Borehole Construction - Bosch Geothermal Heat Pumps Applications Manual

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10.5 Borehole Construction

Prior to borehole construction, the installer should always
locate and mark all existing underground utilities, piping,
etc. All ground heat exchangers should be installed for
new construction before any sidewalks, patios, driveways,
and other construction has begun. During construction,
always accurately mark all ground heat exchanger piping
on a plot plan as an aid in avoiding potential future
damage.
During construction, installers should minimize the
potential for the introduction of contaminants into an
open borehole. During breaks in drilling, boreholes
that are left open should be protected from direct
precipitation, surface water in ow and access by animals
and/or people. The installer should ensure that any open
borehole is securely covered to prevent the entrance of
contaminants, and prevent a safety hazard for animals
and people if construction is not complete and they must
leave the borehole site for any reason. The borehole
should be secured to prevent collapse if the drilling rig is
to be removed from the site before borehole completion.
Boreholes should never be left open for more than ten
days and efforts should be made to avoid having multiple
open boreholes on the site at any particular time.
During construction of a borehole for a vertical closed-
loop system installation, drilling uid consisting of a
bentonite clay viscosi er and water mixture should be
circulated to form a lter cake on the borehole wall to
minimize borehole collapse. The borehole should be
kept full of bentonite drilling uid until the loop piping is
installed. Before grouting, the drilling uid in the borehole
should be thinned until the drilling uid density is lower
than the grout density.
Surface water should not be used as a source of water
during the drilling of a vertical closed-loop system
borehole (unless it is obtained from a municipal water
supply system). Water that is used for drilling purposes
should be potable water that contains a free chlorine
residual of not less than 10 milligrams per liter. Chlorine
test strips are a quick way to check chlorine residual
levels.
Unique geologic conditions may require alternative
construction practices. When necessary, a temporary
casing should be used to maintain borehole stability in
unconsolidated materials.
Where owing or artesian conditions are possible during
construction, the installer should implement appropriate
measures to control or eliminate upward ow in the
borehole.
Data subject to change
If mineshafts, fractures or caverns are encountered in
consolidated material, the borehole should be packed or
sealed above and below the void. Other methods may be
used as necessary to preserve borehole stability. When
drilling through caves, mines, or other cavities the lower
portion of the casing should be grouted in accordance
with design speci cations and a packer or similar bridging
device used to facilitate grouting above the cavity. If rapid
loss of grout material occurs during placement, coarse
material such as sand, gravel, crushed stone, dry cement
or other bridging materials approved for use may be used
in the zones in which the loss is occurring. The remainder
of the annular space should be grouted in accordance with
grout manufacturers and design speci cations. Casing
should be installed, as necessary, in the case of voids
which may cause the loss of excessive amounts of grout.
Applications Manual
Bosch Thermotechnology Corp.