Step 1
Set-Up & Mix Design
The ITM rig is positioned and binder slurry is batched to the design mix. Binder type and dosage are tailored to the target wall strength and permeability, with ground conditions and chemistry informing the specification.
In-Situ Trench Mixing
Continuous stabilised trench walls to 16 m depth — first deployed in New Zealand by GSI.
IN-SITU TRENCH MIXING
In-Situ Trench Mixing (ITM) forms a continuous stabilised soil-cement wall by cutting through existing ground with a rotating mixing chain while simultaneously injecting cementitious binder. The result is a homogeneous wall panel — without excavation, without spoil, and without the risk of trench collapse. GSI's ITM system produces walls 550–950 mm wide to depths exceeding 16 m.
GSI has extensive expertise, design capability, market leadership and a 20-year track record of soil mixing in New Zealand. We were the first contractor to deploy ITM technology in New Zealand, bringing a capability previously only available in Europe and North America. This knowledge is applied directly to every ITM project — ensuring design intent and construction outcomes are aligned under one integrated team.
APPLICATIONS
- —Groundwater cut-off walls for coastal and low-lying developments where seepage or liquefaction are design considerations
- —Continuous cut-off walls managing water inflows into excavations and protecting structures from lateral groundwater pressure
- —Slope stabilisation: a continuous wall of soil-cement installed through the failure plane provides passive reinforcement to the sliding mass
- —Projects requiring combined groundwater control and ground improvement, paired with jet grouting or in-situ mass stabilisation under one contract
GSI NZ CAPABILITY
- —First contractor to deploy ITM technology in New Zealand, with more operational experience with this system in NZ ground conditions than any other contractor
- —Walls 550–950 mm wide to depths exceeding 16 m; integrated with CFA piling and specialist grouting under one contract
- —Full quality assurance records on every programme: binder consumption logs, mixing chain footage, and post-installation testing
- —NZ Transport Agency Waka Kotahi pre-qualified for State Highway geotechnical works, SiteWise Gold accredited, Totika Listed
THE GSI DIFFERENCE
ONE TEAM.
ONE CONTRACT.
- —GSI NZ was the first contractor to deploy ITM in New Zealand — bringing European and North American ground improvement capability to the local market.
- —Continuous monolithic walls with better hydraulic continuity than secant pile alternatives, with no gaps and no interlocking pile alignment risk.
- —Integrated with CFA piling and specialist grouting under one contract, with one engineering team and one point of accountability across all ground treatment disciplines.
HOW WE APPROACH IN-SITU TRENCH MIXING
Step 2
Cutting & Mixing
The mixing chain penetrates to design depth while binder slurry is injected under controlled pressure. Successive overlapping panels are formed to create a continuous wall. Steel sections or reinforcement cages are installed where structural capacity is required.
Step 3
Verification
Wall performance is verified by coring at specified intervals. Cores are tested for UCS and, where required, permeability to confirm the wall meets design criteria. Full QA records and as-built documentation are provided on completion.
CASE STUDY
Wimbledon Road DSM
The Wimbledon Road project for Central Hawke's Bay District Council demonstrated GSI NZ's deep mixing capability in a landslide repair context. 126 soil-cement columns were formed to stabilise an active landslide mass, restoring road access and providing a permanent engineered solution.
The design/build approach (GSI NZ engineers designing and crews building under one contract) meant the column layout was refined in real time as column performance data was returned from the field, achieving the required factor of safety efficiently and within the project programme.
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RELATED PROJECTS
GROUND ENGINEERING
WIMBLEDON ROAD
126 soil-cement columns to stabilise an active landslide mass, Central Hawke's Bay.
View Project →GROUND ENGINEERING
METROSPORTS
Ground improvement and foundation works for major Christchurch aquatic facility.
View Project →GROUND ENGINEERING
MARINE PARADE
CFA piling and GCS wall on a constrained coastal site in Napier.
View Project →Get in Touch
In-Situ Trench Mixing
Specialists.
Our in-situ trench mixing capability delivers high-quality treated soil columns at speed. Let our engineers assess whether it's right for your ground conditions.
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