Three-dimensional Slope Stability Analysis of Embankment Dams
Slope stability analysis plays a significant role in assessing in-service performance of earth dams under static, seismic, and hydrologic loading conditions. Generally, these analyses are performed using 2-dimensional (2D) models. It is well known that the valley form (i.e., valley with: 1. relatively steep or flat abutments; 2. flat or undulating floor; and 3. narrow or wide valley) can have significant effect on the computed factor of safety results of an earth dam of given height and alignment (i.e., dam geometry). However, when the proportions of dam geometry with respect to the valley form are not known as a priori, then the three-dimensional (3D) effects become significant and a 3D analysis should be carried out.
2D analyses are inherently simpler and less time consuming than their 3D counterparts; thus, there are economic as well as technical advantages in developing a good understanding of 3D effects on stability of constructed slopes.
There are three inter-related questions.
1. What are the effects of valley form (shape and size with respect to dam height) on stability of an embankment dam; i.e., limiting proportion of valley width to dam height below which 3D effects are significant and should be considered in making judicious decisions on likely performance of embankment dams under static and seismic loading conditions?
2. What are the effects of material degradation (strength loss, pore pressure buildup) during seismic events on the findings of 1?
3. What is the reliability of 3D computer software (based on limit-equilibrium and continuum-mechanics principles) on the findings of 1 and 2?
Need and Benefit
The three research questions (discussed earlier in this research proposal) on likely performance of an embankment dam during a seismic event routinely come up in risk-based decision meetings with Reclamation staff, as well as in meetings with consulting review boards (CRB) members. At present, estimates on 3D effects are based on individuals' experience and judgment; there is a general lack of consistency in the levels of experience and judgment. Assessing the magnitude of 3D effects based on proposed numerical models will be beneficial in sharpening our in-house skills and judgments with respect to 3D effects on stability of slopes.
Even though the questions during risk deliberations are with respect to likely performance of a dam during a seismic event, static analysis of the dam is necessary because it provides the stress state in the dam prior to the application of seismic load. For this reason, the three inter-related research questions in this proposal include static and seismic loading conditions.
Independent Peer Review
The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.
Discussion of Three-dimensional Slope Stability Analysis of Embankment Dams (interim, PDF,
By Ashok Chugh
Publication completed on March 01, 2012
The original paper is in the Canadian Geotechnical Journal, Vol. 48, Issue 6, pp. 891-904, 2011.
There is no closure to the discussion.
Stability assessment of a circular earth dam (interim, PDF,
By Ashok Chugh
Publication completed on May 04, 2012
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Discussion of “Three-dimensional slope stability based on stresses from a stress-deformation (final, PDF,
By Ashok Chugh
Publication completed on September 06, 2011