Slope Stability of Soils

Slope Stability of Soils

Gokhan Cevikbilen (Istanbul Technical University, Turkey)
DOI: 10.4018/978-1-5225-2709-1.ch011
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Abstract

Slope stability problems in soils underlie most of the landslides that cause losses of human and property in the world. The stability of natural or man-made slopes in soils is an important topic that requires great attention while site exploring, testing, modelling and analyzing. Engineering geology and geotechnical engineering interdisciplinary team work is essential to achieve a sufficient understanding of site geology and the behavior of soil. The developments of urban areas require new sites for settlement. Soil structure interaction in slopes requires more sophisticated numerical analysis methods to develop. This section particularly summarizes the factors cause a slope to fail. In addition, site exploration steps, in-situ and laboratory test methods were mentioned. Slope stability analysis methods such as LEM, FEM, DEM, BEM were discussed in details. The developments of empirical or statistical regional approaches were stated. Remediation techniques were discussed regarding the construction costs. Finally, the necessity of further studies in numerical modelling was emphasized.
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2. Background

Slope stability of soils is one of the major problems since the ancient times. If slope stability is the potential of a slope to landslide, natural or manmade factors that provoke this movement of a mass of soil, rock or debris down a slope have to be well understood to predict or to prevent the problem. While the best known natural causes are weathering and erosion, manmade applications such as cuts, fills, external loadings and changing the ground water level are some of the reasons stimulating a landslide.

The surficial area of a landslide may be smaller than 200 m2 or even larger than 2.000.000 m2. At the hillsides the landslide susceptibility of soils is higher than the soils in the lowlands. Similarly, for manmade structures as the angle or height of a slope increases, the stability of the slope decreases. So, the ground surface geometry of a slope is an important parameter on the stability. Slope angle, β is the angle of inclination of a ground surface. In road engineering applications, β is generally expressed in percent and it equals to meter rise or fall in height, H at 100 m horizontal distance, L. The slope of a ground surface may be composed of a single plane or a series of planes with different inclinations. The plane of rupture below the ground surface is named as sliding surface. The mass of soil between the sliding surface and the ground surface is called as sliding mass that involves head, main body, toe, main scarp, minor scarp as shown in Figure 1. Length, width, depth and initial slope of the sliding mass is useful for describing the size of a landslide. Furthermore, the rate of the movement of landslide material may be as quick as debris or earth fall or as slow as soil creep. Varnes (1978) suggested a classification system for landslides based on type of the material involved and mode of the movement. In the system, the engineering soils are named as debris or earth when the predominant fraction is coarse or fine respectively. He categorized the mode of the movement as falls, topples, rotational slides, translational slides, lateral spreads, flows or creeps. It can also be a combination of two or more of the modes.

Figure 1.

Parts of a landslide (modified from Varnes, 1978)

Key Terms in this Chapter

LEM: Limit Equilibrium Method is numerical analysis of forces and/or moment acting on a body in equilibrium condition.

Drain: Artificially produced drainage paths in the soil for surficial or ground water to pass through.

Fully Softened Shear Strength: The peak drained shear strength of a clay in a normally consolidated state.

Slope Angle: Is the angle between ground surface and horizontal.

Pseudo-Static Analysis: In earthquake engineering to analyze the seismic response of soil embankments and slopes simply adding a permanent body force representing the earthquake shaking to a static limit-equilibrium analysis.

Residual Shear Strength: The minimum and constant shear strength attained at large displacements after the peak shear strength.

FEM: Finite Element Method is a numerical technique for finding approximate solutions to boundary value problems for partial differential equations.

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