Geotechnical News • June 2012
35
THE GROUT LINE
to the work’s success.
Bennett Dam: An extensive array
of piezometers had been installed
adjacent to the area to be grouted.
Maximum allowable pore pressure
increase had been established for each
piezometer, dictating the maximum
grout injection rate and resulting pore
pressure. Initial injection rate was
established based upon analysis and
experience, and should have been
sufficiently slow to not exceed the
allowable pore pressure rise. The real-
ity was, excessive pore pressure rises
occurred on several occasions requir-
ing cessation of all operations until
they were resolved. The recorded digi-
tal record was uploaded into Excel and
viewed at an expanded scale, to show
what was going on within a single
pump stroke. Substantial variation in
the rate at which the piston moved was
observed, even though the average
rate was as intended. The grout pumps
were then replaced with higher quality
pumps capable of uniform operation,
and the excess pore pressure problems
disappeared.
California Aqueduct: Internal erosion
and piping leakage of an embankment
on the California Aqueduct resulted
in an emergency grouting operation.
Time constraint limited the soils inves-
tigation to CPT probes, with this data
supplemented through close monitor-
ing of the injection behavior during
grouting. Each day’s computer moni-
toring data, again uploaded into Excel,
was analyzed overnight, distributed to
team members over the internet, and
injection parameters adjusted for the
following day’s work. Upon comple-
tion of the emergency work, the data
was used to better understand the
existing conditions, facilitating future
action consideration.
Colorado Oil Shale: A perimeter grout
curtain was intended as a component
for environmental isolation of in situ
recovery of hydrocarbons from the
shale. However, initial operations
viewed the ground as ungroutable
with reported observations that grout
“ran away into the formation”. This
project involved greater than usual
depths (more than 400 m working
from surface). Grout data was recov-
ered from the data acquisition system
and uploaded into Excel for detailed
analysis. The following situation was
revealed. Grouting started with water-
filled tubing, and as grout travelled
down the tubing the collar pressure
dropped dramatically because of the
weight of the grout, until the water in
the grout cavitated with consequent
loss of flow control – the reported “run
away” into the formation. The situa-
tion became controlled once sufficient
grout had penetrated the formation to
build enough hydraulic drag to return
the collar pressure to less than that
allowing cavitation of the grout. Excel
analysis of the data determined low
density, high viscosity grouts were
needed for the project.
Amtrak Bridge: This project involved
Computer contol room.
Compaction recording.
