CBD Office Tower Foundation Investigation
Geotechnical investigation and deep foundation design for a 35-storey commercial office tower, with basement levels extending below the water table into Melbourne's Silurian bedrock.
Project Overview
A commercial developer planning a 35-storey office tower in Melbourne's CBD needed specialist geotechnical investigation to support a deep foundation design. With three basement levels extending 22 metres below ground — and below the water table — the project demanded a detailed understanding of the Silurian bedrock and groundwater behaviour beneath the site.
Geotechnical services delivered through our partner network provided the rock coring, pile load testing, and groundwater analysis required to design rock socket piles with confidence. Accurate ground data allowed the foundation to be optimised, reducing construction costs while protecting neighbouring CBD structures during excavation.
Project Challenges
Deep Basement Below the Water Table
Three basement levels reaching 22 metres deep required excavation below the groundwater table. Designing the dewatering and waterproofing strategy demanded accurate permeability data and an understanding of how drawdown could affect adjacent buildings.
High Foundation Loads
A 35-storey tower transfers enormous loads to its foundations. Confirming that bored piles could safely carry 2,000kN required rock socket design verified by full-scale load testing in the Melbourne Formation bedrock.
Protecting Neighbouring Structures
Tight CBD sites sit close to existing — sometimes heritage — buildings. Settlement monitoring and careful groundwater management were essential to ensure construction did not damage adjacent structures.
Variable Bedrock Conditions
Melbourne Formation mudstone weathers unpredictably across short distances. A detailed cored investigation was needed to map rock quality and strength for reliable pile design.
Services Delivered
Cored Ground Investigation
A cored drilling program to 40 metres characterised the soil profile and Melbourne Formation bedrock, with SPT and pressuremeter testing providing the parameters needed for rock socket pile design.
Full-Scale Pile Load Testing
Static and dynamic load testing verified that bored piles could safely carry the design load of 2,000kN, giving the structural engineers confidence to optimise the foundation layout.
Groundwater & Dewatering Assessment
Multi-level monitoring and permeability testing informed the deep basement dewatering design, ensuring groundwater drawdown stayed within safe limits for surrounding buildings.
Construction Monitoring
Settlement markers and verification testing during excavation and piling confirmed ground behaviour matched the design assumptions and protected neighbouring structures.
Technical Approach
Site Investigation
Cored boreholes to 40m depth with SPT, pressuremeter testing, and rock sampling across the building footprint
Bedrock Characterisation
Melbourne Formation Silurian mudstone strength testing to inform rock socket pile design
Pile Load Testing
Full-scale static and dynamic load testing to verify design capacity of bored piles
Groundwater Analysis
Multi-level monitoring and permeability testing for deep basement dewatering design
Settlement Prediction
Numerical modelling of foundation behaviour and impact on adjacent structures
Laboratory Testing
NATA-accredited rock and soil analysis to AS1289 for design parameter confirmation
Project Outcomes
Project Timeline
Desktop Study
Month 1Review of historical CBD geology, adjacent building records, and council planning history
Site Investigation
Months 1-3Cored drilling, in-situ testing, and groundwater monitoring well installation
Pile Load Testing
Months 3-4Full-scale static and dynamic testing to verify bored pile capacity
Foundation Design
Months 4-5Rock socket pile design, basement waterproofing, and settlement assessment
Construction Support
Month 6 onwardsVerification testing and monitoring during excavation and piling
Project Details
Services Provided
Project Progress
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