In light of the importance of study of mechanical parameters of rock mass structural plane
based on a large number of practical projects and the basic statistical principle about error analysis
the applicabilities of least square method and M - estimation method for calculating the structural plane shear strength parameters
are studied. The results show that
when the gross errors are uncertain
it is hard to find the regularity that the two methods are more suitable for some certain condition. Because the data all have the given engineering characteristics
in order to make results more accurate
a new method based on the above two methods is proposed; and it is applied to calculate shear strength parameters of Lijiahe reservoir.