In situ solidification was carried out using a 10 ft diameter mixing auger powered by a crane-mounted rill platform having 400,000 ft-lb of torque. Approximately 52,100 cu yd of sand and gravel were solidified in situ sing the auger mixing technology.
performed at seven days to provide an early indication of
ISS performance. Unconfined compression strengths ranged
from 39 to 351 psi, averaging approximately 180 psi at seven
days. The standard deviation of the sample pool was 70 psi.
Only one sample had strength less than the required 50 psi.
However, its strength increased to 69 psi at 28 days.
Hydraulic conductivity tests were performed at 28 days.
Measured hydraulic conductivities ranged from 5 × 10–8 to
3 × 10–6 cm/s, averaging about 6 × 10–7 cm/s. The standard
deviation of the sample pool was 5 × 10–7 cm/s. Ten samples
failed to achieve the specified criterion of 1 × 10–6 cm/s at 28
days. Subsequent testing, however, demonstrated that the
specified hydraulic conductivity was achieved with additional
curing at 56 days. The data show that it would be necessary to
target a design hydraulic conductivity of about 1 × 10–7 cm/s
to ensure that practically all samples would achieve the required maximum allowable value of 1 × 10–6 cm/s at 28 days.
Among the lessons learned during the ISS process was that
bentonite is clearly beneficial in reducing hydraulic conductivity and controlling strength. However, the use of bentonite requires a high ratio of water to reagent, increasing the
volume of swell and spoils. Accordingly, efforts should be
made during bench studies and field trials to minimize the
quantity of bentonite if it is important to control the volume
of spoils. Furthermore, spoils should be managed to minimize water infiltration, as infiltration increases weight and,
by extension, disposal costs.
Meanwhile, consideration should also be given to other
potential reagents that may achieve suitable results while
also minimizing the required quantity of water. One such
reagent, for example, is granulated blast furnace slag. This
material has successfully been used on other ISS projects with
little or no bentonite addition. Granulated blast furnace slag
has also been used for other grouting applications, including
hydraulic cutoffs in bedrock.
SEPTEMBER 2012 Civil Engineering