Proposal of Elena Kapogianni of National Technical
Reinforced Slope Safety Evaluation
and Design Due to Seismic Loading,
Based on the Determination of the
Critical Slip Surface Using Acceptability Criteria
The design and safety evaluation
of reinforced slopes subjected to seismic loading is a complex problem. Various
methods of analysis are used in order to solve this problem such as the limit
equilibrium method, the limit analysis and the finite element analysis. In most
of the techniques that are based on the limit equilibrium method and on the
limit analysis, the shape of the potential slip surface is predefined (planar,
circular, log spiral etc).
Sarma (2004), Sarma and Tan
(2006) formulated a new procedure for homogenous and non-homogenous unreinforced slopes, within the framework of the limit
equilibrium technique, where no prior assumption of the shape of the surface is
needed. According to this method, the slip surface, which comprises a series of
straight lines, is obtained slice by slice, going from downhill to uphill. The
slip surface and the interslice boundaries are not
predefined. The equilibrium of the slice and the acceptability criteria
determine the slip surface and the interslice
boundaries of the slice.
Main goal of the research
proposed here, is to develop a new solution for the design and safety
evaluation of reinforced slopes with simple and composite geometry, with no
prior assumption of the shape of the slip surface. Similarly to the method
developed by Sarma & Tan, the acceptability
criteria in terms of stresses and cinematics will
determine the slip surface and the interslice
boundaries of the slice. The non- linear equations which will include the
affect of the reinforcement on the slope will be formed and a suitable
optimization technique will be chosen for the implementation of the
methodology. The solution will be programmed with the help of a suitable
software development package (Borland Delphi), creating this way a fast tool
for the design and safety evaluation of reinforced slopes.
The results that will
derive will be compared with correspondent ones from a) analysis with
conventional numerical methods based on the limit equilibrium technique b)
limit analysis and c) finite element stress analysis.
In addition, the analysis
method that will be developed for the design of reinforced slopes with
composite geometry (slopes with berms) will be
compared with an analytical solution for multi-step reinforced earth slope
design that already has been developed and programmed (Kapogianni
& Sakellariou 2008). In this case, the
calculations will be performed initially for each berm
individually (local stability calculations) and then for the whole slope
(global stability calculations). The new procedure will enrich the already
existing one, creating this way a comprehensive and completed tool for the
design and safety evaluation of multi- step reinforced slopes.
Moreover, the forms of the
slip surfaces that will derive form the new procedure will be compared with
already existing predefined possible slip surfaces that are used in other
techniques (such as planar, circular and log spiral). The results will show
which predefined slip surface shape resembles more with the slip surface that
will result from the new method. This comparison will be made for reinforced
slopes with various mechanical and geometrical characteristics and at different
seismic coefficient.
Finally, an experimental
evaluation of the methodology can be planed where the failure conditions can be
determined along with the form of the slip surfaces.
References
[1] Sarma,
S.K. 2004. Critical Slip Surface in Slope Stability Analysis.
In: Advances in Geotechnical Engineering
[2] Sarma,
S.K. & Tan, D. 2006. Determination of Critical Slip
Surface in Slope Stability Analysis. In: Geotechnique
56, No. 8, 539-550
[3] Kapogianni,
E.K. & Sakellariou M.G. 2008. Analytical solution
of multi step reinforced-soil slopes stability due to static and seismic
loading (1st International Conference on Transportation
Geotechnics/ August 2008/ Nottingham-paper accepted)
[4] Kapogianni,
E.K. & Sakellariou M.G. 2008. Comparison of an
analytical solution for multi-step reinforced soil slopes with
conventional numerical methods (4th European Geosynthetics Conference/ September
2008/