Investigation On The Effect Of Natural Fracture On The Propagation Of Model ? Crack In High-Temperature Rock Mass

In the high temperature study of rock mechanics,it is generally considered that 25°is normal temperature,25 ? 900? is high temperature,and above 900? is super high temperature,among which the geothermal research temperature is mainly concentrated in 25 ? 900?.In a large number of geothermal projects,the propagation direction and path of giant hydraulic fracturing will be changed by natural structures(fractures),which will affect the heat exchange efficiency and service life of thermal storage.It is found that during the initiation and propagation of hydraulic fracture,the fractures are mainly model I crack.Therefore,we should focus on the study of the effect of natural fractures on the propagation of model I crack.The mode I crack growth process can be easily observed by the semicircle bending experiment.At the same time,PFC numerical simulation software can simulate the interaction between different mineral particles under high temperature because of its own thermal module.Based on the above factors,this paper establishes semicircle bending experiments with natural fracture by PFC numerical simulation software,and studies the influence of natural fractures with different cementation strength,angles and apertures on mode I crack growth under normal and high temperature(400?)conditions.The main research results are as follows:(1)The applicability and reliability of the model are verified.In this paper,PFC numerical model is established to calibrate the corresponding parameters,and the data of uniaxial compression test,Brazilian split test and thermal fracture test of the past scholars are compared with the numerical simulation results to verify the applicability and reliability of the model.(2)The propagation process of mode I crack includes four stages.The development process of type I crack of natural fracture rock with different bond strength,angle and opening includes the elastic stage before crack initiation,stable crack growth stage,unstable crack growth stage and natural fracture influence stage.(3)The cementation strength,angle and opening of natural fractures all affect the propagation of mode I cracks.The effects of natural fractures with different cementation strength,angles and apertures on the propagation of model I cracks are as follows: If the cementation strength of the natural fracture is larger,the deflection angle of the type I crack will be larger and more complex crack aggregation will occur when the type I crack intersects with the natural fracture;When the mode I crack is close to the natural fracture,with the increase of the angle of the natural fracture,the mode I crack is more likely to deflect towards the natural fracture and the deflection distance is longer;The larger the opening of natural fracture is,the larger the deflection angle of mode I crack will be.(4)High temperature will affect the development of mode I crack.The influence of high temperature on the crack is mainly in two aspects: on the one hand,high temperature will increase the plastic deformation of the specimen and reduce the energy of crack propagation;on the other hand,the thermal fracture in the specimen will change the stress distribution in the specimen,thus increasing the complexity of crack propagation,but will not determine the direction of main crack propagation.