Vereina railway shot cut Feb 1993

The 19km-long Vereina rail tunnel in Switzerland will, for the most part, be excavated through the characteristically strong rocks of the Swiss Alps using a combination of drill+blast and TBM work.

The Klosters portal of the Zugwald Tunnel with the existing rail tunnel to the right. The jetpiling rig is assembled at the portal ready to complete the first round. The grout mixing and pumping station is also on the right

The portal zones of the shorter Zugwald Tunnel, however, pass through weathered and broken rock containing pockets of glacial moraine. Records indicate that this material settles by up to 1-3cm/year.

For safe excavation of these portal sections, horizontal and vertical jet-piling has been specified to provide pre-support of the material while chemical grout injection is applied for consolidation and control of excessive water ingress.

After discussing the project for many years, Rhatische Bahn, the area's privately operated rail company, entrusted Amberg Ingenieurburo of Zurich with the design and construction supervision. This sophisticated tunnel will provide a new route between Klosters and the Engadin Valley. Work on the estimated SF538 million project (in 1988 prices) began in 1991 with award of five major tunnel-related contracts.

The project is split into contract packages by geological and topographical considerations. Trains from the north coming up from the valley will pass on from Klosters into the 2.16km long single track Zugwald Tunnel to the Klosters-Selfranga marshalling yard. Here vehicles which have driven up from the valley will load onto the car rail wagons and will travel the 19km-long single track Vereina Tunnel to the marshalling yard at the other end.

The car trains will operate a shuttle service through the tunnel while through trains for both passengers and freight will join the Valley's existing rail network.

The 19km-long Vereina Tunnel will provide a north-south short-cut through the Swiss Alps between Klosters and the Engadin Valley

The short Zugwald Tunnel is required because of lack of surface space in the village for the new rail track. Again due to limited surface space, part of the marshalling yard extends into the Vereina Tunnel. The first 300m of the tunnel has a 145m² profile and will accommodate three tracks. This then reduces to a 75m² double track profile before stepping down again to the single track profile.

From the opposite portal in the Engadin Valley, the first 2km is also double track with a length of three track cut-and-cover work at the portal.

Of the five contracts, jet-piling is a major part of contract T1 which, with contract T2, has been won by the Arge Selfranga joint venture comprising Walo Bertschinger/Kopp/Schafir & Mugglin/Schmalz/Theiler & Kalbermatter. Contract T1 comprises the first 295 m of the Zugwald Tunnel (T1a) and the first 198 m from the opposite portal (T1b). Contract T2 covers the 2115 m length of three-track and two-track tunnel at the north end of the Vereina Tunnel.

T3, awarded to Pitsch, is for the cut-and-cover portal and surface works at the south end of the Vereina Tunnel in the Engadin Valley.

The TBM, a 7.64m diameter Wirth machine, will be used by the Stuag/ Zublin/J ager/Frutiger/Vetsch/Bordoli joint venture on contract T4 to excavate the central 1,665m of the Zugwald Tunnel as well as about 10.385km of the Vereina Tunnel.

The TBM will work principally in the amphibolites of the Silvretta Fault and will provide a single track proflle.

Plan and geological section of the project. The short Zugwald Tunnel in Klosters leaib; trains to the Selfranga marshalling yard where cars will load onto the trains for the 19km trip through the Vereina Tunnel

T5 is the 6.5km of the Vereina Tunnel from the south portal where the Zschokke/ Murer/CSC/Lazzarini/Torno/Bezzola joint venture is using drill+blast through gneiss and amphibolite. Work started in July 1991 and by mid-November 1992 some 860m of the double track profile tunnel was complete. The full 6.5km length is expected to be finished during 1997 when the single track drill+blast operation junctions with the TBM.

The TBM contract also includes a double track crossover chamber excavated by drill+blast at mid-tunnel point.

Jet-piling

During a site visit in November 1992, the ‘Arge Selfranga’ JV was approaching the end of the jet-piling section of the T1a heading.

As designed by Amberg, the first 210m length is divided into 17 cycles of horizontal jet-piling 16.8m-long drill holes providing 15m long piles and a 2.5m overlap.

While the joint venture is responsible for tunnel excavation and support, the jet-piling work has been subcontracted to specialist contractor GU Tiefbau.

At the end of each horizontal jet piling round, the top heading is excavated in about 1m cycles using an Eickhoff 110 roadheader boom attached to an excavator chassis on tracks.

