Successful infrastructure projects hinge on obtaining a comprehensive geotechnical report early in project planning and design.
That’s according to Wagners Composite Fibre Technologies (CFT) Structural Engineer, Sabin Raut who argues that by revealing critical subsurface conditions at the outset of a project, design decisions can be made early to minimise risk and protect the project from costly delays and complications.
“A geotechnical report is the foundation of design confidence. When it’s thorough and site-specific, it saves time, cost and uncertainty,” Sabin Raut said.
“For Fibre Reinforced Polymer (FRP) structures, where the superstructure is corrosion-proof but lightweight, the soil–structure interaction governs long-term performance,” Mr Raut said.
“Early collaboration between the geotechnical and structural teams ensures a safer, more efficient and more predictable project outcome,” he said.
“Cutting corners or avoiding geotechnical investigations might save a small amount of money at the beginning, however it will be costly to the overall project cost.”
Pictured – An aerial image of a site location that should be included at the beginning of a geotechnical report.
A well-prepared geotechnical report sets the foundation for safe and efficient design, with key details guiding engineers’ decisions from the outset.
“The first thing engineers look at when reviewing a geotechnical report is the date of the geotechnical investigation and the number and depth of borehole logs,” Sabin Raut said.
“Quality and complete reports help avoid any surprises during construction,” Mr Raut said.
“The essential components of a report are sufficient borehole logs and depths of investigation, foundation design parameters (end bearing, skin friction, subgrade modulus) to suit possible foundation types, ground water table information, soil classification and moisture content,” he said.
“These components are crucial because they provide the data needed to assess soil behaviour under loading and determine appropriate foundation solutions.”
Pictured – Undergraduate Structural Engineer, Farhan Khalaf and R&D Technician, Suba Govindaraj conducting a Dynamic Cone Penetrometer (DCP) test at a site on the Gold Coast.
Engaging geotechnical expertise early in a project is key to informed design decisions, accurate cost planning and avoiding gaps in critical foundation data.
“Geotech investigation should be conducted as early as possible in the project to plan the design properly and estimate the budget properly,” Sabin Raut said.
“To ensure you receive a useful geotechnical report, the important things to request are sufficient investigation depths, foundation design parameters and ground water table information,” Mr Raut said.
“Structural engineers should be involved in this stage of a project to ensure the scope and test program capture all data required for foundation design – for example, soil subgrade modulus, settlement behaviour, or uplift resistance,” he said.
“Without their input, critical parameters may be missed.”
Pictured – A map of borehole and DCP test locations completed on site.
Clear, reliable ground data can make the difference between a smooth construction phase and costly redesigns.
“In a recent bridge project, the geotechnical report included detailed boreholes at each abutment and pier location,” Sabin Raut said.
“It also included shear strength and unit weight values summarised in tables and groundwater and acid sulphate soil information,” Mr Raut said.
“Because of this, the pile design was straightforward, construction progressed without delay and no redesign was required,” he said.
“Similarly, on another project with high-quality geotechnical information, potential foundation scenarios were identified during the early design phase. This avoided construction delays that would otherwise have occurred when piles could not be driven to the required depth and the contractor had to return to the engineer for redesign.”
“It demonstrated how good ground information directly translates to a smoother design and delivery process.”
Pictured – A subsurface profile summary provides information about the geological, geotechnical and groundwater conditions beneath a site.
When geotechnical information is incomplete or unclear, the consequences often emerge later in the project through redesign, delays and increased costs.
“Some common issues observed in poor or incomplete geotechnical reports include insufficient investigation depths and an unclear foundation recommendation,” Sabin Raut said.
“For example, there was a case where piles could not achieve minimum required depth as the underlying floaters in soil structures were not captured in the report,” Mr Raut said.
“On multiple occasions I have had to redesign structures due to missing or inaccurate geotechnical information,” he said.
“In some cases, missing soil data forced me to adopt conservative assumptions for bearing or friction capacity, increasing pile lengths and project cost.”
“In other cases, unexpected soil conditions during construction required redesigning the footing or pile arrangement.”
“These situations show that inadequate geotechnical information not only impacts design efficiency but can also lead to significant construction delays, safety risks and financial overruns.”
Pictured – The potential consequence of an inadequate geotechnical report, resulting in failure of an imported FRP pile.
With the right ground data, FRP piles provide a resilient, long-lasting alternative to conventional steel or concrete foundations.
“When designing with FRP piles, a comprehensive geotechnical report is critical for determining the appropriate pile diameter and length,” Sabin Raut said.
“FRP piles offer superior durability in acid sulfate soils and saline environments,” Mr Raut said.
“Where a geotechnical report indicates a high groundwater table, FRP piles can provide a highly resilient foundation solution,” he said.
“These conditions typically accelerate the deterioration of conventional steel and concrete piles, making FRP a more sustainable alternative.”
Pictured – FRP piles used in a boardwalk project on the Gold Coast.
When planning a geotechnical investigation, certain tests are essential for safe and effective foundation design, while others can provide valuable additional insights depending on project requirements.
Sabin’s must-have tests and nice-to-have tests:
Must-have tests:
- Borehole logs to sufficient depth
- Standard Penetration Tests (SPT) or Dynamic Cone Penetration Tests (DCP)
- Groundwater level measurement
- Soil classification, shear strength (c, φ) and unit weight
- Bearing capacity and settlement analysis
Nice-to-have tests:
- CBR values for access or pavement design
- Corrosion potential (pH, sulfate, chloride)
- Permeability and consolidation tests
- Liquefaction assessment for seismic regions
Pictured – Foundation recommendations included at the end of a geotechnical report.
A solid foundation starts with knowing the soil and substructure conditions, a vital step that cannot be overlooked.
“Ultimately, a well-prepared geotechnical report is more than just a collection of data; it provides a roadmap for safe, efficient and cost-effective construction,” Sabin Raut said.
“Understanding the soil and substructure conditions is key to selecting the right materials and construction methods,” Mr Raut said.
“By investing in thorough investigations, engineers can design foundations with confidence, avoid costly surprises and select FRP materials where they offer the greatest benefit,” he said.
“Good geotechnical practice not only saves time and money but also ensures structures stand the test of time.”
Read Wagners CFT Design Guide – https://www.wagnerscft.com.au/app/uploads/2024/07/J7998_WAG_WCFT-Design-Guide-2024_WEB3.pdf
Watch our webinar ‘Footing Fundamentals for FRP Structures’ featuring Impact Structural Engineers Director, Matt Gorring – https://www.youtube.com/watch?v=TxoGxM5q74Y&t=274s
Read ‘Testing finds highly corrosive environment no match for FRP’ – https://www.wagnerscft.com.au/testing-finds-highly-corrosive-environment-no-match-for-frp/
