Study On Confined Creep Properties Of Geogrid

As one of the main products of special geosynthetics, Geogrid has curently become the most prevalent and widespread reinforcing material in the application of reinforced soil engineering, However, its polymer form determines its characteristic of obvious creep. Creep can cause grille stress relaxation which would cause the failure of the reinforce. For certain high structures which are built by using insufficient strength and modulus of materials, the affect of Creep is even worse, Moreover, this affect also is the key factor in deciding weather geogrid can be applied into the permanent works. There have been a lot of research on the creep characteristics of geogrid both domestically and internationally. Nevertherless, most of those studies focus on the creep characteristics only in unconfined restrained tensile condition. It is greatly different from the condition that the geogrid is embedded in the reinforced earth structure in the actual stress state, during which geogrid and soil work together throughout the entire reinforcement process. And those different interfaces will lead to different creep characteristics. Therefore, those studies can not truely reflect the long-term creep behavior of Geogrid in soil.This paper focus on the HDPE geogrid as research object and implemented a series of confined tensile and creep tests of HDPE geogrids in sand. Then the test results were compared with those of unconfined tensile and creep tests in order to analyze the lateral restraining effect on creep characteristics. We utilized those test data to predict the geogrid creep strength in two cases, and further obtained the desired geogrid strength after the elimination of various reduction factor. Finally, applying with the reinforced slope example, this study analyzed the economic impact of the lateral restraining behaviour on the project, The main results are listed as follows:(1) The confining tensile strengths are higher than unconfining tensile strengths, and extension rate is greatly reduced. With growing burden pressures, the secant modulus increase. In certain constraints of lateral limit, the tensile strength is proportional to the elongation rate.(2) The lateral limits showed a distinguish impact on the creep charactistics of geogrid. With the same load pressure, the isochronous creep strain will be greatly reduced and it is proportional to the overburden pressure.(3) The laterally confined creep effects mainly occurs mainly during the loading period and the early period of pressuring period. With the creep load level increases, the isochronous creep rate and creep strain also increase. The time of stablizing is extented, and the creep phenomenon are more distinguished.(4) After processing the date of creep charactisitcs, the study shows that the100kPa confined long-term creep strength increase36%compared with unconfined situations. Similarly, creep reduction coefficient relatively reduces0.642.(5) Applied in reinforced earth engineering, with the same safety coefficient, when considering only the100kPa lateral restraining unconstrained reinforcement material cost savings of16%compared to that of constrained ones.