渭河流域西部局地因素和气候变化对浅层土体冻融过程及水热能运移的影响及其差异机制

In seasonally frozen ground regions in Northwest China，physical and mechanical behavior of shallow soils has always been in long-term dynamic change with external environments. Many diseases of engineering are closely related to water-heat movement and potential transfer caused by environment. In Loess Plateau，freeze-thaw process is obviously affected by complex terrains and surface conditions，so are water-heat movement and potential transfer of shallow soils. This project takes the Loess Hill-Gully Region in the west of Weihe River Valley as an example，and selects local factors including slope gradient，slope aspect，soil type，water content and salt content to be discussed. Based on comprehensive monitoring sites in the field，the quantitative analysis on how local factors and climate change have affected freeze-thaw process，water-heat movement and potential transfer is applied from the angle of field observation. Combined with field observation data，laboratory experiment and theoretical analysis，the evaluation model of seasonally frozen ground is established. Regarding different freeze-thaw processes，characteristics of water-heat movement and potential transfer and their spatial-temporal differentiation rule are both analyzed during typically freeze-thaw period. The moisture-heat coupling model during freeze-thaw process is set up based on local factors. The difference mechanism that various factors have influenced freeze-thaw process and characteristics of water movement and heat transfer is studied thoroughly. In addition，we explore how freeze-thaw process and water-heat movement and potential transfer influence each other under extreme climatic condition. The results provide important parameters and theoretical basis for establishing simultaneously land surface hydrothermal model and getting accurate simulations in Loess Plateau.

西北季节冻土区浅层土体物理力学行为长期受外界环境影响而处于动态的变化中,许多工程病害与环境变化引起的土中水热能迁移有密切关系。在黄土高原，复杂的地形地表条件对季节冻土冻融过程和浅层土体水热能运移影响显著。项目拟选取坡度、坡向、土壤类型、含水量及盐分等局地因素作为研究对象，以渭河流域西部黄土丘陵沟壑区作为研究区，建立野外综合观测场地，从实地观测的角度定量分析局地因素和气候变化对浅层土体冻融过程及水热能运移的作用机理及影响程度。结合实地监测资料、理论分析与室内试验，建立季节冻土局地因素发育评估模型；分析不同冻融过程在典型冻融阶段的水热能运移特征与时空分异规律；构建考虑局地因素影响的土体冻融过程的水热能传输模型，深入研究不同因素对冻融过程及水热能运移特征影响的差异机制，并探索极端气候条件下冻融过程对水热能迁移的影响与响应。研究成果可为黄土高原陆面水热传输模型建立与精确模拟提供重要参数与理论基础。

西北季节冻土区浅层土体物理力学行为长期受外界环境影响而处于动态的变化中，许多工程病害与环境变化引起的土中水热能迁移有密切关系。尤其在黄土高原，复杂的地形地表条件对季节冻土冻融过程和浅层土体水热能运移影响显著。项目选取坡度坡向、土壤类型、含水量及盐分等局地因素作为研究对象，以黄土高原渭河流域西部黄土丘陵沟壑区为研究区域，建立了野外观测场地，对该区域浅层非饱和土体冻融过程及水热运移规律对气候作用及局地因素的响应过程进行了研究与分析。结论：该区域裸露地表土壤的最大冻结深度在20～50cm之间；气温对地温及地温变幅的影响随深度增加而迅速衰减，地温振幅随深度增加按指数规律衰减且温度波的相位随深度的增加而滞后，地表下200cm深度以内地温振幅受气温影响较大；在土壤冻结过程中，深层土壤未冻水逐渐向冻结层运移，导致深层含水量逐渐减少；不同深度土壤冻结系数随土壤深度的增加而减小，融化系数则相反；地表下50cm深度以内的土体含水量受降水影响波动显著；土壤含水量与温度呈相似变化，地温峰值出现的时间总滞后于土壤水分，其变异程度均随土壤深度的增加而减小。在理论分析层面，揭示了在局地因素和气候变化下西部黄土丘陵沟壑区浅层土体冻融过程、水热能运移特征及在冻融环境下土体及土-结构面力学行为。在模型建立方面，基于传热学以及非饱和土渗流理论，以温度和水分作为基本变量，并且结合能量守恒方程和质量守恒方程，建立了考虑水分相变、水分对流传热和水汽扩散潜热的水-汽-热耦合运移模型，预测了在未来暖化和湿化两种气候模式下季节性冻土区土壤中的水热变化规律；建立了大气对非饱和黄土的作用关系模型，利用该作用关系研究了均质非饱和黄土边坡的稳定性，得到了西北气候环境下边坡安全系数随着季节的变化规律。以上研究成果可为黄土高原陆面水热传输模型建立与精确模拟提供重要参数与理论基础，并对季节冻土区岩土工程设计和防灾减灾提供理论支撑与参考。