封闭系统条件下压实黄土的二维循环冻融变形特性及其评价

道路、渠道和土石坝等工程的冻融为二维冻融,为探索土在二维循环冻融作用下的变形规律和评价方法,以宁夏同心黄土为对象,压实度和饱和度为因素,试验研究了压实黄土在封闭系统条件下的二维循环冻融变形特征,变化规律,分析了因素的作用机理和显著性,提出了二维冻融变形评价方法。试验结果表明:封闭系统条件下,压实黄土的二维循环冻融变形以水结冰膨胀效应为主导,竖向表现为冻胀和融沉,水平表现为冻胀和融胀。水平和竖向冻胀变形的比值随冻融循环次数的增加而增大,最大比值约2倍。水平融胀明显地小于竖向融沉,二者的比值平均约0. 43。较一维封闭系统竖向冻融,二维冻融的竖向融沉变形占竖向冻胀变形的比例大,竖向冻融变形波动明显,且冻融体变率高。压实度和饱和度对压实黄土二维冻融变形的影响均非常显著,是主控因素。评价指标合理,能直接或间接表征冻融对土的几何、物理和力学性能的影响。研究结果对宁夏压实黄土岸坡工程的冻害评价与防治具有重要的现实意义,对土二维冻融效应的深入研究具有引导和促进作用。

Two-dimensional cyclic freeze-thaw deformation characteristics and evaluation of compacted loess under closed system condition

The freeze-thaw of roads, canals and earth-rock dams is two-dimensional. In order to explore the deformation law and evaluation method of soil under two-dimensional cyclic freeze-thaw, the orthogonal test scheme L16(4⁵) was designed with Ningxia Tongxin loess as the object, compactness and saturation as the factors. Using two-dimensional unidirectional cyclic freeze-thaw test method, the characteristics and variation law of two-dimensional cyclic freeze-thaw deformation of compacted loess under closed system conditions were studied experimentally. The mechanism and significance of the factors were analyzed, and a evaluation method of two-dimensional freeze-thaw deformation was proposed. The evaluation index of freeze-thaw deformation is reasonable, which can directly or indirectly characterize the effects of freeze-thaw on the geometry, physics and mechanical properties of soil. The results show that the two-dimensional cyclic freeze-thaw deformation of compacted loess is dominated by water freezing expansion effect under the closed system, while the vertical freeze-thaw deformation is characterized by frost heave and thaw settlement, while the horizontal freeze-thaw deformation is characterized by frost heave and thaw heave. The vertical freeze-thaw deformation decreases gradually along the horizontal frozen surface from the vertical restraint surface to the frozen surface. The horizontal freeze-thaw deformation increases first and then decreases along the vertical frozen surface from top to bottom. The ratio of horizontal frost heave deformation to vertical frost heave deformation increases with the increase of freeze-thaw cycles, and the maximum ratio is about 2 times. Horizontal thaw heave is significantly smaller than vertical thaw settlement, and the average ratio of the two is about 0.43. Compared with the vertical freeze-thaw of one-dimensional closed system, the vertical thaw settlement of two-dimensional freeze-thaw system accounts for a larger proportion of the vertical frost heave, and the vertical freeze-thaw deformation fluctuates obviously, and volume change rate is high. Compactness and saturation have significant influence on two-