Preliminary Explore On Liquefaction Characteristics Of Coral Soils

The strategic position of the South China Sea region is key interest of our country.Land reclaiming is a significant way of safeguarding territorial sovereignty.For the high construction costs and the great vulnerability to earthquake,the evaluation of the seismic stability of reef island is very important,the first question is to answer the possibility of liquefaction of coral soils and its anti-liquefaction intensity level.There is considerable controversy about whether liquefaction of coral soils can occur.The mainstream view in China is that coral soils will not liquefy or liquefy hardly,this is due to the lack of liquefaction damage cases,and the diffculty to stably reproduce the typical liquefaction phenomena in laboratory.This thesis collects and studies the recent seismic damage cases of coral soils liquefaction,takes reclaimed coral soils in an reef island in the South China Sea as the research object,explores the saturation technology of coral soil in unit tests,and conducts experiments on liquefaction characteristics of coral soil based on this.A preliminary understanding of the liquefaction laws of coral soils was obtained.The main work and results of the thesis are as follows:(1)The historical liquefaction damage data of coral soils were collected and analyzed.Confirmed the fact that typical seismic liquefaction occurred in coral soils and caused serious damage to port facilities,transportation systems,underground engineering and housing structures.The answer to the issue of whether liquefaction of coral soils can be happened is affirmative,which makes up for the lack of understanding of seismic liquefaction damage in coral soils.(2)The explanation of the reasons why the laboratory is still difficult to stably reproduce the typical liquefaction phenomenon of coral soil is given.It is pointed out that due to the porous nature of coral soil,the saturation process is relatively difficult compared to general non-cohesive soils.Saturation technology development is the key to solving the research on liquefaction of coral soils in laboratory.At the same time,a new saturation method for coral soil tests is proposed.(3)Three groups of grading samples with different average particle sizes were designed using coral soils from an actual reclamation site in South China Sea region as samples.The dynamic triaxial tests and static triaxial tests of coral soil under uniform consolidation conditions were completed.Dynamic strength,pore pressure development,strain development and stress-strain characteristics were analyzed,and compared with quartz standard sand.(4)Based on the triaxial test results of coral soils,the model for predicting the pore pressure increment for coral soil is given.The model parameters are analyzed and the measured and predicted pore pressures are compared.