汶川地震粗粒土路基震动相变研究

Lots of coarse-grained-soil subgrades of road and railway were severely damaged by the Wenchuan earthquake in mountainous areas.How the physical and mechanical behaviors influenced by earthquake and thus the deformation and damage of subgrade controled are burning key scientific issues. Based on the physics of soft condensed matter, a hypothesis of coarse-grained subgrade under earthquake is given: when seismic intensity is small, shear compression-shear dilatancy transition will happen; when seismic intensity become larger, unjammed-jammed transition will happen. The hypothesis will be validated by field observation, experiments and numerical modeling. Typical phase Transitions triggered by earthquake will be observed throuth site investigation, and the behavior of transition will be recognized by shaking table model test. Combined with numerical calculation of discrete element method, the fabric character, mechanical property and law of motion of coarse-grained granular during phase transitions will be studied, as well as the critical condition, direction and pattern of sesmic phase transition. In the end, the two parameters model of seismic phase transition will be proposed, which is fit for Wenchuan seismic area, as well as three parameters model of seismic phase transition, which can be widely used. The reseach we proposed is aimed to supply a theory support to the seismic damage recognization, seismic damage assessment and seismic damage control, and also promote the general theory foundation of disaster prevention discipline.

汶川地震对山区铁路、公路粗粒土填方路基造成了严重损毁。地震以何种方式影响粗粒土填料颗粒的物理力学行为并进而对路基的变形破坏起主导作用是亟待解决的关键科学问题。项目基于软凝聚态物理学的观点提出假设：粗粒土路基存在震动相变行为，当地震作用强度较小时会发生剪缩-剪胀转变，当地震作用强度较大时会发生流动-堵塞转变。拟通过震区调研分析识别出典型的震动相变现象；利用振动台模型实验重现粗粒土路基震动相变行为；结合大规模离散元数值计算，揭示震动相变过程中粗粒土颗粒的组构特征、力学特征和运动规律，以及震动相变发生的临界条件、方向和相变进行的方式；从而验证以上假设并建立适用于汶川震区的粗粒土路基两参数震动相变模型和具有普适性的粗粒土路基三参数震动相变模型。研究成果可望为粗粒土路基震害识别、震害评估和震害控制提供理论基础，也期对交通土建领域防灾减灾学科的发展起到推动作用。

按照项目执行计划的要求，开展了汶川地震强震区典型路段公路震害调研，完成了有侧限挡墙防护路基震动沉陷（震陷）、无侧限斜坡路基震动破坏这两种震动相变致灾现象的归纳总结；在此基础上，完成了粗粒土路基震动沉陷及破坏振动台试验和斜坡路基震动破坏试验，并进行了相应的离散元数值计算；并针对粗粒土颗粒的离散元模拟提出了基于弹塑性理论的接触模型。研究揭示了宏观震害现象的细观物理、力学机制，证实了有侧限粗粒土路基震陷的地震动强度阈值问题，即存在“震陷阈值”，发现了无侧限路基的震动破坏的阈值问题，及存在“破坏阈值”；弹塑性颗粒接触本构模型从物理本质上反应了颗粒动态接触特性，将成为岩土类材料在低周期循环荷载作用下疲劳及损伤研究的基础。