Field validation of a detectable, magnetic, cementitious grout for rock fracture grouting

This paper presents the development and field-scale demonstration of a cementitious grout that enables detection in the subsurface via the addition of magnetite. Through the strategic use of a grout injection borehole and an array of monitoring boreholes for conducting pre- and post-injection magnetic surveys, combined with a geologically-based model for simulating the magnetic field anomaly, this technology can locate the post-injection magnetic grout volume within the subsurface. A series of laboratory tests were conducted to show that the addition of Bayferrox 318 M magnetite to a microfine cementitious grout does not detrimentally affect grout fluidity, penetrability, gelling, bleed and compressive strength. A magnetic grout with fluid to solid ratio = 0.7 and 15% magnetite content was then injected into a borehole interval at 40-50 m depth, and changes to the magnetic field were measured within six surrounding monitoring boreholes. Field trial results show that the measured magnetic anomalies (due to magnetic grout injection) correspond well to geological features identified in a nearby site investigation borehole and that these anomalies can be detected in monitoring boreholes at a distance of 3 m. By optimising the fit between model simulations of the magnetic anomaly and the field trial observations, the final geometry of the grouted rock features could be determined. Results show that grout preferentially penetrated into two coal beds and along two bedding planes that cross-cut the injection hole.