Sarma method: Difference between revisions

Revision as of 15:08, 29 August 2015

Revision as of 10:19, 27 January 2016

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[[Sarada K. Sarma|Sarma]] worked in the area of seismic analysis of earth dams under [[Nicolas Ambraseys|Ambraseys]] at [[Imperial College]] for his doctoral studies in the mid 1960s.<ref>Sarma S. K. (1968) ''Response characteristics and stability of earth dams during strong earthquakes''. PhD Thesis, Imperial College of Science & Technology, University of London</ref> The methods for seismic analysis of dams available at that time were based on the [[Slope stability analysis#Limit equilibrium analysis|Limit Equilibrium]] approach and were restricted to planar or circular failures surfaces adopting several assumptions regarding force and moment equilibrium (usually satisfying one of the two) and about the magnitude of the forces (such as interslice forces being equal to zero).

Sarma looked into the various available methods of analysis and developed a new method for analysis in seismic conditions and calculating the permanent displacements due to strong shaking. His method was published in the 1970s (the very first publication was in 1973<ref>{{Cite journal | last1 = Sarma | first1 = S. K. | title = Stability analysis of embankments and slopes | doi = 10.1680/geot.1973.23.3.423 | journal = Géotechnique | volume = 23 | issue = 3 | pages = 423 | year = 1973 | pmid = | pmc = }}</ref> and later improvements came in 1975<ref>{{Cite journal | last1 = Sarma | first1 = S. K. | title = Seismic stability of earth dams and embankments | doi = 10.1680/geot.1975.25.4.743 | journal = Géotechnique | volume = 25 | issue = 4 | pages = 743 | year = 1975 | pmid = | pmc = }}</ref> and 1979 <ref>Sarma S. K. (1979), ''Stability analysis of embankments and slopes''. Journal of Geotechnical Engineering, ASCE, 1979, 105, 1511–1524, ISSN: 0093-6405</ref>).

==Method==

===Assumptions===

The method satisfies all conditions of equilibrium, (i.e. horizontal and vertical force equilibrium and moment equilibrium for each slice. It may be applied to any shape of slip surface as the slip surfaces are not assumed to be vertical, but they may be inclined. It is assumed that magnitudes of vertical side forces follow prescribed patterns. For n slices (or wedges), there are 3n equations and 3n unknowns, and therefore it statically determinate without the need of any further additional assumptions.

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==Accuracy==

===General acceptance===

The Sarma method has been extensively used in seismic analysis software<ref>[http://www.finesoftware.eu/geotechnical-software/help/slope-stability/sarma/ GEO 5 Geotechnical Software]</ref><ref>[http://www.slope-analysis.com/html/galena_faq.html slope stability software – Galena software ]</ref> for many years and has been the standard practice until recently for seismic slope stability for many years (similar to the [[Mononobe–Okabe method]] <ref>Okabe, S. (1926) General theory of earth pressures. Journal of the Japanese Society of Civil Engineers, 12 (1)</ref><ref>Mononobe, N & Matsuo, H. (1929) On the determination of earth pressures during earthquakes. Proceedings of the World Engineering Congress, 9.</ref> for retaining walls). Its accuracy has been verified by various researchers nad it has been proved to yield results quite similar to the modern ''safe'' [[Lower Bound]] numerical stability [[Plasticity (physics)|Limit Analysis]] methods (e.g. the 51st [[Rankine Lecture]] <ref>{{Cite journal | last1 = Sloan | first1 = S. W. | authorlink1 = Scott W. Sloan| title = Geotechnical stability analysis | doi = 10.1680/geot.12.RL.001 | journal = Géotechnique| volume = 63 | issue = 7 | pages = 531 | year = 2013 | pmid = | pmc = }}</ref> <ref>[http://bga.city.ac.uk/cms/html/51stRankineLecture.pdf 51st Rankine Lecture – Geotechnical Stability Analysis]</ref>).

===General acceptance===

The Sarma method has been extensively used in seismic analysis software<ref>[http://www.finesoftware.eu/geotechnical-software/help/slope-stability/sarma/ GEO 5 Geotechnical Software]</ref><ref>[http://www.slope-analysis.com/html/galena_faq.html slope stability software – Galena software ]</ref> for many years and has been the standard practice until recently for seismic slope stability for many years (similar to the [[Mononobe–Okabe method]] <ref>Okabe, S. (1926) General theory of earth pressures. Journal of the Japanese Society of Civil Engineers, 12 (1)</ref><ref>Mononobe, N & Matsuo, H. (1929) On the determination of earth pressures during earthquakes. Proceedings of the World Engineering Congress, 9.</ref> for retaining walls). Its accuracy has been verified by various researchers nad it has been proved to yield results quite similar to the modern ''safe'' [[Lower Bound]] numerical stability [[Plasticity (physics)|Limit Analysis]] methods (e.g. the 51st [[Rankine Lecture]] <ref>{{Cite journal | last1 = Sloan | first1 = S. W. | authorlink1 = Scott W. Sloan| title = Geotechnical stability analysis | doi = 10.1680/geot.12.RL.001 | journal = Géotechnique| volume = 63 | issue = 7 | pages = 531 | year = 2013 | pmid = | pmc = }}</ref> <ref>[http://bga.city.ac.uk/cms/html/51stRankineLecture.pdf 51st Rankine Lecture – Geotechnical Stability Analysis]</ref>).

===Modern alternatives===