SA3100 – stoos construction-site report

Stoos is a Swiss mountain village located at an altitude of 1306 m asl in the canton of Schwyz. Construction of a funicular will make it accessible all year round. For the 150 villagers, the new cable railway forms the main connection to the valley below.

In future, it will be used not only for passenger traffic but to handle freight as well. It can transport 1500 people per hour. The cable railway can accommodate 136 persons and 6 tonnes of freight. The new funicular will be world’s steepest model of this design. The slope increases to 110 percent in some places. With a rail length of 1785.4 m, the funicular overcomes an altitude difference of 743.1 m.

Handling this project required the construction, among other things, of two bridges and three tunnels.

One of the bridges is located directly at the lower station, on Muota Lake, at an altitude of 563 m asl. The bridge is 127 m in length and crosses the lake with a rail angle of 35°. The purpose of the bridge is to permit the cable railway to travel from the horizontal into the mountain.

Special challenge

A special technical challenge was to manufacture the foundations of the bridge on a slope with an inclination of up to 50°. All of the work carried out in this alpine terrain took place under extreme conditions, as accessibility, reachability of the drilling points and space conditions on the steep slope demanded everything of man and machine alike.

Several drilling methods were needed to create the foundations. Ischebeck TITAN-type self-drilling anchors were used to temporarily stabilise the excavation site. To divert vertical loads, micropiles with double corrosion protection and 16 m in length were installed. The micropiles used were pre-injected GEWI anchors with a diameter of 43 mm. Permanent ground anchors are used to divert all horizontal loads. Pre-stressed L12 strand anchors with all-round corrosion protection were used here. A borehole 185 mm in diameter and 28 m deep had to be drilled for the ground anchors. In addition, a vertical inclinometer 30 m long was installed for future monitoring of the foundations.

The different drill systems and drilling diameters (self-drilling anchors, overburden drilling for strand anchors, micropiles and inclinometer) as well as the extreme terrain placed special demands on the machine engineering. Due to the alpine terrain, only light drill equipment came in for consideration. At the same time, overburden drilling with a maximum diameter of 185 mm had to be introduced at a depth of 30 m, requiring robust technology due to the forces and torques involved. In this case, the customer had to be furnished with the right solution to successfully complete the project. The material used in the injection technology was subjected to very high demands. Here it was particularly the difference in altitude and the great distances that made it difficult to select the right technology.

Different drill systems

The decision was taken for a SA3100-model earth drilling unit attachment by the Morath company. The SA3100 was attached to a Kaiser S12 allroad walking excavator. This combination was used for all drilling operations.

Two different drilling drives were used to permit use of the various drill systems with an drilling unit attachment. The HB100-GD150 was used for the installation of the self-drilling anchor, and the HD52S by the Morath company was used for overburden drilling. An IS500 was used for all of the injection operations.

The Morath company provided the customer with extensive advice over the entire course of the project. Among other things, the reachability of all of the drilling points with the selected combination of the drilling unit attachment and carrier was simulated prior to the start of construction.

Another challenge for the customer, in which the Morath company was able to assist with its many years of experience in process engineering, was the detailed planning of the workflow involved in the installation and removal of the casing, as well as the installation of the strand anchors.

The new funicular will be commissioned in 2016.