Crack Propagation Mechanism And Damage Characteristics Of Rock Mass With Filled Joints Under Dry-wet Cycles

Due to environmental factors such as rising and falling of the underground water and rainfall,the rock and soil mass in natural state is frequently under the actions of dry-wet cycles.As the common construction media in the engineering,the mechanical properties of jointed rock masses are significantly affected by dry-wet cycles.Damage and macroscopic destruction of jointed rock masses due to dry-wet cycles are significant factors in triggering a series of geohazards such as landslide and bank collapse.Therefore,it is of great theoretical significance and application value to carry out research on the crack propagation mechanism and damage characteristics of jointed rock masses under different dry-wet cycles.It is also important for the rock stability analysis and engineering geohazards prevention.The current research on engineering rock masses under dry-wet cycles mainly focuses on mechanical properties and damage characteristics of intact rocks,and there is a lack of research on the filled jointed rock masses subjected to dry-wet cycles.Therefore,in this paper,a combination of laboratory tests and numerical simulations is used to investigate the crack propagation mechanism and damage characteristics of rock mass with filled joints under dry-wet cycles.The uniaxial compression test,nuclear magnetic resonance(NMR)test,discrete element method(DEM)and other research methods have been used to conduct an in-depth study on this hot topic.The work conducted and the related results are summarized as follows:(1)Prefabricated jointed red sandstone specimens with infillings and intact red sandstone specimens have been prepared,and dry-wet cycling tests are conducted.The mechanical properties and damage characteristics are investigated by uniaxial compression tests.The macroscopic mechanical properties and damage characteristics of red sandstone specimens are compared and analyzed in terms of the number of dry-wet cycles and the structure of the prefabricated filled joints.The results show that the filled joints have a guiding effect on the crack propagation.The peak stress and elastic modulus of the specimens show an exponential decay with the increase of the number of dry-wet cycles.(2)X-ray diffraction(XRD)technology is used to quantify the mineral components of prefabricated filled joint specimens under different dry-wet cycles.The loss of the main mineral components in the specimens is investigated,and the effects of dry-wet cycles on the mineral composition of the filled jointed red sandstone are analyzed.The results show that the mineral composition,mainly the albite,has been gradually dissolved in water or reacted with water under dry-wet cycles.The loss of this mineral composition leads to the increase of the pore volume of specimens,which in turn causes the deterioration of its strength.(3)The porosity variations of prefabricated filled jointed specimens under dry-wet cycles have been analyzed using the NMR test.The pores and pore throats of different sizes are classified,and the transformation law of their contents with dry-wet cycles is studied.The damage and degradation mechanism of filled jointed red sandstone under dry-wet cycles are analyzed from the microscopic perspective.The results show that the dry-wet cycles affect the porosity of the specimens.The pores inside the specimen are transformed from small to large size in the process of dry-wet cycles,which can lead to the development of pore connectivity in the specimen.This phenomenon is a reflection on the deterioration of macroscopic mechanical properties from the microscopic perspective.(4)A numerical model with similar macroscopic mechanical properties to the laboratory tests has been established using two-dimensional particle flow code(PFC2D)based on DEM.The process of dry-wet cycles on rock specimens has also been numerically simulated by a secondary development through the FISH language in PFC2D and a calibration of microscopic parameters.The dry-wet cycle process of filled jointed red sandstone specimens is simulated and the reliability of simulation results is verified based on the macroscopic mechanical parameters and damage characteristics obtained from laboratory tests.(5)Numerical simulations have been performed based on numerical models of filled jointed red sandstone specimens after dry-wet cycles.The evolution patterns of crack propagation,stress field and microscopic mechanical parameters have been monitored.The effects of prefabricated filled joints and dry-wet cycle conditions on the damage modes and microscopic mechanical properties of the specimens have also been analyzed.The results show that the stress difference generated from stress concentration area leads to the initiation and propagation of cracks,which is the main cause of the damage phenomenon of specimens.The stress concentration generated at the tips of the prefabricated filled joints affects the redistribution of the stress field in the specimens,which in turn directs the crack propagation.Meanwhile,dry-wet cycles accelerate the process of stress concentration and the damage of the specimens.