Slope stability

Slope stability

The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock. [ [http://www.usace.army.mil/publications/eng-manuals/em1110-2-1902/entire.pdf US Army Corps of Engineers Manual on Slope Stability] ]

As seen in Figure 1, earthen slopes can develop a cut-spherical weakness zone. The probability of this happening can be calculated in advance using a simple 2-D circular analysis package. [ cite web |url=http://www.wise-uranium.org/cssth.html |title=Slope Stability Calculator |accessdate=2006-12-14 |format= |work= ] A primary difficulty with analysis is locating the most-probable slip plane for any given situation. [ Harvard reference|Surname=Chugh|Given=Ashok|Authorlink=|Year=2002|Title=A method for locating critical slip surfaces in slope stability analysis|Journal=NRC Research Press|Volume=|Issue=|Pages=|URL=http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?_handler_=HandleInitialGet&journal=cgj&volume=39&calyLang=eng&articleFile=t02-042.pdf ] Many landslides have only been analyzed after the fact.

It should be noted that real life failures in naturally deposited mixed soils are not necessarily circular, but prior to computers, it was far easier to analyse such a simplified geometry. Nevertheless, failures in 'pure' clay can be quite close to circular. Such slips often occur after a period of heavy rain, when the pore water pressure at the slip surface increases, reducing the effective normal stress and thus diminishing the restraining friction along the slip line. This is combined with increased soil weight due to the added groundwater. A 'shrinkage' crack (formed during prior dry weather) at the top of the slip may also fill with rain water, pushing the slip forward. At the other extreme, slab-shaped slips on hillsides can remove a layer of soil from the top of the underlying bedrock. Again, this is usually initiated by heavy rain, sometimes combined with increased loading from new buildings or removal of support at the toe (resulting from road widening or other construction work). Stability can thus be significantly improved by installing drainage paths to reduce the destabilising forces. Once the slip has occurred, however, a weakness along the slip circle remains, which may then recur at the next monsoon.

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 near the top of the slope. If the toe is eroded too far, or the swimming pool begins to leak, the forces driving a slope failure will exceed those resisting failure, and a landslide will develop, possibly quite suddenly.

Analysis methods

If the forces available to resist movement are greater 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 earthquake-prone areas, the analysis is typically run for static conditions and pseudo-static conditions, where the seismic forces from an earthquake are assumed to add static loads to the analysis.

Method of slices

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 each slice are obtained by considering the mechanical equilibrium for the slices.

Bishop's method

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 each 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) anphi'}{psi}] }{sum [(W/b)sinalpha] }where:psi=cosalpha+frac{sinalpha anphi}{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

Lorimer's method

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 geotechnical pioneer Karl Terzaghi.

See also

* Mass wasting
* SLOPE/W
* UTEXAS
* STABL

Notes

References

* Coduto, Donald P. (1998). "Geotechnical Engineering: Principles and Practices." Prentice-Hall. ISBN 0-13-576380-0


Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Slope stability radar — The Slope Stability Radar (SSR) is a new application for the monitoring of slope stability at open cut mines. It is a system currently in use across the global mining and civil industries. Slope stability is a critical safety and production issue …   Wikipedia

  • Vegetation and slope stability — are interrelated by the ability of the plant life growing on slopes to both promote and hinder the stability of the slope. The relationship is a complex combination of the type of soil, the rainfall regime, the plant species present, the slope… …   Wikipedia

  • SLOPE/W — Infobox Software name = SLOPE/W caption = SLOPE/W author = developer = released = latest release version = 2007 latest release date = latest preview version = latest preview date = operating system = Microsoft Windows platform = language =… …   Wikipedia

  • Grade (slope) — d = run Δh = rise l = slope length α = angle of inclination This article is for the grade of a topographic feature or constructed element, for other uses see: Slope (disambiguation) The grade (also called slope, incline, gradient, pitch or rise)… …   Wikipedia

  • USAF Stability and Control DATCOM — The United States Air Force Stability and Control DATCOM is a collection, correlation, codification, and recording of best knowledge, opinion, and judgment in the area of aerodynamic stability and control prediction methods. It presents… …   Wikipedia

  • Landslide mitigation — Landslides can be triggered by many often concomitant causes. In addition to shallow erosion or reduction of shear strength caused by seasonal rainfall, causes triggered by anthropic activities such as adding excessive weight above the slope,… …   Wikipedia

  • Landslide — This article is about the geological phenomenon. For other uses, see Landslide (disambiguation). Rockslide redirects here. For the comic book character, see Rockslide (comics). Computer simulation of a slump landslide in San Mateo County,… …   Wikipedia

  • Mass wasting — at Palo Duro Canyon, West Texas (2002) …   Wikipedia

  • Causes of landslides — The causes of landslides are usually related to instabilities in slopes. It is usually possible to identify one or more landslide causes and one landslide trigger. The difference between these two concepts is subtle but important. The landslide… …   Wikipedia

  • Sarada K. Sarma — Sarada Kanta Sarma Born India Citizenship British, Indian Nationality Indian …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”