Abstract: In light of that the, studies of mechanical response of rock under cyclic loading need to be more perfected, taking Yichang sandstone as the research object and using the geotechnical testing system RMT-150C for the test platform, the research on the prediction model of deformation rate in triangular wave unloading segment with the magnitude of ms., is carried out. Unloading process is divided into non-lag and lag time segment; and the required parameters and discrimination basis for each segment is given. Effect of lag time segment is pointed out quantitatively; and the prediction mode in time lag segment is also given. Then the concept of the apparent modulus of elasticity in the lag non-lag time segment is proposed; analysis of the test data shows linear relationship between the apparent elastic modulus of the rock sample before the sample was damaged under loading. On this basis, a prediction model of deformation rate by triangular wave unloading in non-lag time segment is established. As the test platform can not be accurately input triangular wave, after the average loading rate and loading rate is corrected by adding corrected constant term, the predicted deformation rate and stress-strain curves of the model are coincide precisely with the measured values, so as to indicate the rationality of the model.

Key words: apparent elastic modulus, calcareous sandstone, triangular wave unloading segment, lag time segment