Face Slab Dispatch Detection of Concrete Faced Rock-Fill Dam Based on Nature Frequency

Face slab dispatch often occurs when concrete faced rock-fill dam (CFRD) has undergone a large earthquake, such as the Wen Chuan earthquake in China. In this paper, an approach for face slab dispatch detection of CFRD based on measured nature frequency of face slab under varying water level is proposed. The principal component analysis (PCA) method is used to eliminate the effect of water level changes. The advantage of this method is that the actual relation between water level and nature frequency is not need to understand and only reference data of measured frequencies from face slab without dispatch and monitoring data of measured frequencies from face slab maybe with dispatch is necessary. Through PCA on the reference data, the number of principle component and a linear subspace in which environment variable (water level) effects lie is identified. Then the monitoring data from face slab maybe with dispatch is project to the linear subspace identified above and the residual error of this projection is calculated. By performing kernel density estimation (KDE) on the residual error of PCA, the upper control limits of it is calculated to judge whether dispatch occurred. In order to verify the feasibility of this method, the FEM of a face slab is made and the dispatch between face slab and cushion of a CFRD was stimulated by removing some springs between them. The impact of water level on nature frequency is simulated by some theoretical and empirical formulas. Three sets of computer-simulated data of nature frequencies are studied and the dispatch identification result shows the good performance of this method. Since the identification of nature frequency is more convenient and accurate than other modal parameters, this method has a good prospect to apply to practical engineering.