Community Research and Development Information Service - CORDIS

FP5

SELFRAC Report Summary

Project ID: FIKW-CT-2001-00182
Funded under: FP5-EAECTP C
Country: Belgium

Long term evolution of the EDZ around a gallery - In-situ test at Mol (HADES)

A new gallery was realised to extend HADES. In-situ test 3 consists in studying the evolution in function of time of the hydro-mechanical properties within the EDZ around the gallery during a period of three years after its construction. For this purpose two multi piezometers were installed around the connecting gallery so that we can follow the evolution of the flow properties with time and self-boring pressuremeter tests were performed to follow the evolution of the mechanical properties.

We can conclude from in-situ test 3 that gallery construction in Boom Clay at an important depth (223 m in the case of the URF HADES) will always induce fractures. Fracturation is caused by stress redistribution, which is inherent in tunnelling. Fracture extent can however be limited by using appropriate excavation and lining techniques. It was observed that these fractures seal but only heal partially.

In-situ test 3 has shown that no interconnected fracture network exists beyond (at most) a few decimetres into the host rock. Furthermore, hydraulic conductivity around the gallery seems not to be influenced by fractures. Higher k-values (up to about a factor 2) are observed up to 6-8 m and are probably caused by the lower level of effective stress in that zone. With time, k tends to become lower (when measured on a vertical piezometer) although further measurements are needed to confirm this.
Unlike k, pore pressure is influenced up to an important extent by the presence of the gallery. The anisotropic aspect of pore pressure distribution can be explained by stress anisotropy (on the shorter term) and by anisotropic hydraulic conductivity of the host rock (on the longer term). Material parameters are only influenced slightly and up to a limited extent (2-3m).

Related information

Reported by

Euridice
Boeretang
2400 Mol
Belgium
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