极端降雨条件下粗粒土高路堤边坡暂态饱和区时空演变规律及致灾机理研究

Constructing durability roadbed is strategic initiatives to reduce life-cycle costs of road construction and improve road capacity, conform with technological development Twelfth Five-Year Transportation Plan. Under the extreme rainfall, coarse-grained soil high embankment may form transient saturated zone, lead to the strength of soil change significantly over time and space, directly affect the durability of the embankment. Consider with the deterioration of soil strength in the transient saturated zone can significantly improve durability of embankment in the high embankment construction, but the researches in this area is not yet in-depth at home and abroad. This study focus on rainy season coarse-gained soil high embankment instability often occurs, first, launch the study of correlation between coarse gained soil permeability characteristic and soil water characteristic curve (SWCC); and then base on the indoor and outdoor experiments and numerical analysis, reveal the formation condition and spatio-temporal evolution of transient saturated zone of coarse-grained soil high embankment slope under extreme rainfall conditions; Finally, introduced CT damage variable, established the constitutive model which can describe the unsaturated shear strength changed with matric suction and considered the damage characteristic, investigate the evolution of transient saturated zone impact on the slope safety factor variation, reveal the slope instability mechanism considered with transient saturated zone. The research has great guiding significance to perfect the durability roadbed construction technology.

建设耐久性路基是降低公路施工全寿命周期成本，提高公路通行能力的战略性举措，符合交通运输“十二五”科技发展规划。极端降雨条件下，粗粒土高路堤边坡将形成暂态饱和区，导致土体强度随时间和空间的变化而发生显著变化，直接影响路堤的耐久性。在高路堤建造时考虑暂态饱和区内土体强度的劣化能显著提高路堤耐久性，而国内外在此方面的研究尚不深入。本项目针对雨季粗粒土高路堤边坡失稳时有发生的现状，首先开展多因素作用下粗粒土渗透特性与土水特征曲线及两者相关性研究；然后基于室内外试验和数值分析，揭示极端降雨条件下粗粒土高路堤边坡暂态饱和区形成条件及其时空演变规律；最后，引入CT损伤变量，建立能描述土体非饱和强度随基质吸力变化及考虑损伤特征的本构模型，结合非饱和抗剪强度理论，探讨暂态饱和区演变影响下边坡安全系数变化规律，揭示考虑暂态饱和区演变影响的边坡失稳机理。研究成果对完善我国耐久性路基建造技术有重要的指导意义。

在高速公路建设过程中，粗粒土是不可或缺的路基填料，受极端降雨影响粗粒土高路堤边坡出现不同程度的管涌、边坡滑塌、路面不均匀沉降等灾变现象；严重缩短了路堤的使用寿命。本项目从粗粒土路堤填料基本物理力学性质出发，结合室内试验、理论分析和数值模拟等手段，分别从以下几个方面对极端降雨条件下粗粒土高路堤边坡暂态饱和区时空演变规律及致灾机理进行研究：. （1）综合考虑水位线、基质吸力变化，分析了渗透力变化对粗粒土高路堤边坡安全系数以及塑性区分布规律的影响。. （2）根据不均匀系数和曲率系数的定义，将粗粒土调配成符合试验要求的级配；分别按照试验方案控制土样的级配和密度，测量其基质吸力和含水率的数值，并分析其两者的变化规律。. （3）基于室内模型试验、数值模拟软件，提出了一种以粗粒土骨架为研究对象，综合考虑基质吸力、孔隙水压力、渗透力、重度等因素影响下的粗粒土稳定性计算方法。. （4）基于饱和-非饱和渗流理论、抗剪强度理论、相似理论建立室内边坡降雨模型，研究长时大雨、短时间暴雨工况下粗粒土高路堤边坡渗流特性，据此对数值模拟的土水特征曲线进行修正，将渗流计算结果导入到FLAC3D中，探讨了粗粒土高路堤边坡稳定性及塑性区的发展规律，揭示出暂态饱和区演变影响的失稳机理。. （5）将三轴试验与CT试验相结合，具体实施方式为在三轴试验前后两阶段，通过现有的工业CT设备，对粗粒土试样同一横截面进行无损检测扫描与分析，通过CT损伤变量值公式计算出不同敏感因素下粗粒土试样在荷载作用下的CT损伤值。. （6）在极端降雨条件下粗粒土高路堤边坡容易发生失稳灾害，以粗粒土路堤边坡失稳的控制技术为目的，探索出几种新型的边坡位移监测技术和边坡加固技术，并对采取的监测与加固技术效果进行分析。.本项目的研究成果可以为复杂环境下粗粒土路堤的设计、施工及路堤长期稳定性的控制提供参考，研究成果具有重要的理论意义和工程实践意义。