AbstractResearch 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.
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