Abstract

The French National Radioactive Waste Management Agency (Andra) has built the Underground Research Laboratory at Meuse\Haute-Marne (MHM-URL) for research on the feasibility of a possible deep repository dedicated to high level waste and intermediate level-long lived waste. Actually, several types of retaining structure have been constructed and instrumented in the URL to follow stress/strain evolutions, as well as better understanding of the interaction between the concrete structure and the surrounding rock. The lining stress measurement is an important input value in a way to evaluate or optimize the engineering design of lining. It is a complicated measurement and often performed indirectly from the strain measurement. One of the rare direct stress measurement is the flat jack technique, which provides a relatively simple and almost non-destructive punctual measurement of stress. Typically, the flat jack is withdrawn from the structure after the test and the structure is restored to the original state before the test. This is not the case in MHM-URL where the flat jack is kept in place, in a way to follow the stress time evolution by conducting regularly the test. This article proposes an interpretation method of flat jack measurement based on semi analytical methods and numerical modelling to follow orthoradial stress evolution in a tunnel lining as function of time. Those analysis have been conducted on measurements performed at MHM-URL.

1.
Introduction

Clay formations in their natural state exhibit very favorable conditions for repository of radioactive waste, as they generally have a very low permeability, small molecular diffusion and significant retention capacity for radionuclide. In France, the National Radioactive Waste Management Agency (Andra) is in charge of the study on the possibility of disposal for radioactive waste in a deep claystone formation. Following the 2006 Waste Act adopted by the French parliament, Andra started work in preparation for the licence application to construct a deep geological disposal facility called Cigéo. Cigéo will be located at the fringe of the Meuse and Haute-Marne departments at the middle of the Callovo-Oxfordian claystone formation (COx), lying between 420 m and 550 m in depth and overlain and underlain by poorly permeable carbonate formations (Fig. 1).

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