In cement-based grouting, insufficient spread of grout within the rock fractures is one of the major issues, which negatively impacts the sealing performance and service life of underground structures. On the other hand, an excess of the grout spread is neither economic nor environmentally friendly. Hence, optimization of the grout spread is of the greatest concern in rock grouting to provide the most reliable and economical solution for sealing in the construction and maintenance of underground facilities. Accordingly, the Real Time Grouting Control (RTGC) theory is a method that has been developed to analyse the spread of grout in rock fractures. It predicts the extent of the grout penetration over time based on grout properties and the applied pressure. Despite extensive work conducted to verify the RTGC method in both the lab and the field, it has not yet been sufficiently investigated in the lab under inhomogeneous geometry conditions like a more realistic rock fracture with variable, non-subsequent apertures.

This investigation therefore took a novel effort to examine the performance of RTGC theory at presence of variable aperture constrictions. The idea is to investigate how close are the results of predictions of grout propagation of RTGC theory (at different aperture orders) with the experimental results obtained using an artificial fracture with adjustable aperture order. A fair comparison is further provided between the predicted results and the results of numerical simulations under different aperture distributions. The predictions are obtained using both the hydraulic aperture, the way that the theory was previously used in the early stages of development, as well as the mean-physical aperture, the way that the theory is currently used in the field applications. 

An unique equipment, referred to as Variable Aperture Long Slot 2 (VALS II), was designed and produced to meet requirements of this investigation. It consists of multiple short aperture plates attached to a 4m long base plate. The aperture plates have different aperture sizes for representing variable apertures in rock fractures and can be mounted on the base plate in any sequence to form desired aperture size distribution with respect to VALS II inlet for grout inflow.

Test results reveal importance of correct evaluation of grout rheology when applying RTGC theory. Based on them it was concluded that if applying fresh grout rheological properties RTGC theory gave not as precise prediction for grout propagation in time as grout rheological properties at 30 minutes from mixing.