This arrangement was needed for greater flexibility as well as to provide a higher reach and allow manoeuvrability in the very limited working area. Set in the centre of the village of Klosters, the working site is restricted on one side by the river valley over which a new rail bridge is being built concurrently; on the other by the rising mountain; on the right by an existing rail track and rail tunnel (which must remain in service throughout the new tunnel work); and on the left by two houses, one of which provides the site offices.

Once excavated, each metre of advance is supported immediately by 3-4 cm of shotcrete, a layer of wire mesh, and a heavy omega profile steel arch of the type 36/58. This then builds up to a 25 cm thick support lining with a second layer of shotcrete and wire mesh and a final 4 cm layer of shotcrete.

CJFA Spritz System CSS 2 on its first use in a Swiss tunnel

This part of the tunnel is to have a final insitu concrete lining as is the opposite portal length. This is part of the T4 TBM contract. In the interim, the two portal zones of the Zugwald will remain supported by the shotcrete based lining.

With the 12.5m excavation cycle complete, jet piling begins with 12 x 3m deep x 60cm diameter vertical piles along each side of the tunnel on about 1m centres. The horizontal piling follows with 28 piles installed around the 34m² top heading. Each pile is theoretically 60cm in diameter and all are installed on a 10° angle.

As is typical with most grout injection processes, it is very difficult to know exactly where the grout is migrating and exactly how much is needed to attain a well consolidated pile.

At Zugwald, GU Tiefbau is injecting an average 350 kg of the water/ cement grout for every 1m of 60 em diameter pile. Grout is mixed at the hatching plant at the portal and is pumped at 520 bar to the two 2.2 mm diameter injection nozzles.

It takes about 30 to 60 min to drill the 16.8 m long horizontal hole and about 4 to 5 min/m to withdraw the steel and inject the grout. A horizontal and vertical jet-piling cycle takes about 6 to 8 days to complete. Following this, it takes 5 to 12 working days to complete the 12.5 m excavation and support cycle depending on conditions.

Unfortunately, due to the steep narrow road over the mountain to the opposite portal, alternate working of both faces is not possible. The jet piling team and equipment are idle during excavation and support cycles. Due to the proximity of the working site to the village centre and in accordance with Swiss working law, work is limited to two 9 h shifts between 6 am and 12 pm Monday to Friday.

Eickhoff type ET 410- Q ready for work at Vereina tunnel

Excavation of loose glacial moraine deposits have proven more difficult than expected. According to Andreas Weidinger of Schmalz and site manager for contract T1: "We have experienced up to 15 litre of water ingress per second and, on occasion, the face has wanted to break up in the loose material. In addition to immediate support measures we have had to consolidate loose material and control water ingress with chemical grout injection."

The chemical grout used is SikaFix, a two-part polyurethane injection material from Sika. Some 30 sec after mixing, the chemical reaction between the two materials causes an increase in volume of between 10 and 15 times.

It is injected both into the face as well as laterally out through the canopy of horizontal jetpiles. SikaFix injection has been used 8 or 10 times on the T1a section. Some 15 t of the material has been injected and another 5 t is kept in stock. The two components are pumped into a static mixer before entering the injection pipe.

Control of water ingress is needed particularly to prevent washing out of the fines, a major cause of movement in this loose material. Movement is gauged principally by horizontal extensometers and convergence measurements taken inside the tunnel as it advances.

For the first 6m adjacent to the existing rail tunnel, steel arches are set on 48 cm centres. This widens to 98 cm centres in the remaining length where cover rises to about 100 m. In particularly weak zones, the face is covered with a 5-10 cm of flash shotcrete to prevent face convergence while building the steel arch.

Ultimate arrest of movement is achieved with excavation of the 26-29 m² invert section and closure of the ring of support.

Unusually, in this case, the ring is closed with a precast concrete invert segment which has a drainage channel in the cast. The legs of the steel arches support the walls and create the link between the support arch and the invert segment.

The invert section is backfilled for easier access to the top heading and will be re-excavated before casting the final in-situ concrete track bed. Excavation and support of the bench is progressing at about 16m maximum per week and ring closure is achieved within 40m of the advancing top heading face.

A section of the Zugwald Tunnel at a point close to the existing rail tunnel. Horizontal and vertical jet-piling has allowed safe excavation of the 34m² top heading and 29m² invert section. The ring of immediate support is closed with a precast concrete invert segment.

