Since time immemorial, building new structures has always been more glamorous than maintaining and improving existing ones. Although today’s construction materials are diverse, high quality and more sophisticated than those of times past, they also require more maintenance than –for example– the iconic stone structures built by the Romans. 

In order to define a suitable maintenance programme that will maximise a structure’s service life, which begins as soon as the construction work has come to an end, it is necessary to carry out a study. First, it is vital that you obtain data on the real condition of the structure. To do this, you need to go out into the field, visit the structure in question and perform an inspection. In Spain, there are specific guides and instructions that define the different types of inspection. Is the case, for example, the Instruction for the Technical Inspection of Railway Bridges (ITPF-05), which defines three types of inspection: basic, main and special. There are similar documents for other types of structures. 

3D model of the Martín Gil viaduct, created using photogrammetry. / INFOGRAPHIC_INECO

These inspections are visual and the information obtained regarding the functional condition and durability of the structure depends, in large part, on the skills and capacities of the inspector. In the university environment, the focus on new construction has resulted in a lack of learning and knowledge with regard to how existing structures behave over time. This, combined with other factors, makes the assessment process more complex. 

When it was built, the Mattín Gil Viaduct on the Zamora-A Coruña line boasted the world’s longest concrete arch, measuring 192.4 metres across the central span

Examples of these other factors include the extremely wide range of structural types and materials (concrete, steel, hybrid, stone, composite, etc.) and the many different pathologies generated by mechanical, chemical or physical causes. In addition to these factors, there is also the fact that the majority of structures are not designed to be inspected; many of their elements are hidden or difficult to access. Another of the inspector’s enemies is adverse weather conditions, which can make outdoor work very complicated.

Ineco started to carry out inspections of railway bridges in the 1990s. It has been a member of the Association for the Repair, Reinforcement and Protection of Concrete (ARPHO) since 2010 (when the Association was created); and a member of the European Association for Construction Repair, Reinforcement and Protection (ACRP) since 2020. 

Ground plan and elevation of the reinforcement works for the viaduct over the River Miño in Ourense (AVE Madrid-Galicia). / PLAN_INECO

Today, Ineco’s structural inspection specialists not only provide services to external clients, but also work on a cross-departmental basis within the company, helping all of the different units
–including those specialising in airports, railways and roads– to perform analyses on all types of structure: from bridges and stations to airport terminals and port facilities. The work is usually carried out in two stages: a field inspection, which often includes a series of tests; and an office-based stage, in which the inspection report and plans for structural retrofitting and strengthening are prepared. 

Drafting the design project and carrying out the construction work only marks the start of a structure’s service life, although it is a very important stage that creates the base for long-term functionality and durability. However, no structure can exist forever. With a well-defined plan, proper execution with suitable materials and strict supervision during construction, plus preventive and corrective maintenance throughout the structure’s service life, it is possible to reach an age of more than 100 years. However, whether modern buildings can match the longevity of Roman structures remains to be seen!

In the course of the infrastructure inspection campaigns of the high- speed lines, deficiencies were detected in the drainage systems of some sections. These deficiencies are resolved within normal or intense levels of rainfall through enlargements and improvements of the drainage network, based on a localised supply of resources.

However, as has been demonstrated occasionally, there can be catastrophic levels of rainfall that exceed all forecasts or normal schedules. The magnitude of the rainfall, the gentle slope of the land, the low level of the tracks and the insufficiency of the drainage elements are factors that may result in incidents on the rail platform.

This is the case of the incident that occurred on 2 July 2014 on the Madrid-Alicante high-speed line, at the town of Alpera (Albacete). The intense rainfall in the zone caused a great accumulation of water next to the platform. The flow water dragged away the ballast, leaving the track without support and causing it’s settlement. As a result of this incident, preparations began to commission Ineco with the study to determine the potentially floodable zones in the high-speed lines in operation.

To achieve the improvement of the drainage network, it is necessary to realise a hydrological study using two-dimensional models, through the application of net rainfall (associated with return periods of 100 and 500 years) and the joint analysis of the transversal and longitudinal drainage system.

The models allow us to study the behaviour of the flow in interbasins and plain zones, as well as the height of the sheet of water at any point. The simulations consider the effect of flood abatement upstream of the works and the dam effect of existing downstream obstacles. Furthermore, the flow speed can be verified and zones with risk of erosion can be detected.

The magnitude of the rainfall, the gentle slope of the land, the low level of the tracks and the insufficiency of the drainage elements are factors that may result in incidents on the rail platform

METHODOLOGY

Firstly, information about the layout and the drainage system is compiled to carry out an inventory of the crossing works. The existing inspections and the incidents registered are consulted. A hydrogeomorphological analysis of the track layout is carried out, allowing a selection of the sections to be studied with the two-dimensional models, while they are classified in accordance with their priority.

Next, the Digital Terrain Model (DTM) is prepared, for which the model is linked to the mesh size of 5m (data from the LIDAR flight of the PNOA, National Plan for Aerial Orthophotography) with topography at a scale of 1:1,000 for the trace of the line. Thus, a single DTM with a 2m mesh size is obtained, which incorporates the openings due to large crossing works in the line to be studied and in other nearby infraestructuras.

In parallel, rainfall in each of the sections is obtained from the ‘Maximum daily rainfall in the Spanish Peninsula’ publication of the General Directorate of Roads of the Ministry of Public Works, in 1999. The intensity of the rainfall in accordance with its duration is calculated through the IDF (Intensity-Duration-Frequency) curves of the Spanish Meteorology Agency, AEMET. To obtain net rainfall, we consider, in addition to rain, the land retention with data of the GIS layer of the water flow supplied by the Ministry of Agriculture, Food and the Environment through its CAUMAX project.

The next step is to generate the two-dimensional model with the Infoworks ICM program. The model defines the land through a triangular mesh from the DTM data, using fracture lines that mark the main traces of the platform slopes, zones with a different mesh size (finer around the platform) and polygons with different land roughness. The model also includes other elements, including for example small drainage works, which simulate the flow in a one-dimensional way. Once validated, rain data can be uploaded and simulations in ICM can be perfore.

Sections of the line are classified in accordance with it’s risk, delimiting potentially floodable zones. Thus, plans are made showing the potential flood risk and the results of the study of each axis are documented in a report

RESULTS OF THE TWO-DIMENSIONAL MODELS

Firstly, six rain episodes are simulated corresponding to the return period of 500 years, whose duration is related to the concentration time of the most important basin. Once the simulations have been performed, it is checked whether the platform is affected.

If it is not affected, the process ends and the section would be low-risk. In the contrary case, it would be necessary to simulate the same episodes of rain with the return period of 100 years. If it is affected only for T500, the risk considered is medium. If it is also affected for T100, the risk is high.

According to the foregoing criteria the lines are classified in sections in accordance with it’s risk, delimiting the potentially floodable zones. As such, plans are obtained to show the potential risk of flooding classified by sections of all lines. The results of the study of each axis are expressed in a report. In the four axes together 2,351 km of trace of route was studied and 89 2D models were made, with a total length of 810 km.

Lastly, we propose an action plan for all of the high-risk sections and for the medium-risk sections associated with the latter. We recommend analysing the 2D models, identifying necessary complementary data (photographs and detail topography), inspecting the area on the field, defining appropriate solutions, performing new simulations and, where applicable, drawing up the appropriate construction projects. Furthermore, the rest of the sections with a medium risk must be analysed to assess the need to carry out these actions on them as well.

Moreover, we recomend to identify other high-speed lines that will start operating soon, evaluate the available information on incidents, inventories and inspections, the documentation of as built projects and the availability of the topography (aerial photography track flights).