Project Features:
- Soil Bentonite Slurry Wall
- 3,618 Linear Feet. 186,065 Square Feet. Maximum of 51.2-feet deep
- Target Average Permeability of 5 x 10-7 cm/s
Background:
The Inverness Forest Levee is located on Cypress Creek and was originally built in 1993 to protect the Inverness Forest neighborhood of north Harris County. In 2022, the Flood Control District initiated a project to implement modifications to be made to the levee system to succeed local and federal standards for flood risk reduction.
Project Objectives:
GSI was contracted to excavate a Soil-Bentonite (SB) cutoff wall along the toe of the levee system of Cypress Creek to a depth of approximately 51 feet.
Description of Work:
At completion the cutoff wall measured 3-foot-wide by 3,318 feet in length and consisted of 186,065 vertical square feet (vsf) of soil-bentonite (SB) slurry wall. Wall installation had a depth of 51.5 feet below the work platform. A 5-foot-wide section was excavated around an large drainage pipe that was roughly 100 LF.
The cutoff was installed using a CAT 395 excavator, and GSI’s long-reach boom and stick attachments. Bentonite slurry was used to maintain stability during excavation and minimize seepage and overbreak of the sidewalls. The bentonite slurry was mixed onsite in GSI’s custom-made batch plant and pumped to the trench.
Backfill was mixed consisting of trench spoils and bentonite slurry. To meet site specifications trench spoils larger than three inches and any undesirable spoils were removed. Field QC testing was conducted during all operations including initial slurry mixture, in trench slurry mixture, and backfill placement to ensure consistent acceptable mixtures were being used throughout the excavation and backfill process. Backfill samples were collected and shipped to Geotechnics for permeability tests with a target of 5×10-7. The target permeability has been reached in all samples with an overall average permeability of 4.2×10-08.
Maintaining the production schedule was a key factor of this project because Times Construction needed to do earth work and install a geo membrane along the levee system. GSI’s commitment to safety was demonstrated on this project by having no environmental impact on Cypress Creek.
Project Challenges
- GSI worked through the heat conditions of south east Texas along with rain that tapered the work pad effecting the excavators ability to track through it.
- A narrow backfill area restricted movement of the excavators.
- During excavation GSI encountered an unforeseen obstruction within the alignment and a refusal was met per specifications.