The Research On The Long-term Settlement Characteristics Of Soft Clay Subject To Static And Dynamic Loading

In addition to static loading, the soft clay subgrades in service period are also need to undertake the low amplitude dynamic loading which caused by the running of traffic tools. So in order to accurately predict and control the post-construction settlement of soft clay especially its long-term settlement, its generation and development rules of creep subjected to static loading and accumulative deformation subjected to dynamic loading must be deeply analyzed.This paper first studied on the deformation characteristics of the long-term creep (secondary consolidation) subjected to static loading. In detail based on Bjerrum’s creep diagram and Yin-Graham EVP model, we used the tangent slope definition method to analyze the time effect of secondary consolidation coefficient of over-consolidated clay in surcharge preloading engineering. As Bjerrum’s creep diagram is an idealized model, the long-term surcharge oedometer tests were performed to improve the above model for the purpose of achieving a better agreement with the actual grounds situations. It’s found that secondary consolidation coefficient of over-consolidated clay not only decreases with over-consolidated ratio, but also increases with the development time of secondary consolidation. Based on above results, a model considering the time effect of secondary consolidation coefficient for settlement estimation was formulated and a case study to estimate it indicated that the settlement estimated by our method is 1.6～5 times larger than that estimated by the previous method. Moreover, the larger the over-consolidated ratio is as well as the longer the service life is, the bigger the difference between our method and the previous method. So the long-term time effect of secondary consolidation of over-consolidated clay must be taken into account when evaluating the post-construction settlement of surcharge preloading engineering.Then the long-term drainage dynamic triaxial tests were carried on GDS dynamic triaxial test system to simulate the deformation characteristics of soft clay under the long-term low amplitude dynamic traffic loading, and it systematically analyze the effect of the cyclic numbers, the static and dynamic deviator stress, the over-consolidated ratio and the vibration frequency. The experimental results show that the accumulative deformation of soft clay under the long-term low amplitude dynamic traffic loading increases with the cyclic numbers, the static and dynamic deviator stress, and decreases with the over-consolidated ratio and vibration frequency. Based on the observation of the similarity deformation pattern of the static creep and the long-term accumulative deformation, the creep equation in Yin-Graham EVP model was used to derive the formula of the long-term logarithm accumulative strain considering the effect of cyclic numbers, the static and dynamic deviator stress, the over-consolidated ratio and the vibration frequency. But as for the numerical difference between the creep and the accumulative deformation, the results of the long-term drainage triaxle tests were used to revise the above formula, and parameters fittings were also carried out which obtained a good result indicating that it is feasible to simulate the long-term accumulative deformation of soft clay under the low amplitude dynamic loading by the static creep.