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Response laws of pore structure and matrix suction of slip zone soils under action of wetting-drying cycles
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摘要: 非饱和土基质吸力与其微观孔隙结构息息相关。为探究在干湿循环作用下滑带土孔隙结构与基质吸力的响应规律, 以重塑黄土坡滑坡滑带土为研究对象, 采用压汞法分析干湿循环过程中孔隙大小分布规律, 得到不同干湿循环次数下滑带土孔隙分布曲线。在此基础上, 结合分形原理, 将滑带土孔隙划分成三类(大孔隙、中孔隙和小孔隙); 结合毛细管模型, 间接推算出滑带土的土-水特征曲线(SWCC)。研究结果表明:反复干湿循环作用使小孔隙逐渐转化成大孔隙, 颗粒孔隙转化成团粒孔隙; 不同干湿循环次数对应的土-水特征曲线均存在一个共同的拐点, 拐点上侧, 含水率相同时, 随着干湿循环次数增加, 基质吸力逐渐增大, 下侧反之。研究成果有利于深入了解滑带土的干湿循环效应, 可用于库岸滑坡演化机理研究。Abstract: The matrix suction in the unsaturatedsoil is closely related to its micro pore structure.In order to analyze the response laws of the pore structure and matrix suction of the slip zone soil under the actions of the wetting-drying cycles, the remolded slip soil of Huangtupo Iandslide was taken as the research case history.Further, a mercury intrusion porosimetry (MIP) tests are carried out to study the changes in pore size distribution during the wetting-drying cycles and the pore size distribution curves for different cycles have been got.On this basis, the pore of slip soil is classified into three type (large pores, medium pores, and small pores) using the fractal theory, and the soil-water characteristic curves of the slip zone soil is indirectly calculated (SWCC) using the capillary model.The research results show that under repeated wetting-drying cycles, some small pores gradually transformed into large pores, and some particle pores changed into aggregate pores.The curves had a common inflection point, and above the inflection point the matrix suction under the same water content gradually increases with the increase in cycle numbers, however, the opposite behavior was noted below the inflection point.Hence, the results obtained from this research can be helpful in comprehensively understanding the wetting-drying effects of the slip soil, which is of great significant and can be applied to research on the evolution mechanism of reservoir bank landslides.
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图 3 不同干湿循环次数下滑带土孔隙分维
Figure 3. Pore fractal dimension of slip zone soils in different cycles
图 5 特定含水率下基质吸力与循环次数的关系
Figure 5. Relationship between matric suction and cycle numbers at three given water contents
表 1 滑带土基本物理性质
Table 1. Basic physical property parameters of Huangtupo slip zone soils
天然密度/(g·cm-3) 干密度/(g·cm-3) 饱和含水率/% 天然含水率/% 饱和度/% 液限/% 塑限/% 塑性指数 液性指数 2.03 1.79 20.95 15.97 75.5 25.95 13.86 12.09 0.17 
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表 2 各区间孔隙体积百分比
Table 2. Percentage of pore volume in each interval
孔隙类型 干湿循环次数/次 0 1 2 3 4 小孔隙 67.3 65.4 65.9 63.8 60.3 中孔隙 8.7 9.2 11.4 11.3 9.3 大孔隙 24.0 25.4 22.7 24.9 30.4
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表 3 特定含水率下基质吸力与循环次数的关系
Table 3. Relationship between matric suction and cycle numbers at given water contents
含水率/% 不同干湿循环次数下的吸力/kPa 0 1 2 3 4 18.00 7.3 11.63 16.5 37.1 41.5 15.97 89.7 108.6 183.0 244.6 251.7 13.86 444.0 463.0 520.0 602.8 583.9
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表 4 SWCC(Van Genuchten方程)参数拟合值
Table 4. Fitting results of SWCC by Van Genuchten equation
循环次数/次 饱和含水率/% 残余含水率/% a b c R2 0 19.03 5.62 3.7×10-11 0.468 2 148.181 0.988 1 19.40 5.34 1.0×10-10 0.477 1 648.450 0.990 2 19.90 4.87 1.7×10-10 0.520 2 376.940 0.993 3 20.35 5.08 4.9×10-10 0.535 1 712.575 0.994 4 21.20 4.26 9.2×10-12 0.434 2 520.875 0.986
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