How does Progressive Erosion Produce Piping in Dam Foundation?

Dear reader we have preliminary idea about piping in embankment and embankment foundation. Here we will learn how piping is generated with progressive erosion. The water in upstream portion of dam seeps through compacted soil or natural soil of embankment and foundation respectively. A resisting force known as viscous drag is generated that resist flow of water through small interstices of soil.
This resisting force reduce pressure head of water; in other word, the erosive force produced by seeping water has tendency to pull out soil particles along its travel path under the dam (foundation) or embankment itself.
Piping eruption from foundation of dam
Now of these two forces, if the erosion resistance or viscous drag is greater than pull out force no harm or damage will happened. But when erosive force is stronger than viscous drag force, soil particles with seeping water washed away and piping phenomena is commenced.
Now what are the sources of erosion resistance with in compacted embankment soil or natural foundation soil? As we are considering piping through foundation, so foundation is considered pervious, in this discussion. The sources are:
a. Cohesion
b. Interlocking effect
c. Weight of soil particles
d. If as a mitigation measure, we provided downstream filter, it also contribute to erosion resistance.
The piping behavior through homogeneous and zone dam will be discussed in next post elaborately.

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