Numerical calculations for prediction of grout spread with account for filtration and varying aperture

Grouting as a mean to reduce the ingress of water to underground facilities has been used for decades. With an increased demand for tightness and cost efficiency, the incentive to improve the method has also increased, and the need to understand the governing factors has been focused. The knowledge concerning grouting involves several fields of research, for instance pow in fractured rock and the behaviour of the grouting material. An understanding of these fields is essential in grouting research. Numerical modelling of grout propagation in fracture geometries is one means of achieving such understanding The paper presents how numerical calculations of grout spread and sealing effect can be used for predictions of the grouting result. The calculation concerns pow of grout in a network of conductive elements, representing a fracture geometry with the scope to understand the governing parameters when grouting. The spread of grout is significantly affected by the spatial variability of the fracture aperture. Measurements on grout properties and laboratory experiments show that the grout possesses a limited penetration ability and that filtration of the grout occurs if the aperture of a constriction is smaller than a critical value, i.e. when a filter cake forms in front of constrictions in the pow and the great that passes is filtered. In the paper, a model for filtration of grout is presented. When filtration and limited penetration ability are incorporated in the calculations, additional strong effects are observed. This underlines the need of both a representative geometry, including the fracture variability and measurements of grout properties. (C) 2001 Elsevier Science Ltd. All rights reserved.