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Seepage path modelling
Petrula, Lubomír ; Baroková, Dana (referee) ; Brouček, Miroslav (referee) ; Říha, Jaromír (advisor)
One of the most dangerous processes that can occur on water retaining structures is deformation due to seepage. During these processes, a rearrangement of individual grains within the material happens and, in some cases, grains may be carried out of the material entirely. The dangerousness of such processes is given due to difficulty of their detection. A special case of deformations due to seepage is a backward erosion piping that occurs in the foundation of the structure (dams, weirs and such). During the process, a material is flushed out of the foundation due to forces induced by groundwater flow which leads to formation of the seepage pipe. The result of pipe progress may be a complete connection of spaces upstream and downstream the structure. Along with the pipe’s backward progression, its widening and increase in depth may be observed. Conditions of initialisation of backward erosion piping have been a topic for research since the beginning of 20th century. However, the data from experiments or even from direct observations on water retaining structures were focused mainly on general conditions and it did not pay enough attention to local conditions within the pipe nor on its tip where erosion occurs. Also, the speed of the whole process and the rate of backward erosion were not researched either. The pipe cross-sectional changes were researched only for materials with high contains of clay. The reason for using only clayey materials was given by ease of sample preparation. The goal of this work was to describe a process of the backward erosion piping that occurs in structure foundation. For this goal, a new device was designed, tested, and used for experimenting on picked uniform sands. After evaluation of obtained results, a new formula for calculation of backward erosion rate was derived. Based on the knowledge on hydraulic conditions in the sample and the pipe, a numeric model of the pipe progression was proposed.
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