Asphalt Paving at the Highest Level
Work on the A9 motorway in the Valais canton between Siders and Brig (approximately 32 km long) is a challenging project on many fronts. With a revised alignment, the route is designed to bundle the traffic lanes as efficiently as possible given the narrowness of the Rhône valley. About 50% of the new A9 motorway route through the Upper Valais runs underground, which makes the construction work particularly difficult. Ammann machinery, in the form of an asphalt-mixing plant, a road paver and vibratory and pneumatic tyred rollers, supports the demanding paving work in the tunnel. A consortium of businesses named ARGE ATV was assigned the multi-phased project. Ulrich Imboden AG handled the paving portion of the roadbuilding.
The Valais, a mountainous canton, has topographically little space and few location choices for upgrading major transportation routes, given the constrictions of the Rhône valley. Successfully extending this motorway, without isolating the canton from the rest of Switzerland, is a difficult task and has been under discussion for decades. Construction of the new A9 circumvents the problem by including numerous tunnels and improves connections between the whole Valais region and Switzerland’s national road network.
Routing Through Tunnels
The construction site is 31.8 km long in total and is fraught with many challenges. For example, two tunnels linked by a bridge take drivers on a route some 7 km long around the town of Visp. The asphalt paving crew faces huge challenges here. First, the Swiss authorities stipulate maximum standards for paving quality in road tunnels to extend intervals between servicing work. Second, the high volume of traffic on this section will severely impact the asphalt.
This means that the work of laying the asphalt paving must be of the highest quality. For the surface layer, a special mix formula with PMB (polymer modified bitumen) is used because of its robust nature. Because of its high quality requirements and its special composition, this layer also necessitates particularly high compaction standards. Achieving this quality requires an experienced crew and machinery that is ideally matched to operate together throughout the paving process – from the asphalt-mixing plant, to the paver and to the rollers.
Work in the tunnel has even more complications for the paving crew from Ulrich Imboden AG. Laying asphalt paving creates vapours, which do not easily disperse inside a tunnel. This makes ventilation for the new road tunnel a key factor, even at the asphalt paving stage.
Because the wind in the Valais constantly changes direction, the ventilation system must repeatedly be adjusted to extract the vapours from the tunnel.
At the Heart of the Process Chain
Since 2004, Ulrich Imboden AG has been operating a stationary Ammann asphalt-mixing plant in the immediate vicinity of the tunnels. The plant is an Ammann Global 160, which in 2018 was fitted with an RAH feed to process recycled asphalt (RAP). This plant, designed to be at the cutting edge of technology, produces the asphalt for various projects in the Valais. It has sufficient capacity to reliably supply mix for a major project such as the extension to the A9.
The proximity of the construction site is ideal. Lorries take only a few minutes to transport the mix from the plant to the paver. In terms of its output, the plant must always be well geared to the day-to-day needs of the asphalt paver. Ultimately, the AFT 700-3 from Ammann is the “heart” and so dictates the pace of the whole paving process. Because of its size, the AFT 700-3 from Ammann can pave across the entire width of the 7.3-meter wide carriageway in a single pass. This eliminates the possibility of weak points in the layer, which could occur where two separate lanes have to be joined together.
In this sort of construction project, the entire paving crew is expected to work with maximum precision and productivity in order to be on top of the work in the mandated timeframe. This requires precise coordination of the various work flows and a thoroughly experienced, highly skilled team.
High-Level Compaction and Fast Paving
An ARP 95 Pivot-Steer Tandem Roller with ACE technology and an AP240 Pneumatic Tyred Roller, both from Ammann, work behind the paver. The latter has a higher static weight than the tandem roller, with its pneumatic action creating a “kneading” effect that increases the compaction performance.
Ammann Compaction Expert (ACE), the company’s proprietary Intelligent Compaction system, is a key piece of the puzzle. This built-in, automatic compaction control shows the machine operator the current compaction status as he works. This enables him to avoid unnecessary repeat passes and to monitor the degree of compaction achieved in every section. Finally, this saves both valuable time and fuel and also eliminates the need for expensive reworking.
Only the tandem roller is needed to compact the PMB surface layer. The roller’s vibrations enable compaction goals to be reached.
All the quality standards of the Swiss authorities were met by the seamless interplay of the individual machines and the experienced Imboden crew. This was all accomplished while adhering to a tight schedule.
Key Role for Project and Partnership
The asphalt work in the Visp South tunnel is finished. The Ulrich Imboden AG team and the Ammann machinery played an important part in keeping the project on schedule while also meeting the required quality goals. If all goes according to plan, the tunnels will come back into use in 2022.
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