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The Soft Soil Effect of Marine Soil on Ground Motion Parameters

Session: How Well Can We Assess Site Effects So Far? [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

Most offshore seabed is covered by a thick layer of soft soil that is nearly in the viscous liquid state or semi-plastic state. It magnifies or reduce the seismic site effect, thereby it is an important factor for the determination of seismic design parameters of offshore facilities and the compilation of ground motion zonation map of marine area. This research is based on the dynamic property experimental data of marine soil and the nonlinearity site response simulation to investigate the effect of soft soil on site ground motion parameters. The liquidity index or the shear wave velocity is recommended as the index of marine soft soil. The soil volume with a liquidity index less than 1.0 or the shear wave velocity less than 150m/s is considered as soft soil and it should be paid more attention on its seismic site effect. The investigation shows that the thickness of the soft soil is the key factor to determine its effect on ground motion parameters. The soft soil with a thickness less than 4 meters will magnify the peak ground motion acceleration. With the increasement of input ground motion, the amplification becomes more remarkable, and the characteristic period extends to the lower frequency. When the thickness of the soft soil is greater than 4 meters, it deamplifies the site ground motion parameters. The equivalent shear wave velocity of the top 40m soil is recommended as the site classification index of marine site. And the site is classified into 4 classes. It presents the initial study of the characteristic and site effect of thick soft sediment on the seabed, the marine site classification index and site types.The research can provide the assessment of site effects for the seismic ground motion zonation in the marine area and the determination of seismic design parameters for the offshore facilities. This will benefit the structural safety of offshore facilities and speed up the compilation of ground motion zonation map in China.

Presenting Author: yanju peng

Student Presenter: No

Authors