Influence of Dry Density and Wetting-Drying on Hydraulic Characteristics of Compacted Loess

doi:10.11988/ckyyb.20230377

Abstract

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

CLC Number:

TU444黄土与地基

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 Changjiang River Scientific Research Institute, 2024, 41(8): 128-134.

Figures/Tables 13

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

Fig.1 Particle grading curves

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%

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

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

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

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

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

Fig.4 Relationship between air intake value and dry density

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

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

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

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

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

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