The limit state for settlement of expansive soil roadbed isn’t so absolutely definite as “critical point” since those factors

such as water content

void ratio and consolidation degree

are unstable and stochastic. Basing on the fuzzy mathematics theory

the paper prescribes the limit state as an incertitude section closing by “zero” when analyzing the reliability of expansive soil roadbed

introduces “fuzzy critical section” and “fuzzy limit state”

brings forward the conception “fuzzy reliability”

and expounds the method and processes for analyzing fuzzy reliability of expansive soil roadbed. Furthermore

the paper takes a typical expansive soil roadbed as example to calculate the fuzzy reliability of settlement. The result indicates that the fuzzy invalidation probability of exceeding allowable settlement may be a little big when expansive soil roadbed is designed according to intensity and stability principle.