Study of size effect of rock mass deformation modulus based on in-situ test

It is the key step for geotechnical engineering stability evaluation to determine suitable mechanical parameters of rock mass due to random distribution of its parameters. The statistical analysis of 110 data from borehole jack tests conducted from earlier research of a hydropower station shows that the deformation modulus more closely matches the Weibull distribution. Then the cube rock masses of various sizes, each of which comprises a number of cube elements, are simulated numerically. The size of each element is identical with that of bearing plate of borehole jack test instrument; and the deformation modulus of each cube element is given randomly by Weibull distribution. Each of rock masses is simulated by 5000 uniaxial compression tests; and then the change of equivalent deformation modulus with rock mass size is obtained, which determines the REV of equivalent deformation modulus. It is a new attempt to survey the macro parameters of rock mass by combination of in-suit test and probability statistics theory, so as to provide a useful reference for the parameter determination of rock mass in this hydropower station.