Abstract: The strength reduction method, which is popular at present in the slope stability analysis, is used to analyze the relative error of calculation results by using software MIDAS/GTS, FLAC, ANSYS with D-P and M-C yield criteria in three cases (soft clay, hard clay, weak expansive soil). In the case of soft clay the relative error of calculation results by using D-P criterion and M-C criterion is relatively small. For hard clay slope, the relative error of calculation results by using D-P criterion and M-C criterion increases significantly. The calculation results by using three kinds of software with two yield criteria all indicate that sliding surface in hard clay is shallower than the sliding surface in weak expansive soil and soft clay. Under the same circumstances, sliding surface determined by MIDAS is shallower than the result by ANSYS. When the slope is small the safety factor of the calculation by MIDAS is smaller than that by FLAC (M-C); when slope is large the result is opposite. When slope is small the calculation convergence is realized after the breakthrough of plastic zone, but for large slope calculation divergence occurs before the breakthrough of plastic zone. In the case of small slope the difference between reduction factors upon appearance of calculation divergence and upon breakthrough of plastic zone is significant. But the difference between reduction factors is relative small in the case of large slope, even breakthrough of plastic zone does not occur upon the calculation divergence, which is more remarkable when using MIDAS software.

Key words: slope, method of strength reduction, strength criterion, safety factors