Abstract: The process conversion of PBA method is complex, and it is easy to cause surface settlement. It is difficult to clear the settlement law under different stratum conditions, especially under bad geological conditions such as waterbearing silt formation, which would cause certain safety hazards to the surrounding environment. As a result, the distribution of PBA stations in fine silty sand stratum of Beijing Metro is investigated, the surface settlement laws of PBA station under different precipitation conditions are analyzed based on monitoring data, and the calculation and verification are carried out according to the finite element method. The research results show that: (1) The relationship between occurrence probability of surface settlement value greater than correspondance and maximum surface settlement shows a normal distribution; the maximum surface settlement values of effective precipitation and noneffective precipitation station are -85.31～-93.29 mm and -126.16～-131.35 mm, respectively, and the probabilities of the maximum surface settlement value exceeding -60 mm are 53.30% and 74.96%, respectively according to data fitting. (2) The settlement deformation mainly occurs in the construction stage of the pilot tunnel and the arch lining, accounting for about 90%, and the settlement ratio in typical construction stage of top heading excavation,lower bench excavation,beancolumn system construction and arch lining construction is about 4∶3∶1∶2. (3) The settlement trough is consistent with Peck curve, the settlement trough width is 9.82～15.51 m, and the settlement trough width in the effective precipitation station is 3～5 m wider than that of the noneffective precipitation station. (4) The ground loss rate is 0.56%～0.70% generally, and settlement trough width parameter is affected by precipitation effect significantly, ranging from 0.51 to 0.89. The conclusions can be used to preliminarily judge the maximum surface settlement of PBA station．

Key words: metro station, PBA method, fine silty sand stratum, settlement, settlement trough