Study on the Methods for Evaluating the Location of and Preventing Seepage Failure using Acoustic Emission

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Seepage failure is a problem in hydraulic structures, cofferdams at the location of high groundwater level, etc. Once the seepage failure occurs, it causes serious damage to the work itself and/or neibouring places from the economical point of view. There are still many problems unknown, in the seepage failure phenomena, which have to be made clear.In this study, the seepage failure problem of soil within a cofferdam was mainly considered. First, the case history of piping occurred in a subsoil of a bridge abutment within a cofferdam during dewatering was reported and the analytical consideration of the problem was given. The causes of the piping were then considered.Second, theoretically, the existant theories of seepage failure were examined and classified to the several categories. The prismatic failure was also presented as a new method for analyzing seepage failure of soil behind a sheet pile wall. The typical three examples were analyzed using these theories, and the characteristics of these theories of seepage failure were then clarified precisely.Finally, experiments were made on the seepage failure of soil column and on the failure of soil within a cofferdam. Analyzing the changes in the distribution of equipotentials, the state of soil, the relationship of hydraulic head difference versus discharge, the remarkable result was obtained that the points of these changes are identical altogether. In the two-dimensional seepage failure experiments, accoustic emission was measured and analyzed, as a result the possibility of the evaluation of the time and the location of seepage failure was demonstrated.