Two TF 100 cutter heads were key to performing excavation works to create the longest pedestrian tunnel inside a glacier.
In May 2015, two Simex TF 100 cutter heads completed excavation of a pedestrian tunnel inside the Icelandic glacier of Langyökull. Stretching 536 meters, the tunnel cuts through formations of ice created over centuries, allowing a view of this spectacular natural phenomenon from its very inside.
Only now are we giving news of this successful project performed by our attachments, because for almost four years the TF 100 and TF 50 cutter head models had been object of a dispute with a German manufacturer regarding the patent on some of the technical solutions used for the design. An agreement reached in the spirit of fair competition recently saw the resolution of the situation.
Excavating inside the glacier
Langjökull (Icelandic for “long glacier) measures 953 sq. km, 50 km in length and 15-20 km in width, and is the second largest in Iceland, smaller only than the colossal Vatnajökull.
Situated some 200 km northeast of Reykjavik and at an altitude of 1,450 m, the glacier has a maximum thickness of about 580 m and extends over a large system of volcanoes (two of them still active). Because this natural phenomenon is so unique and is relatively difficult to reach from the part exposed to the southwest, Langjökull has long been a destination for hikers from all over the world.
In 2010, Baldvin Einarsson and Hallgrimur Orn Arngrímsson imagined a tunnel that would penetrate inside the glacier. With the aid of geophysicist Ari Trausti Gudmundsson and the engineering company Efla, who performed the studies for the project, they proposed the excavation of a pedestrian tunnel that would allow the mass of ice to be admired from the inside. The project went through a long gestation period not only to obtain government approvals, but also to make a thorough evaluation of the many geological, environmental, logistical and construction factors.
Special attention was placed on the plan to guarantee worker safety during the construction phase and visitor safety after the tunnel opened to the public. The project’s execution involved the excavation of a tunnel with a total length of 536 m reachable from an 80 meter “corridor” and accessed from the outside through a portal.
At the end of this first part of the linear walkway is a large chamber, then the circuit splits into two other tunnels each with an irregular-shaped loop; regardless of the direction taken, the visitor is always led back to the chamber and the access corridor. Along the irregular loops of the circuit, which reaches a maximum 30 m depth with respect to the surface, larger areas have been created for information and snack areas, and even a chapel that can accommodate about 50 people.
Following excavation, the tunnel was outfitted with a ventilation system and lighting system with special effects powered by solar panels and wind generators installed externally in order to minimize environmental impact. Now, three years after its inauguration, the pedestrian ice tunnel is hailed a success with the number of yearly visitors estimated to reach 20,000.
Simex offers the excavation solution
Due to the practical difficulties of operating at an altitude and in a remote area, Into the glacier, the company promoting the project, assigned construction of the tunnel to a contractor familiar with operating in the large area at the foot of the glacier. The organization and planning of the project was complex from many standpoints, especially because the area identified for the tunnel excavation would not always be accessible due to weather conditions.
To respect the schedule -- opening to the public was planned for June 1, 2015 – a special machine was locally designed and built to perform the works. Thanks to the solutions used for this machine, excavation times would theoretically have been shortened, but during 2014, the system was already demonstrating the limits of the mechanical solutions adopted, and did not seem to be able to ensure a satisfactory output, since it was advancing only 2 m per day.
The contractor then searched for a new excavation system that would guarantee greater reliability and especially a higher production output in order to stay on schedule. The solution was provided by the Simex dealer for Iceland, Vèlfang, who after evaluating the size of the excavation proposed the TF 100 cutter head, judging it the best suited to the application.
The solution essentially involved a roadheader system of excavation using a carrier machine and a properly sized attachment for the small tunnel measuring 3 meters in height and, depending on the area, 2-5 meters in width, to create an excavation face of 6-15 square meters.
The attachment also had to be able to excavate niches and large chambers without affecting the timeframe. After using the TF 100 on a trial basis on a straight section of the entrance, it became clear that production could be doubled immediately, even tripled, once the operators had worked out the best technique for using the machine and attachment together. The method, as a result, proved the most efficient and quickest solution for guaranteeing the required production and was thus adopted immediately adopted.
After excavating the access corridor and reaching the point where excavation of the large chamber (departure point for the loop) was to begin, two excavation faces were created that would meet approximately halfway. Two TF 100 cutter heads were put to work, one coupled to a Terex TC 40 mini-excavator and the other to a JCB 8026 mini-excavator, which excavated in the opposite direction to then meet at the breakthrough point practically at the same time and complete the circuit. A third TF 100 was purchased as a spare cutter head to assure advancement in case one of the two attachments required maintenance (a precaution that turned out to be unnecessary). The job of removing the milled ice was assigned to a telescopic handler with bucket, which would enter alternating sides of the tunnel after the mini-excavators pulled out in order to allow access.
Throughout the works, the TF 100 demonstrated an excellent ability to excavate the packed, thousand-year old ice of Langjökull, as validated by Einar S. Traustason, one of the two heads of the contracting company who performed the works: “The TF 100 attachments really made the whole project possible. Excavating ice might not seem a job that presents special challenges, but when we’re talking about material that has overlapped and compressed over centuries, like what you’d come across at a 20-30 m depth on a high-altitude glacier, that’s something else. So we’re very pleased with these attachments, which really enabled us to complete the excavation on schedule.”
According to the depth (as mentioned, the maximum depth of the tunnel with respect to the surface is 30 m), the ice in a mass of that extent is very compact and has a low quantity of empty spaces and, depending on the zone, can have a uniaxial compressive strength of 5-10 MPa. A glacier is formed by the compression of various layers of snow that are accumulated and compressed over time due to the weight of the upper layers (i.e., the metamorphosis of ice crystals). The two small TF cutter heads were consequently put to work on a job more similar to the excavation of a rock mass with a moderate compressive strength than of a glacier formed by a frozen body of water.
Simex TF 50 and 100 cutter heads: the smallest of a range of 10 models
The TF 100 can be mounted on 2.5 - 4 ton mini-excavators and, together with the even smaller TF 50 designed to fit 1.2 - 4 ton mini-excavators, is part of the range of Simex cutter heads comprising ten models.
Small but powerful, the TF 50 and TF 100 are cutter heads that can excavate for their entire width, thanks to an innovative system with central chain that leaves no zones unmilled. This allows the work capacity of the attachment to be fully maximized (from the TF 200 up all the cutter heads have no central chain and are driven by a coaxial motor, a solution patented by Simex).
Especially suited for nursery and forestry applications, such as cutting trunks and roots, these attachments are very efficient for excavation of small trenches in rocky terrain, or for installing manholes or utility vaults for water, telephone or electrical lines.
The TF 50 and TF 100 can also be used effectively for milling concrete walls or removing plaster, and thanks to the weight and to the limited size of the carrier machines they are mounted on, they are ideal for refurbishing civil and industrial buildings, applications where they offer low noise levels, also in confined spaces. In addition, these attachments are extremely efficient for profiling of horizontal or vertical surfaces that need to be made uniform.