The Research Of Influence Factors And Formula For Dynamic Stress Reduction Coefficient

Since the Professor H.B.Seed and I.M.Idriss published a methodology termed the “simplified procedure” or “CSR method” for liquefaction evaluated,this method has been developed and improved for decades,and gradually became the most commonly used method for liquefaction evaluated.The calculation method of dynamic stress reduction coefficient rd is the most important factor for the evaluation result and the core technology for CSR method.The research of more reliable and practical rd calculated method is not only meaningful for liquefaction evaluation,but also an important mark of the improvement in seismic response analysis.In this thesis,the appropriate site response analysis program is selected to perform dynamic response calculations on a large number of working conditions.The obtained rd curves are statistically analyzed,and the basic form of the rd curve is found.The significance of various factors influencing rd is quantified by variance analysis,and the important factors are selected to establish a new three-factor formula and a simplified one-factor formula,which provides support for the regression of more accurate liquefaction trigger curves.The main work and conclusion of this thesis include:(1)Summarize the existing key researches,draw the critical curve or equal liquefaction probability curve for each rd calculation method and its corresponding liquefaction evaluated method.The critical curve is bended back,and the equal probability curve increases infinitely with depth,which is inconsistent with the existing experience of liquefaction induced by earthquake.(2)Use SHAKE 2000,Deep Soil and Soil Quake three site response analysis programs to perform the seismic response analysis of 508 earthquake input motion at 32 sites in Ki K-net database.The analysis results given by each program were similar,especially there is little difference in rd curves.For comparing with the existing researchs,the results of the SHAKE 2000 are selected for statistical analysis.(3)Compare the rd average curves of different levels of each factor,and find that the magnitude and shear wave velocity have a significant influence on the rd curve,while the peak ground acceleration has little effect.Through univariate and multivariate analysis of variance,it is found that depth is the most important factor for rd and plays a decisive role.Magnitude and shear wave velocity have a significant effect on rd and play an important role.Peak ground acceleration has no significant effect on rd and can be ignored.(4)Establish a new three-factor rd calculation formula.It is recommended to be used both in CSR re-evaluation of liquefaction history-cases and in liquefaction evaluation for the engineering project.The single factor rd calculation formula is simplified and recommended in the general engineering project liquefaction evaluation.(5)Compare with the existing multi-factor calculation formulas,it is found that the calculation results of the three-factor rd formula represent the results of site response analysis results better.At the same time,the formula is simpler and easier to use in engineering practice.It is improved both in accurate and practical.Compared with the existing single-factor calculation formulas,the single-factor calculation formula in this paper is more able to reflect the average curve of site response analysis results.