Cement-Bentonite (C-B) slurry trench cutoff walls utilize
a bentonite slurry containing cement to stabilize the trench during the
excavation phase. After completion of the excavation, the cement causes
the slurry to harden to a strength comparable to that of a stiff clay,
thereby eliminating the need for trench backfilling. The cement-bentonite
slurry contains no aggregate other than some suspended soil particles from
the excavation process, The bentonite provides the media to keep the cement
in suspension until initial set occurs.
Strength and plasticity of the hardened cement-bentonite
slurry will vary, depending mostly on the cement/water ratio and the type
of cement, with higher strengths having lower plasticity. Mixes can be
designed to achieve unconfined compressive strength from 5 psi to well
over 20 psi at 28 days.
Additives, including setting retarders, can be incorporated
in the mixture to achieve certain operating characteristics, or for economy.
For example, flyash is sometimes used as a filler to increase the density
of the slurry and to reduce the cement content. The permeability of C-B
cutoff walls depends on the proportions of bentonite, cement and flyash
used in the mix. Permeability can normally be achieved in the range of
10-5 to 10-6 cm per sec. Lower permeabilities can
be achieved if required.
Some of the primary reasons for selecting C-B cutoff walls
instead of soil-bentonite cutoff walls are:
Design requirement for strength of the backfill.
Potential for trench instability due to soft and loose soil zones
or adjacent surcharges.
The panel method of excavation can be employed where these conditions
are critical.
Site conditions restricting the working area and preventing the preparation
of the S-B backfill mixture alongside the trench.
Unavailable or costly materials suitable for soil-bentonite backfill.
INQUIP has experience in the installation of C-B cutoff walls since 1977,
and has access to advances in mix technology through license agreements.
If you have an immediate or future application for any
of our specialty construction techniques, please
contact us. If you need additional information please e-mail us at:
info@inquip.com,
or call one of our offices.
