Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3
G.M. Volkmann; DYWIDAG-Systems International GmbH, Pasching, Austria
B. Moritz & K.M.; Schneider Austrian Federal Railways, Graz, Austria

The Koralm Tunnel (KAT), part of the Austrian railway system, forms an important link of the Trans European Railway Network (TEN). Upon completion, this twin-tube tunnel with a length of 32.9 km will be one of the longest railway tunnels worldwide. The project is divided into three main construction lots. Lot KAT 1 was constructed by using the principles of the New Austrian Tunnelling Method (NATM), while Lot KAT 2 the central part under the Koralpe is mainly driven with two double shield tunnel boring machines (TBM). Lot KAT 3, which is already partly excavated as exploratory tunnels, is constructed both by the New Austrian Tunneling Method (NATM) and one Tunnel Boring Machine (TBM) depending on the tunnel section.

After a project overview this paper focuses on a shallow section of the tunnel in tertiary sediments excavated with NATM, where a pipe umbrella system (AT-114, L = 15 m) with a newly developed squeezed connection type was successfully applied. Main reasons for the selection of this new connection type were the optimization of the pipe umbrella tubes with respect to structural capacity and weight. In addition to these technical advantages, time savings and safety gains during pipe umbrella installation are important points. All technical features and additional advantages will be explained with this site example.


Starting in 1990 the European Union adopted the Trans-European Transport Network (TEN-T), which consists of a planned set of road, rail, air and water transport networks. The Trans-European conventional rail network is part of the TEN-T and consists of nine core network corridors. The Baltic-Adriatic Corridor is one of these. It starts in Poland at the Baltic Sea, leading to the south via Vienna (Austria) to Ravenna (Italy). In Austria the Semmering Base Tunnel and the Koralm Tunnel are main parts of this corridor.

The Baltic-Adriatic Corridor is among the most important cross-Alpine lines in Europe with about 24 million tons of freight per year. This high-capacity railway connection from the Baltic Sea to the Adriatic (Figure 1) is therefore a necessary precondition for further economic development along the corridor. On its way from the Baltic Sea to the Adriatic Sea the rail corridor crosses numerous important traffic routes. It therefore provides an efficient transport chain to other important economic regions in Europe. This close integration makes the Baltic-Adriatic Corridor a backbone of the Central European transport infrastructure.

The Koralm Railway connects the Austrian cities Graz (Austrian State Styria) and Klagenfurt (Austrian State Carinthia) with a total length of 127 kilometers and maximum speed of 250km/h. An important link on this alignment is the Koralm Tunnel, which is constructed as base tunnel under the Koralpe mountain range. After completion the Koralm Tunnel will consist of two single-track railway tunnels with a length of 32.9 km.

At the western portal (Carinthia) the tunnel alignment is situated in sandstone and siltstone formations. These formations needed to be additionally supported by pre-support measures so a pipe umbrella system was installed prior to excavation to ensure stable and safe excavation conditions. This pipe umbrella system was equipped with a newly developed coupling system that increases the performance as well as safety during installation processes.

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Figure 1: Location of the Baltic-Adriatic Corridor in Europe (I-Net, 2015)

2.Koralm Tunnel

The Koralm railway (Austria) represents an important section of the Baltic-Adriatic axis (Harer & Schneider, 2013) and includes more than 15 new stations, more than 100 bridges and allows a max. speed of 250 km/h; its new capacity creates significantly improved conditions for passenger and freight transport by rail. Core piece of this railway line is the Koralm tunnel with a total length of 32.9 km (Figure 2), which upon completion, will be one of the longest railway tunnels worldwide. The project is divided into three contract sections (KAT 1, KAT 2 and KAT 3). The tunnel system consists of two single-track tunnels that are connected every 500 m by cross-passages. In the middle of the tunnel is an emergency stopping area. In addition to a multi-phase exploration program using engineering and hydrogeological mapping as well as extensive subsurface exploration, an exploratory tunnel system with a total length of about 10 km, consisting of the sections near Leibenfeld, Mitterpichling and Paierdorf, was carried out to assist the preparation for construction tenders starting in 2003.

