Filling of old silver mines in Pradal

Under supervision for years by the Department of Prevention and Mineral Safety (DPSM) of the Bureau of Geological and Mining Research (BRGM), silver-lead mines are located under the town center of the PRADAL commune. The potential risk for the overlying constructions and roads required filling the galleries with the URETEK Cavity Filling® process in order to secure the site sustainably.

This large-scale project took place under the delegated project management of the BRGM and the project management of ANTEA. Nearly 600 m3 had to be filled while respecting the many constraints of the specifications (deadlines, security, controls, etc.).

To add to the complexity of the site, this filling had to be entirely carried out from the bottom of the galleries. Usually, vertical drilling is preferred to carry out injections from the top, but this technique from the bottom was imposed by the difficulty of access to the site in urban location. To meet the typology of the site, the phasing required the installation of dams (masonry and shotcrete) by EIFFAGE to partition the cavity in several volumes.

Balls of expanded clay were then introduced into each of the sections to be filled before injecting an exclusive expansive resin until perfect bonding was obtained. This much lighter filling material than traditional grouts preserves the porosity of the cavity while allowing possible hydraulic circulation.

This delicate intervention was carried out in the space of 5 weeks and without any hindrance for the neighboring dwellings, which are now secure. The speed of intervention and the perfect adaptability of the solution offered by URETEK^® to the constraints of the site were able to convince the BRGM which is currently considering the use of Cavity Filling on other monitored sites.