Failure Criterion Of Natural Loess Under Dynamic Loading

Studying and solving the dynamic problems of loess intensively is the key to solve the problems of seismic geological disasters in loess regions.The failure criterion of the loess under dynamic loading is particularly prominent.Furthermore,with the increasing impact of earthquake disasters,the failure criterion of original loess under dynamic loading needs to be solved.The results have great significance for enriching and developing the theory of loess dynamics,and it also accords with the objective development trend of loess dynamics.In order to solve the failure criterion of original loess under dynamic loading,the idea adopted by the author can be briefly summarized as: by analyzing the concept and relation of destruction and yield,the author tries to understand the concept of loess failure clearly.The dynamic failure process of loess is studied by using the test data.The parameters that describe loess failure are provided.The failure criterion of original loess under dynamic loading is established in combination with the dynamic failure process.Finally the applicability of the failure criterion is tested by test results.In this dissertation,three principal problems are discussed concretely,including the analysis of concept of failure and yield and their relationship,expression parameters of natural loess failure and its failure criterion,and the applicability of failure criterion of natural loess.There are a few research progresses in this thesis and the details corresponding above three principal problems could be summarized as follows.(1)On the view of concept,yield and failure are different.The failure criterion is also different from the yield criterion.In fact,most failure criteria are actually yield criteria.Yield is the boundary between the elastic and plastic of a material.For a unit body,failure is the state where the stress no longer increases and the strain or displacement reaches a certain limit value.For a structure,first,failure means that the structure as a whole cannot sustain the load,and external loads cannot continue to be applied.Next,the failure point is connected to form an overall failure surface,and the strain and displacement on the failure surface are abruptly changed,there are significant and relatively large-scale relative movements along both sides of the failure surface.(2)We comb the concept of average distance to describe particle contact density and its mathematical expression,then applied the stress ratio that figures the endurance capacity of loess to resist external dynamic loading.We also put forward an estimation method of the failure dynamic stress of loess based on the critical influencing properties.The results show that the mean value of particle contact density can reflect the micro-scale contact characteristics of soil,which agrees well with the shear strength of loess.As a link between relationships of dynamic strain and micro-scale parameters,shear strength could be effective to make sure the failure criterion of loess under dynamic loading.(3)The calculated results of the failure criterion based on average distance are in good agreement with testing data and perform well on controlling the data error.This means the estimation method has rationality at a certain extent.This method should theoretically have applicability to other soil types.Based on this,the empirical formula of estimating the failure dynamic stress of loess by using the void ratio is proposed,we can distinguish whether the loess is in a state of failure.