Modeling Of Vibroflotation Treatment Of Reclaimed Liquefiable Silty Fine Sands

At present,there are many practical engineering applications of the vibroflotation without packing in the backfill fine sand foundation.But its theoretical derivation and numerical calculation method are still in the primary stage.Under this background,it is increasingly important to explore the internal mechanism of the vibroflotation without packing in the backfill fine sand foundation,of which it is great theoretical significance and engineering value.Based on the energy attenuation model and pore pressure model put forward by Thevachandran Shenthan,this paper deduces the relationship between"energy—pore pressure—standard penetration"through proper hypothesis and simplification.Finally,this paper obtains four calculation values of standard penetration,and combines the measured values of standard penetration of practical engineering cases to verify the rationality and feasibility of the theory.The specific study contents and conclusions are as follows:?1?The energy dissipation mechanism is adopted to analyse and explain the variation of pore pressure in the backfill fine sand foundation during"vibroflotation process"and"after vibroflotation".In the vibroflotation process,the pore pressure variation caused by consolidation is ignored,and the total pore pressure ut in the vibroflotation process is completely represented by the pore pressure u_g,which caused by cumulative energy dissipation.The feasibility of the theoretical simplification is verified by the practical engineering cases in this paper.?2?The pore pressure variation in vibroflotation process is associated with the standard penetration.The calculation values of the standard penetration before and after vibroflotation are obtained by using four semi-theoretical and semi-empirical standard penetration formulas,which are analyzed comparing with the measured standard penetration values in the practical engineering cases supported by this paper.The results show that for the practical engineering cases in this paper,the formulas come up with by Tokimatsu&Seed and Meyerhof G G are applicable to calculate the standard penetration value of fine sand;the formula put forward by Cubrinovski M&Ishihara K is applicable to calculate the standard penetration value of silt;the formula proposed by Zhu-longgen is not applicable to calculate the standard penetration value of the foundation soil.These results are further confirmed that the scientific and rationality of the theoretical system.?3?Through analysising regressionly the standard penetration value calculated by formula put forward by Tokimatsu&Seed and Meyerhof G G before the vibroflotation,a modified formula is put forward.By comparing the calculated values of the modified standard penetration with the measured values before and after the vibroflotation,it is found that the difference between the calculated values of the modified standard penetration and the measured values is smaller and more consistent,which confirms the applicability of the modified formula.?4?This paper analyses the sensitivity of the attenuation coefficient which is a influence factor of energy transfer caused by vibroflotation in the foundation of backfill fine sand to the calculated value of standard penetration after vibroflotation.According to analysis results for the practical engineering cases in this paper,the attenuation coefficient of fine sand should be 0.03 m^-1;the attenuation coefficient of silt should be0.04 m^-1;the attenuation coefficient of the"lower boundary"should take a large critical value of 0.05 m^-1,which can improve the calculated value of standard penetration and narrow the gap between it and the measured value;the energy ball at the"upper boundary"is broken,so the attenuation coefficient is appropriate to take a small critical value of 0.0165 m^-1.