高海拔寒区桩土动力相互作用机制及桥梁桩基地震稳定性研究

As the main foundation form of the major construction project in unstable and ice-rich permafrost regions, the pile foundation is widely used, which also has great application foreground when the permafrost is degrading. In terms of the strong geological tectonic activities of the Qinghai-Tibet Plateau and the frequent earthquake activities, it is necessary to conduct a systematic study on the dynamic interaction mechanisms of pile-soil interface in cold regions, the seismic responses of the permafrost sites and the influencing mechanisms, and the evolution process of deformation instability of the pile foundation under the seismic load. Based on the dynamic shear tests of pile-soil interface under different test conditions, the dynamic mechanical properties of pile-soil interface and the influencing factors are to be investigated; the dynamic response characteristics of the permafrost sites will then be analyzed, and the dynamic responses of the typical pile foundations under seismic load and the deformation mechanisms are studied eventually. The research will provide a dynamic stress-strain model of the pile-soil interface considering temperature effect, and determine the spectral characteristics and intensity indices in permafrost regions. Moreover, with considering the effect of global warming and the local site effect on strong ground motion, the analytical model of the pile foundation instability under strong earthquake will be developed, and the seismic stability of the pile foundations at permafrost region will be evaluated eventually. The results of this research will have important scientific significance and application value for preventing and controlling the disasters of pile foundations at permafrost regions.

桩基是不稳定和高含冰量多年冻土区重要的工程结构基础形式，在青藏高原冻土面临大幅度退化的背景下被大量应用。鉴于青藏高原属于地质构造活动强烈区并且地震活动频繁，因此有必要对不同温度条件下寒区桩土动力相互作用机理、多年冻土场地地震动效应及影响机制、地震荷载作用下寒区桩基变形失稳演化过程及稳定性等科学问题展开系统研究。本项目以寒区桩土接触界面动力直剪试验为切入点,研究桩土接触界面动力学特性影响因素及变化规律，多年冻土场地地震动力响应特征及不同气候变化情景下桩基地震动力响应过程及变形失稳机制。研究成果将构建考虑温度影响的桩土接触面动应力应变关系模型，确定多年冻土区场地随机地震动频谱特性和强度指标，进一步提出不同气候变化情景下的桩基及桩周土体的变形破坏模式，形成地震荷载作用下考虑桩基整体效应的工程结构稳定性综合评估体系，对于提高我国多年冻土地区桩基工程的灾害预测和防治水平具有重要的科学意义和应用价值。

项目考虑青藏高原多年冻土区地震活动性和地质构造背景，以多年冻土区广泛应用的 以桥代路”桩基结构形式为研究对象，开展动荷载下桩土相互作用力学行为及典型桩基结构的地震动力响应及其稳定性的系统研究。主要成果包括：基于冻土动力学特性试验，分析了多年冻土的动力学参数随温度，围压，荷载频率的变化特性；搭建了适应于低温条件下土与结构界面动力直剪试验系统，开展了不同温度，法向压力，动荷载频率和加载次数作用下界面直剪试验，并根据接触面动剪切应力-剪切位移的关系曲线，系统研究了桩和冻土接触界面的动强度特性及变化规律；其后，应用数值计算的手段模拟天然冻土场地地震响应特性，进一步探讨了地层结构及地震动本身对场地地震效应的影响；更进一步地，以典型的“以桥代路”桩基工程为对象，考虑冻融作用下活动层的不同温度状态条件，对不同超越概率青藏人工地震荷载动作用下冻土桩基础进行了地震响应分析，并对桥梁桩基础的稳定性做出评价。综合上述成果，本研究为形成地震荷载作用下考虑桩基整体效应的工程结构稳定性综合评估体系奠定了坚实的基础，对于提高我国多年冻土地区桩基工程的灾害预测和防治水平具有重要的科学意义和应用价值。项目资助发表论文6篇，获授权发明专利1项，培养硕士研究生3名。项目投入经费24万，目前共花费15.02万，计划用于本项目研究的后续支出。