Vereina advance

Over on contract T2, the 2.15 km length of three and two-track tunnel at the north portal of the 19 km long Vereina Tunnel is being advanced by the same joint venture. During the site visit, the 300 m of three-track tunnel was completed and fully lined with its in-situ concrete final lining. A 10 m long form from Bernold was used to cast the 500 mm thick x 27 m span lining which is complete with a membrane waterproofing system from Sika.

An Eickhoff 410 roadheader was bought to excavate the sediments of the Arosa Imbricated Zone comprising dolomite, sandstone and slates. This however proved a little too hard for the roadheader. Drill+blast was used instead and is now advancing on the remaining 30 m of the bench before trying the roadheader again to complete the last 1280 m of two-track section where the TBM will pick up. The two-track section is finished with a single shell lining of shotcrete, wire mesh, steel arches (if necessary) and rock bolts. Weidmann Fibreglass rock bolts were specified by Amberg because they eliminate the risk of corrosion.

Shotcreting

Wet shotcrete is being used on the T2 Vereina Tunnel contract. This is applied using a shotcreting unit from CIFA of Italy, the first in Switzerland. With a 13m³/h capacity, the mobile unit is equipped with a 4m long sliding boom carriage. From one location, the nozzle can cover approximately 8m length without moving the unit.

The unit is also fitted with an automatic doser for two shotcrete additives. CIFA's BiFlux control system is managed directly by the concrete pumping circuit giving precise synchronism between the pumping cylinder and the hydraulic actuator of the batching pump. The batching pump consists of a rack actuator with two additive-feeder cylinders keyed to it mechanically. By rotating a register, the percentage of additive can be varied from 0 to 10% even when the machine is in operation.

On both Tl and T2 contracts, Sika additives are being used. In the wet shotcrete process, a concrete mix of about 1,730kg aggregates, 430kg cement, 200 litre water, 20kg Sikafume TU, 1% Sikatard 902 superplasticiser/stabiliser, 2% SikaTell 200, a cohesive agent and 2% of Sigunit 120 accelerator, the shotcrete is achieving a 28 day-compressive strength of 40-50N/mm². Additional layers of wet process shotcrete contain SikaTell 200 without accelerator to achieve a far greater compressive strength. Rebound when using the wet shotcrete process and 0-16mm aggregate is limited to 8-10%.

A section through the GU Tiejbau drilling and jetting system. 1) Connection piece. 2) Internal drillsteel drive. 3) External drillsteel drive. 4)Backstream holes. 5) External drillsteel. 6) Internal drillsteel. 7) Ring crown. 8) Grout. 9) Stopvalve. 10) Drillhammer.

In the smaller single track profiles of the Tl Zugwald Tunnel, dry shotcreting is being applied using an Aliva 260 unit. Here the aggregate size is 0 to 8mm and 3-5% of Sigunit 162 liquid accelerator is added with the water supply at the nozzle. Powered Sikafume TU, added at the mixing plant, is said to provide a tighter, better quality shotcrete.

Work on both contracts started in April 1991 and T2 is expected to be completed by mid-1994.

Horizontal jet-piling on contract T1a is expected to be finished in December 1992. Following the horizontal jet-piling work, tunnelling will continue for a further 90 m into the rock where an assembly and launch chamber is to be excavated ready for arrival of the Wirth TBM in mid-1993.

Although 17 horizontal jet-piling cycles were envisaged for T1a, another was needed before reaching the rock.

Jet-piling and excavation of the T1b portal is expected to start in Jan-Feb 1993 and finish by Dec 1993.

On T2, nearly 835m of the full 2.15km length was complete to November 1992. This heading will also finish in about mid-1994 with the excavation of a TBM launch chamber.

When opened in 2000, the Vereinalinie is sure to attract a huge influx of both commercial and private traffic. At present the most direct route from the north into the Engadin Valley is via the mountain road over the Fluela Pass which is subject to frequent closure during the winter. A second alternative is the longer route through the Albula rail tunnel which adds another 2hr to the journey. Once open, the Vereinalinie will cut the current 295 min train journey from Zurich to Scuol-Tarasp, for example, to just 160 min.

With careful and efficient handling of this traffic, the character and environment of the famous village of Klosters can be preserved while accommodating important transportation facilities for the future.