The online civil calculator which helps you to calculate the critical gradient for flow net and seepage calculation from the given input.
The critical gradients for fine sand are considered most relevant in this context, as both tailings and glacial till are relatively fine grained materials. Empirical studies thus show that the critical gradient can be lower in a water retaining structure compared to laboratory test results. Hence, current tailings dam design does not provide sufficient safety against piping and erosion.
Internal erosion is a process not yet completely understood; it is related to the seepage rate, which in turn connected to the hydraulic gradient, internal structure, particle size distribution etc.
Values for critical gradients determined in laboratory conditions are difficult to handle due to the varying procedures and definitions of a critical gradient, i.e. whether the critical gradient describes a limit at which particles start to move or whether a certain amount of erosion occurs.
Formula:
ic = γ’ / γw
where,γ’ = Submerged unit weight of soil
γw = Specific weight of water
ic = Critical gradient