PROJECT RESULTS / Annual Technical Results

Year 4 : ESDRED TECHNICAL RESULTS to January 2008

Module 4: Low pH shotcrete for rock support and plug construction technology

Summary :

The construction of the full-scale (4 m-long, 3.5 m in diameter) low-pH shotcrete plug was carried out in the Grimsel Test Site during the first quarter of 2007. Firstly the 1 m-long bentonite buffer was constructed at the back end of the gallery, which involved the installation of 16 588 kg of bentonite with 33 embedded sensors and six hydration mats.

Immediately afterwards the low-pH shotcrete plug was constructed by spraying seven successive vertical layers. They were given a curved shape in their periphery to improve the contact with the rock. The installation of the Water Injection System, the Data Acquisition, Display and Control System and the gallery instrumentation followed, leaving the test ready to be operated and monitored with the 86 sensors installed in total to measure water and mechanical pressures, displacements and humidities.

The operational phase started on March 29, 2007 with the injection at a pressure of 2 bar through the hydration mat located at the back end of the bentonite buffer. A water leakage was detected through the contact of the rock with the bottom of the plug, and the injection was stopped. After several different attempts to stop the leakage, in September 2007 a retaining dam was constructed close to the plug front up to mid height of the gallery, so to allow the retention of water and favor the swelling of bentonite. The water injection was resumed in November 2007 and total pressure and humidity started rising after a few weeks.

Work completed:

Work Underway:

Important Events Planned For 2008:

The operational phase will continue until end of 2008, including the increase of the hydration regime by injecting water through all the six mats, and at higher pressures if necessary, so reach if possible the target pressure of 4.5 MPa in the bentonite buffer.