Numerical analysis of the interaction between rock and structure in drifts excavated in Callovo-Oxfordian claystone

Abstract:

Built and operated by the French National Agency for Radioactive Waste Management (ANDRA) since the early 2000s, the Meuse/Haute-Marne underground research laboratory (M/HM URL) is designed for scientific experiments and demonstrations aimed at proving the feasibility and constructability of geological disposal of radioactive waste in Callovo-Oxfordian claystone (Cigéo project). It consists of a network of drifts excavated in the directions of the main horizontal stresses (…~12.4 MPa et ….~16.1 MPa). Some drifts are designed to analyse rock-structure interaction and to test and to improve different support systems. Analysing the behaviour of these types of drift will provide valuable insights for the design of future Cigéo Project structures.

In this context, the current PhD work is divided into two main areas: (1) In-situ monitoring analysis: convergence and extensometric data, and deformation and load in support structures of different rock-structure interaction configurations. (2) The implementation of an engineering design numerical model that reproduces the short-term behaviour of support structures and extrapolates the long-term behaviour.

This presentation will focus on the 5.40 m-diameter GER drift, which was excavated in the direction of the minor horizontal stress, thus under an initial anisotropic stress state. This drift is composed of five different sections with various types of temporary support and final lining (Djizanne et al., 2019). In-situ observations revealed an anisotropic response: (i) the extension of the induced excavation fractured zone along the drift is more developed in the vertical direction of the cross section; (ii) vertical convergences are four times larger than horizontal ones; (iii) deformations and load in the temporary support and final lining are anisotropic.

Building on previous work by Lara et al. (2025) and complementing in situ monitoring analysis, a numerical model that explicitly incorporates the fractured zone is implemented. A Burgers-Mohr constitutive model is assumed for the rock mass (CVISC law) with different viscoelastic parameters for the fractured zone and for intact rock. The extent of the fractured zone is simply correlated to convergence measurements. The results successfully replicate the development and anisotropy of the in-situ convergences observed. Furthermore, analysing stress and strain measurements in the GER drift support system has enabled us to identify various factors influencing the loading of the final lining, such as the stiffness of the temporary support and the installation delay of final lining.

Short bio:

After his engineering studies at Ecole Nationale des Ponts et Chaussées (ENPC), Blaise-Pascal ALLO started a PhD at Laboratoire Navier under supervision of Jean Sulem, Lina-María GUAYACAN-CARRILLO and Eric Boidy (ANDRA). His research focuses on rock mechanics and the numerical modeling of underground structures. By combining in situ data with numerical simulations, he aims to develop an engineering-based approach for designing support systems for drifts excavated in Callovo-Oxfordian claystone.