Study on the effect of fissures in expansive soils on permeability and engineering effects of canal slopes
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摘要:
膨胀土是一种特殊的非饱和土，也是南水北调中线渠首段土体的主要成分。与一般黏性土相比，膨胀土具有裂隙性，裂隙的存在会对其渗透性产生影响，进而影响到膨胀土渠坡的实际排水效果。为了探究膨胀土渗透性与其裂隙和含水量之间的关系，采用自制的渗流装置对相关地区的非饱和膨胀土进行渗流试验。试验结果表明，不同初始条件的土样在饱和环境中渗流时其渗透系数都会随着渗流的进行而逐渐减小。在同等初始含水率情况下，土样的裂隙率越大，渗透系数越大，渗透系数到达稳定状态所需的时间就越长；在相同初始裂隙率情况下，初始含水率低的土样，渗透性小但基质吸力大，吸水后会迅速膨胀导致渗透性越来越差。通过分析土体从不同初始条件开始渗流至饱和状态期间土体渗透系数的变化过程，可以发现在渗流开始的2 h以内，渠坡排水设施的排水效果最好，在8 h内渠坡排水设施都具有一定效果，超过8 h后排水效果有限。
Abstract:Expansive soils represent a special type of unsaturated soil and constitute a major component of the soil structure in the initial canal section of the middle route of the South-to-North Water Transfer Project(MR-SNWTP). Compared to typical cohesive soils, expansive soils exhibit fissures that can impact their permeability, subsequently influencing the drainage efficiency of expansive soil slopes. To investigate the relationship between permeability of expansive soils, fissures, and moisture content, percolation tests were carried out on unsaturated expansive soils in the relevant region using a self-made permeability apparatus. The experimental results indicate that the permeability coefficient of soil samples with different initial conditions decreases gradually during percolation in a saturated environment. At the same initial water content, the greater the fracture ratios of the soil sample, the greater the permeability coefficient and the longer it takes for the permeability coefficient to reach a steady state. Under equal initial moisture content, greater fissure rates of soil samples result in higher permeability coefficients, and the time required for the permeability coefficient to stabilize increases. Under the same initial fissure rate, soil samples with lower initial moisture content exhibit lower permeability but higher matric suction; however, rapid expansion due to water absorption leads deteriorating permeability. By analyzing the changes in soil permeability coefficients during the transition from different initial conditions to a saturated state, it is observed that the drainage effectiveness of canal slope drainage facilities is most significant within 2 hours of the start of the seepage, remains noticeable within 8 hours, and becomes limited after 8 hours.
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Key words:
- geological engineering /
- expansive soil /
- seepage test /
- fissure ratios /
- drainage effectiveness
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表 1 试样基本参数指标
Table 1. Fundamental parameters of test samples
编号 含水率/% 重度/（kN·m−3） 黏聚力/kPa 内摩擦角/（°） 1 12.4 19.1 14.0 11.0 2 10.1 22.1 20.0 14.0 3 25.4 19.7 24.0 16.0 4 29.1 19.9 61.3 22.8 5 28.2 20.3 72.5 25.0 
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表 2 不同工况试验参数表
Table 2. Experimental parameters for different working conditions
试样 初始裂隙率/% 初始含水率/% 工况1 14.0 5 工况2 11.5 10 工况3 9.0 15 工况4 6.5 20 工况5 4.0 25
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