Three-dimensional GPR contact antenna used to study the infill structure in land reclamation projects


Radargrams showing layer structure and deformation of a land reclamation infill


Top: Radargram acquired on a landfill reclamation project. Bottom: Structural interpretation of the radargram

Civil Engineering applications


The correct maintenance and conservation of harbor infrastructures guarantees its functionality and operability. A preventive maintenance approach of these infrastructures avoids the economic costs associated with interruptions in the activity due to the development of ground subsidence that can ultimately lead to the appearance of sinkholes in the pavement of land reclamation areas.

The global increase in freight traffic has motivated expansion projects in most ports around the world. The port site must have infrastructures such as piers, basins, stacking or storage areas, warehouses, and equipment such as cranes, all of which involve larger and larger areas. Therefore, land reclamation projects have been the solution to such demands.

The added land facilitates the streamlining of container terminal operations, allow the construction of new deep-water berths capable of handling the largest container vessels, and open-up new space for related industry investment and activity.

Due to the large volumes involved and for practical and economic reasons it is quite common to use available materials from the vicinity of the project.

One of the main determining factors in the structural behavior of infilling projects is the bearing capacity of the underlying materials (from the undisturbed natural ground to the surface). On roads and other land transport infrastructures, pavements lie on top of a properly compacted embankment or base course or on the bottom of a road cut on firm soil or rock. However, in ports, the main body of the infill is generally constituted by a fine-grained material located totally or partially below sea level (which is why direct compaction with standard mechanical methods is not possible).

Finally, the pavement on the crest of the infilling is placed above the water level, with selected materials, in sufficient thickness and duly compacted. It must withstand the large weight of trucks, trains, cranes, and freight.

In this context (large areas that need to be monitored continuously in a very hostile environment) the use of geophysical methods become especially important.

The continued erosive action of the sea can produce a displacement of the infill material. Therefore, the topmost layers can suffer subsidence that ultimately lead to a sinkhole on the surface. This is a hazard not only for the activity on the surface (vehicles, personnel, and freight) but also for the integrity of the buried services beneath the surface (sewers, power lines, gas pipelines, oil pipelines, etc).

The best technique for detecting and evaluating the condition of a port infill and pavement is three-dimensional ground coupled GPR. Thanks to the rapid acquisition of field data, the use of contact antennas guarantees greater penetration capacity and enables the study of large areas (tens of hectares) in a very short time.

With this technique it is possible to know the existence of incipient zones of deformation under the surface before the sinkhole occurs. It is possible to limit accurately the dimensions and the depth of the affected area. On the other hand, it is possible to identify different layers of the top of the infill, to obtain information about the grain size of the material that makes up the infill and the identification of buried objects.

Depth to Base Course Layer derived from a GPR3D survey of a land reclamation infill project. Several sinkholes were rapidly detected

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