The Debris Flow Movement Characteristics and Risk Assessment in the Lamaxi Gully, Sichuan Province, China

The Lamaxi Gully is a tributary of the Liusha River and there have been difference scale debris flow in history. The Lamaxi Gully stratum belongs to Xigeda Formation Tertiary, the rock and soil has poor engineering properties. The trench is enriched in unconsolidated deposits of Quaternary. It would most likely outbreak of debris flow disasters under the heavy rainfall condition, because the water erosion and gravity erosion happened seriously in this catchment. The Lamaxi Gully Bridge of Ya’an-Lugu Lake expressway crossing the Lamaxi Gully, Sichuan province, therefore, the debris flow disaster will bring great danger for bridge safety operation. On basis of the flied investigation in the Lamaxi Gully, analyses the characteristics of Lamaxi Gully development, identify the debris flow forming conditions and movement characteristics. Calculating the debris flow velocity, peak flow, one total debris flow of Lamaxi Gully under the different design probability, and make the debris flow risk disaster classification and evaluation. Through above research, it considered that the loose materials source may evolve into the debris flow under a 100-a rainstorm in Lamaxi Gully catchment, which impacted on the safety operation of bridge. It has a practical significance for safety of Lamaxi Gully Bridge under the debris flow.