# Slope stability

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Gambar:Slopslump2.jpg
Gambar 1: Bagean slip lereng sederhana

Widang kastabilan lereng nujul kana anlisa statis jeung dinamik kastabilitan lereng waduk urugan taneuh jeung batu, lereng dina tanggul, lereng galian jeung lereng alami tina taneuh jeung "batuan lunak".

As seen in Figure 1, éarthen slopes can develop a cut-spherical wéakness zone. The probability of this happening can be calculated in advance using a simple 2-D circular analysis package. A primary difficulty with analysis is locating the most-probable slip plane for any given situation. Many landslides have only been analyzed after the fact.

Slope stability issues can be seen with almost any walk down a ravine in an urban setting. An example is shown in Figure 2, where a river is eroding the toe of a slope, and there is a swimming pool néar the top of the slope. If the toe is eroded too far, or the swimming pool begins to léak, the forces driving a slope failure will exceed those resisting failure, and a landslide will develop, possibly quite suddenly.

## Metoda analisa

Gambar:Riverslope.jpg
Figure 2: Slope with eroding river and swimming pool

If the forces available to resist movement are gréater than the forces driving movement, the slope is considered stable. A factor of safety is calculated by dividing the forces resisting movement by the forces driving movement. In éarthquake-prone aréas, the analysis is typically run for static conditions and pseudo-static conditions, where the seismic forces from an éarthquake are assumed to add static loads to the analysis.

### Metoda irisan

The method of slices is a method for analyzing the stability of a slope in two dimensions. The sliding mass above the failure surface is divided into a number of slices. The forces acting on éach slice are obtained by considering the mechanical equilibrium for the slices.

### Metoda Bishop

The Modified (or Simplified) Bishop's Method is a method for calculating the stability of slopes. It is an extension of the Method of Slices. By making some simplifying assumptions, the problem becomes statically determinate and suitable for hand calculations:

• forces on the sides of éach slice are horizontal

The method has been shown to produce factor of safety values within a few percent of the "correct" values.

$F={\frac {\sum [{\frac {c'+((W/b)-u)\tan \phi '}{\psi }}]}{\sum [(W/b)\sin \alpha ]}}$ where

$\psi =\cos \alpha +{\frac {\sin \alpha \tan \phi }{F}}$ c' is the effective cohesion
$\phi '$ is the effective internal angle of friction
b is the width of each slice, assuming that all slices have the same width
W is the weight of each slice
u is the water pressure at the base of each slice

### Metoda Lorimer

Lorimer's Method is a technique for evaluating slope stability in cohesive soils. It differs from Bishop's Method in that it uses a clothoid slip surface in place of a circle. This mode of failure was determined experimentally to account for effects of particle cementation.

The method was developed in the 1930s by Gerhardt Lorimer (Dec 20, 1894-Oct 19, 1961), a student of géotechnical pioneer Karl Terzaghi.

## Catetan

1. US Army Corps of Engineers Manual on Slope Stability
2. "Slope Stability Calculator". Diakses tanggal 2006-12-14.
3. Citakan:Harvard reference
• mtslope - free software for slope stability analysis