SCOUT - Sustainable Construction of Underground Transport Infrastructures
Overview
Background & policy context:
The development of the Trans-European Transport Network requires the construction of many new railways, highways and waterborne connections. In urban centres, burying transport infrastructures underground is the best option to avoid congestion, noise impact at the surface. In many projects, it is the only possible choice to build intermodal connections linking underground stations and airports, parking lots, pedestrian access, etc.
For such underground infrastructure, the cut-and-cover method is a cost-effective alternative to tunnels, and the best option when the tunnel is relatively shallow (maximum depth < 20 m) and the surface is free from buildings. The method is very safe, does not create subsidence, and the phasing of works allows surface traffic to be restored at a relatively early stage, when the cover slab is completed. This method has a huge number of references over the world for the construction of underground roads, subways, railway lines and stations.
Cut-and-cover tunnels are therefore a vital tool for the construction of transport infrastructures which are needed for the development of the TEN-T Network. But this method was confronted with a new set of requirements: the urgent need for safer and more cost effective techniques, and a reduction of environmental impact from the construction (use of natural resources, noise, disruption of traffic, etc).
Objectives:
The main objective of the project was to develop a new concept for sustainable construction of 'cut-and-cover' tunnels that optimises the safety and life-cycle cost of the construction, and eliminates or drastically reduces most nuisances to urban environment, which are classically associated with construction projects: noise, dust and large construction equipment causing long traffic disruption at the surface.
Methodology:
The project concentrated on the construction of tunnel walls and, using a holistic approach, addressed the three complementary domains of construction: materials, design and construction process.
The project core activities were:
- Development of new methods for design: starting from the analysis of a selection of reference cases, the project developed:
- new methods to optimise the engineering of cut-and-cover projects, using the concept of a 'doubleskin' structure and aiming at reducing the cost of construction materials by 15%;
- a methodology and relevant documentation to apply the observational method to cut-and-cover tunnels on a wide scale, with the objective of eliminating the extra delays and increased costs classically related to soil heterogeneity.
- Development of a breakthrough construction method: a radically new concept for the construction of tunnel walls was developed, where the drilling process is continuous and horizontal, with the objectives of minimal environmental impact and maximum workers' safety. Modular architecture of the equipment will allow the adaptation of a large variety of tunnel projects in a number of different European soil types. The environmental advantages will be minimal noise and dust, and no drilling through mud. The concrete structure will be cast in situ and equivalent in quality to that of superstructures.
- Study of new composite materials, and material recycling: the project investigated how fibre-reinforced concrete materials can be used in both temporary and permanent structure members to optimise structural design. New materials were developed and tested at full scale. The recycling of excavated soil was analysed (soil conditions, plant equipment, quality control requirements, costs), so as to identify the current blockages and to establish a roadmap towards the implementation of soil waste recycling.
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