| According to the investigation on the collapse of travertine earth dam in the spark seascape area induced by the 7.0-magnitude Jiuzhaigou earthquake in 2017,it is found that the dam has the characteristics of high angle and short sliding distance,with strong damage,great harm and serious derivative disasters.The formation mechanism of travertine soil has been paid more and more attention,and the research on its structural characteristics and dynamic damage mechanism is rare.The dam body collapsing area in the spark seascape area induced by Jiuzhaigou earthquake was selected to carry out field investigation,basic physical and mechanical properties test of travertine soil,microstructure scanning electron microscope test,dynamic liquefaction test,etc.according to the characteristics of the uneven structure of travertine soil in the dam site area,and according to the corresponding specific structure and the main characteristics of statics and dynamics,various explorations were carried out.This paper discusses the Dynamic Liquefaction Characteristics and control factors of the saturated travertine soil,reveals the generation and development law of excess pore pressure in the liquefaction process of the saturated travertine soil under the action of dynamic load,and discusses the development trend of the strength and deformation of the saturated travertine soil after liquefaction.On this basis,further analysis of the geological prototype of the collapsing dam body,combined with numerical simulation,the earthquake induced collapse of the saturated travertine soil is carried out The formation mechanism of the powder is demonstrated.Through the research,the following main understandings are preliminarily obtained:(1)In this study,the sample dam site area is spark sea research area,the upper part is quaternary Holocene alluvial diluvium,the material composition is mainly block stone,gravel,clay,etc.,the lower part is composed of dolomitic limestone with chert limestone and other rocks.There are different types of groundwater in Jiuzhaigou.According to the characteristics of rock,the dynamic characteristics of groundwater and the different types of water storage space,groundwater can be divided into three types: interstitial water,karst water and fissure water.Through the continuous movement of the earth’s crust and the change of valleys,and the erosion and erosion of many factors such as long-term water flow and wind,some valleys appear multi-level water drop and waterfall,forming a V-shaped topographic feature of the middle depression in this area.(2)Based on the analysis of travertine soil structure,the corresponding data analysis is carried out from the composition and characteristics of travertine soil,strength index,saturation parameter and other aspects.It is found that the loose travertine soil has some properties of sand,such as loose soil,good permeability and permeability,which provides a reference for the subsequent analysis of the properties of travertine sand.In addition,travertine sand also has Its own particularity(for example,the biogenetic influence on its primary structure,the average cohesive force of 32.65 kpa,the average internal friction angle of 39.87 °)shows that the distribution of mechanical properties of travertine soil is uneven,which lays a scientific foundation for the formulation of relevant dynamic parameters.(3)By means of scanning electron microscopy,we found evidence that biological factors play a role in matrix and framework during Travertine Deposition,further revealed the biological mechanism of travertine,and controlled the organic matter content artificially by means of burning loss in direct shear test,and compared the experimental results after removing the organic matter content with the original experimental results.That is to say,the C value and Φ value of travertine soil are reduced by 43.08% and 37.5% respectively in the state of burning loss compared with that in the state of non burning loss,that is to say,cement plays a role of connection and framework for the structural strength of travertine soil,and the strength of travertine soil is also significantly reduced after the structure is damaged.Because of the anisotropy of calcareous cementation of travertine soil,with the increase of sampling depth,the better the cementation degree is,and the greater the damage of cementation structure after burning is,the more obvious the strength reduction of travertine soil with deeper depth is.(4)Based on the analysis of the collapse mechanism of the dam,it is found that the travertine soil,which is unevenly distributed on the dam body and the degree of cementation will change to some extent,is the material foundation for the dam body to break,and the underlying liquefied sand layer provides favorable conditions for the dam break.Under the earthquake,the corresponding structure of the underlying travertine sand is damaged,which makes the excess pore pressure in the saturated zone accumulate continuously.Through a certain degree of development,the liquefaction of travertine sand emerges upward and expands and separates to both sides.The tensile fracture of the overlying travertine earth dam results in the dam collapse due to the uneven settlement.Based on the comprehensive analysis,the formation mechanism of the dam break in sparking sea is as follows: the erosion of external forces causes the formation of free surface-the formation of liquefaction zone-the earthquake causes the liquefaction upwelling of sand in the saturated zone and the lateral spread-the tension crack of overlying travertine soil-the overall collapse of the dam body.(5)On the basis of the above research,the pore pressure model(Finn)in FLAC3 D is used to reduce the change rule of stress and strain under the condition of vibration load and the deformation and failure process of dam body,and the formation mechanism of dam body collapse induced by earthquake is demonstrated.Through FLAC simulation,the change and development of excess pore pressure in the process of strong earthquake impact on dam body can be well demonstrated.It describes the whole process from the generation and accumulation of excess pore pressure,the change of stress and the development of displacement under shear stress to the dam collapse.The formation mechanism of vibration collapse of saturated travertine soil induced by strong earthquake is revealed. |
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