Pilkington Glass in the Alpine summit
The glass platform “Le Pas dans le Vide” is a new attraction for tourists visiting one of the most popular terraces in the French Alps, located on the top of the Aiguille du Midi (3,842 meters above sea level). The platform “Le Pas dans le Vide” can be reached via cable car from the famous ski resort of Chamonix. On arriving at the upper station of the cable car (3,802 meters above sea level), the final ascent of 40 meters is by an elevator built inside the mountain. Once you’ve arrived at the top you can visit the remarkable extension of the traditional observation deck known as “Le Pas dans le Vide”.
The new viewing platform was opened to visitors on Dec. 21, 2013. On stepping into the viewing platform, tourists will be, surrounded by the transparent walls, a glass roof overhead and a glass floor, which creates an extraordinary sensation of “floating” above the 1,000 metres precipice. The new viewing platform appears to be "suspended" in the clouds not only because of the material used, i.e. glass, but also due to the frameless glass walls being practically invisible.
Glass with a view of Mont Blanc
“Suspended” at an altitude of 3,842 meters above sea level vantage point “Le Pas dans le Vide” is a glass structure in the form of a box with dimensions of 2 meters wide x 2.45 meters high and a depth of 1.70 meters. The glass box was installed on a steel bracket fixed to the observation deck. The design of this small but unique project meant it was vital to ensure an uninterrupted view of the alpine panorama. Therefore extra clear Pilkington Optiwhite™ was chosen for the viewing platform. Each of the three walls, ceiling and floor of "Le Pas dans le Vide" are made of three panes of toughened 12 mm Pilkington Optiwhite™ laminated with two SentryGlas® interlayers (each with a thickness of 1.52 mm). SentryGlas® was specified as the structural interlayer, rather than a standard PVB interlayer, because of its increased strength, and the key fact that it is more transparent than standard PVB. This type of interlayer in combination with extra clear glass achieves improved transparency, even in laminated glass. The use of laminated glass made with Pilkington Optiwhite™ and SentryGlas® interlayer for the construction of the project, provided very highlight transmission (LT = 88.3 %) and high colour rendering (CRI = 98.1 %) despite the considerable thickness of the glass (over 39 mm).
Safety above the clouds
In addition to the stunning aesthetics of the platform, a key element in the design of “Le Pas dans le Vide” was to provide the highest level of safety. Therefore it was essential that the glass that was specified - Pilkington Optiwhite™ underwent several stages of glass processing: each pane of glass was toughened, heat soak tested and laminated with SentryGlas® interlayer. The process of toughening increased the resistance of glass, preventing it from cracking in areas of high stress concentration, i.e. in the glass fixing points. Additional heat treatment called “heat soak test” reduces the risk of spontaneous breakage of glass. Application of SentryGlas® interlayer makes the glass stronger and more durable. SentryGlas® interlayer retains a residual strength even when the glass panes are damaged. Therefore, its use is particularly recommended in areas exposed to extreme conditions and weather phenomena and where the possibility of maintenance is difficult. Increased stiffness of the SentryGlas® interlayer reduces the likelihood of deflection of glass pane subject to wind and snow loads and continuous loads. All of these characteristics perfectly met the needs of this innovative high-altitude construction.
Proven glass processing techniques were essential for the construction of the Alpine viewing platform to ensure the whole structure could withstand wind speeds of up to 220 km/h and a temperature differential ranging from -35°C up to 60°C.
Construction of “Le Pas dans le Vide” began in August 2013, but the preparations for the implementation of this pioneering and highly demanding structure in terms of technical investments have taken more than two years. A number of calculations and stress tests have been performed and were critical to ensure the best performance of the final design. Prior to installation in high altitude conditions, the glass box was made and thoroughly tested “on the ground”.
Several specialized partners were involved in the implementation of this prestigious project. NSG Group, manufacturer of Pilkington glass, supplied the glass to the processing company Dania Vitrage and the installation of glass was by Laubeuf. The financing of the entire project was by Compagnie du Mont Blanc, who manage the cable car at Aiguille du Midi and also supports other ski slopes in the Mont Blanc area.
Photography: Bertrand Delapierre