Conductive grout with multiwalled carbon nanotubes for water cut-off self-monitoring in underground tunnels

In underwater and underground tunnels, grouting methods are used to prevent water inflow. However, the effectiveness of water infiltration blocking is difficult to verify after construction, and the long-term performance of grout in terms of water tightness is hard to assess. This study proposes a technology for monitoring the water infiltration capacity of grout that incorporates multiwalled carbon nanotubes (MWCNTs) as conductive nanomaterials. Grout containing conductive nanomaterials exhibits lower resistance compared with conventional grout, facilitating electrical flow and enabling the detection of water infiltrating the grouted area. MWCNTs-incorporated grout specimens were fabricated to analyse their electrical characteristics during water infiltration. According to electrical resistivity tests, the optimal amount of MWCNTs incorporated into the grout was 1.0%. A quadratic relationship was established through water infiltration tests with different residual depths and spacings of electrodes. Additionally, multiple regression analysis was performed to express the relationship between the water detection time, electrode residual depth, and electrode spacing in a functional form. This enables the calculation of the appropriate residual depth and spacing of electrodes based on the desired water detection time. This study proposes an efficient water detection configuration using rock bolts for grout reinforced system in a tunnel.