Abstract
This paper contains the theoretical considerations on the basis of Coulomb-Navier's theory.The rock with parallel weak planes fails along the weak planes, before a new fracture plane cuts planes in the solid rock, if the angle between the planes and principal stress lies in some range in the two dimensional case. This range can be determined from the conditions for failure in solid rock and weak planes.The active Rankine's earth pressure of the rock with weak planes is not smaller than that of an intact solid one, and the passive Rankine's earth pressure of such rock is not larger than that of an intact solid one.In case of three dimensional development of parallel weak planes, failure along weak planes takes place before a new fracture plane arises in the solid rock, if direction cosines of the normal to the planes with principal axes lie in a certain range. The medium principal stress, in this case, plays a very important role in failure along weak planes and determining the dangerous range of the direction cosines.
