Some Key Problems on Debris Flow in Wenchuan Earthquake Area

After the Wenchuan earthquake on May 12, 2008, some initial treatments, such as silt dams and drainage ditches which were built in debris flow gullies in the earthquake area for debris control, showed a poor performance and went into a failure condition because of the underestimated launch quantity of loose material resource, the insufficient design capacity of the silt dams, and the small cross sections of drainage grooves. To deal with these problems, the formation characteristics and outbreak regularities of debris flow in the earthquake area were analyzed, and a systematic summary of experience was obtained from the lesson of insufficient understanding of the continuous, massive, and group-occurring of the debris flow. There are some significant differences between the earthquake debris flow and general debris flow in the starting mechanism, block and break, lasting time and break-out quantity of loose materials, and so on. Through the engineering practices in exploration, design and management of two giant debris flow in 2010 and 2013, some experiences are summarized as follows: (1) reasonably determine the blocking collapse coefficient and the discharge of debris flow; (2) put forward effective treatment plans according to different types of debris flows and the preserved objects; for example, effectively combine the block, slope reinforcement, drainage ditches and silting field; (3) reasonably distribute the effective height and number of silt dams; and, (4) choose reasonable structure types for dams, such as entity dam, crack dam and comb dam. The above experience has been successfully applied and verified effective in the investigation, design and management projects of large debris flows in Wenjiagou gully in Qingping town of Mianzhu County, Hongchungou gully, Qipangou gully and Taoguangou gully in Wenchuan County, and Lenmugou gully in Baoxing County.