西藏贡觉县泥石流灾害研究

Study on debris flow hazard in Gongjue County,Tibet

西藏自治区贡觉县境内对居民存在影响的泥石流沟有3条,即者龙洼Ⅰ沟,者龙洼Ⅱ沟,克西林沟,均位于该县东南部的高山峡谷区。泥石流沟长度均超过2km,沟床平均纵坡降130‰,地表松散物质的厚度都在6 5m以上,其来源有所不同,克西林沟泥石流的固体物质来源于沟谷两侧的也古、拉巴滑坡堆积物;者龙洼Ⅰ、Ⅱ泥石流的固体物质来源主要为岩石风化物质及崩、坡积物。固体物质颗粒粒径分布范围很广,分布曲线均呈三峰型。说明该区泥石流中固体物质含量较高。贡觉县境内泥石流的诱发因素是降雨,为降雨型泥石流。文章根据非饱和土强度理论对贡觉县降雨型泥石流的成因机理进行了研究,提出降雨型泥石流的形成过程可以划分为2个阶段,第1个阶段为基质吸力引起的抗剪强度丧失阶段,与前期实效降雨量有关;第2个阶段为泥石流发生阶段,与短历时强降雨有关。运用上述理论方法,对降雨型泥石流的预测模型进行了探讨。建议用临界雨量线模型框架来建立贡觉县泥石流的预测模型,并依据者龙洼Ⅱ沟泥石流爆发前20d的降雨量数据进行拟合分析,结果表明:文中建议的2个临界雨量线模型框架均适于用建立贡觉县降雨型泥石流暴发的预报模型。

There are three debris flow gullies which are harmful to resident in GongJue County Tibet, includeing Zhelongwa Ⅰ gully, Zhelongwa Ⅱ gully,Kexilin gully,and the three debris flow gullies are located at alpine valley area in the south-east of GongJue county. The length of the debris flow gullies is more than 2 km, the average gully ratio is 130‰ and the thickness of surficial loose material is more than 6.5 m. The surficial loose material have varied source:debris flow material in Kexilin gully is from Yegu and Laba slidemass situated in the gully, and debris flow material in Zhelongwa Ⅰ gully, Zhelongwa Ⅱ gully is from weathering residues colluvium and diluvium. The debris flow material with a wide range of grain size distribution and triple humped grain size distribution curve show the debris flow with a high content of solid loose material. The debris flow in GongJue County is induced by rainfall, so it is a rainfall-type debris flow. In this paper, according to theory of unsaturated soils mechanics, the genetic and mechanic analysis of debris flow due to rainfall in GongJue County is researched. The formation process of debris flow due to rainfall can be divided into two stages. The first stage is loss of shear strength due to suction, relation with antecedent effective precipitation, and the second stage is debris flow forming, relation with heavy precipitation at short time is put forward. The forecasting model of rainfall-type debris flow is studied in this paper. Establishing the forecasting model of debris flow in GongJue County according to framework of critical rainfall curve model, regression analysis is done based on the 20 day-rainfall data before Zhelongwa Ⅱ debris flow took place, the result shows that two framework of critical rainfall amount curve model given in this paper are suitable for establishing the forecasting model of debris flow due to rainfall in GongJue County.