Application Of Ultrasonic Phased Array To Identify Fractures In Model Test

Rock mass has been subjected to various geological structures during the long geological history,and a large number of joints and fractures have been formed under the action of in-situ stress field,which has brought great hidden dangers to the stability of underground engineering in rock mass.Therefore,the detection and recognition of fractures and their fracture evolution in rock mass has always been one of the hot and difficult problems in the field of rock mechanics.Combined with the project of National Natural Science Foundation of China(51404255)and ultrasonic phased array detection technology,this paper use the physical model test to detect and locate the typical cracks and research the methods to improve the accuracy and efficiency of identifying cracks in the surrounding rock during the model test combined with the mechanical characteristics and fracture evolution law during the loading failure process.The main findings and conclusions are as follows:(1)The influence factors of parameter setting and the imaging characteristics of different fracture shapes are obtained,and the parameters setting range and suggestion of using A1040 MIRA to detect imaging in model test are determined by the analyze of the basic principle of commercial nondestructive detector(A1040 MIRAA)based on ultrasonic phased array technology and the contrast study of testing and imaging with prefabricated fracture model.(2)The setting of wave velocity has a great influence on the imaging results.When the deviation between the set velocity and the actual velocity is less than 10%,it has little influence on the imaging result,when the deviation is more than 20%,it will have a serious effect on the imaging result.The difference between the crack location and the actual value is too large to detect the existence of the crack.(3)The directivity of the beam is enhanced if the working frequency is increased properly(25 ~ 45kHz),and the ability and accuracy of identifying cracks can be improved effectively.When the frequency of work is increased to 60 kHz,small size anomalies begin to appear in the image,and the recognition ability to crack defects is gradually weakening as the frequency increases.(4)This paper studies the methods to improve the accuracy and efficiency of different dip angles,bifurcation fissures,and multiple sets of parallel fissures based on the detection and recognition of different fractures,draws the characteristics and differences of the imaging images under different fracture patterns and establishes the relationship between the imaging map and the actual fracture.(5)This paper detect and analyze the deformation and failure process of fracturespecimens with different initial morphology by the use of ultrasonic phased array imaging technique.The length,position and shape of the crack in the imaging map are consistent with the actual situation of the fracture,which can detect and identify the fracture evolution in the process of deformation and failure of the specimen.It lays a good foundation for identifying and analyzing the generation and evolution of cracks in the model.