Blast-Furnace-Slag-Cement-Bentonite (BFSCB, SCCB) and Soil-Bentonite (SB) Slurry Wall
Legacy Rochester Hills Apartments
Rochester Hills, MI
Significant Project Features:
- Sloped site – 12%
- Self-hardening slag-cement-cement-bentonite (SCCB) slurry wall on sloped legs.
- Soil-bentonite slurry wall on flat legs.
- 950 Linear Feet -> 22,000 SF
- Maximum of 47-feet deep
- Target permeability of 1 x 10-7 cm/s. Actual average permeability of 7.7 x 10-8 cm/s
- Target UCS > 30 psi. Actual UCS: 50 psi.
Background:
The site is a historic unregulated dump site being redeveloped into apartment buildings. Hazardous waste was encountered throughout the 9-acre site. The waste in the majority of the site was shallow enough to be removed by conventional excavation and off-site disposal (by Others). About 1-acre of the site contained waste at depths up to 40 ft which were too deep to efficiently be removed with the excavation technique so a cutoff wall and cap system was designed. The cutoff wall extended from ground surface to the confining unit clay layer at the bottom.
Project Objectives:
Geo-Solutions, Inc. (GSI) was contracted by HM Environmental to install the cutoff wall. The cutoff wall is needed to further mitigate the site contaminants from seeping into groundwater. We performed a cost-benefit analysis to determine the best-fit approach since the cutoff wall was required to be installed around the perimeter of the remaining waste, which included the 12% sloped topography. Self-hardening blast-furnace-slag-cement-bentonite (BFSCB, SCCB) slurry walls were chosen for the sloped leg sections of the site, and soil-bentonite (SB) slurry walls were selected for the non-sloped legs to reduce cost.
Description of Work:
The slurry wall included the installation of a 950 ft long wall at 2.5 feet wide. The wall was installed to a maximum depth of 47 feet below ground surface (fbgs). In total, the installed wall was 22,000 vertical square feet (VSF), length x depth.
A unique challenge was the need to install the cutoff wall in areas where a previous contractor was unsuccessful at completing the cutoff wall leaving behind overly loose and soft soils. Cobbles, boulders and gravelly soils were also present and required careful cutoff wall installation processes and tight control of the cutoff wall materials to overcome these challenges.
Another complication was the limited workspace. Everything outside the cutoff wall alignment had been previously “closed” for regulatory compliance so everything associated with our work (materials, mixing areas, spoils, equipment, etc.) had to be confined to our 1-acre work site. Our crew worked closely with the general contractor, HM Environmental, to manage the restrictive site challenges.
Excavation was accomplished using a Komatsu PC800 excavator fitted with a custom long stick and boom configuration. Slurry for trenching was produced onsite in GSI’s mix continuous batch plant and pumped to the trench.
GSI’s commitment to safety was demonstrated on this project as it was completed with no incidents, accidents or near misses. The project was also completed on schedule. We utilized 100% of our own specialized labor force to complete this work. The Client and Engineer have worked diligently over the past 3 years to design and implement the project, and both were thrilled to have the cutoff wall installed successfully.
