The Effect of Blasting On The Grout-PPT Presentation

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The study examines whether drilling and blasting damage grout used to control water inflow during tunnel excavation, and whether standard post-grouting waiting times are necessary. In Scandinavia, crews commonly wait 5–7 hours, sometimes up to 12, before drilling resumes.<br /><br />Researchers conducted a field test using 4-m boreholes. After hydraulic testing and grouting selected holes, they detonated a contour-style charge in one borehole three hours after grouting, measured vibrations, and retested water flow. They also estimated blasting-induced shear strain and characterized grout using its shear modulus and the strain needed to make it flow.<br /><br />The grout’s resistance to flow increased as it hardened. At three hours, its measured yield stress was 14–16 Pa, and an estimated shear strain of about 0.05 was required to make it flow. The tested blast produced substantially lower strain, even near the blast hole. After blasting, three of four adjacent boreholes remained tight; one showed flushing or erosion during water-loss measurements.<br /><br />The authors conclude that, for the tested charge and conditions, blasting did not significantly affect grout at distances of 1 m or more. They argue that drilling and blasting need not be governed by an arbitrary general waiting time. Instead, grout should be characterized by its shear modulus and resistance to flow, with testing and grouting design tailored to the excavation cycle. The findings apply specifically to the tested contour-hole charge and should not be generalized to all blasting conditions.

Keywords

tunnel excavation

grout

drilling and blasting

water inflow control

post-grouting waiting time

contour charge

shear strain

yield stress

hydraulic testing

blast-induced damage