The existing methods of calculation of the coal excavation performance of hydraulic giants lack an adequate scientific basis. The destructibility criteria used, either are incapable in principle of describing the true properties of coal (Ry) or reflect the specifics of hydraulic destruction to a limited extent and characterize the interaction of the jet with the coal mass incompletely (ψ0).
Attempts at developing a general criterion of coal destructibility by a hydraulic jet, as well as a phenomenological theory of strength, have been unsuccessful because of the extreme complexity of the phenomena and the large number of factors of different nature contributing to them.
It is necessary to study the interaction of the jet with the coal mass to determine the patterns of the process and develop a scientific basis for hydraulic mining.
The most promising trend of research is the development of continuous theory of defect accumulation and the theory of macrocracks. For practical purposes, it is desitable to develop a method for calculating the parameters of hydraulic excavation for given basic conditions.