Siphoning check

The difference in water level existing between the upstream part and the downstream part of the weir involves the possibility for the problem of siphoning to occur. By siphoning we mean that physical phenomenon capable of lifting the part of ground situated on the downstream toe of the weir, generating the collapse hazard for the work. The criterion followed in the programme consists in checking that the speed in the porous means is such – in each point - as not to remove then finest particles of the ground. In mathematical terms - calling the critical piezometric slope ic and the outflow piezometric slope ie – the siphoning safety factor is expressed by:

Where:

ie is the piezometric water slope calculated in the maximum hazard point for the siphoning, usually on the downstream toe of the work. The siphoning check can be executed with the aid of specially provided software which carries out the analysis of the filtration in a porous means. In order to execute the filtration analysis, proceed as follows:

1. From the calculation menu or from the relevant tool bar, select "Filtration analysis";

2. A window will open through which you can generate a file compatible with the software used for the filtration analysis;

3. In the open window, select the type of weir for which you want to analyze the filtration (Silted-up weir or Non-silted-up weir);

4. At this point, click on the Export button and select the path of the file to be exported;