干密度和增减湿对压实黄土水力特性的影响

doi:10.11988/ckyyb.20230377

摘要/Abstract

摘要：

研究非饱和土的水力特性对分析工程建设活动中黄土的渗流和变形问题具有重要意义。以西安市南郊黄土为研究对象,采用滤纸法和饱和盐溶液法测得3种干密度下的黄土增减湿土-水特征曲线,并通过Childs & Collis-George模型预测试验黄土的非饱和渗透系数,探究干密度和增减湿对非饱和渗透特性的影响。结果表明:经历增减湿的土样的非饱和渗透系数曲线应结合土样的含水状态和对应的土-水特征曲线来预测;土体非饱和渗透系数随体积含水率的增大而增大,随基质吸力的增大而减小,在0~5 MPa范围快速衰减4~5个数量级;受瓶颈效应和减湿收缩的影响,土体增湿阶段渗透系数变化幅度小于减湿阶段的变化幅度;渗透系数随干密度增大而减小,干密度从1.719 g/cm³增大到1.834 g/cm³,渗透系数减小2个数量级;压实黄土在增减湿阶段的非饱和渗透系数最大可相差3~4倍。

关键词: 压实黄土, 土-水特征曲线, 干密度, 增减湿, 非饱和渗透系数

Abstract:

The study of hydraulic characteristics in unsaturated soils is crucial for analyzing seepage and deformation of loess during engineering activities. This research focuses on loess from the southern suburbs of Xi’an City. The filter paper method and saturated salt solution method were employed to measure soil-water characteristic curves under three dry density conditions with varying degrees of wetness. The Childs & Collis-George model was used to predict unsaturated permeability coefficient, examining the impacts of dry density and wetting/drying cycles on these characteristics. Results indicate that unsaturated permeability coefficient increased with volumetric moisture content and decreased with matric suction, dropping significantly by 4-5 orders of magnitude within the 0-5 MPa range. Due to bottleneck effects and moisture-reduction-induced shrinkage, the variation in permeability coefficient during wetting stages was smaller compared to drying stages. Furthermore, with dry density increasing from 1.719 g/cm³ to 1.834 g/cm³, permeability coefficient decreased by two orders of magnitude. The unsaturated permeability coefficient of compacted loess varied by a factor of up to 3-4 between wetting and drying phases.

Key words: compacted loess, soil-water characteristic curve, dry density, wetting and drying, unsaturated permeability coefficient

中图分类号:

TU444黄土与地基

胡梦玲, 张小龙, 许文昊, 王治文, 陈豪. 干密度和增减湿对压实黄土水力特性的影响[J]. 院报, 2024, 41(8): 128-134.

HU Meng-ling, ZHANG Xiao-long, XU Wen-hao, WANG Zhi-wen, CHEN Hao. Influence of Dry Density and Wetting-Drying on Hydraulic Characteristics of Compacted Loess[J]. Journal of Yangtze River Scientific Research Institute, 2024, 41(8): 128-134.

图/表 13

表1 试验黄土的基本物理性质指标

Table 1 Basic physical properties of the test loess

孔隙比e	相对密度 G_s	液限 ω_L /%	塑限 ω_p /%	最优含水率 ω_opc /%	最大干密度 ρ_dmax/ ( g·cm^-3)
0.998	2.69	31.57	17.26	13.2	1.91

图1 颗粒级配曲线

Fig.1 Particle grading curves

表2 不同干密度的SWCC增减湿试验方案

Table 2 Wetting and drying scheme for the SWCC test on compacted loess with different dry densities

干密度/ (g·cm^-3)	减湿制样路径	增湿制样路径
1.719 1.776 1.834	饱和→23%→21%→19%→17%→15%→13%→11%→9%→7%→5%	饱和→风干→5%→7%→9%→11%→13%→15%→17%→19%→21%→23%

表3 不同饱和盐溶液对应的基质吸力[18]

Table 3 Matric suction values corresponding to different saturated salt solutions[18]

