INNOVATIVE GROUTING TECHNIQUES FOR INSTALLATION OF A SEEPAGE BARRIER AT BARRAGE DES QUINZE DAM (QUEBEC, CANADA)

摘要

The Barrage des Quinze dam is a concrete sluice dam consisting of 19 spillway sections, each of which is approximately 7.6 metres wide and 14.5 metres deep. Rehabilitation efforts being performed on the dam including demolition and improvement of the roadway and spillway sections and grouting to mitigate underseepage. Initially, conventional cement grouting was attempted and was successful in 14 of the spillway sections, but unsuccessful in 5 of the sections due to the high water flows which washed the grout away. The removal of the roadway and portions of the piers during construction temporarily reduced the stability of the structure limiting grouting pressures that could be applied. This and the substantial high water flows (leakage) beneath the dam between the concrete/rock contact and within fractures in the upper rock formation created a challenging situation to create a cutoff. A grouting solution was developed that involved implementing several different grouting methods and materials including balanced high mobility grouts (HMG); low mobility grouts (LMG); polyurethane grouts; and sodium silicates. Because of the critical scheduling for the work, multiple approaches were planned and made available on site so that the work could proceed with the best technology with little, if any, time loss. The end goal of the grouting program was to create a seepage cutoff beneath the 5 sections of the dam in a stepwise process. The initial step was to fill the large openings and create a grout barrier to reduce the high water flow. The second step was to seal the contact between the base of the dam and the bedrock; and the third step was to complete closure by grouting a deep grout curtain into the underlying rock. Other features of the work included an extensive grout mix testing program, water pressure testing, borehole camera survey, and monitoring of the grout injections. Critical to the success of the project was the careful planning and execution of the hole pattern and injection sequence to minimize grout loss due to high water flows and optimize cutoff of the high flows to permit closure with a HMG grout curtain. A novel use of a sodium silicate as a setting agent together with a balanced stable cement grout proved to be a highly effective technique to stop the high water flows streamlining the operation and eliminating the need for LMG and polyurethane grout. The project was successfully completed through the winter months in northern Quebec Province using special measures to protect the work space and provide heating for grout materials for proper injection and cure. The work was completed within the required schedule to enable use of the dam gates to manage spring flows.