Design, testing, and evaluation of a water injection grouting system. Final report
The necessity of grouting vertical ground heat exchanger boreholes is well established. The use of chip bentonite was investigated as an alternative to slurry grouting methods for backfilling geothermal bores. Grouting a geothermal bore with chip bentonite has many potential benefits if the bore can be completely grouted from bottom to top. High solids content grouts that are possible with chip bentonite could increase the thermal conductivity of the grout and make it less susceptible to performance reductions associated with drying of the grout. The lower price of chip bentonite compared to powder bentonite grouts would reduce the cost of grouting. Chip bentonites would also have an advantage over powder bentonite grouts by reducing the amount of dust created during the grouting process. The proposed grouting system would use water to transport chip bentonite through a tremie pipe into the bore. The properties of chip bentonite grouts were first examined by pouring chip bentonite into a standing column of water. Chip bentonite grouts had percent solids ranging from 50% to 60% and thermal conductivity from 0.46 to 0.52 Btu/hr ft F. Tests were also performed with a thermal additive mixed with the bentonite chips. Additives tested included pea rock, masonry sand, and crushed quartzite. The additive in the wet grout accumulated in pockets, creating possible avenues for hydraulic movement. Total percent solids of bentonite and additive mixtures ranged from 60% to 80%. Thermal conductivity results were varied, but generally increased with increasing percentages of additive. The feasibility of transporting bentonite chips with water through a tremie pipe was studied with two types of water injection systems. Both systems incorporated a pressurized solids tank to keep water from hydrating the chips prior to entering the water stream. A low pressure system was able to transfer pea rock successfully through a short length of tremie pipe. The use of bentonite chips caused plugging at the feeding point. A higher pressure system was built to handle the higher pressures caused by the transportation of material through longer tremie pipes. An auger was used to transfer chips out of the solids tank and drop them into a cone mixing chamber. Difficulties in trying to balance air and water pressures to keep the water level below the height of the auger proved to be too complex for further experimentation. Neither system is recommended as a model for a practical grouting system.
- Research Organization:
- Electric Power Research Inst. (EPRI), Palo Alto, CA (United States); National Geothermal Support Center, Brookings, SD (United States); South Dakota State Univ., Mechanical Engineering Dept., Brookings, SD (United States)
- Sponsoring Organization:
- Electric Power Research Inst., Palo Alto, CA (United States)
- OSTI ID:
- 353215
- Report Number(s):
- EPRI-TR-109162; TRN: AHC29923%%46
- Resource Relation:
- Other Information: PBD: Nov 1997
- Country of Publication:
- United States
- Language:
- English
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