Design principles and guidelines of filters

The design criteria of Terzaghi filter layer have laid the foundation for the researches on filter layers, which are safet enough for uniform cohesionless soil, but not secure for uneven cohesionless soil, and they are not suitable for other types of soil. The existing research results are reviewed based on the design criteria of Terzaghi filter layer for various types of filters with different permeability damages. The control principles and methods are put forward to determine the control grain sizes of different types of soil so as to expand the scope of the criteria. The research results show that for the uneven non-viscous filter layer of soil, the fine particles should be protected. Some experiments are performed to confirm the principles and methods to get the particle sizes of the fine materials. In the process of experiments, Using of fine materials to be the control grain size, and the regression method is used to get the results to determine the control grain sizes of the entire soil. Finally, the design criteria of filter layers for different kinds of soil are obtained. The results may provide reference and guiding significance for engineering design of practical filter layers.