Jean Louis Chazelas

Dynamic Response of Shallow Rectangular Tunnels in Sand by Centrifuge Testing

A series of dynamic centrifuge tests on rectangular tunnel models embedded in dry and saturated sands is presented. The tests were carried out at the geotechnical centrifuge facility of IFSTTAR in Nantes, France, within the Transnational Access action DRESBUS II funded by the SERIES research project. The experimental program focused on salient parameters controlling the dynamic response of the soil-tunnel system such as soil-to-tunnel relative flexibility, soil-tunnel interface characteristics, soil saturation and characteristics of the input motion. Among the innovative features of the experimental set up were sand pluvation, models saturation and tunnels waterproofing techniques. A dense monitoring scheme was implemented, including accelerometers, displacement sensors, pore pressure sensors and specially designed extensometers for measuring side-wall deformations and diagonal distortion of the tunnel. A preliminary interpretation of the experimental data revealed the effect of the above parameters on the racking deformation modes of the tunnel sections.

The SERIES Virtual Database: Exchange Data Format and Local/Central Databases

At the beginning of the project, the access and exchange of data within the European scientific community was highly fragmented and the diffusion of information among laboratories was not sufficient. The outcome of an inquiry performed among partner laboratories at the beginning of SERIES showed that data storage in an unstructured way was the common approach in most of the cases. Naturally, access to and elaboration of the data was restricted only to the local users, a fact leading to a very low impact of the results on practice because of their limited dissemination and the difficulties in collaboration among researchers. SERIES (Networking Activity NA1) aimed, among others, at overcoming this state by establishing a culture of preservation of data in a structured way and by facilitating data exchange and collaboration with the broader research community. A structured database in which data are stored according to a commonly agreed Exchange Data Format has been implemented at the SERIES laboratory sites; tools for the management and automatic data import have been developed to facilitate data supply from participating laboratories. The data stored in the local databases are then made publically accessible to external users by means of a Data Access Portal, hosted in the University of Patras. The elements of the so-called SERIES virtual database are here described.

Experimental and Numerical Investigations of Nonlinearity in Soils Using Advanced Laboratory-Scaled Models (ENINALS Project): From a Site-Test to a Centrifuge Model

The SERIES project “Experimental and Numerical Investigations of Nonlinearity in soils using Advanced Laboratory-Scaled models” (ENINALS) was focused on the centrifuge modeling of seismically-induced strains vs. stratigraphic features and it was applied to the heterogeneous alluvia of the Tiber River in the Rome historical centre. Four soil samples, representing two homogeneous soil columns (only clay and only sand respectively) and two heterogeneous soil columns (including a clay level between two sand ones) were tested in the IFSTTAR centrifuge. The applied dynamic input represents the maximum expected seismic action in Rome and it was reproduced at the centrifuge shaking device following three approaches: (i) a natural time history, (ii) an equivalent sinusoidal signal, and (iii) a multifrequential equivalent signal derived by the recently proposed LEMA_DES approach. The here reported preliminary results: (i) demonstrate the reliability of a “cut and install” procedure for realizing the saturated multilayer samples; (ii) give new insights on the reliability of multifrequencial dynamic equivalent signals for scale-reduced analogical modeling.