Keller constructed a set of jet grouted soil-cement columns to form a portion of an environmental barrier wall at a large remediation project in Toronto.
The project as a whole was undertaken to remove contaminated soils above the water table, to treat impacted soils below the water table and to construct a deep perimeter containment structure in order to immobilize remnant contamination and eliminate future migration of contaminants. Proximity to a neighbouring high-rise structure and the presence of abandoned steel H-piles precluded the use of conventional barrier wall construction techniques across a portion of the property's perimeter. Jet grouting, with its ability to target specific soil layers and to create large diameter elements using only small-diameter drill tooling, provided the solution to the problem.
A pre-production test program was performed on site in ground representative of the targeted soil mass in order to optimize the selection of jet grouting design parameters for use in constructing the permanent work. Four sacrificial jet grouted soil-cement columns were constructed and exhumed 48 hours later for examination.
Production jet grouting was performed using the double-fluid method employing the combination of flow rate, rotation rate, lift rate and injection pressure that resulted in the largest diameter test column. Between the elevations of 10.5 metres and 13.2 metres below grade and over a lateral extent of 5.3 metres, 8 watertight and contiguous soil-cement columns were constructed. Advance to underside of jet grouted columns was achieved in a single stroke by Keller's Casagrande C8 drill rig, using mud-rotary drilling with cement grout acting as the drilling fluid. Jet grouting took place during retraction upwards from the bottom of each hole to the top of the target zone. Thereafter, the drill string was retracted out of the hole without further injection of grout. Each jet grouted soil-cement column’s entire construction progress was monitored, displayed, controlled and recorded using a Jean Lutz LT3 automatic parameter recorder.
Quality assurance HQ3 coring was completed in order to confirm as-built jet grouted soil-cement column diameters, to confirm the integrity of the interface between conventional and jet grouted elements, to capture in situ soil-cement samples for visual inspection and laboratory testing and, most importantly, to test residual in situ permeability of the jet grouted soil mass.
Two parallel strategies were employed to mitigate the risks associated with the combination of the high grouting pressures inherent to jet grouting and the work’s proximity to the neighbouring structure. The jet grouting process itself was monitored to ensure uninterrupted evacuation of grout spoil from target zone to atmosphere. Concurrent to this measure, an array of electro-levels located through-out the basement of the neighbouring structure was tied into a data logger with the ability to send a real time alarm to the grouting operation upon detection of movement of the structure. No grouting induced movements were detected.
Keller Business Unit(s)
Keller Foundations Ltd.