following conclusions have been obtained:lower modulus of elasticity,higher peak strength and higher strain values obtained in uniaxial compression tests for rock-like specimens with ice filling at the same angle of circularity a and angle of inclination ?,change in damage mode from brittle damage to ductile damage when not filled with ice,analysis of the microscopic electron microscopic images of the fracture surface obtained by scanning electron microscopy shows that the filling of the ice intensifies the squeezing effect between the particles inside the specimen and increases the microcracks on the fracture surface and leads to a larger roughness of the overall fracture surface.(3)Based on the above laboratory experiment test results for rock-like specimens with arc-shaped flaws,the two-dimensional particle flow software PFC2D is used to construct a numerical model of a specimen containing arc-shaped ice flaws,the specimens were calibrated for fine mechanical parameters,secondary development of a simulation program for uniaxial compression of specimens with arc-shaped ice flaws after F-T cycles using PFC2D's own FISH language,numerical simulations of uniaxial compression processes in specimens containing ice-filled flaws(including both unfrozen-thawed and frozen-thawed conditions)have been carried out using the corresponding procedures.The feasibility and validity of the secondary development procedure is verified by comparing the laboratory experiment results and numerical simulation results of the specimens with arc-shaped ice flaws under the condition of no F-T cycles,and the F-T damage characteristics and crack extension mechanism of the specimens with prefabricated arc-shaped ice flaws are further analysed and studied,and the following conclusions are obtained:a)Sandstone-like specimens containing ice have higher peak strength,peak strain and F-T coefficients but lower modulus of elasticity for the same circular angle ?,dip angle ? and number of F-T cycles n compared to non-ice filled rock-like specimens.b)During the uniaxial compression simulation tests shear cracks develop slowly and evenly around the ice filled cracks,followed by a rapid increase in tensioning cracks and the formation of main cracks.c)The higher the number of F-T cycles,the faster the stress-strain curve decreases and the more brittle the damage is,with the highest peak strength for specimens containing prefabricated arc-shaped flaws with a 90° circular angle and a 90° angle between the two endpoints of the arc-shaped flaws and the horizontal line(?=90°,?=90°)and the lowest peak strength for specimens containing prefabricated arc-shaped flaws with a 90° circular angle and a 45° angle between the two endpoints of the circular fissures and the horizontal line(?=90°,?=45°)... |
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