Hydraulic Gradient

Question

Hello 
 I want to ask about hydraulic gradient in your tutorial that stability of a dam under rapid drawdown. 
 I realized that i takes big value in phase_1 (rapiddrawdown) at clay core. 
 Is this okey for piping? Can we say that it is unimportant because maybe clay is not dispersif. 
 
 Thank you.

Faseel Khan · Answer

The hydraulic gradient that is present in this tutorial reaches a maximum value of 5.4 and that is in the rapid draw down phase as shown in the screenshot below. Other phases show an even lower value of hydraulic gradient. Please check your inputs and material properties as detailed in the manual of this tutorial.

Faseel Khan · Answer

Piping depends on the critical hydraulic gradient which is the hydraulic gradient with which when water flows in the soil in an upward direction, the seepage force or drag exerted by water on soil particles, which pushes them up, completely balances the weight of these particles, and they seem to be suspended in water. You will have to calculate that based on the weight of soil above that zone and if that weight is larger than the uplifting force, then there will be no piping. As far as internal erosion is concerned, it depends on the soil gradation between the two adjacent soils such that if one of the materials has bigger voids, then the smaller particles from the other soil will erode in to the larger voids. This erosion criteria is usually found in the filter design criteria which you can find in many text books.