黄土沉积序列的地质力学演进规律与定量评价

Loess soils have been the subject of large amounts of research effort, arising from their geological environmental importance. However, it is still lack of high precision profile of loess mechanics as well as the spatial distribution within the whole Chinese Loess Plateau. This is very importance, arising from their economic importance in China and elsewhere and also because of the severe geohazards that they are subject to, notable collapse failures. A key problem remains that much of this research is specific to one topic or particular soil, and there is a lack of linking framework between soil mechanics and geological properties. This means that diverse opinions exist in the literature on many principal mechanisms of behaviour, for example the relative roles of inter-particle cementing and suction. This research project will provide an innovative umbrella framework for the mechanical behaviour of loess soils using the latest techniques for examining the relationships between loess geology backgrounds and mechanical behaviour of soils within the context of their geological origins and history. For example, loess soils of differing composition will be tested in high quality laboratory triaxial apparatus at strains that are resolved from the elastic region to failure, using the latest instrumentation and techniques. An initial framework based on the behaviour of the soils in saturated states will be derived from comparisons of the behaviour of intact and reconstituted samples. Geological properties such as depositing environment, physical-chemical properties, micro-fabric and mineralogical studies will be used to confirm what forms of soil mechanics correspond to. The project will therefore provide a solid basis for future work to build a unifying soil mechanical model of loess soils.

黄土第四纪环境地学研究已取得了巨大进展。但之于地质剖面当前仍缺乏高精度黄土力学剖面；之于黄土风成分区，仍缺乏与之对应的力学分区。本研究拟以黄土成土化过程为主线，按照“物源沉积→环境控制→结构生长→应力固结→结构力学”的研究思路，以地质与力学融合为研究手段，以典型剖面为研究对象，开展黄土沉积序列地质力学演进规律与定量评价研究。分析黄土沉积序列物性和沉积环境特征获取黄土地质属性；模拟沉积环境，制取重塑样品，揭示黄土微观结构生长及应力固化机制；针对原状黄土和重塑黄土分别开展土力学实验研究，重构黄土固有力学和结构力学剖面，揭示结构效应及其产生机制。分析黄土力学特性与剖面沉积环境演化、物性规律、微观结构和应力历史的对应关系，以黄土堆积过程为演进参照，定量评价黄土沉积序列地质力学演进规律。本项目不仅可以推动黄土科学集成纵深发展，也为进一步建立黄土统一地质力学模型打下基础。

黄土第四纪环境地学研究已取得了巨大进展。但之于地质剖面当前仍缺乏高精度黄土力学剖面，之于黄土风成分区，仍缺乏与之对应的力学分区。本项目按照“物源沉积→环境控制→结构生长→力学响应”的地质历史思路，以黄土成土化过程为主线，以黄土沉积序列为研究对象，将黄土地质和力学深度融合，以实验的可靠性和精准性为支撑，开展“黄土沉积序列地质力学演进规律与定量评价”研究，取得了如下进展：（1）饱和黄土结构力学特性：揭示了长期渗流条件下黄土结构的劣化机理，发现了黄土原状结构的各向异性现象，揭示了黄土颗粒在沉积过程中的方向选择性，定量刻画了黄土结构的破坏过程；揭示了区域尺度上黄土力学特性异同，建立了颗粒级配指标与变形强度指标的相关关系，初步构建黄土地质力学本底数据库；系统总结了黄土高原尺度盐分含量分布规律，揭示了增加难溶盐含量与改良颗粒级配对黄土强化结构抵抗变形的正向作用；发现了黄土颗粒在高应力条件下的破碎行为，揭示了黄土颗粒间的接触模式对颗粒破碎行为的控制作用。（2）非饱和黄土灾变力学特性：从实验室尺度和现场尺度揭示了水-力-热耦合作用下黄土灾变过程，精细刻画了非饱和黄土的变形特性和持水特性，揭示了温度和孔隙比变化对黄土灾变的影响机制，构建了考虑孔隙比和温度变化的黄土水-热-力耦合模型，并将其运用到预测现场大尺度的黄土湿陷；分析了加载速率和增湿路径对黄土水力特性的影响机制，证实了非饱和黄土的变形和屈服特性与加载速率的相关性，揭示了力学增湿和水力增湿对持水特性影响的差异，并评价了常见考虑孔隙比变化的持水模型在黄土的适用性。（3）黄土力学特性定量评价：借助数学方法构建了黄土力学参数的多维概率模型，揭示了非饱和黄土物性参数与力学参数之间的非线性相关性，提出了黄土力学参数的非线性概率估计方法；证实了非高斯性对黄土力学参数估计的影响，并评价了常见多维概率模型在黄土物理-力学参数上的适用性；分析了不同结构的vine copula模型在黄土力学参数建模的适用性，通过R vine-copula构建的多维概率模型对未知的黄土力学参数进行合理估计。通过本项目持续攻关，将黄土力学研究放在黄土第四纪地质学框架内加以研究，考虑沉积环境和应力历史，突破以往黄土力学关注个例的研究局限，将黄土地质与黄土力学深度整合，推动黄土科学集成纵深发展，也为进一步开展黄土高原土力学分区提供基础，具有广阔的应用前景。