Bentonite grout is quickly becoming the accepted standard backfill material for geothermal bore holes.  Bentonite grout in a geothermal bore seals the hole and prevents surface water from contaminating underground aquifers and also prevents inter-aquifer communication if grouted from bottom to top.  Grouting a geothermal bore hole ensures a continuous heat transfer path between pipes and bore wall, and also gives the design engineer the advantage of specifying the thermal conductivity of the backfill material.  Bentonite grouts can be mixed in certain ratios with a silica compound to produce thermal conductivities ranging from .45 to 1.2 Btu/hr-ft-F.  Geothermal Supply Company is a supplier of GeoPro Inc. grouting product, which uses the highest quality bentonite products from Black Hills Bentonite L.L.C.  For more information about our grouting products, grouting practices, or pricing information, please contact us.      

 

Once backfilling is complete, the bentonite slurry quickly sets up to a pliable clay consistency.  The permeability of the bore hole to water is reduced to 6.9 E-8 cm/s which is well below the maximum allowable permeability standard of 1 E-7 cm/s.  Underground aquifers are protected from surface water and from other contaminated aquifers.   

The grouting components are mixed together in a paddle mixer to produce a slurry which is then pumped via a positive displacement pump through a tremie tube to the bottom of the bore.  The bore hole is filled from bottom to top with the slurry to ensure no voids are created during backfilling.

The thermally enhanced grouts consist of three components:  bentonite, silica compound, and water.  The components mixed in different ratios yield thermal conductivities ranging from .45 to 1.2 Btu/hr-ft-F.