Laboratory characterization of mining cemented rock fill by NDT methods: Experimental set-up and testing

Abstract

Many types of back fill are used as supporting technique in underground mines to optimize ground control stability and to minimize environmental problem at the surface. In theory cemented rock fill can yield optimum strength resistance, yet it is the least implemented in practice due to difficulties related to laboratory analysis of coarse particles in the material. This paper focuses on finding an appropriate protocol to use nondestructive testing techniques to characterize a cement-based material and to study the evolution of the properties during a curing period of 120 days. The testing techniques are the electrical resistivity and sonic methods. The resistivity technique highlights the changes in resistivity caused by hydration processes and the bond developing between the back fill constituents. The sonic technique measures the P and S waves. Knowing the velocity of the waves, changes of the geotechnical properties can be evaluated using known relationships between velocities and mechanical properties. Overall the mechanical strength can be indirectly monitored by these two techniques. Both techniques are complementary to one another and their joint application should improve the interpretation of strength. A concrete sample was made to test these two techniques on a slightly heterogeneous material. The experiment shows that the techniques are sensitive to the physical property changes and they enable monitoring of hardening and strength development. The far-reaching outcome of this research could help assess the properties of different compositions of mining rock fills in the laboratory before using them in mines. Alternatively, these techniques may be used on other cement-based material with coarser particles. © RILEM 2013.