箭竹特大桥堰塞沉积特征及工程地质特性分析

Analysis of the Sedimentary Characteristics and Engineering Geological Characteristics of Dammed Lake Deposits of Jianzhu Bridge

研究目的:堰塞沉积地层是我国西南山区河流中常见的第四纪湖湘沉积地层。本文在地质调查的基础上,通过勘探、物探、原位测试及室内试验等综合勘察方法,阐明箭竹特大桥沉积环境特征,分析堰塞沉积物工程地质特性及桥梁面临的工程地质问题,以期为设计提供准确的基础资料。研究结论:(1)箭竹泥石流堆积体为堰塞坝址所在位置;(2)堰塞沉积物以深色软塑粉质黏土为主,两色韵律纹层不明显,沉积环境存在较长的干旱气候期;(3)堰塞区下游至上游沉积物颗粒和厚度均逐渐增大,最大厚度约35 m,单个沉积韵律层厚度15~26 mm,推测沉积时间大于500年;(4)对室内试验及原位测试成果进行分析,得出沉积物相关物理力学指标供设计参考;(5)软弱地基、砂土液化及潜在的堰塞坝是桥梁面临的主要堰塞工程地质问题;(6)本研究成果可为完善堰塞沉积区铁路选线及工程防护提供借鉴和参考。

Research purposes: Dammed lake deposit is a common Quaternary lacustrine deposits stratum in mountainous rivers in Southwest China. On the basis of geological survey, this paper expounds the sedimentary environment characteristics of Jianzhu bridge, analyzes the engineering geological characteristics of dammed lake deposits and the engineering geological problems faced by the bridge, through comprehensive survey methods such as exploration, geophysical exploration, in-situ test and laboratory test, in order to provide accurate basic data for design.Research conclusions:(1) The debris flow accumulation body of Jianzhu is the location of dam site.(2) The dammed lake deposit is mainly dark soft plastic silty clay, and the two-color rhythmic lamina is not obvious. There is a long dry climate period in the sedimentary environment.(3) The sediment particles size and thickness from the downstream to the upstream of the damming area are gradually increasing, and the maximum thickness of dammed lake deposit is about 35 m, and the thickness of single sedimentary rhythmic layer is 15 ~ 26 mm. It is speculated that the deposition time is more than 500 years.(4) Based on the analysis of the results of in-situ test and laboratory test, the relevant physical and mechanical indexes of sediment are obtained for design reference.(5) Weak foundation, sand liquefaction and potential barrier dam are the main engineering geological problems of the bridge.(6) The research results can provide reference for improving railway route selection and engineering protection in dammed lake deposition area.