Study On Creep Behaviour Of Geogrids And Analysis Method For Evaluation Of Long-term Performance Of Geogrid-Reinforced Earth Structuress

In this paper, the geogrid is taken as a typical geosynthetics and the retaining wall reinforced by geogrids is taken as a representative reinforced earth structures. The creep behaviour and visco constitutive model of geogrids are studied through experimental creep tests in laboratory. Through the archetypal observation and the indoor creep tests, the mechanical properties of the reinforcement wall is seriously discussed and spot analysis of the typical defects of the strong reinforcement retaining wall is done. Hereafter, the model shall be analyzed by using visco-elasticity plasticity finite element merical number of grid reinforcement retaining wall with the consideration of the soil mass visco-elasticity plasticity rheology and grid visco-elasticity plasticity creep to discover the long-term working properties of the geogrid and the reinforcement retaining wall. In accordance with the large scale deformation of the reinforcement retaining wall, the reinforcement wall mechanics parameter inversion analysis and calculation method based on Plastic Finite Element Method and the Complex variable derivative inversion is built to investigate the reasons and the prevention of the typical defects of grid reinforcement wall and to provide the important reference for the evaluation of reinforcement retaining wall working properties and the engineering design. Precisely, the main investigations and achievements are composed of following portions.1. Through the spot survey and analysis of the partial reinforcement retaining wall at home and abroad, the problems of reinforcement wall design, construction and use have been discovered; especially the defects and mechanical rules of long-term working reinforcement wall and the destroyed position and means of the reinforcement wall in long-term work have also been discovered. In accordance with the analysis of the relation between the wall deformation and the whole security, the conclusion that the creep properties of the grid and the soil rheology are the key elements of the reinforcement long-term properties is put forward.2. The creep experiments are carried out in accordance with the CAT steel-plastic complex grid and high density HDPE, and the systematical analysis of the experiments result is done. On the basis of the test results experimentally achieved under different conditions, the general characteristics of variations of geogrids with time and the change law of with the level loads are examined for a given environmental temperature. The creep test data obtained for different temperatures are correlated to the creep behaviour for a given temperature by the time shift factor and then all the revised data are used for curve fitting to determine the creep reduction coefficient of the two kinds of geogrids when it is fifty years.. Furthermore, two types of empirical constitutive models including an exponential-type model and a hyperbolic-type model based on visco-elasticity are proposed for geogrids to reproduce the nonlinear creep properties of geogrids, then rational procedures for defining the relevant parameters respectively by experimental tests are presented. In addition, both proposed models are verified by comparing the prediction given by the models with experimental results.3. In order to investigate the long-term working properties of the reinforcement retaining wall, the experimental tests of the 12m grid reinforcement retaining wall of Meihe express way stone section class-three steps in GuangDong province have been conducting for two years. At the same time, the 4.5m reinforcement wall indoor model experimental tests of the three steps in the chamber are underway. Through the tests and analysis of the spot archetype and indoor models, the conclusion got is that the reinforcement mass strength is not changing in accordance with the banking, and the bar tension is keeping steadily. The nonlinear distributing foundation tension and the influencing factors of it are analyzed and so are the relation between the rules of the reinforcement mass change with the wall height and the basal supporting conditions. Afterwards, the precise analysis of the hidden fracture plane in reinforcement mass is carried out.For the deformation of the large-scale reinforcement retaining wall, the spot observation and analysis and the study of the reinforcement remaining intensity are carried out. Through the systematical compared analysis, five typical wall deformation of the large-scale reinforcement wall are discovered. Further more, the production reason, the relation between wall deformation and the mechanical properties of the reinforcement wall are analyzed to get the pertinence between the reinforcement wall stability and the wall deformation.4. Numerical analyses of long-term performance of geogrids reinforced retaining earth walls considering both rheological behaviour of backfill soils and creep property of geogrids based on visco-elasto-plasticity theory by nonlinear creep properties. Through the secondary development of the large-scale general finite element soft, the finite element iterative process can be carried out and through the use of the subprogram Umat of the user, the grid Viscoelastic and the soil mass creep properties are carried out. Nonlinear computation is numerically implemented by hybrid procedure which combines the incremental method with iteration scheme based on initial-strains and unbalanced forces. The comparison between the calculation result and the model testing result proves the reliability of the mathematical model and in accordance with which, the precise long-term working properties analysis of the reinforcement wall is deep investigated. Through the analysis, the relation between the reinforcement wall and the soil tension, the distribution rules of the reinforcement tension and the soil tension, and foundation tension curve and the effective elements are discovered. The rule that the distributing rule of the hidden fracture plane of the reinforcement wall will disappear in given time is put forward, and the failure mode of long working reinforcement wall is achieved.5. Based on the spot observation and the reinforcement wall deformation, the Complex Derivative analysis is adopted and the visco-elasticity plasticity finite element analysis program of the reinforcement wall is used. The mechanical parameter cohesion c and frictional angleφof the reinforcement wall need refutations when it is stratified filling. Through the analysis, the relation between the reinforcement wall deformation and the reinforcement mechanical parameter is got. And through the deformation mode of the reinforcement wall deformation in the normal working conditions and the reasons of other deformations of the wall, the relations of between the wall deformation and the reinforcement wall stability is put forward. In accordance with which, the reasonable inspecting part of the strong reinforcement wall and the relation between the wall deformation and the whole structural security.