GEOWEB® Geocells

Project Name: Mining Soft Shale Slope Repair

Project Location: Tumbler Ridge, British Columbia

What is Shale?

Shale is the most common sedimentary rock on Earth. Typically formed from mud, it contains tiny fragments of clay minerals and silt-sized particles of other minerals, such as quartz and calcite.

Shale accounts for approximately 70% of the sedimentary rock in the Earth’s crust and is prevalent worldwide; however, the physical properties of shale can be problematic. It often exhibits characteristics such as fissuring, dilation movements, weathering, and softening soils. These properties make shales in prone to landslides, surface excavations, and erosion due to the underlying soil properties.

Project Problem: Shale Slope Erosion

Nestled in the foothills of the Canadian Rockies, a coal mining community in British Columbia was dealing with an abundance of shale slopes that had formulated over time.

One particular soft shale slope was degrading due to geomorphic processes, causing scour and erosion to the hillside. This slope is located above a mechanically stabilized earth (MSE) wall that is supporting a new coal conveyor, so a long-term soil stabilization solution was critical to this project.

Project Solution: GEOWEB® Slope Protection System paired with a non-woven geotextile

The initial plan, which relied on only topsoil and natural vegetation, proved insufficient due to the risks of snow loading and natural erosion.

The project owner and TetraTech (Consulting Engineer) reached out to Layfield Group, Presto Geosystems’ material provider, to help find a solution to the eroding hillside. A few complimentary project evaluations were completed on the slope by Presto Geosystems’ engineering team to assess several different slope lengths and anchorages to compensate for snow loadings.

The project evaluations provided product recommendations based on the specific characteristics, structural values, and specifications from the site. Based on the results, the GEOWEB® Geocells with exclusively designed ATRA® geocell accessories were selected as a long-term, cost-effective slope stabilization solution. The GEOWEB System maintains the slope angle, while keeping granular material in place.

Partnering closely with TetraTech’s engineer of record and Duz Cho Construction, Layfield Group forged a deployment plan that promised stability and resilience.

Installation Process

The project installation began by digging a trench for a deadman pipe on top of the slope, then placing a non-woven geotextile separation layer along the sidehill cut slope area using a man-lift.

Once the geotextile sections were laid down, the GEOWEB Geocells were expanded down the 1.43H:1V cut slope and the tendons were tied to the deadman anchor on top of the slope. The project evaluation called for the GEOWEB (GW30V4) mid-sized cell, 4 inches deep panels.

The integral ATRA® Tendon Clips were tied to each tendon at every sixth GEOWEB cell.

The ATRA Tendon Clips “lock” with the GEOWEB cell wall for the most secure connection, and a looped tie off assures that tendons stay bound to the device. The “locked with the cell” design also allows for easy preassembling off-slope, a huge time saver, especially on steeper slopes that are difficult to access.

After the GEOWEB sections were expanded, the contractor backfilled the deadman crest area with on-site siltstone bedrock. Then continued to backfill the GEOWEB Geocells with topsoil starting at the crest of the slope all the way down towards the toe.

The GEOWEB® sections were slightly overfilled to allow for consolidation and compaction of the backfill as per the specifications, and the area was seeded for vegetation growth.

Project Conclusion

Layfield Group’s on-site technical support was pivotal, guiding the contractor through best practices to ensure a safe and successful installation. The deployment was executed swiftly and without incident, thanks to meticulous planning and on-the-fly adjustments. These included pre-assembling the GEOWEB sections before deployment and realigning the anchor trench for optimal effectiveness and ease of construction.