Understanding geotechnical investigations: Key words and definitions
Geotechnical and hydrogeological conditions
Geotechnical and hydrogeological conditions describe the subsurface materials and groundwater behaviour along the proposed railway alignment. While distinct, these aspects are closely interrelated in infrastructure projects and are critical for assessing ground-and-groundwater-related risks and ensuring the safety and reliability of the infrastructure.
Why conduct geotechnical investigations?
Geotechnical investigations provide site-specific information on subsurface and groundwater conditions to support infrastructure design and construction planning. They also help assess earthwork requirements, the potential reuse of excavated materials, and opportunities to improve cost efficiency while reducing construction risks.
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What does a geotechnical investigation involve?
A geotechnical investigation involves the analysis of data collected during fieldwork, including:
- Drilling boreholes, soundings and test pits
- Sampling and in situ testing of soils and rock, including geophysical methods
- Groundwater monitoring using instruments such as regular piezometers, vibrating wire piezometers and monitoring wells
- Drone and airborne LiDAR (Light Detection and Ranging) surveys
- Laboratory testing of collected samples
This information is used to assess how well the proposed works are adapted to existing ground and groundwater conditions and to develop technical recommendations that support the safe construction and long-term performance of the infrastructure. These recommendations may relate to:
- Track subgrade conditions
- Construction material requirements (including ballast and granular fill)
- Earthwork design and slope stability
- Frost susceptibility
- Settlement mitigation measures and ground improvement techniques
- Foundation design (shallow and deep foundations)
- Design of underground structures (tunnels, shafts and utilities)
- Temporary and permanent earth-retaining structures
- Seismic considerations (such as site classification, stability, and liquefaction); and
- Assessment of soil and groundwater corrosivity
