Preliminarily Research On Non-destructive Testing In Anchorage Quality Of Anchor Cable

As the main supporting method, the working condition of pre-stress anchor cables is related to the safety and stability of the whole project, so the anchorage quality non-destructive testing is very urgent. At present, the theoretical research on non-destructive testing of anchor cable is laging, and its engineering practice is still using the detection method of bolt. However, anchor cable structure is very complicated, stress wave transmission mechanism whether consistent with bolt is not clear, the test rusults require to be demonstrated if it was directly introduced into anchor cable anchorage system.Considering the above situation, this paper researches the propagation characteristics of stress wave in anchor cables, analyses the feasibility that stress reflected wave in anchorage quality testing by collecting dynamic response signal of the anchorage specimens and processing it with self-compiled program, and proves the applicability in field testing based on the nondestructive testing theory of bolt. The main achievements are as follows:1) There is uncertainty between the first bottom reflection and the second fixed end reflection in time line, when the stress wave transmited in the (anchorage) anchor cables. The bottom reflection is quite easily disturbed by the fixed end reflection:the peak of bottom reflection will be weakened, even obscured completely and produced a reflection blind area; it also may be moved forward or back, and made the deviation between the test value and real value. Therefore, revised the existing correlation function algorithm. That can identify bottom reflection more accurately, and provide a theoretical basis to improve the analysis program.2) Conduct test and bearing analogous simulation experiment for the different sizes of anchorage speciments in the laboratory, and the analysis results show:stress wave will spread with two speeds along the different cable lines, and form two reflected signals at the anchor cables bottom, it is also the main difference from bolt; the actual anchor cable wave speed between peripheral spiral cable lines and center of straight line; the free-segment wave speed and consolidating wave velocity will decrease regularly as the increase of anchorage segment diameter, however, they won’t change as the anchorage segment length in the anchorage cable.3) Based on tracking and testing concrete mortar-anchor cable in the different anchorage strength(curing time), obtain the following conclusions:the laws between consolidating wave velocity and anchorage quality(concretion strength) in anchorage cable, is the same as the anchorage bolt. That is, if the anchorage quality is poor, the consolidating wave velocity will close to the wave speed of freedom anchor cable; If the anchorage quality is excellent, the consolidating wave velocity will trend to the anchorage medium wave speed; otherwise, consolidating wave velocity in between. The smaller consolidating wave velocity is, the more excellent anchorage quality of anchor cable will be; and vice-versa. It can provide theoretical support for the non-destructive testing of the anchorage quality, through the consolidating wave velocity of anchor cables.4) Within a certain limits, the bigger working load is, the smaller wave velocity of anchor cable will be; when the working load increases to a certain value, the wave velocity isn’t change anymore. In addition, the relationship between the working load and the fundamental frequency of the end-anchored cables presented a power function, however, it hasn’t been verified in the experiment under the load.5) To prove the feasibility of stress wave in testing the anchorage quality of anchor cable, conduct a test in the6#foundation pit of Yellow River extra-large bridge and Yao Qiao mine of the China Coal Group based on the propagation characteristics of stress wave.