The Research On The Creep Properties Of Geogrid And Constitutive Model Of Reinforced Soil

In recent years , the application technologies of reinforced soil are changing continuously,and reinforced soil structures have been widely used in highway engineerings because of its advantages of simple construction and low cost. However,the theoretical analysis and design of reinforced soil still lagged behind engineering practices. In the past,geogrids were regarded as elastic materials in a lot of researches,which made it difficult to consider the effect on the work performance of reinforced soil structures caused by the creep of geogrid as the polymer under a long-term load.Therefore,this paper centered on the creep properties of geogrid under a long-term load and its effect on the stress and deformation of reinforced soil structures,mainly carried out the following experimental and theoretical studies:(1)This paper selected some home-made high-density polyethylene geogrids for the tests,so as to study the creep properties and relaxation effects of geogrids under the environmental temperature and different load conditions by the creep tests of geogrids,then determined the calculation mode of the long-term creep strength of the geogrids at a certain temperature. Then, this paper categorized creep model of geogrids from previous studies and evaluated their applicabilities and reliabilities.(2)Combining with the experimental creep results , this paper established the viscoelastic constitutive model and viscoelastic-plastic-damaged constitutive model of the geogrids , then analyzed the dependence of the model parameters on its influencing factors after the model parameters were obtained based on the utmost optimization theory(.3)Constitutive model of reinforced soil considering viscoelasticity of geogrid was established,and the constitutive model parameters of reinforced soil were solved based on the utmost optimization theory,then the law of change of stress-strain characteristics of reinforced soil as the different influencing factors change was studied.In the process of carrying out experimental and theoretical studies,several useful conclusions have also been obtained such as:(1)Power function type has the highest precision in the previous typical creep models studied for the geogrids. However,these three types of typical creep models are only suited to describe the attenuation mode creep at a low-stress ratio,not suited to describe the non-attenuation mode creep at a high-stress ratio.(2)Three parameters viscoelastic model of geogrids can relatively accurately reflect two-stage attenuation creep properties of geogrids at a low stress. The viscoelastic-plastic-damaged model established for the geogrids through considering the viscoplastic deformation and damage characteristics of geogrids,can relatively accurately reflect the three-stage non-attenuation mode creep properties of the goegrids at a high-stress ratio.(3)The micro-stress of geogrid in the reinforced soil unit is related to the tensile strength of geogrid,reinforced layer spacing,soil properties and time;When the macro-stress of reinforced soil unit remained unchanged,the stress relaxation of geogrid would lead to the gradual decrease of micro stress of geogrid unit and gradual increase of micro stress of soil unit,and the micro stress of unit wouldn't tend to remain stable until the time of Tp while the reinforced soil arrived plastic state;The effect of model parameters of geogrid and the deformation and strength parameters of soil on Tp have different sizes.It is hoped that the research results in this article could provide some references for analysis of stress and deformation or the security design of reinforced soil structures on considering the creep properties of geogrids.