Test and Evaluation of Monitoring Systems (TEM) - ESDRED low-pH shotcrete plug
The low-pH shotcrete plug was completed at the Grimsel Test Site in March 2007. The aim of the full-scale set-up is to demonstrate the support capacity of such a sealing plug under realistic conditions. The necessary pressure is applied by a swelling bentonite buffer at one side of the plug.
The low-pH concrete used for the construction of the plug must meet two key requirements:
Its pH has to be as low as possible (below 11) in order to minimise any chemical interaction of the plug with the bentonite and the surrounding geological medium.
It must be suitable for emplacement with the shotcrete technique.
Appropriate concrete formulations were developed and a short low-pH shotcrete plug was constructed in the framework of one of the earlier full-scale demonstrations for ESDRED
at the Äspö URL. Based on the results and lessons learned, a full-scale low-pH plug was constructed at the Grimsel Test Site with the shotcrete technique.
The second step has been to test and monitor the plug‘s support capacity under the realistic conditions of a filled emplacement gallery, i.e. in a gallery of appropriate diameter, with an actual granite-shotcrete interface and with the load of a swelling bentonite buffer at one end. An artificial hydration system in the buffer has accelerated the saturation process and imposes a pore-water pressure in the bentonite. The plug is monitored by a network of sensors for total pressure, water pressure and water content.
Construction of the bentonite backfill (left) and hydration system in vertical mats (right)
Completion of the plug with a shotcrete robot