With waterproofing and drainage needs leading to various solution to challenges in tunnels, a relatively recent addition to the offerings includes a mesh module of inter-connected channels – the Dolenco Drain – that can be attached easily to walls and also covered with shotcrete.

Once in place, a grid of narrow channels is then established around the full tunnel profile, to permanently prevent waterpressure. The network of slim, low density polyethylene (LDPE) channels is able, says Danish manufacturer Dolenco Tunnel Systems, to drain 8m3 of water per linear metre per hour – and be in place with a design life of more than 120 years.

By permanently preventing pressure on the structure, it is possible to eliminate or reduce problems with seeping water during construction, and significantly reduce maintenance costs during the lifetime of the structure managing director Johnny Poulsen tells T&T. He adds that complementing current construction methods reduces construction time and costs. By optimising design it is also possible to reduce CO2 footprint.

During design studies, the company had input from an external tunnelling consultant to optimising the structure and this helped to estimate the potential project savings in direct costs, construction time and CO2, compared to standard solutions in hard and soft rock tunnels.

“The calculations shows the significant savings and have been made without including savings by avoiding short and longterm injection costs and changing membrane after 60 years,” says Poulsen.

With a background of more than 20 years in waterproofing, the business was built on this basis, says Poulsen. Development and worldwide patenting for its Dolenco Drain product started six years ago, he adds. The product is a mesh of channels only 14mm thick.

It is 800mm x 1200mm and the mesh can simply be nailed to walls at provided hanging points. The standard module designed sheets are then connected together, allowing for extensive areas of drainage coverage – for permanent solutions or even temporary drainage support, during construction, by different excavation methods. The mesh design makes it possible to have adhesion between primary and secondary lining. As a consequence, only a very slim secondary layer is needed, which also makes it an ideal solution for existing structures says Poulsen.

Manufacturing takes place in Denmark where the company also continues its research and development activities, adapting “to the specific need and niches in the market”.

There is a variety of application areas for Dolenco Drain. Some current tunnel projects using the drainage mesh include metro station walls and tunnels, and different secant pile structures.

PROJECTS

Project have been undertaken to install the drainage mesh in a number of countries, including Canada, the US, India and Russia.

Canada

In Montreal, the Reseau Express Metropolitan light rail system is under construction to link up with the existing main metro network. The new transit system is to add 67km of network and 26 stations. It is the province of Quebec’s largest public transport project in the last 50 years.

With construction underway since 2021, Dolenco says the designed drainage system, based on spray membrane, had been showing early problems with water ingress and led to a change in approach, adding in its drainage layer. The drainage mesh is mounted on top of the 300m initial shotcrete and then covered with 25mm-40mm of smoothening layer shotcrete upon which the spray membrane is then applied, and further shotcrete added.

US

For the refurbishment work outside a portal of Tuscarora Mountain Tunnel, in Philadelphia, the Dolenco Drain system is being mounted on a high retaining wall for extra drainage provision. The tunnel is owned by the Pennsylvania Turnpike Commission.

The tunnel was built in the late 1960s. Difficulties with water ingress at the portal’s high retaining wall came during refurbishment work.