Mapping the underground for a new metropolitan railway in Dublin

Over the last ten years Ireland has had one of the highest growth and development rates in the European community.

With this view, construction has started on a modern transport system based initially on a surface metropolitan railway, to be followed by the construction of an underground metropolitan railway.

The Railway Procurement Agency (RPA), which has the task of designing, constructing and managing the first lines of the surface railway, has recently finished the first two lines which have been perfectly integrated into the urban environment and in record time.

During the design phase, and above all, during the construction phase of these first two lines there was a significant economic and timescale impact caused by the lack of mapping of the underground utilities. The delay caused by the lack of knowledge of the distribution of underground utilities and structures caused consequent delays in the execution time required for the work and increased the costs with respect to those initially programmed.

After a first phase, in which the mapping was performed using traditional methods (opening manholes, checking available maps, interviewing personnel from the companies managing the utilities networks), it became clear that the mapping had to be performed following a more industrial and technological method, taking into consideration the use of noninvasive methods that would interact with the existing database and surface information.

The RPA quickly activated a study to find an alternative that would provide maximum efficiency, organising a series of tests of the available nondestructive technologies. Once the phase of investigation of the various methods was completed, the RPA offered the companies in the sector of underground utilities mapping the possibility of performing field measurements to compare and evaluate the practicality and precision of the service offered.

Different methods were evaluated in these last two phases, with particular attention being focused on radar apparatus. One of the evaluation parameters considered, apart from the high precision level required of the measurements (>5cm), was the interactivity of the information generated by the different detection methods with the existing database.

A key element in the engineering of this project was the active integration of the field information with the project and execution phase requirements and formats. The test data permitted the specifications and terms of reference to be set for an international tender, including the detailed detection of the networks and structures located along the path of the project and the presentation of results on a digital map, perfectly referenced in 3D CAD format integrated with designers’ maps. The technical offer for the tender, won by TST Engineering – an Italian company with international expertise in multidisciplinary mapping of utilities – was based on techniques that included the application of the ground penetrating radar (GPR) method in multichannel – multifrequency mode. The no dig systems proposed and used in the project were based on IDS GPR technology, which offers an integrated solution allowing for mapping the underworld in a complete 3D format delivering the final results in a CAD or GIS compatible format.

The IDS GPR is an array system specifically designed for mapping utilities. This system uses a series of antennas with different frequencies to provide “÷illumination’ with optimal resolution at various depths and increases the possibility of characterising underground elements. The uniqueness of the system and the interface software permits a particularly high degree of productivity and accuracy, directly producing GPR interpretation maps in CAD format.

Over and above the decision regarding the methodology, the quantity of data acquired and the overall complexity of the task led to the TST engineers to work in close collaboration with the RPA technical staff to develop an optimised synergy in both the acquisition and data integration phases.

The optimisation of the categorisation of the multidisciplinary and GPR information and its integration with the existing information represented the main difficulty in reaching a layout easy to use by all sectors – principally the design group, personnel responsible for moving the utilities interfering with the lines under construction and technical staff employed in constructing the infrastructure. The field work was performed using different multidisciplinary work groups – GPS, manholes, etc. These groups included one exclusively specialised in radar detection. The work groups permitted the collection of an average of 30 m of road detection per day along the path designated for the metropolitan tunnels.

The Dublin RPA project represents an idealised application scheme for the integration of GPR technology with multidisciplinary mapping methods of traditional utilities. The IDS GPR technology has been integrated with the surface maps to offer the design engineers the detailed information (both in terms of identifying objectives and in resolution) that on one had has permitted the work to be optimised, and on the other represented an instrument for controlling and reducing risks for the companies contracted to perform the remodelling and construction work. In this framework, the TST field experience and IDS technology represented an ideal match to the RPA engineering requirements.

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