Spain is already an arid part of the world, and in early 2008 it experienced its worst drought in 60 years, with the Catalonia region in the northeast one of the hardest hit areas. Up until September 2008 this region had experienced almost no rainfall for 18 months and reservoirs reached only 20 percent of capacity, posing serious threats to its agriculture.

The 84km Segarra – Garrigues canal, of which 42.5km is currently being constructed is planned to both help save water and increase productivity in the region. The canal will service a region of approximately 70,150 hectares and 17,000 farmers and stretch from the Rialb dam in the west to the Albages catchment area in the east. The canal which will have a capacity of 35m3/sec will be made up of a combination of open waterway, aqueducts and tunnels.

Section II of this project was awarded to a Joint Venture of Acciona Infastructures and M. y J. Gruas. The US$39.5M contract is comprised of the 4.8m diameter Oliola water tunnel of which 4,470m was to be a bored tunnel, 521m cut and cover and the remaining 3,000m an open canal.

After the awarding of the contract, the Joint Venture proposed a redesign of the tunnel alignment which increased the length of the tunnel from 4,470m to 7,100m thus negating the need for the open canal. This re-design allowed for the full optimisation of the TBM drive and in turn significantly reduced the environmental impact on the area which would have resulted from constructing an open canal.

Excavation and primary support

The geology of the tunnel alignment is predominantly sedimentary rock of limestone, greystones and gypsum. Sandstones and limestones account for approximately 4.7km of the bore length with an average RMR 55-60 and 2.3km of massive gypsum with an expected RMR 45-50.

The preconstruction investigation included boreholes approximately every 260m along the proposed tunnel’s alignment.

Excavation commenced in May 2008 using a refurbished 5.4m diameter Robbins 182-129-4 TBM owned by Acciona Infraestructuras.

Three types of ground support are specified dependent on ground conditions. These consist of:

• S1 – 4 rock bolts and 50mm shotcrete (upper part) every 1.2m

• S2 – 7 rock bolts and 100mm shotcrete (upper part) every 1.2m

• S3 – Steel arches (THN 16.5kg/m) every 1.2m and 100mm shotcrete all around (except segment)

All shotcrete is macro fibre reinforced with Barchip Shogun synthetic structural fibre. Full site trials were undertaken and the performance criterion of 700 joules in an EFNARC1 plate test achieved with a dosage of 5kg/m3.

Shotcrete is batched from an onsite batching plant, which will also supply the concrete for the final lining.

As excavation advances a specially designed precast invert segment is placed behind the TBM. The segment is part of the tunnel’s final lining and is designed, in terms of loading and configuration, to take the excavation equipment as well as the travelling formwork. The segment is reinforced with a steel cage which has a steel concentration of either 50kg/m3 or 100kg/m3 depending on the ground conditions. Macro-synthetic fibre is used in conjunction with both cage configurations to impart impact and abrasion resistance. Unlike the steel cage, no concrete cover is required for the synthetic fibre, so the full depth of the segment can be reinforced, ensuring that any crack propagation is significantly reduced; critical where water may cause corrosion over the life of the asset. The segments are manufactured at a nearby casting yard and transported to site.

Secondary lining

Both the methodology and equipment used for the cast in-situ tunnel lining is critical to ensure that project costs and time remain within the schedule. To achieve this, the secondary lining is to commence while excavation of the tunnel continues. The obvious disadvantage of only one entry and exit for all materials and muck and the coordination of two major activities make for a challenging environment.

Within one 24-hour cycle the activities of muck removal in order to continue excavation and the setting, pouring and stripping of the formwork are bound to occur simultaneously and cause a bottleneck in the running tunnel.

To overcome this, a specially designed switch system allows for 100m of track to become, in effect, a single track through the centre of the formwork.

This allows the outer rails to carry the formwork. The formwork’s frame allows full and empty muck wagons to pass through its centre. Wagons can be held either side of this single track if required and then dispatched through the formwork when allowed. This process becomes even more important as the distance between the formwork and the portal increases.

The secondary lining has a thickness of 300mm in thickness and the formwork consists of two 15m lengths, each capable of being moved and positioned individually using the outer rails.

Concrete is batched from the onsite batching plant and transported using cigar concrete mixes to be delivered to the concrete pump near the formwork. Originally the secondary lining was designed with two layers of wire welded fabric (150mm x 150mm x 8mm) which has been replaced by 5kgs/m3 Barchip Shogun synthetic fibre. The WWF was specified for crack propagation control purposes. Replacing it with macro fibre significantly reduces cycle times due to the lack of installation time associated with conventional WWF reinforcement. Additionally, the use of fibre increases safety by eliminating what could be a difficult task. Unlike the WWF, the fibre reinforces the full depth of the concrete, thereby enabling optimum resistant to crack propagation that might occur throughout the concrete structure.

The concrete is Class 30/35 using sulphate resistant cement.

The relatively high slump concrete is able to flow behind the formwork with minimal vibration. Curing times for the in-situ concrete will depend on the distance from the portal to the face, internal and external air temperatures and large seasonal temperature variations. These factors will have a significant bearing on stripping times and therefore cycle times. The expectation is for 30 linear metres per day to be poured allowing 10 – 14 hours for setting, pouring, curing and stripping the form fol-lowed by 8 – 10 hours for the concrete pour.

The formwork leaves an aesthetically pleasing finish which is both smooth and fibre free.


The proposed completion of the Segarra – Garrigues canal by 2012 will add much needed irrigation infrastructure to the drought affected region and so ensure the best possible availability of arable land for agriculture. T&T

Macro synthetic fibre reinforcement

Both the primary and secondary linings and the precast segments use a macro-synthetic fibre, Barchip Shogun, as reinforcement in place of steel fibre and/or WWF.
Macro-synthetic fibres have been used in the con-struction industry for 15 – 20 years[2]. However, developments in the last 10 years have enabled their performance to exceed that of steel fibre reinforced concrete on a performance versus cost basis. There are now many examples of major tunnelling projects around the world using macro synthetic fibre for the reinforcing of primary and secondary support[3].
Andrew Ridout from Elasto-Plastic Concrete (Europe) Ltd explains “There has been a significant move to macro-synthetic fibre in recent years; principally due to the fact that it is a more cost effective, non-corrosive reinforcement, lighter and safer to handle, greatly reduced labour requirement for installation and with reduced wear on pumping equipment. Additionally, there is a growing amount of evidence showing that macro-synthetic fibre outperforms steel fibre over the longer term[4]. Durability is also a significant issue for steel fibres. Where concrete does crack, research has shown that steel fibre reinforced concrete loses 45% of its per-formance within one year at crack widths over 0.1mm[5]. Macro-synthetic fibre can offer significant long-term durability giving the owner a more durable asset”.
Barchip Shogun has been specially developed for shotcrete and concrete reinforcement and is certified to EN BS 14889-26 a mandatory requirement for synthetic fibre in some countries. Barchip Shogun is also fully CE mark registered, in line with mandatory requirements from the European Construction Products Directive, for fibres to be used in concrete.

The formwork for the final lining