Global and internal stability calculations
We are covering most of the embankment dam safety issues, namely global and local stability analysis with all its special tasks like rapid drawdown etc, but we can also handle some problems with internal erosion or upstream concrete face slabs stability. Most recently we are dealing with dam cores and grouting performance assessment. Currently we use a specialized geotechnical software GeoStudio 2007 by GEO-SLOPE Int. A SLOPE/W is used for slope stability using the limit equilibrium methods, a SEEP/W is used for groundwater calculations using the finite element method (FEM) and a SIGMA/W is used for stress/strain and deformation calculations using the FEM as well.
Global stability
Calculations of the global stability of the upstream and downstream part of dams are probably the most common ones. Usually, the limit equilibrium methods in SLOPE/W are used for assessing the safety factor on the slip surface.
Calculations of internal stability (suffusion, suffusion, etc.) can be done using the hydraulic criteria, resp. the critical hydraulic gradients limits. These limits are given in the literature by various authors while this field is still the target of intensive research worldwide. Using the SEEP/W, we can calculate the field of hydraulic gradients at different load conditions including the unsteady flow (e.g. for rapid drawdown or flood routing). Then we can easily compare calculated gradients with limit gradient values for a particular soil type.
Rapid drawdown of water level in the reservoir is a special load condition, which can be dangerous for some types of embankment dams, especially the ones with homogenous impervious soils in the whole cross section. These dams are usually quite old, while the more recently built rockfill dams with central clay core are not so sensitive to the rapid drawdown. Due to the very slow dissipation of pore pressures in the upstream part of the dam, the safety factor can significantly fall in case of rapid drawdown for some dams. Therefore, the dam operators demand information about the limits of reservoir drawdown speed, so that the safety of upstream face is still ensured. These limit values are usually later implemented into the dam handling regulations.
There are also many variations of classic tasks, e.g. at rapid drawdown, we can calculate the uplift pressure and forces which are impacting the concrete slabs on the upstream face. Another task we meet is the extreme high reservoir water level at flood routing and assessing the crest safety with the sealing membrane size and position optimization. Quite frequently we can encounter problems with the drainage elements optimization, especially considering the polders and small dams. Finally, we are experienced in problems with the flood protection dikes along the river, where the internal erosion and hydraulic rupturing can occur and where we can model the groundwater flow to reduce the occurrence of these phenomena.
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