The impact-echo (IE) method is a popular non-destructive testing (NDT) technique widely used for measuring the thickness of plate-like structures and for detecting certain defects inside concrete elements or structures. However, the IE method is not effective for full condition assessment (i.e., defect detection, defect diagnosis, defect sizing and location), because the simple frequency spectrum analysis involved in the existing IE method is not sufficient to capture the IE signal patterns associated with different conditions. In this paper, we attempt to enhance the IE technique and enable it for full condition assessment of concrete elements by introducing advanced machine learning techniques for performing comprehensive analysis and pattern recognition of IE signals. Specifically, we use wavelet decomposition for extracting signatures or features out of the raw IE signals and apply extreme learning machine, one of the recently developed machine learning techniques, as classification models for full condition assessment. To validate the capabilities of the proposed method, we build a number of specimens with various types, sizes, and locations of defects and perform IE testing on these specimens in a lab environment. Based on analysis of the collected IE signals using the proposed machine learning based IE method, we demonstrate that the proposed method is effective in performing full condition assessment of concrete elements or structures.

Aiming at the key design problems of large pumping station in area of high seismic-intensity on weak foundation, this paper proposed a new type of reinforcement scheme combining with plate rib underground continuous wall and soil grouting technique based on China's South-to-North Water Diversion Project. According to the layout characteristics of jointed structure, a three-dimensional nonlinear finite element model was established, and the static and dynamic finite element analysis of the plate-rib underground continuous wall were achieved with consideration of different rib width, grouting depth and soil strength parameters. The displacement principles of structure and foundation, contact state of construction joints, the influences of different arrangement modes of retaining wall and grouting effect on the overall safety performance of structure were studied respectively. The results showed that the reinforcement method is feasible and effective, and it can solve the base consolidation problem of soft-based foundation of large pumping station in meizoseismal area.