川西北某泥石流沟发育特征及易发性评价

Development Characteristics and Susceptibility Evaluation of a Certain Debris Flow Gully in the Northwestern Sichuan

川西北某泥石流沟位于汶川“5.12”8级地震中心影响区域岷江河谷,该区域地质构造复杂,新构造运动强烈,强震频发,加之受岷江河谷深切,地形陡峻,出露地层以软质岩为主,沟道及两侧物源十分丰富,强降雨条件下易引发泥石流灾害。通过收集区域地质资料、遥感解译、现场地质勘察和力学计算等方法相结合,从地形、物源和水动力条件等方面,研究了该区域某泥石流沟的发育特征并开展易发性评价,提出了相应的工程防治对策。研究结果表明:(1)川西北某泥石流沟为暴雨崩滑沟谷型泥石流,泥石流沟流域面积20.8 km^(2),固体物质总储量约258.9×10^(4) m^(3),可能的动储量约64.5×10^(4) m^(3);(2)100年一遇的泥石流重度为1.74 t/m^(3),平均流速为5.12 m/s,最大峰值流量为535.4 m^(3)/s,泥石流最大冲起高度为1.34 m,预测100年一遇的泥石流淤积厚度为4.8 m,具有中度易发性风险;(3)针对工程区的泥石流发育特征及易发性程度,建议以桥梁工程形式并留足净空通过泥石流沟,提出了泥石流防治对策与建议。研究成果对川西北山区铁路勘察设计和施工建设具有一定借鉴价值。

Located in the Minjiang River Valley,a major area affected by the 8.0 magnitude Wenchuan“5.12”earthquake,a particular debris flow gully in Northwestern Sichuan has complex geological structures and intense new tectonic movement.The prevalence of strong earthquakes,coupled with the deep incision of the Minjiang River,has created steep terrains.The main exposed stratum is soft rock,and the gully and its surroundings are abundant in material sources,making the area prone to debris flow disaster under heavy rainfall.By collecting the geological data of this region,conducting remote sensing interpretation,on-site geological investigation,and mechanical calculation,the paper studied the development characteristics of this debris flow gully and evaluated its susceptibility from aspects of terrain,material sources,and hydraulic conditions,and proposed corresponding preventive and control measures.The results show:(1)The debris flow gully in Northwestern Sichuan is caused by a rainstorm-induced collapse valleytype debris flow,with a catchment area of 20.8 km^(2),total solid material storage of approximately 258.9×10^(4) m 3,and a probable moving storage volume of about 64.5×10^(4) m 3.(2)The debris flow density is 1.74 t/m^(3) for a 100-year event,with an average flow rate of 5.12 m/s,a maximum peak flow rate of 535.4 m^(3)/s,and a maximum flow uprush height of 1.34 m.The predicted deposition thickness for a 100-year event is 4.8 m,bringing a medium susceptibility risk.(3)Based on the debris flow development characteristics and susceptibility level in the engineering area,it is suggested to use bridge leaving enough clearance to pass the debris flow gully,and corresponding debris flow prevention measures and recommendations were proposed.The conclusions of this study can provide a useful reference for railway and highway investigation,design,and construction in the mountainous area of Northwestern Sichuan.