Abstract
Grouting is a geotechnical process involving, for example, injection of a cement sand and water mixture or chemical resins into the ground to improve the strength and to decrease the permeability of rocks and soils. The efficiency of grouting operations is generally assessed by carrying out permeability and loading tests. Additionally, the comparison of the seismic field velocities of a rock mass obtained before and after the grout infection operation can give a qualitative indication of the effectiveness of grouting. However, for a quantitative assessment of grouting efficiency, more complex analysis of the rock mass seismic velocity is required.
Analysis of field seismic velocity data from different dam sites in the U. K. (Knill, 1970), according to the time average equation has given a relation between the field seismic fracture index and the field P wave velocity of the rock mass that is best repressented by a curve. The relation between the fracture index and the seismic P wave velocity is extended by assuming a P wave velocity of 1.46 km/s for groundwater, 2.40 km/s for grout and taking the intacts rock P wave velocity value from the analysis of data given by Knill. The results are presented as a diagram which can be used for grout efficiency assessment of the rock mass. Comparison of the published results from various dam sites with the diagram indicates that the diagram gives an upper bound curve. Additionally, a dimensionless version of the diagram is also presented for practical application.
Résumé
La consolidation par injection est une méthode géotechnique qui consiste à inecter par exemple un mélange de mortier de ciment et d'eau ou de résines chimiques dans les sols et les roches afin d'en améliorer la résistance et de diminuer la perméabilité. L'efficacité des injections est vérifiée en général au moyen d'essais de chargement et de perméabilité. En outre la comparaison des vitesses de propagation des ondes dans une masse rocheuse en place avant et après les opération d'injection peut donner une idée qualitative de l'efficacité de ces dernières. Copendant une estimation quantitative de l'efficacités des injections néssite une analyse plus complexe de la vitesse de propagation des ondes dans le massif rocheux.
L'analyse des mesures de vitesse des ondes sur un certain nombre de sites de barrages en Grande Bretagne a permis d'établir und corrélation entre l'indice de fracturation du massif et la vitesse de propagation de l'onde P. Pour établir cetter corrélation, on a admis que la vitesse de l'onde P dans l'eau souterraine est de 1,46 km/s, dans le coulis injecté de 2,40 km/s et que les vitesses de propagation de l'onde P dans la roche saine sont celles indiquéesppar Knill. Les résultants sont présentés sours forme d'un diagramme qui peut être utilisé pour vérifier de l'injection dans un massif rocheux. La comparaison des résultats publiés sur différents sites de barrages avec le diagramme montre que ce dernier donne une courbe située en haut du fuseau.
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Turk, N., Dearman, W.R. Assessment of grouting efficiency in a rock mass in terms of seismic velocities. Bulletin of the International Association of Engineering Geology 36, 101–108 (1987). https://doi.org/10.1007/BF02600944
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DOI: https://doi.org/10.1007/BF02600944