Study On Characteristics Of The Xiali 2# Debris Flow And Its Potential Perniciousness On A Engineering Project

Debris flows are a kind of geological disaster that is suddenly unpredictable and has fast movement speed and strong impact force.It often causes serious loss of people's lives and property and damage to engineering construction and operation.The topography and geomorphology of Qinghai-Tibet Plateau are characterized by extremely complex,while the active fault are well developed often inducing seismic activities.Resultantly,shattered mountains and fragmented rock masses are ubiquitous in this region.Landslide and rockfall deposits and shattered mountain slopes provide plentiful source materials for debris flow initiation.Consequently,debris flows occur with increased frequency in this region.Xiali 2#debris flow gully is located in Xiali Township,Basu County,Changdu City,Tibet,and on the left bank of the Walayong.According to an engineering project plan,a proposed line will pass through its deposition fan from the northeast and downstream side of Walayong in the form of the Xiali Bridge.Due to the steep terrain of debris flow gully,abundant loose deposits in the catchment and favorable water convergence conditions,large-scale debris flows are prone to occur in this gully,posing a threat to the proposed line.This paper reveals the topography,source materials and rainfall conditions via the collected geological data and field investigations.The development characteristics of loose source materials and their possible failure mode are analyzed,and the initiation mechanism of debris flow is clarified.Moreover,the kinetic parameters of Xiali 2# debris flow are calculated,and the key parameters of the gully mouth profile are obtained,involving velocity,peak discharge,the total volume of debris flow mobilized,the total volume of solid material and the overall impact pressure.Furthermore,the risk degree of debris flow is determined.CAD,Sufer and ANSYS softwares are conducted to construct a three-dimensional geological model,and CFX software is performed to simulate the movement process of debris flow and predict the dangerous area of debris flow.The results suggest that the debris flow with return period of 20 years will block Walayong river,and the 50 years and 100 years return periods debris flow will not only block the main river,but also directly impact and even bury the piers of Xiali Bridge,which constitutes a threat to the construction and operation safety of the proposed line.Finally,according to the range of debris flow dangerous area obtained by numerical simulation,the prevention and control suggestions of building deposition works on debris flow accumulation fan are put forward for the proposed line.