• Gibelhorn Upgrades—An Ambitious Construction Project

Gibelhorn Upgrades—An Ambitious Construction Project

Published on 01.11.2013

The Muotathalerstrasse in Schwyz Canton is being rebuilt.

The Muotathalerstrasse [Muota Valley highway] in Schwyz Canton was first built in 1860, then slightly altered and widened in some places in 1940 and 1960. It is now being redeveloped and widened.

This road was seriously deficient from the standpoint of its alignment and safety. So the cantonal legislature approved a 46.33 million CHF redevelopment and widening loan for the 900-m stretch around the Gibelhorn. After prep work and natural hazard mitigation (protection from falling rocks, cliff stabilisation), four new concrete retaining walls—250 m long and up to eight metres high—are built on the side of the mountain, and the road is widened by cutting into the cliff. Extending to the valley are four new angle retaining walls with a length of 380 m. Along the remaining 520 m, the existing support structures are reinforced by the addition of subjacent support pilings, advanced concrete ribs, injected material, partial shear connections, bracing, and new cantilevers and concrete slabs to the existing walls. The highway’s drainage system and crust are completely rebuilt.

About 5,500 vehicles use the Muotathalerstrasse every day, which is a real challenge for the project engineers considering the very tight space and the longest wait times tolerated for traffic signals (only 3-4 minutes). The Muotathalerstrasse is the only link between the Muota Valley and Schwyz that is built for heavy vehicles, and it gives access to the entire valley. “This is the most difficult construction site the Canton has ever had to manage”, said Bruno Kaelin, the head of the Department of Engineering Structures at the Office of Civil and Underground Engineering. The site poses enormous difficulties: precipitous slopes, tight spaces, and short deadlines. To allow the work to proceed, traffic is reduced to one lane during the day. However, alternating traffic is feasible only between March and November due to ski tourism and snow removal during the winter. If the road is closed completely (possible only at night), long detours must be set up.

Through the former ARP Ingenieure und Berater AG in the engineering consortium Horn, BG is responsible for SIA sub-phases 32-53 (representing about 60% of the services of the engineering consortium). It is handling overall site management and acting as the lead construction manager as well as providing project planning for the road construction/drainage and mountainside supporting structures, construction-phase and traffic planning, and most of the invitations to tender and on-site supervision work.

One impressive feature of the construction site is the scaffolding that has to be erected on the vertical and sometimes even overhanging face of the 100-metre-high cliff. The workers dangle almost directly above the chasm, so comprehensive safety measures are a priority. The work is to be completed in 2016.

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