| Both natural and artificial gravelly soils sites have been damaged by liquefaction in the past but did not cause enough attention.Wenchuan Earthquake in 2008 witnessed the largest liquefaction of natural sedimentary gravelly soils in the world,with the gravel content of liquefied soil ranging from 5% to 85% or more,which is far higher than before,overturning the traditional understanding that the natural gravelly soils site is an excellent natural foundation.Considering the wide application of gravelly soils engineering,the liquefaction of gravelly soils with broad gravel content has become a front and hot topic in geotechnical earthquake engineering in recent 10 years.The liquefaction resistance is one of the essential parts of soil liquefaction research.As a fundamental way to obtain the mechanical properties of gravelly soils,the triaxial test still has several critical problems to be solved.The first is the membrane compliance and the its correction method;the second is the real influence of the gravel content and relative density on the liquefaction resistance of gravelly soils;the third is the evaluation method of the liquefaction resistance of gravelly soils in the non-horizontal site.In the past 20 years,the development of the correction method of membrane compliance is limited,which severely blocks the development of gravelly soils liquefaction theory and site evaluation technology,and is the key and bottleneck of gravelly soils liquefaction research.Gravel content,the most crucial factor that distinguishes gravelly soils from sand,has no unified conclusion on the ite effect on liquefaction resistance,which restricts the improvement of basic liquefaction theory and evaluation technology.Relative density is an essential factor that affects the liquefaction of coarse-grained soil.Still,its influence law on liquefaction strength cannot be explained correctly all the time,which makes the liquefaction evaluation theory lack a reliable quantitative basis.The liquefaction evaluation method of non-horizontal gravelly soils field with initial shear stress ratio has attracted much attention.Still,there is a lack of reliable analysis theory,which makes it challenging to evaluate the liquefaction of non-horizontal gravelly soils field.Based on the GDS large-scale dynamic triaxial apparatus of the Institute of Engineering Mechanics,CEA,this paper extensively collected the existing research on the gravelly soils liquefaction,expanded the existing database,and carried out the research on the test technology and gravelly soil liquefaction resistance.Taking the real liquefied soil in Wenchuan earthquake as the primary research object,a series of scientific,systematic and reliable correction methods of membrane compliance were established as the the core,and the development law of the liquefaction resistance of gravelly soils under different conditions was taken as the basis and reference of the study of liquefaction mechanism and evaluation method.Under the isotropic consolidation condition,the real influence law of the gravel content and relative density on the liquefaction resistance was explored,and the scientific and reasonable prediction model and formula were proposed pertinently;under the anisotropic consolidation condition,the analysis principle and method of the influence of the initial shear stress ratio were put forward,and the influence law and calculation model of the initial shear stress ratio on the gravelly soils liquefaction resistance were obtained.The study provides an essential basis and reference for the study of liquefaction mechanism and evaluation method of gravelly soils.The main achievements and innovations are as follows:1.The measurement and calculation of membrane penetration of gravelly soils were studied.The two-scale method was first applied to coarse-grained soils and largescale equipment to demonstrate the feasibility of the method and the reliability of the results,achieved the accurate measurement of the membrane penetration of gravelly soils in the conventional instrument.The influence conditions of membrane thickness were put forward by using the quantitative relationship between film thickness and particle size.The new calculation formula for the membrane penetration of coarse-grained soil was established,which overcomes the defect of the present single variable formula that can not adequately deal with the gradation diversity.The volume deformation law of gravel soil during water compensation was pointed out,and the limitations of isotropic hypothesis in different gravel soil were demonstrated.2.The correction technology for the membrane compliance of gravelly soils was studied.Based on the principle of calculation correction,the pore pressure increment model of gravelly soils considering the membrane compliance was established,the reliability of calculation results was analyzed by comparing with the results of instrument compensation method;the new non-linear development law of membrane correction factor of coarse-grained soil was revealed,and the empirical calculation formula of the modification coefficient was proposed.Based on the correction results,the new error prediction model and formula of membrane compliance on the coarse-grained soil liquefaction resistance were proposed.3.The effect of gravel content and relative density on the gravelly soils liquefaction resistance of under the triaxial isotropic consolidation were analyzed.By the development of gravelly soils modelling technology,the phenomenon of gravelly soils liquefaction was successfully reproduced in the laboratory,and the liquefaction characteristics of gravelly soils with different gravel content and compactness were compared.Based on the membrane compliance correction,the influence law of gravel content on gravelly soils liquefaction resistance was revealed,the concept of threshold gravel content and the prediction formula of gravel content correction factor were proposed,which provide the critical basis for liquefaction evaluation.The real relationship of gravelly soils liquefaction resistance with different compactness was analyzed.4.The effect of initial shear stress ratio on the gravelly soils liquefaction resistance was analyzed under the triaxial anisotropic consolidation condition.Based on the defects of the existing research methods,a new analytical method for the influence of initial shear stress ratio was proposed by using the spherical stress standardization method and the maximum cyclic shear plane theory,which had been verified in a variety of test conditions.A new method of the correction factor of initial shear stress ratio was proposed,and the recommended value of the correction factor of gravelly soils was obtained based on the triaxial test,so as to achieve the evaluation of gravelly soils liquefaction resistance with the influence of initial shear stress ratio. |
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