Technical CommunicationThree-dimensional slope stability assessment of two-layered undrained clay
Introduction
Geotechnical engineering problems such as trench stability [1], [2], tunnelling [3], [4] and slope stability [5], [6] have been investigated for years. Slope stability is generally influenced by the slope’s physical properties, the strength parameters of the soil and the slope geometry while a slope’s profile is affected by its construction approach. In general, a slope can be classified as a cut slope, natural slope or fill slope based on the method of construction. Duncan et␣al. [7] shows that slopes with two-layered of undrained clay are commonly encountered in the construction of embankments or levees.
Slope stability has traditionally been analysed considering plane strain condition. However, various investigators have pointed out that the stability of a slope can be influenced by the 3D boundary of the slope. In the study by Cavounidis [8], it was shown that the factors of safety (F) from three-dimensional (3D) analyses are higher than those from two-dimensional (2D) analyses. Additionally, Gens et␣al. [9] indicated that a 2D back analysis will overestimate the mobilized shear strength and thus lead to an unsafe prediction. As such, many 3D slope stability analysis methods have been developed in recent years. However, many of the methods were extended from the existing 2D limit equilibrium method (LEM). In addition, most 3D assessments utilizing limit analysis methods have been based on the upper bound method alone [10], [11], [12], [13]. This is due to the inherent difficulty in manually constructing the statically admissible stress fields for lower bound limit analysis.
Although many methods have been developed for slope stability assessment, only a few sets of slope stability charts have been produced to date [9], [13], [14], [15], [16], [17], [18], [19], [20]. Furthermore, only some of those charts have considered 3D boundary effects. The conventional limit equilibrium analysis is the most popular approach to assess slope stability and thus the earliest slope stability charts have been proposed based on the LEM [9], [14], [21], [22]. Gens et␣al. [9] and Taylor [22] both investigated slopes with undrained clay. In particular, Gens et␣al. [9] proposed the first set of 3D slope stability charts. In recent years, stability charts have also been developed using limit analysis method. Michalowski [19], Viratjandr and Michalowski [23] and Kumar and Samui [15] performed their study based on a 2D analysis while Michalowski [13] considered 3D effects in his study. Their studies only used the upper bound limit analysis which is not conservative, therefore rigorous solutions have not been widely applied to slope designs.
Unfortunately, stability charts for fill slopes are limited. Therefore, this study aims to investigate the 3D stability of fill slopes using both the upper and lower bound finite element limit analysis methods developed by Lyamin and Sloan [24], [25] and Krabbenhoft et␣al. [26]. The obtained results will be presented in the form of comprehensive and convenient chart solutions that can be used by practicing engineers. These charts are particularly useful for quick first assessments of slopes. It should be noted that 3D boundary effects on slope stability will be investigated thoroughly in this paper. In addition to the stability charts, the 3D failure mechanism will also be discussed. In this study, the fill slopes are made up two layer of undrained clay.
Section snippets
Previous studies
Although many LEM based 3D analysis methods have been developed in the past, most of them are extended from the existing 2D methods [27], [28], [29]. Thus, the inherent limitations of LEM still exist within the formulations. As previously mentioned, several LEM based stability charts have been developed to date [9], [14], [21], [22]. In particular, Gens et␣al. [9] considered 3D effects in their study of undrained clay slope stability and presented their results in the form of stability charts.
