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Table 1 Requirements to grouting materials and BHE sealing modified after IEA ECES (2020)

From: Impact of operational temperature changes and freeze–thaw cycles on the hydraulic conductivity of borehole heat exchangers

Belgium The permeability needs to be less than 10–8 m s−1. Mostly cement–bentonite grouts and clay pellets are used
Denmark The only requirements are related to the sealing properties. So far only bentonite-based grouts have been used in DK. The legislation demands “impermeable materials”. This means that materials other than bentonite, with the same permeability properties, may be allowed
Finland Not specified
Germany In almost all cases a cementitious grouting slurry is used. Rarely are swelling clay pellets used for grouting in case of fissures in combination with groundwater. Thermal enhanced clay pellets and a special pumping device have been developed. The permeability of the backfill needs to be ≤ 10–10 m s−1 according to the VDI 4640 guideline. However, this value is under discussion in Germany
Japan Not specified
Netherlands The permeability needs to be less than 10–9 m s−1. Clay from the drilling itself cannot be used
Sweden Alternative sealing by different forms of sealing plugs that are attached to the collector. These are used to avoid salt or brackish water to enter higher levels in the boreholes, but also to seal-off potential leakage between aquifers
Turkey Not specified