土工格栅加筋土挡墙的加载历史效应研究

Loading history is closely related to the time that can be considered through another concept "loading rate". Creep, relaxation and cyclic loading can also be characterized by loading rate. Generally, the geosynthetic- reinforced soil retaining wall is subjected to the arbitrary loading during the construction and service stages, and the loading rate is usually not constant. Therefore, it is more general and applicable to use loading rate as the research perspective to perform experimental and theoretical studies on the effect of loading history of geosynthetic-reinforced soil retaining wall. Using the underground engineering model test system, a series of model tests are performed on geogrid-reinforced sand retaining wall under the various loading histories to study their deformation and strength characteristics. The interaction between sand and geogrid as well as the mechanism of loading history effect are explored through digital photography-based deformation measurement technique. On the basis of the model test results, the elasto-viscoplastic constitutive models for the reinforcement, soil and interface are developed to describe the deformation and strength characteristics of geogrid-reinforced sand retaining wall under arbitrary load historical conditions. The corresponding nonlinear numerical method is presented to quantitatively predict the deformation and strength characteristics of geosynthetic-reinforced soil retaining wall during the entire process from construction, service to the design life. It has theoretical significance to promote the prediction research on the failure of geosynthetic-reinforced soil engineering.

加载历史与时间密切相关，加载速率隐含时间的概念，而蠕变、松弛和循环均可通过加载速率表征。土工合成加筋土挡墙在施工及服役过程中所经受的载荷通常是任意变化的，同时加载速率不完全是持续不变的。因此，以加载速率为研究视角对土工合成加筋土挡墙的加载历史效应进行试验与理论研究更具有一般性和适用性。本项目利用地下工程模型试验系统和数字照相量测技术，对土工格栅加筋砂土挡墙在不同加载史下的变形强度特性及影响规律进行研究，探讨砂土和土工格栅之间的相互作用以及加载历史效应的作用机理。在分析试验结果基础上，从筋-土-界面三方面考虑，建立能反映任意加载历史条件下土工格栅加筋砂土挡墙变形强度特性的弹粘塑性本构模型理论。最后提出相应的非线性数值计算方法，定量预测土工合成加筋土挡墙从施工、服役使用直至设计使用寿命的整个加载历史过程中的变形强度特性。研究成果对于促进土工合成加筋土工程失稳破坏的预测研究具有理论指导意义。

加载历史与时间密切相关，加载速率隐含时间的概念，而蠕变、松弛和循环均可通过加载速率表征。土工合成加筋土挡墙在施工及服役过程中所经受的载荷通常是任意变化的，同时加载速率不完全是持续不变的。因此，以加载速率为研究视角对土工合成加筋土挡墙的加载历史效应进行试验与理论研究更具有一般性和适用性。本项目基于室内模型试验结果，对土工格栅加筋砂土挡墙的加载历史效应进行分析，包括速率相关特性、蠕变以及应力松弛，发现土工格栅加筋砂土挡墙的加载历史效应与砂土和土工合成材料的加载历史效应相似，揭示了加载历史效应发生机理在于加载速率不会发生突变而加载速率的变化量（加速度）会发生突变。在三要素模型框架下，针对岩土材料所表现出的速率相关特性，以应变速率为基本内变量，构建了统一的弹粘塑性本构模型，该模型既可以描述砂土材料也可以描述土工合成材料的加载历史效应。将统一的弹粘塑性本构模型嵌入到基于动态松弛法的有限元程序中，从而对土工合成加筋土挡墙的加载历史效应进行弹粘塑性有限元模拟，实现了包含加载速率变化加载、蠕变加载和应力松弛加载在内的全过程模拟。数值计算结果表明，综合考虑砂土材料和土工合成加筋材料粘性特性的有限元计算方法能很好地模拟土工合成加筋砂土挡墙的加载历史效应，包括速率相关特性、蠕变变形以及应力松弛现象，分析了墙背土压力、基底应力及筋材中张拉力的分布特征和演化规律。研究成果对于促进土工合成加筋土工程失稳破坏的预测研究具有理论指导意义。