Measurements on back-fill grouting at Groene Hart Tunnel (GHT) are described and analysed. The research utilises TBM data, monitored grout pressures and measured rheological properties of tunnelling fluids. Grout injection strategy and vertical grout pressure distribution behind the TBM were found to agree with established theory, like found in other tunnelling projects. However, on some occasions different smaller vertical grout pressure gradients were found, which might have been caused by an incidental upward movement of the tunnel. It is shown that the consolidation of grout determines the decay of grout pressures. The associated net hydraulic resistance of surrounding soil is substantially higher than according to radial flow theory. This higher resistance is attributed to bentonite originating from the face of the TBM, having invaded the grout-soil
interface.