Numerical Approach to Design Warning Systems Based on DTSS Technology for the Detection of the Early Stages of Embankment Piping Failures
Embankment dams, composed of excavated materials like gravel, sand, and clay, are the most common dam type around the world (about 78 % according to the ICOLD – International Commission on Large Dams). Despite compliance with strict design and construction regulations and their currently low probability of failure, dams pose a high risk, due to the associated extent of damage involved, especially in densely populated downstream. Piping erosion is one of the main causes of historical embankment dam failures (Fry, 2007). This phenomenon involves the progression of a continuous conduit between the upstream and the downstream embankment shoulders. Its detection at an early stage is very difficult. Any delay in problem identification results in a considerable reduction of the warning time and, consequently in a risk increase.
A review of historical failures of embankment dams indicates that in most of the cases, a significant deformation at the dam crest was visible in an early phase of the breach development. Consequently, this work proposes a conceptual design of an early dam break warning system at the dam crest based on distributed temperature and strain sensing technology (DTSS). This warning system allows real-time monitoring of strains along the dam crest with high sensitivity and the detection of the exact problem location. Therefore, the system is able to extend the warning time because of a faster and automated failure recognition. To evaluate the application scope a 3D finite element model controlled by parametric variables is used to calculate strains in embankment dams during hazard situations. The erosion initiation is modeled in a simplified way by defining an erosion pipe characterized by a low strength material, its position, angle, length, and radius. The simulation of its progression is done by modifying the geometric parameters of the pipe. In a final step, the resulting strain distributions at the dam crest are compared with the known DTSS sensitivity. Thus, it is possible to quantify the advantages of the proposed dam warning system for a wide range of embankment dam geometries and piping erosion failure stages.