An Approach to Evaluate the Efficiency of Compensation Grouting
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 140, Issue 12
Abstract
Compensation grouting is often employed as a mitigation technique to reduce the settlements induced by tunneling. The efficiency of compensation grouting, defined as the ratio of the volume of heave induced at the ground surface to the volume of injected grout, is strongly dependent on grout properties, injection characteristics, and soil properties. In clayey soils, site observations and laboratory tests show high values of compensation efficiency immediately after injection. However, the efficiency can decrease with time if positive excess pore-water pressures develop in the soil during the injection process. Conversely, in sandy soils, a loss of volume occurs because of pressure filtration of the grout during and soon after the injection process, which reduces the compensation efficiency. This paper describes an analytical model that can be used to evaluate the volume loss produced by pressure filtration of cement-bentonite grouts as a function of soil, grout, and injection parameters. The magnitude of pressure filtration is evaluated as the grout efficiency, which is given by the ratio of the volumes of the final grout body to the injected grout. Results show that the grout efficiency increases with decreasing soil permeability and with increasing grout bentonite content. The result of a grout injection test on a silty soil is back-analyzed using this approach in which the grout efficiency is first evaluated through the proposed filtration model and then used to calibrate a numerical simulation of the test. The good agreement between experimental data and computed results shows that prediction of the efficiency of compensation grouting can be improved using the proposed approach.
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Acknowledgments
The authors acknowledge Professor Adam Bezuijen (formerly Deltares, currently Ghent University) for the fruitful discussions and the support given during the execution of the filtration tests carried out at Deltares and throughout the development of the study.
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Information & Authors
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 140 • Issue 12 • December 2014
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Nov 15, 2013
Accepted: Jul 21, 2014
Published online: Aug 27, 2014
Published in print: Dec 1, 2014
Discussion open until: Jan 27, 2015
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