The New Railway Link through the Alps (AlpTransit), is a Swiss federal project focused on building faster North-South rail links across the Swiss Alps by constructing base tunnels several hundred meters below the level of the current tunnels.

Several million cubic meters of excavated, non-utilisable materials from the Ceneri Base railway Tunnel are to be stockpiled close to the main construction site of the intermediate portal, on a 5,000m² area near Sigirino, Switzerland. A reinforced soil structure was to be built to stabilise this stockpile and Maccaferri’s ‘Paramesh’ System, a combination of Green Terramesh® and ParaGrid® geogrids, was chosen for this purpose.

The construction of the 15.4km long dual tube railway tunnel under Monte Ceneri in Southern Switzerland started in 2009 and should be completed in 2018. In order to manage the excess of material excavated from the tunnel jobsite in Sigirino, which is expected to produce a total of 3.6 million cubic meters of a non-recyclable, inert material, a 5,000m² area was selected to store such a quantity of crushed rock / bulk material within the limited jobsite area.

A reinforced soil structure was to be built to stabilise the mass of excavated material. The structure had to be highly flexible to accommodate the potential deformation and settlement induced by the overburden load on the soil below which is characterised by alternating layers of sands, gravels and normally consolidated silts of fluvioglacial origin. Moreover, a key factor in the final choice was the speed of execution.

Maccaferri’s Green Terramesh® System and ParaGrid® geogrids were eventually determined as the most suitable solution to the problem. The geosynthetic reinforced soil wall is 200m in length, has a height of up to 42m and has a face angle of 70°.

Since the site-won backfill material is quite angular and aggressive in terms of its capacity to mechanically damage the soil reinforcement product, a specific installation damage test was carried out to determine the performance of the geogrids. Maccaferri’s primary reinforcement Paragrid® geogrid showed excellent performance considering the aggressive nature of the fill material. Three geogrid grades, with ultimate tensile strengths of 65kN/m, 100kN/m and 175kN/m respectively, were used in order to provide the long-term stability of the structures.

This solution enabled the contractor to effectively manage the material generated from the tunnel excavation as the speed of reinforced slope construction was quicker than that required by the rate of excavation at all stages. This avoided the payment of heavy penalties which would be imposed upon the contractor in the event of not fulfilling this requirement and stockpiling excavated materials.

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