The drill and blast rock excavation cycle involves several processes that affects the grouting; vibration from drilling, borehole flushing, the blasting itself and water-loss measurements in boreholes. This research project focused on the effects of water-loss measurements, drilling (both vibration and flushing) and blasting on the grout and during the first five hours of the hardening process. A conceptual model was derived to explain what forces acts on the grout and how the forces can be interpreted in order to reveal how these forces effects the grout. The model suggests that the shear modulus of the grout is a key parameter for understanding the degradation of the grout. The different forces/stresses during an excavation effects the grout differently but the blasting is by far the most difficult process to describe. One starting point of the project is that the grout does not reinforce the rock and by that should not hinder the gas expansion. The blasting should generate new fractures around the blast hole and the gas will penetrate these cracks and finally the expansion of gases should cause fragmentation and movement in the rock mass. The paper describes the results from the field test and how the grout has been characterized using a rheometer. The field test was conducted in a short tunnel niche. The effects from the drill- and blast cycle were studied i.e. vibrations from drilling, boreholes flushing/water-loss measurements and vibrations from blasting. Five boreholes with a centrum distance of 1 m were chosen to be monitored, due to its hydraulic connectivity between the boreholes. Four of these boreholes were successfully grouted by following a grouting design and one borehole was left un-grouted and used for blasting. The effect on grouting in the rock mass from hole of blasting was measured using water-loss measurements in adjacent boreholes. One result of the field test is that the grout was not affected by the blasting under the circumstances used. Instead the study revealed that the water loss measurements affected the connected boreholes negatively.
Rock Excavation Cycle and Its Effect on Grouting
Funehag, Johan, Janson, Thomas, Jern, Mathias, Svahn, Victoria, and Rasmus Trygg. "Rock Excavation Cycle and Its Effect on Grouting." Paper presented at the ISRM 9th Nordic Grouting Symposium, Helsinki, Finland, September 2019.
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