Abstract: The energy mechanism of material damage in thermodynamic theory was introduced to slope engineering. An energy conservation equation that was applicable in strength reduction period was deduced. Then, a calculation procedure for the slope energy was developed with FLAC3D, which was applied to a traditional slope example. Compared with the result from Spencer method, the slope’s energy change was closely related to its stability in the strength reduction method, hence four new slope failure criteria-energy catastrophe criteria which were theoretically in unity were proposed. By comparison, the criterion of the kinetic energy catastrophe is in correspondence with the criteria of numerical calculation non-convergence, the loss of gravitational potential energy catastrophe is in correspondence with the criteria of dramatic increase in the marked nodal displacements, and the dissipated energy catastrophe is in correspondence with the criteria of a plastic zone going through the slope. In summary, the aforementioned correspondences demonstrate the unity of the three common failure criteria. Several examples demonstrate that the different results from the three common failure criteria are because of artificial factors such as mesh generation precision and numerical convergence criteria. In essence, the different results stem from the fact that numerical calculation is a kind of approximate solution. In application, the accuracy of safety factor can be evaluated by the consistency of the results from various slope failure criteria. The better the consistency is, the higher the accuracy is. The basic method of improving the accuracy of safety factor is strict convergence standard and fine mesh precision, but achieving strict convergence standard and fine mesh precision may require extremely long numerical calculation time. Therefore, a moderate numerical calculation time should be chosen to maximize the computational efficiency.

Key words: slope, strength reduction finite element method, failure criterion, energy, unity