Shear modulus as a new parameter to characterize grout

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When tunnels are excavated by drill and blast there are several processes that generates forces/tensions on the grout, such as vibrations, blast induced forces, water flow etc. Extensive laboratory work was conducted to find crucial parameters on grout to assess a fundamental understanding on how a grout can be characterized to cope with future demands on grout. The work comprised of advanced laboratory testing on cement compared more traditional testing. The shear modulus is measured in this study for cement grout over five hours of hardening time. It is shown that grout with lower w/c hardens faster i.e., more rapid growth of shear modulus. Cement grout has a relatively high shear modulus which increases over time, where the viscous and elastic shear moduli intersect at a point which is believed to correlate to a change in failure mechanism Rheological tests are performed to study the first five hours of the hardening process of the grout. The setup was with oscillating concentric cylinder, with both constant amplitude and frequency. The shear moduli over time can be computed, which in this case can be seen as a first attempt to describe a shear moduli of cement grout. This could help to describe the characteristics of a grout, to understand the forces that the grout encounters during a full drill-and blast cycle.

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