Compressible valley beds

Over the years, the development of transport infrastructures has continued and intensified. As a result, these projects are faced with increasing difficulties related to the environmental and geotechnical context of the new sites they cross. In particular, this has led contractors to consider building structures in areas crossing sensitive compressible valleys, which are likely to cause problems in the short or long term. Depending on the nature of existing or future structures, it is therefore necessary to define the risks to which they are exposed and to determine the actions to be taken to control these risks.

The purpose of this document is to provide a basis for understanding the challenges posed by crossing compressible valleys, and the methodologies for resolving these challenges through the choice of appropriate constructive arrangements. This choice is based first and foremost on optimizing the combination of cost and time factors (consolidation time).

The presentation is based on a specific practical approach, as implemented in the earthworks sector.

The file does not go into the principles of the mechanical behavior of compressible soils. For these elements, please refer to the relevant dossiers in Techniques de l'Ingénieur and, if further research is required, to the many technical works devoted to this subject, or to the treatises on soil mechanics cited in the bibliographic list.

It should be noted, however, that we have chosen to describe only a certain number of the most representative tests of compressible soil behavior, and on this occasion we recall the scientific approaches to some of the phenomena encountered.

The concepts that we will briefly discuss are as follows:

• the main phenomena encountered, the nature of the potential disorders they may cause and the consequences on the structures to be prevented;

• the main families of high-risk soils ;

• the surveys and tests to be carried out in order to determine the constructive provisions ;

• Soil consolidation measures ;

• the instrumentation needed to check soil consolidation.

This dossier is devoted to the geological context and the geotechnical approach to the phenomena encountered. The following dossier, , deals with the choice of consolidation methods and instrumentation.