Summary: To achieve a sealed area in rock, the grout should be sufficiently penetrated through the fractures while the filtration is an obstruction. By reducing the filtration, penetrability will be increased resulting in a more reliable grouting. Decrease in time, costs and the environmental impacts of the projects are of the benefits of reducing the filtration as well as increasing the safety margins of the projects during both construction and operation.
Use of variable pressure is a method for reducing the filtration which has been studied both in lab and field for many years. However there is still a lack of knowledge on the most efficient shape of the variable pressure. The effects of frequencies, magnitudes, ramp rates, pick and rest periods of the applied pressure on reducing the filtration are still unknown. To find out the answers of these questions a pneumatic pressure control system will be utilized together with the short slot (Draganovic & Stille, 2011). The aim is to study the use of variable pressure at a constriction through a fracture and to compare the results with constant pressure.
Backround: Cement grouting delivers the required sealing efficiency in tunnels, dams, hydropower plants and nuclear waste repositories provided that the sufficient penetration length can be achieved during the injection. The filtration, defined as separation of solid and liquid phases of the grout mix, prevents the grout to reach the sufficient penetration length. This limits the efficiency of rock grouting in underground facilities.
To solve the problem and increase the penetrability of cement grout, the filtration should be controlled efficiently. The effects of various parameters on reducing the filtration and improving the grout penetrability have been investigated by several researchers so far. These parameters are e.g. cement particle size, w/c ratio and grouting pressure increment. Regularly the applied pressure in rock grouting in field is based on constant pressure. However according to some recent investigations, variable pressure might have a significant influence on reducing the filtration and improving the penetrability.
Although the influence of dynamic grouting on improving the penetrability was satisfactory both in lab and field, the mechanism of action is not clear so far. Furthermore, the most efficient shape of the pressure, frequency, magnitude, ramp rate and duration of the pick and the rest periods have not been discovered yet.
This project is planed to be reported in a BeFo report during 2015.