| Title | Grouting Quality of Borehole Heat Exchangers |
|---|---|
| Authors | Tim LUTZ, Yannick REDUTH |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | grouting, quality, ground water flow, filtration, NPI |
| Abstract | In Central Europe borehole heat exchanger (BHE) boreholes are usually grouted with cement-based suspensions in order to assure the heat transport between the heat carrier fluid in the BHE pipes and the underground and in order to seal the borehole. The borehole must be sealed for hydrogeological reasons to prevent the intrusion of possibly polluted surface water into the underground and to prevent the connection of different groundwater layers. In Germany several research projects have been carried out in the last years in order to examine the grouting quality of borehole heat exchangers and to determine the main influence factors for the grouting quality. Therefore, test rigs with a height of 6 m were developed in which the grouting process could be visualized. In a second step grouting experiments were done with 30 m deep borehole heat exchangers in a special test rig, that allows a non-destructive removal of the examined borehole heat exchangers. The results concerning the grouting quality that were gained from analysis of the dismantled 6 and 30 m long BHE were compared to the suspension properties of the grouting materials and other factors of the grouting process (e.g. geometry of the borehole, type of mixing machine for the grouting suspension). The suspension properties were measured in laboratory as well as on-site during the grouting process of the tested BHE. Based on these comparisons the main influence factors for the grouting quality have been determined and recommendations for the design and construction of BHEs as well as for the grouting process supervision have been derived. In the latest research projects the examinations described have been extended to the aspect of water exchange between the suspension and the underground. This water exchange can be either due to groundwater flow or due to filtration of the suspension in a water-permeable underground. The results of the research described above is used in national and international technical as well as legislative guidelines and standards like VDI 4640, IEA ECES Annex 27 (Quality Management in Design, Construction and Operation of Borehole Systems, CEN/TC 451 (Water wells and borehole heat exchangers) etc. In this contribution the research methods for determining the main influence factors of BHE grouting quality and the most important outcomes are presented. |