Congrès annuel 2008 de la SCGC CSCE 2008 Annual Conference Québec, QC 10 au 13 juin 2008 / June 10-13, 2008 1 OPTICAL BOREHOLE ACOUSTIC IMAGERY FOR STRUCTURAL DAMAGE ANALYSIS S. Kabir; P. Rivard Group for Research in Analysis and Instrumentation University of Sherbrooke, Sherbrooke, Québec, Canada Abstract: This research provides a comparative study of various techniques for their effectiveness in analyzing deterioration in concrete structures using digital acoustic imagery obtained with an Acoustic Televiewer from a borehole in a concrete lock. The methods evaluated consist of spatial domain filters, as well as transform and statistical based methods. The spatial domain filters employed are the low-pass, median and directional filters, and the Sobel, Roberts and Laplacian edge-detectors. The transform- based method used is the Haar discrete wavelet, and the grey-level cooccurrence matrix is the statistical based approach. An unsupervised clustering technique is employed to characterize and quantify the damage in the imagery. The results of the study indicate that the statistical based approach of the grey- level cooccurrence matrix is the most efficient among the techniques evaluated, followed by the Haar wavelet transform. Among the spatial filters, the low-pass filter provided the best results. The damage analysis conducted on the acoustic imagery provided quantitative information concerning total damage, and crack-width opening, which was calculated using the max and mean opening along single cracks. 1. INTRODUCTION The aging of concrete structures is resulting in reduced levels of safety and serviceability, the assessment of which is often complicated due to a lack of original design details. Standards concerning the safety and design of these structures have changed with time; consequently, many structures must be rehabilitated. Large dams are among the most critical structures. Their safety and stability are closely related to their resistance to sliding, which strongly depends on the condition of the concrete and bedrock. Frequent inspection is thus necessary for the collection of condition information in order to detect problems in concrete dams. Information about the location and extent of deterioration, stains, voids and the length and width of cracks are recorded in order to assess the condition of the dam. Structural health data provide invaluable records of changing conditions. Assessing the safety of a dam against sliding requires a detailed investigation of the cracks and other anomalies in the concrete structure and the rock foundation underneath. This is achieved through characterization of the mechanical properties of the concrete and rock materials, and especially the shear strength of the different types of irregularities found throughout the structure and foundation. Traditionally, cores are drilled in the structure being investigated in order to collect data about the existence of any anomalies. This method has the advantage of providing specimens for petrographic examinations and allows the testing of specific properties, such as compressive strength or permeability. However, information on the condition of the anomalies is sometimes altered or lost due to drilling operations, even if a triple-tube coring system is used. For instance, cracks might be created during drilling or transportation of the samples. Also, planes of cohesive weakness can separate after drilling,