Quality Control and Troubleshooting for Grouts Used with Geothermal Heat Pumps

Abstract

Vertical boreholes for geothermal heat pumps (GHPs) are completed with grout materials to provide heat transfer and prevent groundwater contamination. Typically, grouts are either bentonite or cementitious. Modifications to these materials are usually made in order to improve thermal conductivity. The efficient performance of GHPs relies on the properties of the grout and the quality of the grout placement. Therefore, it is necessary to ensure that the grouting material conforms to specification requirements and that appropriate quality control testing is undertaken to verify mix proportions and pumpability. This paper considers field quality control and post-grouting tests applicable to bentonite and cementitious grouts and how these can best be implemented. In addition, problems that can arise during mixing and placement of grout are discussed and recommendations are made on how these pitfalls can be avoided.