Significant Project Goals and Features:
- Installed cutoff wall using excavators and cranes/clamshells;
- Installed 773 linear meters (2,500 lf) of Soil-Cement-Bentonite (SCB) cutoff wall from 32 to 40m deep (105 to 131 feet) for approximately 29,700m2 (320,000 ft2);
- Used approximately 8,000,000 lbs of cement and 6,300,000 lbs of bentonite;
- Worked 24 hours per day for 8 months;
Description of Work:
Geo-Solutions was subcontracted to install a cutoff wall for Husky Energy’s White Rose Extension Project in Argentia, Newfoundland. The SCB cutoff wall was installed through porous soils/boulders to prevent groundwater seepage of the adjacent Atlantic Ocean bay, from entering into an open excavation. The excavated area inside the cutoff wall was taken to approximately 21 meters (70 feet) below the elevation of the ocean water and will be used to construct the base for an oil well platform.
Cutoff Wall Construction:
The SCB wall was designed with two intersecting segments to prevent the seepage of groundwater from the ocean into the Graving Dock excavation. The cumulative length for both walls was 773 linear meters with approximate width of 0.9 meters and depths up to 40 meters. The total area of the cutoff walls was 29,712 m2.
The cutoff wall was excavated using Komatsu PC1250 excavators equipped with long stick and boom setup that is capable of reaching up to 27 meters, and several Liebherr 855 cranes equipped with clamshells attachments. Additional equipment was mobilized to assist with the difficult excavation conditions. For a majority of the project, there were three Liebherr 855 cranes with clamshells, two Komatsu PC1250 excavators, two 100-ton crane with drill attachments, and a 100-ton chisel crane.
The SCB backfill material had the following target properties:
- Approximately 6% cement and 1.5% bentonite;
- Permeability of 5×10-7 cm/sec at 28 days
- Minimum shear strength of 100 kPa (UCS = 30 psi) at 28 days
Due to extreme weather conditions, a structure was needed to contain the batch plant for mixing cement and bentonite slurry. The batch plant consisted of 3 mixer tanks, 2 silos, and 2 storage vessels. Two mixing pits for blending the SCB backfill were constructed outside of the structure, and the backfill was remote mixed and hauled to the trench.
Project Challenges:
- Extreme weather conditions;
- Difficult excavation due to the presence of significant boulders;
- Significant equipment damage caused by soil conditions;
- Continuous schedule of 24 hours/day, 7 days/week for 8 months;
- Remote project location;
