Vertical Closed-Loop Grouting Recommendations; Grout Material - Bosch Geothermal Heat Pumps Applications Manual

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10.9 Vertical Closed-Loop Grouting
Recommendations
The borehole should be grouted immediately after pipe
installation, ideally within 24 hours and in accordance
with the grout manufacturer's mixing and installation
requirements (Fig. 67)). Drilling uids should be ushed
from the borehole prior to pipe installation, with the
exception of boreholes where groundwater exhibits
artesian conditions. Grouting should be completed in a
manner that prevents the introduction of surface or near
surface contaminants into an aquifer, the interchange
of water from different aquifers, or the loss of natural
artesian pressure from an aquifer.
The void space between the vertical closed-loop system
piping and the borehole should be grouted in a continuous
operation from bottom to top using grout placement
procedures set forth in the IGSHPA Grouting for Vertical
Heat Pump Systems, Engineering Design and Field Manual.
A Tremie pipe (grout pipe) not less than 1¼ inches
nominal diameter should be placed to the bottom of the
borehole before grouting. The Tremie pipe may be used
to push the closed-loop piping into the borehole. The
Tremie pipe should be removed from the borehole upon
completion of grouting. Grout should be pumped through
the Tremie pipe till the density of the grout owing from
the borehole at the ground surface equals the density of
the grout being pumped in. The installer should monitor
each borehole for settling for a period of not less than
12 hours. Additional grout should be added if necessary
and the monitoring period should be extended until the
settling of grout stops. A borehole drilled using horizontal
directional drilling techniques should be grouted by
pumping grout as the Tremie pipe is retracted through the
borehole. Grout manufacturers' product speci cations
should always be followed for mixing and pumping grout.
Fig. 67
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
Data subject to change

10.10 Grout Material

Grout material is typically used to ensure contact between
the inserted pipe and the earth and helps promote heat
transfer (Fig. 68). The grout material also serves to seal
the hole off from any aquifers or groundwater supplies
that may have been penetrated during the drilling process.
Fig. 68
A proper grout for vertical loops will have the following
properties:
f
high thermal conductivity to allow heat transfer
f
low viscosity to allow the grout to wrap around the
pipe
f
low shrinkage volume to ensure that the grout will not
pull away from the pipe
f
low permeability to prevent the migration of antifreeze
solution in the event of a line breakage
Grout materials, which do not include drilling muds, uids
or gels, are typically divided into two types:
f
cement-based
f
bentonite-based
Cement-based grouts with 5-10 percent bentonite are
occasionally used. However, cement-based grouts are
prone to shrinkage and heat of hydration and they may not
adhere to the HDPE plastic pipe.
Therefore, bentonite-based grouts are typically
recommended in lieu of cement-based grouts (Fig. 69).
Silica can be added in speci c proportions to both grout
types to increase thermal conductivity ability.
Applications Manual
Bosch Thermotechnology Corp.