The area of the Koralm tunnel project is mainly located in the Koralpe crystalline complex (Figure 3), with a tectonic boundary to the tertiary sediments of the Lavanttal Basin in the west and plunges under the likewise tertiary deposits of the Western Styrian Basin in the east. The rock units mentioned before are covered over wide areas by quaternary sediments. The Koralpe massif is composed of various gneiss subtypes, schists and (to a lesser degree) silicate marbles. The overburden varies from 5 m at the portal area to approximately 1200 m in the central section of the advance.

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Figure 2: Project overview of the Koralm tunnel – Schematic layout showing the shafts, running tunnels, cross-passages and emergency stopping area as well as the sub-division of the main contracts KAT 1, KAT 2 and KAT 3 (Source: ÖBB)

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Figure 3: Geological longitudinal profile through the Koralm tunnel (simplified) showing the main contract sections KAT 1, KAT 2 and KAT 3 and the section with the exploration tunnels (EKT) at Leibenfeld, Paierdorf and Mitterpichling (Moritz et al. 2011)

2.1 Koralm Tunnel Lot 1 (KAT 1)

Lot KAT 1 was constructed by using the principles of the New Austrian Tunnelling Method (NATM), due to the limitations of establishing a large construction site near the portal and the short tunnel length of about 2.3 km. This lot is the shortest of the three tunnel sections – started in May 2010 and has already been finished.

2.2 Koralm Tunnel Lot 2 (KAT 2)

In January 2011, construction commenced on section KAT 2 with up to 18 km, the longest section of the Koralm tunnel. Besides NATM sections it is mainly driven with two double shield tunnel boring machines (TBM). The construction started at the Leibenfeld exploratory shaft (EKS) because of the available construction site area and the relatively favorable infrastructure for access. After the construction of an additional construction shaft the components of the two double shield TBMs were lifted into the tunnel and assembled in two installation caverns in the crystalline rock, where continuous mechanical tunneling is used exclusively. The remaining tunnel sections in this construction lot still comprise more than 5 km and are located both in crystalline and in tertiary rock sequences. NATM is applied likewise for the cross passages, the 900 m long rescue area at the emergency stop and to enlarge the existing 1.7 km long Leibenfeld exploratory tunnel in the south tube.

2.3 Koralm Tunnel Lot 3 (KAT 3)

In January 2014, construction works started on lot KAT 3 having a length of about 13 km. This lot is already partly excavated as exploratory tunnels, and it is constructed both by NATM and a TBM. The tertiary formations and the main Lavanttal fault zone in the north tube are being excavated by a shield machine with earth pressure components (Moritz et al. 2011). After entering the crystalline bedrock the EPB machine will be converted to a single shield TBM for the remaining advance in hard rock to the boundary with section KAT 2. In the following a shallow tunnel section near the western portal in tertiary sediments excavated with NATM is highlighted, where a pipe umbrella system with a newly developed squeezed connection type was successfully applied.

3.Pre-support System

At the western portal in Carinthia (Austria) the northern tube is excavated under the protection of a consecutively installed, 15 m long pipe umbrella support. This type of pre-support system is also called “canopy tube system”, “umbrella arch method”, or “long forepoling method” worldwide. This section is situated at shallow overburden in claystone, sandstones and several fault zones. The AT-114 pipe umbrella system was applied, which has an outer steel tube diameter of 114.3 mm with a tube wall thickness of 6.3 mm. When using this system the supporting tubes are installed piecewise with conventional drilling machinery (in this case Atlas Copco E2) and a squeezed connection was chosen for connecting the single tube pieces. The main reason for the selection of this new connection type was that tube connections are the weakest link in a pipe umbrella system (Volkmann & Schubert, 2008), the ultimate moment in the coupling section was therefore defined to be higher than the elastic moment of the regular pipe. Further reasons were the optimization of the pipe umbrella tubes with regards to cross-section and weight, as well as time savings and safety gains during pipe umbrella installation.

3.1 The AT – Pipe Umbrella System

The AT – Pipe Umbrella System was originally developed as pre-support in sequential tunneling to create a supporting umbrella in difficult ground conditions (UCS < 1 MPa). Here, the pipe umbrella support is applied due to the risk of ground shear failures around the heading and to reduce ground subsidence due to the excavation induced stress transfer processes. These points gain in importance because of existing housing and infrastructure on the surface. One precondition in the development of the AT – Pipe Umbrella system was that installation should be possible by normal tunnel crew with machinery available on site. This feature has enabled pipe umbrellas, which at that time were regarded as special measures, to be used more often as a regular support measure (Volkmann et al. 2011).

