Numerical Simulation Study On The Reaction Rules Of Earthquake In Tianjin Soft Soil Foundation And Its Seismic Subsidence

Tianjin is a big city in the BoHai ring that is located in cenozoic subsidence basin inside the large city. Its underground is made of soft soil foundation what has the characteristics of high sensitivity, high compressibility, low strength, low permeability and consolidating long time in the thick sedimentary layer. This foundation has a unique frequency characteristic, for the low frequency earthquake motion and the surface deformation and displacement have magnifying and extending vibration’s duration of effects. As the same time, the building build on soft soil foundation under the action of seismic load will be occurred suddenly excessive subsidence and uneven settlement, seismic subsidence and liquefaction which will be lead earthquake damage to the foundation, so it is very bad for the high and span of building. This paper carried out the following research according to the rules of seismic response and conditions of the soft soil site’s seismic subsidence in Tianjin Binhai New Area.(1)This article elaborates the background and significance of selected topic, summaries and analysis about the earthquake’s response and research methods and making progress in the seismic subsidence’s study of domestic and foreign.(2)Through the collection of drilling and geological data, discusses the geological background, seismicity, distribution of soft soil,physical and mechanical indexes and microstructure of Tianjin Binhai New Area in detail.(3)Elaborates the equivalent linear method of seismic response of soil layer and the way of nonlinear analysis of soil dynamic that Flac3 D software used, summaries the principle of Flac3 D software based on the finite difference method that’s including the physical and the motive equations which is between the units. Introduces the basic methods and steps of Flac3 D software’s dynamic analysis which is how to solve some key problems in the calculation, recommends the proportional coefficient and the trigonometric series of method of earthquake motion synthesis.(4)Analyses the seismic response to the soft soil foundation in Tianjin Binhai New Area through the Flac3 D software, Numerous simulate the acceleration, velocity and displacement spectrum and amplified effect of earthquake wave through the silt, silty clay and powder clay of soft soil foundation which has been filtered. Discusses the influencing factors of the physical composition and thickness of soft soil layer that is to affect the amplified effect.(5)The someone architecture engineering site of dredger fill with in Tianjin Binhai New Aera is as the research object. This site belongs to soft foundation that is main made up of powder clay and sand lens. It is with the high plasticity index, high natural moisture content and ratio porosity, low natural unit weight, high compressibility and low strength. According the results of numerous simulate the acceleration, velocity and displacement spectrum and amplified effect of earthquake wave through the silt, silty clay and powder clay of soft soil foundation to establish the calculating model which uses the trigonometric series method to synthetic ground of 63%, 10%, 2% of exceeding probability in 50 years which based on that three bedrock acceleration duration. Using the Flac3 D software to enter the synthetic earthquake motion to calculate the situation of the seismic subsidence in the soft soil site, extracting the mechanical parameters, and preliminary revealing the site of dredger fill in its mechanism of the seismic subsidence, and the results will be carried contrast analysis with Yu ShouSong’s calculation formula of seismic subsidence quantity which obtained by the three axle test, Meanwhile it offers preliminary evaluation the seismic depression level of the soft soil.