| Xigeda formation was originally called "Hundan formation" and was renamed "Xigeda Formation" in 1938. It is mainly spread over the south and northeast of the Sichuan with the course of Qinghai-Tibet Plateau uplifting. Xigeda formation is a lacustrine deposit stratigraphic, which is mainly of rhythmically alternating layers of fine-grained sandstones, siltstones, pelitic siltstones and siltstones and dark-gray mudstones. For 70 years of researching, we has deepened understanding of the formation time of the Xigeda and evolution process including palaeogeography, palaeoceanography and paleoenvironment. But there are many questions about Xigeda formation because of lacking of the research areas and fossils.From the view of supporting the project of the Panzhihua Iron and Steel Company's new basis of the V-Si in Xichang, formation mechanism and dynamic stability analysis are introduced through the dynamic triaxial test and numerical simulation. The tasks done are follows:(1) Analysis of the Xigeda's sediment unit's spatial distribution and formation mechanism by studying the data of bore holes. Existing researches about the Xigeda's formation background always rely on an outcrop or two, which are large difference to each other. However, there are widely distributed in Xichang of the Xigeda, which will help the further research of formation mechanism.(2) R-mode Factor analysis method was used to analyze for experimental data and to probe parameters correlation among the silty clay, silty sand mixed clay, silt and clay; Find out linear equations by the regression analysis and the least square method. The result shows that moisture, void ratio, liquid limit and plastic limit are the central event in the physical and mechanical parameters.(3) Seismic response analysis by the three seismic waves which are FA5→0.25 g1→parameterⅤ,FA5→0.25 g2→parameterⅤand FA5→EL→parameterⅤ. The result shows that the effect of height to Z-axis acceleration is considerable.
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