饱和盐溶液	相对湿度RH/%	基质吸力/MPa
LiBr	6.6	367.54
LiCl·H₂O	12.0	286.70
CH₃COOK	23.1	198.14
MgCl₂·6H₂O	33.1	149.51
K₂CO₃	43.2	113.50
NaBr	59.1	71.12
KI	69.9	48.42
NaCl	75.5	38.00
KCl	85.1	21.82
K₂SO₄	97.6	3.29

图2 3种干密度下的增减湿土-水特征曲线

Fig.2 SWCCs of compacted loess with different dry densities under wetting and drying cycles

图3 VG模型拟合的增减湿土-水特征曲线

Fig.3 SWCCs of compacted loess under wetting and drying cycles fitted by VG model

表4 不同干密度下增减湿SWCC的VG模型拟合参数

Table 4 Fitting parameters of VG model for the SWCCs of compacted loess with different dry densities under wetting and drying cycles

干密度/ (g·cm^-3)	阶段	VG模型拟合参数					进气值/ kPa
干密度/ (g·cm^-3)	阶段	θ_r	θ_s	$α$	$n$	$R 2$	进气值/ kPa
1.719	减湿	0.052 9	0.361 0	2.42×10^-3	1.423 1	0.995	204.633
1.719	增湿	0.055 9	0.312 9	3.08×10^-3	1.427 6	0.997	129.945
1.776	减湿	0.061 7	0.339 7	8.71×10^-4	1.525 8	0.986	513.052
1.776	增湿	0.057 2	0.300 7	1.74×10^-3	1.470 4	0.987	204.633
1.834	减湿	0.062 5	0.318 2	6.42×10^-4	1.528 5	0.993	657.129
1.834	增湿	0.058 5	0.285 2	7.86×10^-4	1.488 8	0.997	548.245

表4 不同干密度下增减湿SWCC的VG模型拟合参数

Table 4 Fitting parameters of VG model for the SWCCs of compacted loess with different dry densities under wetting and drying cycles

干密度/ (g·cm^-3)	阶段	VG模型拟合参数					进气值/ kPa
干密度/ (g·cm^-3)	阶段	θ_r	θ_s	$α$	$n$	$R 2$	进气值/ kPa
1.719	减湿	0.052 9	0.361 0	2.42×10^-3	1.423 1	0.995	204.633
1.719	增湿	0.055 9	0.312 9	3.08×10^-3	1.427 6	0.997	129.945
1.776	减湿	0.061 7	0.339 7	8.71×10^-4	1.525 8	0.986	513.052
1.776	增湿	0.057 2	0.300 7	1.74×10^-3	1.470 4	0.987	204.633
1.834	减湿	0.062 5	0.318 2	6.42×10^-4	1.528 5	0.993	657.129
1.834	增湿	0.058 5	0.285 2	7.86×10^-4	1.488 8	0.997	548.245

图4 进气值随干密度的变化关系

Fig.4 Relationship between air intake value and dry density

图5 预测非饱和渗透系数的Childs & Collis-George模型示意

Fig.5 Childs & Collis-George model for predicting unsaturated permeability coefficient

表5 不同干密度下增减湿阶段饱和渗透系数实测值

Table 5 Measured values of saturated permeability coefficient of compacted loess with different dry densities during wetting and drying stages

阶段	干密度/(g·cm^-3)	饱和渗透系数K_s/(m·s^-1)
	1.719	5.430×10^-6
减湿	1.776	6.440×10^-7
	1.834	5.640×10^-8
	1.719	3.289×10^-6
增湿	1.776	4.054×10^-7
	1.834	2.313×10^-8

表6 不同干密度下增湿阶段饱和渗透系数预测值

Table 6 Predicted values of saturated permeability coefficient of compacted loess with different dry densities during wetting and drying stages

阶段	干密度/(g·cm^-3)	饱和渗透系数K_s / (m·s^-1)
	1.719	2.563×10^-6
增湿	1.776	3.073×10^-7
	1.834	1.647×10^-8

图6 ρd =1.719 g/cm3时非饱和渗透系数随基质吸力和体积含水率的变化曲线

Fig.6 Variations of unsaturated permeability coefficient with matric suction and volumetric moisture content when ρd =1.719 g/cm3

图7 3种干密度下的非饱和渗透系数变化曲线

Fig.7 Curves of unsaturated permeability coefficient at three dry densities

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