Empact Study Of Silt Content On Sandy Soil Liquefaction Potential Covering Full Relative Density

Most studies generally believe that the liquefaction potential of sand decreases first and then increases with the increase of fine particle content,showing a ’ parabolic ’ trend.This is due to the use of equal void ratio or equal dry density principle in sample preparation.The relative density of the sample decreases first and then increases.In the dynamic triaxial liquefaction test,the reaction is more the influence of relative density on the test results.The sample preparation principle,whether it is equal void ratio,equal skeleton void ratio,or equal relative density,cannot fundamentally solve the problem.Therefore,it is of great practical significance to systematically study the liquefaction of fine-grained sand,including the new understanding based on the existing test methods,the analysis of historical seismic liquefaction data and the exploration of new sample preparation principles.In this thesis,from the perspective of different sample preparation standards,the classical literature on liquefaction of fine-grained sandy soil is studied and analyzed to obtain reasonable sample preparation principles.Through relevant experiments,the influence of silt content on liquefaction potential and liquefaction characteristics of saturated sandy soil is studied and discussed.The specific work and results are as follows :(1)The indoor compaction test was used to simulate the field standard penetration test,and the variation trend of the number of hits,the tangent slope of the compaction settlement curve and the change trend of the silt content were analyzed.The variation law of the sand soil was studied when the silt content was different.The results show that with the increase of relative density,the sample is more and more difficult to be compacted,which is consistent with the trend of SPT blow count with relative density.Therefore,the indoor compaction test can be used to simulate the field standard penetration test.(2)Collect the liquefaction data of liquefied sites and non-liquefied sites in historical earthquakes,refer to a large number of seismic liquefaction survey data based on in-situ tests and analyze the laws to verify the real representativeness of the relationship between the number of indoor compaction tests and the silt content in Chapter 2,and establish the relationship between indoor compaction tests and historical seismic liquefaction data.The results show that the indoor compaction test results in the second chapter have similar distribution forms with the standard penetration test results in the earthquake site,which confirms that the indoor compaction test is comparable to the historical seismic liquefaction data,and can reflect the overall change trend of the standard penetration number with the silt content.(3)According to the third group of sand and silt in the second chapter,in order to approach the particle size range of real fine sand and silt in nature,the ’ fine ’ Fujian standard sand(0.075mm-0.5mm)and the Yellow River silt(0.005mm-0.075mm)were mixed to prepare samples,and the ’ fine ’ Fujian standard sand with different silt content was prepared according to the equal relative density of 30 % and 70 %,respectively.(4)On the fitting curve of cyclic stress ratio and vibration times,the cyclic stress ratios of 20 times and 30 times are intercepted respectively and their changing trends with the increase of silt content are analyzed respectively.The results are compared with the relationship between the number of indoor compaction tests and the content of silt in the second chapter and the relationship between the number of standard penetration tests and the content of fine particles in the third chapter.The results show that the dynamic triaxial liquefaction test results and the third chapter historical earthquake liquefaction survey data are verified in the NCEER liquefaction discrimination method.The cyclic stress ratio decreases with the increase of powder content,but the overall decline rate is slower than that of standard penetration blow count,which leads to the result that the liquefaction critical curve moves to the left with the increase of fine content.