Problem definition
Fig.␣1 shows the typical 2D and 3D slope geometry and boundary conditions for the problem considered in this study. The fill materials and foundation which have been divided into Region 1 and Region 2 will have an undrained strength of cu. The cohesive strength in the fill materials (Region 1) will be assigned as cu1 while the cohesive strength in the pre-existing soil (Region 2) is assigned cu2. The strength difference between both layers are considered using cu1/cu2 ratios which range from
Results and discussion
Due to similar obtained trends in the stability charts for various slope inclinations and L/H ratios, the stability charts in Fig.␣3, Fig.␣4, Fig.␣5 only present the solutions for β = 15°, 45° and 75° with L/H = 1, 3 and 5. For simplicity and demonstration purposes, only lower bound numerical solutions from the 3D analyses are shown (the full results, including upper bound results, can be found in the tables in Appendix A). Also they are more conservative and thus the results can be utilized in
Assumed application examples
A case study will be used to demonstrate the convenience of using the stability charts, consisting of a fill slope with the following parameters: cu1/cu2 = 4.5, a soil unit weight of γ = 18 kN/m3, a depth factor of d/H = 2, and a fill material cohesion of cu1 = 50 kN/m2.
Conclusions
This study uses the finite element upper and lower bound limit analysis methods to investigate the stability of slopes specifically for two-layered undrained clay slopes. The results obtained are bracketed to within ±10% or better. In fact, this study has shown that as slope 3D boundary (L/H) increases, the stability number increases which leads to a slope with higher risk. Furthermore, cu1/cu2 ratio is also found to have an effect on the stability number. When cu1/cu2 ⩾ 1.25, the stability of
References (61)
- et al.
Tunnel stability and arching effects during tunneling in soft clayey soil
Tunn Undergr Space Technol
(2006) - et al.
Stability of a circular tunnel in cohesive-frictional soil subjected to surcharge loading
Comput Geotech
(2011) - et al.
Stability charts for pseudo-static slope stability analysis
Soil Dyn Earthq Eng
(2006) - et al.
Limit analysis solutions for three dimensional undrained slopes
Comput Geotech
(2009) Rotational stability of unreinforced and reinforced embankments on soft soils
Geotext Geomembr
(1994)- et al.
Finite element slope stability analysis by shear strength reduction technique
Soils Found
(1992) - et al.
Influence of heterogeneity on 3D slope reliability and failure consequence
Comput Geotech
(2014) - et al.
Influence of heterogeneity on the reliability and failure of a long 3D slope
Comput Geotech
(2010) - et al.
Simulation of the progressive failure of an embankment on soft soil
Comput Geotech
(2009) - et al.
Finite element simulation of an embankment on soft clay – case study
Comput Geotech
(2013)
A three-dimensional slope stability analysis method using the upper bound theorem Part II: numerical approaches, applications and extensions
Int J Rock Mech Min
A three-dimensional slope stability analysis method using the upper bound theorem: Part I: theory and methods
Int J Rock Mech Min
Analytical solutions for stability of slurry trench
J Geotech Geoenviron Eng
Trench stability under bentonite pressure in purely cohesive clay
Int J Geomech
The use of the slip circle in the stability analysis of slopes
Géotechnique
Slope stability analysis by finite elements
Geotechnique
Analysis of the stability of I-Walls with Gaps between the I-Wall and the Levee Fill
J Geotech Geoenviron Eng
On the ratio of factors of safety in slope stability analyses
Géotechnique
Three-dimensional analysis of slides in cohesive soils
Géotechnique
Three-dimensional analysis of nonhomogeneous slopes
J Geotech Geoenviron Eng
An extended limit analysis of three-dimensional slope stability
Geotechnique
Three-dimensional analysis of locally loaded slopes
Géotechnique
Limit analysis and stability charts for 3D slope failures
J Geotech Geoenviron Eng
Stability determination for layered soil slopes using the upper bound limit analysis
Geotech Geol Eng
Three-dimensional stability charts for slopes based on limit analysis methods
Can Geotech J
Stability of uniformly reinforced slopes
J Geotech Geoenviron Eng
Stability charts for uniform slopes
J Geotech Geoenviron Eng
Stability charts for 3D failures of steep slopes subjected to seismic excitation
J Geotech Geoenviron Eng
Stability charts for homogenous soil slopes
J Geotech Geoenviron Eng
Stability of earth slopes
J Boston Soc Civ Eng
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