Project Overview:
PCA Ground Engineering was contracted to stabilise a sensitive slope adjacent to key SEQ Water infrastructure at Mount Crosby. The project’s primary objective was to prevent any rock debris larger than 15mm in any direction from falling onto the access area beside the settlement basin. Due to the site’s constraints—including a heritage-listed reservoir at the crest and a protected settlement pond at the base—traditional methods and heavy machinery were not feasible.
PCA was required to complete the works using rope access techniques and manual equipment, ensuring minimal disruption and complete control over debris and dust during the descaling process.
Challenges
- Prevention of rock debris >15mm falling into access areas
- Strict environmental controls due to proximity of settlement pond
- No tolerance for dust or foreign materials entering water infrastructure
- Restricted access between a heritage-listed reservoir and steep slope
- No use of large machinery permitted on site
- Need for a mesh system with aperture smaller than 15mm
Innovative Solution
PCA proposed and installed the Pyramat system, a high-strength UV-stabilised polypropylene mesh with fine apertures that meet the project’s debris control requirements. Benefits included:
- Aperture smaller than 15mm to meet slope retention criteria
- Encouraged future vegetation growth by trapping native seeds
- Installed using rope access and hand tools for minimal impact
- Slopes cleared back 1 metre at the crest for secure anchoring
- Concrete access path constructed between terraced slope sections
Geotechnical Assessment & Design
Prior to implementation, PCA conducted a geotechnical stability assessment to evaluate risks of raveling and face instability. This included:
- Preliminary visual assessment and mapping of upper and lower slopes
- On-site inspections during and after descaling operations
- Integration of slope data into the final design
- In-house design and documentation through PCA’s independently audited quality system
PCA’s long-standing experience in deep foundation and slope stability design enabled a safe, reliable solution for this highly constrained and sensitive site.
