Protection of rockfill dams with toe berms for moderate unit discharges. A downloadable version (in Spanish)

Protection of rockfill dams with toe berms for moderate unit discharges. A downloadable version (in Spanish)

This thesis is the result of a research project that aimed to define criteria to design rockfill toe protections for existing dams with a highly‐permeable downstream shoulder.

The proposed protection consists of a rockfill toe berm situated downstream from the dam with specific characteristics with respect to the rockfill that integrates the shoulder of the main dam. The function of these protections is to prevent mass slides due to an abnormally high water flow circulation through the dam’s shoulder. This accidental seepage flow may be caused by such reasons as overtopping or the loss of sealing at the impervious element of the dam or its foundation. According to data from the International Commission on Large Dams (ICOLD 1995), 70% of the causes of failure or serious damage in embankment dams in the world are within that described previously.

This accidental seepage of water through the rockfill shoulder, typically turbulent, is usually called through‐flow. The physical phenomenon which causes the breakage of the rockfill shoulder during such through‐flow processes is complex, involving a diversity of parameters (often not deterministic) and coupling among processes, not only seepage but also internal erosion, drag or mass slide.

In this thesis, numerical and experimental research is conducted in order to analyze the effects of the main parameters that define the toe protection, i.e. the toe crest length, its slope, and maximum height. Additional studies on significant factors that influence the seepage, such as the anisotropy of the material and the increase of the unit flow at the dam toe due to the valley shape are also performed. In addition, conclusions regarding the effectiveness of this type of protection are obtained based on the results of physical and numerical models.

The main result of the thesis is a design procedure for this type of protection to avoid mass sliding. In order to complete the design criteria, additional recommendations about internal and external erosion based on the state of the art are included. Finally, new lines of research are suggested for the future to expand the level of knowledge of the complex phenomena that influence the behavior of this type of protection, such as the effects of scale, rockfill anisotropy, non‐linear seepage laws in turbulent seepage through granular media, effects of erodible foundations, or new procedures to characterize the properties of dam rockfill as a construction material.

About Rafael Morán