The AT – Pipe Umbrella System essentially consist of the following components (Plate 1):

  • starter unit with a single-use drill bit,
  • extension tubes,
  • end tube (without injection holes and valves).

The drill bit adapter and the drilling rods, which are necessary for force transfer during installation, can be withdrawn after drilling and be reused. The casing pipes remain in the ground after drilling and are ready for use after installation. The usual drilling depths with this system are up to 18 m, although the drilling of holes up to 30 m is possible. The maximum achievable depth does, however, always depend on the properties of the surrounding rock. For example, very abrasive rock can increase the wear on the drill bit and reduce the practical drilling depth.

3.2 Installation Procedure

The pipes are installed prior to excavation and should be located at the outer perimeter of the following excavation profile. Its installation position must consider emerging pre-settlements due to the excavation process. Thus, it is important that the starting point of the drilling as well as its direction is as exact as possible. Therefore, the starting point as well as the orientation of the drill boom is usually determined by a theodolite before installation.

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Plate 1: System components of the AT – Pipe Umbrella System

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Plate 2: AT – Pipe Umbrella System ready for the installation

When using the AT – Pipe Umbrella System, one umbrella pipe consists of single pipe pieces that have a common length of 3 m. While rigging the boom, the first pipe piece (referred to as “starter unit” including the drill bit), and the drill rod are already placed on the boom. Consequently, the boom is brought into the correct drilling position, and the first pipe piece is installed (Plate 2). After installing this first pipe piece, the boom remains in position. The shank adapter is disconnected from the drill rod and moved to a backward position. The next pipe piece including another drill rod can be placed either manually or automatically on the drill arm. A basket is usually used to carry the pipes when the drill arm is at a high position. As soon as pipe and drill rod are placed on the drill arm, the drill rod as well as the extension tube are connected to the already installed parts so the next pipe piece is ready for the drilling process. This process is repeated until the installed pipe has reached its designed length. If the drill jumbo is equipped with two booms, both can of course be used parallel to save time.

3.3 Squeezed Connection

Different connection types are available on the market these days.

Very common is a standard threaded connection. Standard threaded connections are generally not well suited for connecting pipe umbrella pipes. By mechanically removing a certain portion of the steel tube for a thread (Plate 3a), the effective cross-section is reduced. This fact drastically decreases the load-bearing capacity and stiffness in the connection area (Table 1). At most standard pipe umbrella dimensions the maximum elastic moment (design value) of the regular pipe is at the level of the ultimate moment (failure) of the standard threaded connection at laboratory conditions. Hence, to achieve certain given pipe umbrella design parameters, an over-dimensioning of the un-weakened pipe section is a practical way – though highly inefficient – to overcome this limitation.

As a result of dangerous problems when using standard threaded connections during construction, the so called nipple coupling was developed. Nipple connections consist of threaded connection fittings, which are pressed and welded into the ends of standard pipes (Plate 3b). This connection type provides an elastic design load as well as stiffness properties equal to an un-weakened pipe (Table 1). By using this connection type, default design parameters are constant over the entire length of installed, connected pipe umbrella drills.

The latest development in the field of pipe connections is the squeezed connection, this connection type results from the attempt to provide a tough and easy-to-connect alternative to conventional threaded systems (Plate 4a). By means of the squeezed connection, non-threaded pipe ends are mechanically connected in terms of force-fitted squeezing using a boom-mounted press (Plate 4b).

In detail the pipes are delivered to the side with one reduced end that fits into the other unedited end. So after feeding an extension tube with its drill steel to the boom the drill steel is conventionally screwed together and the smaller pipe end is simply moved into the regular pipe end at the squeezing console position. Then the squeezing unit on the front end of the boom is activated by remote control by the driller and the pipes are squeezed together by using the hydraulic pressure of the drilling machine after a 2 seconds long squeezing process. This squeezing process creates a force-fit connection. So there are on one hand fewer rotating parts, which increases safety and simplifies handling and on the other hand there is no thread, which increases the system security and decreases the coupling time for the installation process.

