Stability analysis of layered slopes in unsaturated soils

doi:10.1007/s11709-022-0808-2

Front. Struct. Civ. Eng.

2022, Vol. 16

Issue (3) : 378-387 https://doi.org/10.1007/s11709-022-0808-2

RESEARCH ARTICLE

Stability analysis of layered slopes in unsaturated soils

Guangyu DAI^1,², Fei ZHANG^1,²(

), Yuke WANG³

¹. Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China
². Jiangsu Province’s Geotechnical Research Center, Nanjing 210098, China
³. College of Water Conservancy Engineering, Zhengzhou University, Zhengzhou 450001, China

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Abstract

This study presents stability analyses of layered soil slopes in unsaturated conditions and uses a limit equilibrium method to determine the factor of safety involving suction stress of unsaturated soil. One-dimensional steady infiltration and evaporation conditions are considered in the stability analyses. An example of a two-layered slope in clay and silt is selected to verify the used method by comparing with the results of other methods. Parametric analyses are conducted to explore the influences of the matric suction on the stability of layered soil slopes. The obtained results show that larger suction stress provided in unsaturated clay dominates the stability of the layered slopes. Therefore, the location and thickness of the clay layer have significant influences on slope stability. As the water level decreases, the factor of safety reduces and then increases gradually in most cases. Infiltration/evaporation can obviously affect the stability of unsaturated layered slopes, but their influences depend on the soil property and thickness of the lower soil layer.

Keywords slope stability suction stress unsaturated soil layered slope limit equilibrium

Corresponding Author(s): Fei ZHANG

Just Accepted Date: 16 February 2022 Online First Date: 08 April 2022 Issue Date: 31 May 2022

Cite this article:

Guangyu DAI,Fei ZHANG,Yuke WANG. Stability analysis of layered slopes in unsaturated soils[J]. Front. Struct. Civ. Eng., 2022, 16(3): 378-387.

URL:

https://academic.hep.com.cn/fsce/EN/10.1007/s11709-022-0808-2
https://academic.hep.com.cn/fsce/EN/Y2022/V16/I3/378

Fig.1 Modeling of unsaturated slope stability analysis.

Fig.2 Normal and shear stress acting on the log-spiral surface.

Fig.3 Flow chart of the optimization procedure to determine the factor of safety.

Tab.1 The value of several typical unsaturated soil parameters [7]

Tab.2 Typical values of infiltration and evaporation rates [7]

Tab.3 F_s for unsaturated slopes with the same soil properties in each layer

Fig.4 Comparisons of F_s between the presented method and Spencer method for: (a) Case 1: the upper layer is clay and the lower layer is silt; (b) Case 2: the upper layer is silt and the lower layer is clay.

soil type	n	α (kPa^?1)	k_s (m/s)	$? ′ (°)$	c' (kPa)	γ (kN/m³)
clay	1.7	0.005	5 × 10^?8	20	10	18
silt	4.0	0.05	1 × 10^?7	30	5	18

Tab.4 Typical values of the unsaturated soil properties

Fig.5 (a) SWCC for clay and silt soils; (b) SSCC for clay and silt soils.

Fig.6 Variation of F_s with the thickness of soil layer for: (a) Case 1: the upper layer is clay and the lower layer is silt; (b) Case 2: the upper layer is silt and the lower layer is clay.

Fig.7 Distribution of suction stress along vertical elevation of an unsaturated slope in uniform clay/silt (H = 10 m, H_w = 0).

Fig.8 Variation of F_s with water table level for: (a) Case 1: the upper layer is clay and the lower layer is silt; (b) Case 2: the upper layer is silt and the lower layer is clay.

Fig.9 Effects of the groundwater level on the critical sliding surface of Case 1 (θ = 45°) with: (a) H₁ = 0.2H; (b) H₁ = 0.5H; (c) H₁ = 0.8H.

Fig.10 Influence of the infiltration/evaporation rate on the factor of safety (θ = 45°, H_w = 0) for (a) Case 1: the upper layer is clay and the lower layer is silt; (b) Case 2: the upper layer is silt and the lower layer is clay.

Fig.11 Influence of the dimensionless infiltration/evaporation rate on the safety of the unsaturated slope in clay or silt (θ = 45°, H_w = 0).

Fig.A1 Different calculations on the moment of the self-weight gravity when (a) β_F > β_E and (b) β_F ≤ β_E.

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