Abstract: The studies with development of piping and filters, two mutualized problems, are reviewed. Meanwhile our studied results are also given for comparison. This part II, with respect to filters we indicate that the developing tendency of controlled grain size is one point of average grain size first and then to two points as well as to many points along the grain size grading curve. Terzaghi’s filter criterion is conservative and it should be revised by hydrodynamics in spite of sand gravel filter or geotextile filter. When filter used to protect clay the key problem will be cracked or not and the design criteria for these two situations are very discrepant. As to clogging of filter, such as relief wells, the suction washing method to restore the drainage effect is the better.

Key words: Terzaghi’s filter, sandy gravel, clay, geotextile, grading curve