Project Overview
As part of ground improvement works along Brisbane’s Kingsford Smith Drive upgrade, PCA Ground Engineering implemented Controlled Stiffness Columns (CSC), also known as rigid inclusions, to improve foundation performance in compressible soils. This technique increases the soil’s bearing capacity, reduces compressibility, and provides a cost-effective alternative to deep piling or large-scale excavation.
The solution was particularly suited for the project’s geotechnical conditions, where traditional foundation methods would have been inefficient or uneconomical. By combining the benefits of piles and shallow foundations, CSC technology enabled reliable load transfer while minimising settlements and environmental impact.
Applications
Controlled Stiffness Columns are suitable for:
- Residential, industrial, and commercial buildings
- Embankments for highways and railways
- Harbour structures
- Compressible soils where settlement must be minimised
Advantages & Limitations
- Settlement reduction by a factor of 8–10 under high loads
- Allows construction of strip footings and slabs designed like a slab-on-piles system
- Compatible with load distribution layers to spread structural loads
- Requires careful design consideration for additional bending moments in slabs and footings
- Most effective in compressible soils with controlled installation sequencing
Installation & Quality Control
PCA delivered a robust quality assurance program during construction, including:
- Precise layout of column locations within tolerance
- Electronic logging of every column installed, recording:
- Column number, diameter, and length
- Penetration depth and pump stroke count
- Start/end times and grout/concrete volume
- Crowd pressure or rotary torque
- Real-time monitoring via PCA’s custom data logging software, with results transmitted to a central database
- Routine sampling and cylinder testing of grout/concrete for compliance
This ensured not only compliance with design specifications but also provided complete traceability and quality verification for the client.
Outcome
- Delivered effective soil reinforcement under challenging site conditions
- Achieved significant settlement reduction and increased bearing capacity
- Ensured high-quality installation with near real-time monitoring and QA reporting
- Provided a cost-effective, low-impact alternative to conventional piling systems