Mapei waterproofing systems for tunnels

Mapei’s UTT (Underground Technology Team) division offers an extensive range of solutions for underground construction projects. Among them are Mapelastic TU System and Mapeplan TU waterproofing systems. These products are ideal for repairing and strengthening tunnels lined with shotcrete, which are widely used in road and railway tunnels.

Mapelastic TU System

The Mapelastic TU System polymeric membrane is highly flexible, features high tensile strength and adheres very firmly to cementitious substrates like shotcrete.

Once applied to the substrate, Mapelastic TU System forms a waterproof barrier with excellent adhesion properties, making it suitable for creating ‘sandwich’ type waterproofing systems applied between layers of shotcrete or cast-in-situ concrete (with the substrates properly prepared) and shotcrete.

This product is ready to use and needs to be spray-applied with a high-pressure, airless pump. Such application is more practical, faster and cleaner without emitting dust into the environment, and enables other activities to take place in the tunnel at the same time.

The consumption rate is around 4 kg/sq m every 3 mm of thickness, which achieves a certified waterproofing capacity of more than 15 bar water column. It can be applied in a single layer or in two steps (two layers at a rate of 2.0 kg/sq m) – applying a first layer of white Mapelastic TU System followed by a second layer of green Mapelastic TU System a few hours later.

Applying the system in two layers gives better final results and has several benefits, including: better control of how it covers the substrate, thanks to the contrasting colours (a first white layer over grey concrete and a second green layer over the white one); consistent final thickness over the entire surface where it is applied; and better control of consumption.

The excellent adhesion properties of the membrane means that the substrate and the new lining work as one from a structural perspective, while strengthening of the concrete can be performed by using synthetic fibres or structural metal fibres.

The Mapelastic TU System membrane can also serve as a preventive waterproofing system, or be used in areas where the amount of water infiltrations is not particularly high. Existing water infiltrations must be treated beforehand by injecting resin.

Mapeplan TU line

Synthetic membranes from the Mapeplan TU line, with their distinctive orange signal layer, are specifically designed for waterproofing tunnels, usually in which the final lining is created using formwork; although they may also be used in those with a shotcrete lining. In this case, it is fundamental to apply a reinforcement mesh before applying the spray-applied coating because there is practically no adherence between concrete and PVC.

When using this system, it is recommended to install a membrane from the Mapeplan Protection line over the Mapeplan TU membrane to prevent damaging the waterproofing membrane when installing reinforcement meshes or during application of the shotcrete lining.

Thanks to a watertight anchoring element, Mapeplan Anchoring, it is possible to anchor the reinforced shotcrete to the substrate mechanically, thereby guaranteeing the maximum level of waterproofing for the system. 

Mapeplan Anchoring is a precast element consisting of a steel bar embedded in a robust PVC case, which is installed into the concrete with the use of Mapefix VE SF resin, to form an anchor point with a load capacity of more than 120 t. Once installed, the in-built flange is heat welded to the main membrane to seal the hole.

The Mapelastic TU System and Mapeplan TU line can be interconnected, or a transition zone can be formed between the two systems by applying Mapeplan Tape PVC, flexible PVC sealing tape to create a continuous waterproofing system, both widthways and lengthways, according to specific project requirements.

This article courtesy of Realtà Mapei International 95.