The presented report is a summary of the laboratory investigation conducted in collaboration between RISE CBI Betonginstitutet and Division of Soil and Rock Mechanics, KTH Royal Institute of Technology during 2017-2018 with the aim to improve the grout spread in rock fractures using dynamic grouting technique. The dynamic grouting, which has been developed to improve the spread of grout in rock fractures, has been studied in both the lab and the field since 1985. The focus of all the previous investigations was however on application of high-frequency oscillating pressure to reduce the grout apparent viscosity. This was achieved by destructing the grout internal structure and reconstructing to a lower viscosity suspension. Even though some improvements were reported in the corresponding literature, the major remaining issue was yet quick dissipation of the oscillations along the fractures and consequently inadequate spread of grout.
Recent investigation performed by the authors, presented in BeFo-Report-149, illustrated a significant improvement (up to 11 times) in the total volume of grout passed through the apertures smaller than 70 µm in a short slot by applying low-frequency rectangular pressure impulses compared to the static pressure. In this study, the mechanism of improvement of the grout spread was interpreted as successive erosion of the produced filter cakes due to the variation in flow pattern at the constrictions caused by the pressure change in consecutive cycles. However, since the laboratory experiments conducted in this study were carried out using a short slot, the dissipation length of the applied pressure impulses along a longer fracture was yet questionable.
The present study first aimed to investigate the dissipation of the dynamic pressure impulses along a much longer artificial fracture, so-called varying aperture long slot (VALS). The investigation was conducted by applying two selections of the peak/rest periods in two steps. In each step, the extent of the improvement of the grout spread was examined in different pressure conditions.
Even though the project was a limited study based only on the laboratory experiments, the results obtained in terms of both the extent of improvement of the grout spread and the extent of dissipation along a fracture were promising showing the potential of the method. Finally, the study suggests further development of the method to full scale field tests, to demonstrate the capacity of the new technique to the stakeholders in industry.