Creep Properties And Calculation Model Of Rockfill Under Complex Loading Condition

Several super high earth-rockfill dams will be constructed in China in the near future.Deformation control is the key issue in the construction and operation of these projects.Especially the control of post-construction deformation is one of the most critical problems.At present,Shen's creep model,which is widely used in earth-rockfill dam engineering,is based on the constant load creep test.However,whether the model is applicable to complex loading conditions remains undiscussed and needs further research.This dissertation focuses on the coupling effect of stress loading and creep of rockfill materia ls,which was investigated by using laboratory test,mechanism analysis,calculation models and engineering applications.The main achievements of the thesis are as follows:1.Using Nuozhadu granite rockfill,multi-step loading triaxial creep tests with large stress increment and small stress increment were carried out.Based on the experimental results,the creep process and its influence on the subsequent loading process were investigated.According to the hardening characteristics of creep,the concept of hardening creep is proposed,which can help explain the segmentation characteristics of the specimens before and after creep.2.According to the results of multi-step loading creep tests,the influence of stress loading process on the subsequent creep development was investigated,and a new accumulation rule for the creep of rockfill was proposed,which states that the current creep deformation at a certain moment in the rockfill unit is equal to the additional hardening creep deformation at that time.The unity of the hardening characteristics and the accumulation rules of creep were discussed.It is found that the influence between the two is mutual and uniform,and at physical level it's also harmonious and symmetric.3.The influence of the stress unloading process on the subsequent creep development was investigated.It was found that after the stress unloading,there exists the positive creep area,non-creep area and reverse creep area in the rockfill material.The proposed creep accumulation rule o f rockfill is also applicable to the case of stress unloading.4.Combining the general elasto-plastic model,Shen's double-yield surface model and Duncan and Chang's EB model,the calculation methods of equivalent strain hardening and hardening creep stra in were proposed and the calculation methods considering the stress loading and creep coupling effects of rockfill materials were established.The model was verified using triaxial creep test results.5.The new creep calculation model was embedded into th e large scale Contana FEM code.Based on the numerical analysis of the post-construction deformation characteristics of Gushui Dam,it is found that the main creep process of rockfill is only started after the completion of dam construction when the new calculation model is adopted.After the post-construction creep deformation,the rock mass of the dam will be in a similar “over-consolidation state”.