Long-term Properties Of Geogrid And Its Effect On The Response Of Reinforced Soil Retaining Wall At Small Strain

With the development of reinforced soil technology,geosynthetic-reinforced retaining walls have been widely used in a large number of engineering projects.The geogrid is one of the most commonly used reinforcement materials,and its creep and stress relaxation properties have always been co-existing in the normal service life of the retaining walls,and these two long-term properties influence and interact with each other.The long-term properties of geogrid have a direct influence on the performance of geosynthetic-reinforced retaining walls,and the strain of the reinforcement materials is generally not more than 2% under the normal working condition of the retaining walls,so it is particularly important to investigate the long-term properties of geogrid at small strain.This thesis is targeted at the long-term properties of the HDPE geogrid at small strain.The long-term stiffness fitted formula of the geogrid under small stress / small strain has been obtained from laboratory tests,then the long-term stiffness was employed to study the effect of the long-term properties on the reinforcement loads and lateral facing displacements of geosynthetic reinforced soil retaining walls.The main contents and conclusions are presented as follows.(1)By literature survey,this study summarized the long-term properties of geogrid and its influencing factors,the evaluation methods of long-term stiffness,and the various indoor testing methods of long-term properties;(2)The long-term creep and stress relaxation properties of the geogrid(<1000 hours)have been obtained,through conventional laboratory tests under three levels of small stress or small strain by using the tri-head electronic creep testing machine.(3)The long-term creep and stress relaxation properties of the geogrid in the design life have been predicted,through conducting the time-temperature superposition method tests under the same stress or strain levels.The results of the accelerated tests have been compared with those obtained from the conventional tests,the errors in the acceleration tests have been analyzed,and the repeatability of the test results have also been verified.Finally,both the long-term creep stiffness formula of the geogrid under small stress and the long-term stress relaxation stiffness formula of the geogrid under small strain have been derived by combining the results of the conventional tests and the accelerated tests,and the accuracy of these formulas have been verified.(4)By establishing the numerical models of the reinforced retaining walls with the formulas of long-term stiffness,the internal forces of the reinforcement and the lateral facing displacements of geosynthetic-reinforced soil retaining walls after different years of service have been obtained by using the iterative method.The influence of the long-term stiffness on the response of reinforced retaining wall have been analyzed and summarized.