ISC7

How to get a good match for consolidation coefficient

  • Gómez Escoubès, Ramiro (ACCIONA INGENIERÍA)
  • Peña Fernández, Santiago (SIEMENS)

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One of largest gaps in geotechnical projects is got when permeability is involved in. It is difficult to get accurate magnitudes when dealing with consolidation coefficient, decisive when clays and clayey silts, are compressing, especially if secondary consolidation is in play. This is a typical condition in harbors when new areas are to be reclaimed to get more and more loading/unloading extension. There are several approaches to assess consolidation rate. The oedometer cell is the main lab test used to get the compressibility parameters. It is accepted that 24 hours is a good time for each pressure. However, some soils are too slow to be consolidated, and they need more time. Especially when slope is far from horizontal. On the other hand, “true” consolidation coefficient is obtained when surpassing the preconsolidation pressure. Thus, values obtained below preconsolidation pressure are usually discarded. Horizontal coefficient of consolidation can be assessed with dissipation tests from piezocones. This paper also displays some outputs of oedometer test with trimmed samples perpendicular to the usual way, trying to get the horizontal consolidation coefficient, Ch, instead of the usual vertical one, Cv If piezometers are installed within the consolidating layer, comparing with the theoretical isochrones we may derive the “true” consolidation coefficient. If settlements are measured, a comparison with theoretical ones can be informed on the predominant consolidation phenomenon. Much care is to be applied and not misunderstand the process in play. Dissipation tests give way to much higher consolidation values than laboratory tests. This could be due to anisotropic effects, but the main reason is that dissipation occurs in a reloading process, while oedometer tests are in primary consolidation, at least from the preconsolidation pressure and on. This paper shows some ideas to properly assess the process involving consolidation