Dam materials properties (PCI-1.1)

Problematic A; Compacted till core

As the main goal of the core is to limit water seepage through the dam, the material constituting the core must have, after placement and compaction, very low permeability and good rigidity to sustain vertical and lateral deformation when it is time to fill the reservoir. Particle stability in the core material submitted to water seepage forces must be assured for the whole lifespan of the structure in order to avoid piping failure by the migration fine particles. The placement conditions of the till, often the core material, play a crutial role on the properties of the material. It as been shown that tills placed at a water contain lower then the water content determined by the normal Procor test are susceptible to develop a heterogenus stucture (aggregated or honeycomb structure). These discontinuities reflect the presence of macropores where seepage water flows at a higher flow rate that it would in a structure charaterized by micropores. Furthermore, water travelling in those macropores could foster the migration of small particles. Variations of the grain-size distribution within the accepted grading range may also influence seepage characteristics and core material rigidity.

Problematic B; filter zone

The sand filter zone has two main functions: 1) prevent te migraion of small particles from the core material and 2) effectively drain off seepage water passing through the core. This zone must be constructed with material having a much more important permeability than the core material and, at the same time, the filter material must also have a small pore size distribution in order to retain particles that could move from the core. Filter material should have a good rigidity and small compressibility in order to offer a good lateral support for the core. Filter material must also meetthe internal stability criterion against piping phenomena. The variability of the grain-size distribution and placement conditions of the material will greatly affect hydric and mechanical behavior of the filter.

Problematic C; transition zone

As the name says, the transition zone, made of sand or a mix of sand and gravel, serves as a transition between the filter zone and the rockfill shell. The transition zone must retain small particles that could come from the filter material and it must also offer adequate lateral support for the filter in order to avoid stress concentrations that could occur during the filling of the reservoir as well as prevent differential déformations. 

The main objective of the project is to shed light on the effect of the of grain-size distribution variability and placement conditions of the different material used in an embankment dam on the hydraulic conductivity, internal stability, rigidity and compressibility and this, for moist and quasi-saturated states.

Subprojects:

-Characterization of the pore-size distribution and particles arrangement of material in general (team)

-Characterization of the pore-size distribution and particles arrangement of tills (MSc1)

-Characterization of till hydraulic properties and internal stability (MSc2 and PhD1)

-Characterization of till mechanical properties and compressibility (MSc3)

-Characterization of hydraulic properties, internal stability and pore-size distribution of sand, gravel and crushed stone mixtures (MSc4 and MSc5)

-Characterization of mechanical properties, compressibility and particles arrangement of sand, gravel and crushed stone mixture (MSc6 and MSc7)