1、The filling coefficient theory was put forward, a criterion for the filling coefficient of soil stratum failure and a critical hydraulic gradient chart were formulated.
3、Finally, we suggested that the problem on stability of the bench mark may be settled in certain area by using the bench mark with a casing pipe buried in the proper depth of soil stratum.
2、By use of 453 groups of piping test data, verification was made to the existing 7 analytic methods for stability of soil stratum permeability at home and abroad.