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Plate 3: a) standard threaded connection and b) nipple coupling

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Table 1: Examples of elastic design values for 114.3 x 6.3 pipes with different connection types. (Volkmann, 2014)

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Plate 4: a) squeezed connection and b) squeezing console mounted on a drill boom

This connection type features a higher elastic design load in the connection area compared to standard threaded connections as well as a slight reduction in stiffness (Table 1) compared to the regular pipe (Volkmann, 2014). The ultimate moment in the connection area is at least 50 percent higher than the maximum elastic moment of regular pipes so at correctly designed support cases a failure can be excluded at the coupling area. Besides simple design and handling, this connection type provides operational benefits due to decreased time intervals required for pipe connection. Similar to the nipple connections the squeezed connections also reduce the inner cross-section of the pipe umbrella pipes so an installation in combination with sacrificial, single-face drill bits is required.

3.4 Performance at the Koralm tunnel

The day before pipe umbrella drilling, the squeezing units were mounted on the drill booms and connected to the drill rigs hydraulic system. The entire process needed about 5 hours including a performance test of the squeezing units and their hydraulic connections prior to mounting the completed system on the drill boom (Plate 5). Further optimization led to changing times between 3 and 4 hours.

The drilling works started in the northern tube of the KAT 3 in the night from April 2nd to 3rd 2014. At the beginning the workers were introduced to the system and were instructed about the processes and the correct sequence for a successful installation routine. For this reason a 15 m long pipe was installed with one drill boom and then another pipe with the other drill boom. These installation processes were finished after 40 minutes and 41 minutes after the de-installation of the drill steel respectively. Then both drill booms were used parallel and the basket in the middle were used to feed the extension tubes with the drill steel onto both drill booms (Plate 6). Approximately 24 hours later the first pipe umbrella were installed with 34 pieces of 15 meter long pipes.

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Plate 5: Both squeezing units mounted on the drill booms – drilling machinery ready for the installation

Application of the Pipe Umbrella Support System at the Koralm Tunnel KAT 3

Plate 6: Pipe umbrella installation with two squeezing units mounted onto the drill booms during drilling and a feeding basket in the middle.

With further system experience it was possible to typically install one pipe umbrella consisting of 34 pieces 15 meter long pipes in between 18 and 20 hours. So, the establishment of fast and safe connections for pipe umbrella pipes was proven in the course of Lot KAT 3 whilst time consumption for the working step “tube connection” could be reduced by more than 50% compared to typical installation times with threaded couplings. The finalizing grouting process was performed as a onetime grouting process from the mouth of the installed tubes with a pressure value as stop criteria. Typically the inside of the pipes is filled first, and then the annular gap between steel pipe and ground is filled and finally existing open joints or access able pores of the ground. Due to the differing grouting volume, which is typical for shallow tunnel alignments, the grouting times varied as well so the grouting process needed about 12 hours as guidance value at this site.

3.5 Main advantages of the squeezed connection

  • Installation with conventional drill jumbos equipped with a squeezing console
  • Execution of pipe umbrella drilling with on-site personnel
  • Simple and robust system components
  • Higher maximum elastic moment compared to standard threaded connections
  • Clearly higher maximum ultimate load compared to the design load of normal pipes
  • Fewer moving / rotating parts during elongation
  • Easy handling
  • No risk for damaging threads due to handling on site
  • No risk for jamming threads during coupling processes
  • Dirt insensitive
  • Quick coupling times
  • Faster construction of a pipe umbrella support system


The newly developed squeezed connection for the AT – Pipe Umbrella System was introduced at the Koralm tunnel, one of the longest railway tunnels worldwide. With the successful application at this project it was shown that the developed connection type and auxiliary equipment can improve both the structural behavior and construction performance of pipe umbrella support systems, in particular ensuring a quicker installation, higher safety for the involved workforce and last but not least a high cost efficiency for the installed steel tube sections.

2 replies
  1. vivek pratap says:

    if you are a manufacturer of umbrella pipe roofing then provide your contact no. I have some requirements for pipe roofings.

    • Jeff says:

      Hi Vivek,

      Please send me your requirement for roofing pipes, we have all the materials made in Asia for tunnelling & underground mine support. Cheers.

      BuildPac Ltd.


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