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.