DISCUSSION OF SAFETY FACTOR DEFINITIONS AND COMPUTATION METHODS FOR GEOTECHNICAL STRUCTURES

Taking common geotechnical problems, such as the bearing capacity of soil foundations and slope stability, as examples, two different definitions for the safety factor of structures, i.e. the ratio of limit load to allowable load and that of the available strength to required strength, are discussed. It is noted that the first definition is valid only for certain types of structures, whereas the second can be used for any type of structures. When both definitions can be employed, the proper choice depends on the characteristics as well as the loading environment of a specific structure, and different values for the required safety factor should be specified to reach the same level of reliability when a different safety factor definition is adopted. Moreover, the available methods for the computation of safety factors are reviewed, including the classical methods such as the slip line method, the limit analysis method, and the limit equilibrium method; as well as the modern methods such as the ordinary elasto-plastic finite element method, the strength reduction finite element method, and the finite element limit analysis method. The advantages and disadvantages of each method are discussed, and some suggestions are also presented with regard to their applications.