Abstract: Uniaxial compressive tests were carried out to investigate the dilatation behaviour of phyllite samples under different loading azimuths. There were four types of samples taken from the Chengdu-Lanzhou railway. The results showed that the samples generally expanded before the peak stress reached, and the dilatation behaviour was influenced by the loading azimuth and degree of anisotropy. The vertical strain rate was greater than the horizontal one before the dilatation occurred, and vice versa after expansion. When the volumetric strain of phyllite samples converted from a positive value to a negative one, three conditions existed: pre-peak stress, post-peak stress and not-converted. Besides, the probability of the conversion was related to the participation degree, the form, and the failure mode of the original cracks during the loading process. The maximum dilatation rate appeared at the moment when the axial strain reached its maximum value, and the high azimuth angle was more sensitive to the dilatation capacity. The initiation stress of the dilatation was usually low, and the difference between the loading azimuth and lithology was large. The deformation and failure process of phyllite under loading was significantly reflected by the elastic modulus and Poisson ratio which were greatly affected by the dilatancy.

Key words: phyllite, dilatancy, uniaxial compressive test, elastic modulus, Poisson ratio