A compression model for non-brittle soft clays and peat

Abstract

A simple and effective model is presented for the calculation of the compression of non-brittle soft clays and peat. It is based on a unique relationship between stress, strain and creep strain rate. It combines features of existing models in an eclectic fashion and some new features. The treatment of unload–reload behaviour is unique to this model, as is the use of natural strain. A new measure—intrinsic time— is introduced to describe creep. The constitutive behaviour is combined with hydraulic storage and flow in a finite strain consolidation equation. A simplified derivation of the finite strain equation is presented. The model is shown to fit accurately the entire stress—strain—time response of a soft organic clay and a peat subjected to incremental loading oedometer tests. Some special effects of the model are shown. L'article présente un modèle effectif simple permettant de calculer la consolidation déargiles molles non friables et de tourbe. Ce modèle est fondé sur une relation contrainte déformationvitesse de fluage tout à fait particulière. Il combine, de manière éclectique, certaines caractéristiques des modèles préexistants è de nouvelles caractéristiques. Le traaement du comportement en déchargement–rechargement ainsi que la prise en compte de la déformation naturelle sont particuliers à ce modèle. Une nouvelle variable, appelée temps intrinsèque, est introduite pour décrire le fluage. Le comportement constitutif est associé au coefficient d&quo;emmagasinement et au débit hydraulique par l’intermédaire déune équation de consolidation à déformation fine. Une dérivation simplifiée de cette équation est proposée. Le modèle montre un bon ajustement avec la réponse contrainte– d6formation–temps d’une argile molle organique ou d’une tourbe soumise à des essais oedomé triques avec pas de chargement. Certains résultats particuliers à cc modèle sont présentés.

Disentangling and Parameterizing Shallow Sources of Subsidence: Application to a Reclaimed Coastal Area, Flevoland, the Netherlands

“…Both models depend on effective stresses exerted on the sediments situated above and below the phreatic groundwater level and increases herein when water levels are lowered. An alternative model that is widely applied in the Netherlands, the a/b/c Isotache model, uses a rate type formulation like the NEN-Bjerrum model but it is based on natural strain rather than linear strain (Den Haan, January 1996;Visschedijk & Trompille, 2009). For the small compression strains that we encountered, the a/b/c Isotache model is equivalent to the NEN-Bjerrum model; we have therefore not used it.…”

“…For changing vertical effective stress, these contributions are combined as (Bakr, 2015;Den Haan, January 1996;Visschedijk & Trompille, 2009):…”

Atlantis, a tool for producing national predictive land subsidence maps of the Netherlands

“…This caused shrinkage of the soils, and oxidation of peat above the lower groundwater level and consolidation and compaction of underlying saturated Holocene deposits (e.g. Erkens et al, 2016). The subsidence gradually decreases the thickness of the unsaturated zone.…”

“…1). In areas with thick peat layers, this process can continue for many centuries and cause subsidence of several meters (Erkens et al, 2016).…”

“…Adaptation to land subsidence, generally by further lowering of the surface water levels to lower phreatic ground water levels, has occurred relatively unconsciously for about a millennium already (e.g. Erkens et al, 2016). Over the last few decades, awareness of subsidence and its impacts has grown with government bodies and has started to become integrated in policy making.…”