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Frontiers of Structural and Civil Engineering

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ISSN 2095-2449(Online)

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Front. Struct. Civ. Eng.    2014, Vol. 8 Issue (3) : 252-259    https://doi.org/10.1007/s11709-014-0260-z
RESEARCH ARTICLE
Stability analysis of a high loess slope reinforced by the combination system of soil nails and stabilization piles
Jiu-jiang WU,Qian-gong CHENG(),Xin LIANG,Jian-Lei CAO
Department of Geological Engineering, Southwest Jiaotong University, Chengdu 610031, China
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Abstract

While the soil nails and the corresponding compound technology are widely used as the support techniques for deep foundation pit and normal slopes, few related engineering cases are found for high loess slopes. By utilizing the finite element software of PLAXIS 8.5, the behavior of a high loess slope reinforced by the combination of soil nails and stabilization piles (hereinafter for CSNSP) is studied in this paper. It can be found that the potential slide surface of the slope moves to deeper locations during the process of the multi-staged excavations. The measure of reducing the weight of the top of the slope is a positive factor to the stability of the loess slope, while the rainfall is a negative factor. The slope can’t be stable if it’s reinforced only by stabilization piles or soil nails during the process of the multi-staged excavations. The soil nail contributes greater to the overall system stability when the excavation depth is relatively shallow, while the stabilization pile takes it over when the excavation depth reaches a large value. Compared to the results from the Sweden circular slip surface, the data derived from the method of phi/c reduction is relatively large when the slope is unreinforced or reinforced only by stabilization pile, and the data turns to be small when the slope is strengthened by soil nails or the combination system of soil nails and stabilization piles.
Keywords high loess slope      CSNSP      PLAXIS      phi/c strength reduction method      Sweden circular slip surface     
Corresponding Author(s): Qian-gong CHENG   
Issue Date: 19 August 2014
 Cite this article:   
Jiu-jiang WU,Qian-gong CHENG,Xin LIANG, et al. Stability analysis of a high loess slope reinforced by the combination system of soil nails and stabilization piles[J]. Front. Struct. Civ. Eng., 2014, 8(3): 252-259.
 URL:  
https://academic.hep.com.cn/fsce/EN/10.1007/s11709-014-0260-z
https://academic.hep.com.cn/fsce/EN/Y2014/V8/I3/252
Fig.1  Geological profile and excavation process of the test section
staged constructionsdescriptionduration
stage 1excavating the front soil of the pile to the depth of 2 m10 days
stage 2reducing the weight of the head of the slope due to a landslide is generated2 days
stage 3excavating the front soil of the pile to the depth of 4 m4 months
stage 4excavating the front soil of the pile to the depth of 9.5 m during rainy season1 month
stage 5excavating the front soil of the pile to the depth of 13.5 m, a 6 m width of soil platform is remained to facilitate the construction1 month
stage 6excavating the front soil of the pile to the depth of 16.3 m15 days
Tab.1  The process of excavation
Fig.2  FEM model
Itemsshell bolting spray layerstabilization pilesoil nail
axial rigidity (kN/m)1.53 × 1062.98 × 1082.6 × 105
flexural rigidity (kN·m2/m)4593.05 × 108–
equivalent thickness (m)0.103.50–
bending strength (kN·m/m)2.2––
unit weight (kN/m/m)1.382.4–
axial strength (kN/m)35–156
Tab.2  Parameters of the structural element
itemsloessloess in rainfallfully weathered sandstonehighly weathered sandstoneslightly weathered sandstone
unsaturated unit weight (kN/m3)15.915.9192123
saturated unit weight (kN/m3)1717202224
modulus of Elasticity (kN/m2)1.45e41.20e41.68e42.38e44.85e4
Poisson ratio0.170.170.20.170.15
cohesion (kN/m2)606615103
angle of internal friction (°)2018253542
Rinter0.650.600.680.750.85
Tab.3  Parameters of the soil and rock layers
Fig.3  (a) Distribution of shearing force for the stabilization pile in each stage and (b) distribution of shearing force for the stabilization pile varying with construction stages
Fig.4  (a) Distribution of moment for the stabilization pile in each stage and (b) distribution of moment for the stabilization pile varying with construction stages
Fig.5  Distributions of the local slide surface
construction stagesKS0KS1KS2KS
stage 11.0931.2001.0971.331
stage 21.1501.2331.1451.354
stage 31.0621.1651.1011.290
stage 4–––1.061
stage 5failure–1.1541.186
stage 6failurefailure1.0301.058
Tab.4  Calculation results of the overall stability based on the phi/c reduction method
Fig.6  The potential slide surface in different construction stages. (a) stage 1; (b) stage 2; (c) stage 3; (d) stage 4; (e) stage 5; (f) stage 6
Fig.7  The analysis model of overall stability
construction stagesKS0KS1KS2KS
stage 11.0721.3311.0851.377
stage 21.0951.3481.1331.385
stage 31.0441.2811.0891.324
stage 40.7790.9290.9081.088
stage 50.8611.0181.1521.194
stage 60.7630.9110.9871.075
Tab.5  Calculation results of the overall stability based on the Sweden circular slip surface
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