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Detailed cell design documentation in Rochedale

Detailed cell design documentation in Rochedale

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CLIENT

Cleanaway

SECTOR

Waste

SOLUTIONS

Geo-environmental engineering

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Colin Stapleton

Senior Principal

Overview

Senversa was commissioned by Cleanaway Solid Waste Pty Ltd, under the Resource Recovery Innovation Alliance, to prepare detailed design documentation for the final capping of the Western Slope at Brisbane Landfill, Rochedale, Queensland. The capping footprint spans approximately 4.7 hectares, covering Cells 6B, 7, and 8, and overlays interim capped areas with vegetated overgrowth and soil stockpiles.

Scope

The scope of consultancy work included:

Preparation of a comprehensive design report, technical specifications, construction drawings, and supporting assessments.
Integration of site-specific data including topography, geology, hydrology, climate, and existing infrastructure.
Compliance with Queensland Landfill Guidelines (DETSI, 2025), Environmental Authority (EA) permit conditions, and stormwater guidelines (DES, 2021).

Key design elements comprised:

A geosynthetic capping system including coated Geosynthetic Clay Liner (GCL), subsurface drainage (GCD and subsoil pipes), reinforcement geogrids, and vegetated cover soils.
Stability assessments using SlopeW software, evaluating long-term, short-term, and seismic loading conditions.
Veneer stability and anchor trench assessments to ensure slope integrity and resistance to tensile forces.
Stormwater management infrastructure including contour banks, bench drains, chute B6, and reinforced concrete box culverts.
HELP modelling to assess seepage performance and inform drainage design.
Safety-in-design (SiD) risk assessments addressing construction and operational hazards.

Senversa also reviewed and optimised the final landform geometry to reduce cut/fill volumes, enhance long-term stability, and align with operational constraints. The design incorporated erosion protection, landfill gas (LFG) interface management, and provisions for future passive venting.

Challenge

Reconciling discrepancies between the provided subgrade design surface and actual surveyed topography, necessitating iterative redesign.
Managing landfill gas infrastructure during construction, including coordination with LMS Energy for pipe disconnection, sealing, and reconnection.
Ensuring veneer stability across steep slopes, requiring geogrid reinforcement and detailed interface shear strength assessments.
Mitigating construction risks such as interaction with heavy vehicles, exposure to LFG, and premature GCL hydration.
Designing stormwater infrastructure to reduce flow velocities and erosion risk while maintaining conveyance capacity under 1% AEP events.

Senversa addressed these challenges through rigorous engineering assessments, stakeholder coordination, and incorporation of safety and environmental controls. The project outcome supports long-term landfill closure objectives and environmental protection.

Outcome

The Western Slope Cap Design successfully delivered a robust, compliant, and environmentally sound solution tailored to the unique conditions of Brisbane Landfill.

The final design achieved:

Reduced earthworks volumes (from ~80,000 m³ to ~33,000 m³) through slope geometry optimisation.
Compliance with landfill guidelines and EA permit conditions for leachate containment, stormwater management, and gas control.
Enhanced slope stability with acceptable Factors of Safety across all loading scenarios, including seismic events.
Effective stormwater conveyance and erosion control through redesigned drainage infrastructure.