Land geophysical surveys

A geophysical survey is a non-intrusive, remote sensing method for assessing subsurface conditions by measuring variations in physical properties of the ground, such as density, seismic (elastic), magnetic, and electrical parameters. Used in geophysical site investigations and geological research, these surveys help identify underground geological structures, geo-hazards, buried objects, assess soil and rock characteristics, and provide in situ data to inform design parameters.

Fugro’s survey and mapping services support both land and marine projects. Our offshore geophysical surveys provide critical data for offshore wind, oil and gas, and subsea infrastructure. Our land geophysical surveys are applicable in a range of environments including urban, coastal, and brownfield sites for construction, energy, and ground infrastructure development or remediation. The data captured through geophysical investigations can be used to help build a robust ground model and inform further intrusive investigative works needed to build the full subsurface picture.

Geophysical surveys collect critical subsurface data to support geotechnical investigation, infrastructure development and monitoring, and environmental assessments. These surveys provide insights into:

• Subsurface structure and composition; identifying rock formations, fault lines, and sediment layers.

• Soil and rock properties; measuring density, porosity, and stiffness to assess ground stability for construction and resource exploration.

• Seismic activity and ground movements; detecting potential geohazards, such as earthquake liquefaction potential and subsidence risks.

• Groundwater and fluid movement; locating underground water sources and monitoring fluid migration and contaminants to aid environmental planning.

• Buried infrastructure and anomalies; mapping pipelines, utilities, and objects that may be hidden beneath the ground.

• Assessing the construction and health of existing man-made structures; for example concrete slab construction, road pavements, structural defects, voiding and corrosion.

• Allows for 2D and 3D data coverage to fully understand site variability

• Generally non-intrusive methods mean lower environmental site impact

• More cost-effective than invasive drilling methods

• Rapid results and efficient data gathering over large areas

• Improved safety by screening the site prior to boots on the ground works

• Better planning and refined scope for site investigations and project design and execution

Geophysics should be included as part of any required ground investigation for the best possible data on site or structure conditions. Geophysical surveys are very flexible and can be carried out in most types of geology and applied to support project objectives across a wide range of sectors. These include:

• Energy infrastructure onshore and offshore

• Nuclear projects

• Renewable energy including geothermal, hydropower and wind farms

• Mining infrastructure

• Transport infrastructure including tunnels and bridges

• Construction including mega-structures and data centres

• Urban development

• Utilities

• Groundwater monitoring and management

Duration depends on the methods used, the site conditions, the complexity of the area and the project objectives. Small, accessible sites with simple targets can often be assessed in one or two days, while larger or more complex sites may take weeks to months. Fugro’s geophysical experts can advise on and build an optimised investigation strategy based on site-specific variables.

We provide a range of geophysical survey and mapping techniques to deliver precise subsurface data for geophysical site investigations and geological research. Our key survey methods include:

• Seismic refraction and reflection surveys Analysis of elastic waves as they move through layers of geology to detect and map the structure of layers and anomalies.

• Multi-channel analysis of surface waves (MASW) measures surface (Rayleigh) wave energy to derive shear wave data to allow assessment of ground stiffness variations.

• Ambient noise tomography (ANT) provides a 3D representation of shear wave velocity distribution of the subsurface from which ground risk can be assessed (stiffness variability, geohazards).

• Ground penetrating radar (GPR) surveys Employs radar waves to locate and map underground features, such as voids, pipes, cable, foundation and to forensically investigate existing built structures.

• Electrical resistivity tomography (ERT) surveys Uses electrical currents to map subsurface resistivity distribution to identify geological layering, geo-hazards such as cavities and solution features and buried objects.

• Electromagnetic (EM) methods Assesses electrical properties (conductivity) of the ground to identify buried structures, soil/rock variability, groundwater contamination, landfill and shallow cavities.

• Magnetic surveys Detects small changes in the Earth’s magnetic field associated with shallow buried magnetic materials, for example, buried foundations, pipes, cables, UXO and magnetic rock types.

• Micro gravity surveys Measures variations in the Earth’s gravitational field to map subsurface density variations associated with weak ground, cavities, fault zones etc.

• Borehole wireline geophysical surveys Provides in-situ measurement of geotechnical, geological and hydrological parameters during the borehole investigation phase. This uses techniques such as caliper, televiewer, PS logging, full wave sonic, downhole magnetic resonance, resistivity, formation density, and natural/spectral gamma.

• Marine geophysical surveys Conducting geophysical surveys offshore to map seabed conditions for offshore wind farms, cable routes, and oil exploration.