Experimental Study Class Rock Joint Rock Damage Fracture

The jointed crack is considered as one of structural defects in natural rock mass, whose structural characteristics as well as physical and mechanical properties affect and even decide whole physical and mechanical features to some extent. The mechanism for instability and failure of jointed rock mass is the most cutting-edge direction but it is badly in need of solution at present.In order to research the failure mechanism of crack damage about jointed rock mass under the uniaxial compression, the model was developed regarding cement mortar as the similar material. Based on theory of prefabricating joints, the specimens were made. The compressive test of uniaxial gradation loading was conducted for maintained specimens through universal electro-hydraulic machine that was controlled by WAW-10000 C.During the compressive process, the specimens' ultrasonic wave velocity could be measured with the help of ZBL-U520 which is a nonmetal wavedetector. Meanwhile, the ultrasonic wave velocity could be recorded under the different loading. In addition, the width of joint could be obtained by PTS-C10 which is the width gage of crack. The part of jointed width could be also measured. During the whole process of loading, high-definition digital device was adopted to observe and record situation of new crack such as conception, development and cut-through. Its main conclusions are shown as follows:(1) Theory of crack model for rock sliding was suitable to initiation analysis of jointed tip under uniaxial compression and it could also explain jointed crack phenomena. Meanwhile, the accumulative damage theory reflected well attenuation laws of ultrasonic wave velocity in this test.(2) During process of uniaxial loading, the jointed tip would produce three kinds of new capillary crack such as wing cracks, secondary inclined cracks and secondary coplanar cracks. Of course, it's not all. Tension cracks would produce in the edged of specimen. In terms of crack appeared successively, tension cracks appeared early in general. In terms of jointed tip cracks appeared successively, wing cracks often appeared firstly, and then secondary coplanar cracks appeared. However, there was this case between wing cracks and secondary coplanar cracks at times but secondary inclined cracks often appeared after wing cracks. As for specimens including three discontinuous joints, various joints often had overlapping phenomena.However, the overlapped amount of cracks, location and kinds of lap would have a great difference because of change of geometrical distribution. There were three kinds of lap such as tension, shear and combined tensile and shear as a whole. In addition, the vertical and horizontal joint specimens only presented overlapping of tension and combined tensile and shear but no kind of shear. It is obvious that cracks of geometrical distribution have a great effect on pattern of overlapping.(3) Due to the difference about groups of joint and geometrical spatial distribution for specimens, there were great differences between the patterns of stress-strain curves. The peak stress, residual stress and strain when the stress reaches peak also had apparent differences. However, the characteristics of curves all presented brittle failure. Compared all values of initial crack at the same time, where the horizontal stress was lower than the vertical instead of inclined joints. When the distance between jointed tip and specimens' edged was smaller, initial stress would be lower. As to the effect on angle of dip to initial stress, there were no obvious laws. As regards two joints or three joints of specimens, compared the vertical, horizontal joints and inclined joints of specimens, the compressive strength would be larger and the stability would be better.(4) Compared with the variation characteristics of all specimens' wave velocity, the ultrasonic wave velocity of specimen would have differencesowing to groups of joints and geometrical spatial distribution before loading.However, the jointed angle of dip and angle presented some laws in the same kind of specimens. When the specimen was in load application, all wave velocity presented a tendency of decrease and attenuation. As for inclined joints, its wave velocity would attenuate fast in the same loading as a whole instead of the vertical or horizontal joints. Meanwhile, it had close correlation between the sizes of loading, descend range and kinds of joints,combined form when the wave is in a sharp fall.