Back Filling Bentonite powder manufacturers
When soils and ground conditions are highly acidic, or alkaline, or suspected of being so, backfill earthing compounds or materials such as Bentonite can significantly extend the life cycle of bare copper earth tapes and earth rods. Furthermore, Bentonite retains water increasing the surface contact area with the soil and consequently reducing grounding resistance. Carbon-based backfills often contain other contaminants, such as sulphur and other elements which are harmful to copper and should be avoided.
Pictured: a chemical-filled earth rod surrounded by Bentonite backfill (the white slurry) to improve electrical connectivity to the copper earthing system.
How To Use Bentonite
The plasticity and viscosity of the earthing compound ensures simple installation and use by the utility or civil engineering contractor – there is no precise mixing ratio and this varies according to local electrical utility and DNO engineering standards and preferences related to ground conditions and resistivity readings. The compound should be mixed thoroughly and vigorously with water to achieve an even consistency in slurry type form to suit pouring into the cable trench, bore-hole or worksite.
Mixing Bentonite
The expansion rate of Bentonite is relative to the volume of water used to create the earthing compound mixture. As a rule of thumb we recommend to assume a 2:1 expansion ratio.
1 x 25kg Bentonite = 1cu ft or 0.0283m³ (Dry)
1 x 25kg Bentonite = 2cu ft or 0.0566m³ (Wet)
For Example…
To backfill a cable trench containing 10no. copper earth rods in 3.6m deep, 0.1m diameter boreholes will require the following volume of Bentonite clay compound:
Volume Of Boreholes
= 10 x π r² x h
= 10 x π x 0.05² x 3.6
= 0.28m³
Number of Bags = 0.28 / 0.0566 = 5 Bentonite Bags
Installation Of Bentonite Into Boreholes
For the installation of an earth rod or electrode into a borehole the following procedure is recommended.
1 Bore/auger a hole at the desired earth rod location of 75-100mm (3-4 inches) diameter. The depth of the bore hole should be determined by the earthing system designer.
2 Insert the copper earth rod into the borehole – ensure that the top of the eartth rod is at the correct level for connection.
3 Backfill the borehole with Bentonite – this will be mixed with water an now in a slurry condition. Regular stirring or agitation of the earth rod should ensure that no voids are formed within the backfill of the underground trench.
4 Remove any standing water from the top of the borehole.
5 Make final inspection to the earth rod and make good i.e. fit the earthing inspection chamber.