Study On Mechanism And Discrimination Of Sand Liquefaction Based On Shaking Table Test

Sand liquefaction is an important topic of geotechnical engineering.The liquefaction of sand induced by dynamic load always causes the foundation failure,water spraying and sand emitting as well as the building damaged.Thus,it will also result in a great loss to the national economy and a serious threat for the people's life and property.Along with people's increasing attention to the liquefaction problem,it has been found that there are many of unsaturated sand liquefaction cases in the practical engineering.However,it has been noted that the research on the liquefaction of unsaturated sand is few.Therefore,the study of mechanism and discrimination for liquefaction of unsaturated sand is necessary for its engineering applications.Firstly,the shaking table experiments are carried out for the sand with the saturation of 100%,95%,90%,85% and 80%,respectively.The results show that the saturation has an important effect on the sand liquefaction.With the decrease of saturation,the liquefaction resistance will increase.The liquefaction of sand arises always from bottom to top during the load,that is to say,the pore water constantly flows upward from the bottom of the model box,along with the lower and middle layers of sand first liquefied till the entire sand model foundation following.After the end of the load,the excess pore water pressure will dissipate gradually,and its velocity will increase with the depth of the sand model.Secondly,as the discriminant methods have not been developed,it will result in the existed methods couldn't be applied widely.Based on the Bayes discriminant analysis theory,40 groups of typical sand samples collected from Tangshan and Sanshui earthquakes are firstly constructed as a database for our analysis in the thesis.Then,a seven-factor Bayes discriminant analysis model is established in terms of the earthquake magnitude M,the peak ground acceleration gmax,the standard penetration hammer number N63.5,the penetration resistance Ps,the relative density Dr,the average particle diameter D50 and the groundwater depth dw seven evaluation indicators.According to the influence weight of each evaluation index in the seven-factor Bayes model,a new five-factor Bayes model and a new five-factor Fisher model are developed in terms of the earthquake magnitude M,the peak ground acceleration gmax,the penetration resistance Ps,the relative density Dr,the average particle diameter D50.Finally,comparing the results of the five-factor models and those of the seven-factor models,it can be found that the five-factor models are more accurate than the seven-factor models,which means the five-factor model has a higher accuration with fewer indicators.Thus,the five-factor model will not only catch the effect of main factors on the discriminant of sand liquefaction,but also save the construction cost,which will be more applicable in practical engineering.