The ultimate capacity of piles is always determined using a failure criterion. Due to the differences in failure criteria

the ultimate capacity of piles and the reliability index obtained using different failure criteria may not be the same. It is necessary to analyze the reliability levels corresponding to various failure criteria

especially S-lgt criterion used in Chinese technical code for building pile foundations. For this purpose

a bias factor defined with respect to S-lgt criterion is introduced; and one database for static load tests of bored piles is utilized for detailed evaluation of the bias arising from failure criteria

the corresponding reliability are further analyzed. The results indicate that there is a considerable bias of different failure criteria. Moreover

the failure criteria have a significant influence on the reliability of pile foundations. The reliability index based on S-lgt criterion is on the high side among seven failure criteria used in this paper. The actual safety levels of designs with the same nominal reliability index are not the same.