Numerical study on the pipe flow characteristics of grouting repairing pastes used in slab track

Abstract

In this study, the pipe flow characteristics of the grouting repairing pastes (GRPs) used in slab track were investigated based on three-dimensional flowing models taking into account the hydration effects. Firstly, the rheological properties of GRPs at different hydration times were measured and fitted to obtain key rheological parameters of GRPs. Then the flowing models of GRPs in pipes were established based on these rheological parameters and were verified by comparing with theoretical values. Finally, the effects of pressure gradients, pipe diameters and cement hydration on the flow characteristics of GRPs were systematically studied in terms of four indices including plug diameter, plug velocity, average velocity and the velocity ratio. Results show that the increases of pipe diameters and pressure gradients both lead to the growth of flow velocity, causing an inhomogeneity flow of GRPs in pipes. Yield stress of GRPs has the greatest influence on the flow indices. Consistency index contributes more to plug velocity and average velocity while fluid behavior index dominates the velocity ratio. To achieve a homogeneous flow at high flow rate, it is recommended to prepare a grouting repair material with moderate yield stress and low consistency index and fluid behavior index. Moreover, cement hydration causes noticeable decreases of plug velocity and average velocity under the coupling effects of rheological parameters, which may lead to the setting of GRPs near pipe wall and eventually to the occurrence of pipe blockage during transportation. In order to satisfy efficient repairing in short skylight period, it is suggested to adopt a special grouting repair material featured with slow hydration during grouting but rapid hardening after filling in the debonding area.