藏东地区斜坡土壤冻融侵蚀力学机制及敏感性分析

冻融侵蚀是青藏高原草甸覆盖区的主要侵蚀方式,以气候条件一致的藏东地区斜坡表层土壤侵蚀为对象,基于区域地质条件和土体赋存特征,分析了土壤剥蚀输移的力学过程,探索了缓变的隐性因子和灾变的显性因子对冻融侵蚀的作用机制。结果表明：① 地表冻融侵蚀是自基岩风化和土壤演化起始,经历冻融拉裂破坏与沙土输移,到重新裸露基岩的一个循环演化过程;② 冻融侵蚀输移驱动力为受全因素控制的重力和径流动水压力,抗侵蚀力则由土壤二元结构特征和植被根系锚固力控制,多因素耦合作用下,冻融侵蚀演化具有“多因素,同表观”的特征;③ 基于土体极限平衡状态的破坏机制,冻融侵蚀分为牵引式的逐级崩解型和牵引—推移复合式的多级崩解型,两者在侵蚀强度和触发因素上均存在显著区别;④ 引入冻融侵蚀强度特征参数并建立其与构造、地形、植被、岩性等因子之间的关系式,提出基于小流域土壤侵蚀观测的冻融侵蚀强度估算公式。基于力学过程和土体破裂机制建立的侵蚀强度多因素估算方法,可有效减小区域适宜性产生的误差,并且为制定精细化的不同工况下的冻融侵蚀防治对策提供理论基础。

The mechanism and sensitivity analysis of soil freeze-thaw erosion on slope in eastern Tibet

Freeze-thaw erosion is the main erosion in the Qinghai-Tibet Plateau. In this study,both the failure process and the transport process of the soil on a slope are analyzed under a similar climatic condition in eastern Tibet. It reveals that the sensitivity factors should be divided into the latent factor and the dominant factor. The latent factors change gradually over time, which include the geological structures, the lithology, and the slope direction. The dominant factors with catastrophe include the climate, the sloping topography, and the vegetation cover. The driving forces of freeze-thaw erosion are the gravity force and hydrodynamic force, while the erosion resistance is controlled by the dual structure of soil and the anchoring force of vegetable roots. On a temporal scale, the freeze-thaw erosion is a cyclic evolution process. It begins with the weathering of bedrock and soil formation, goes through the freezing-thawing and the tensile failure process, and ends with the re-exposure of bedrock after the soil is transported. Generally, this cycle should last a long term, but it could only last several years or decades of the period due to the structure of the soil. Based on the failure mechanism of the limit equilibrium state of the soil, freeze-thaw erosion can be divided into trailed progressive disintegration and multi-level disintegration type, both of which have the characteristics of ’multi-pathogenesis and same symptoms’. The characteristic parameter of freeze-thaw erosion intensity is introduced to describe how those influence factors affect the mechanism of freeze-thaw erosion. The formula is established by the relationship between the intensity value and the factors including both latent factors and dominant factors. It can be used to forecast calculate the amount of soil erosion when there is a standard-value in the study.Although there are still a few discretization errors in the formula building because of the randomness of sensitivity factors, the fitting results can still explain more than 90% of the evolution trend. Moreover, a new model of freeze-thaw erosion intensity based on soil erosion observation is proposed. Therefore, different from previous research, in this paper, the new model of erosion intensity can effectively reduce the errors caused by regional suitability and provide a theoretical basis for formulating countermeasures under different conditions.