Tunnel construction projects are subject to a very high level of complexity. Variations in soil conditions, different rock types, and high water pressure are factors that place high demands on the materials and machines used.

In order to meet the customer’s needs at all times while offering the best possible sealing solutions, companies such as industrial supplier Datwyler are continuously advancing the development of their products. Datwyler’s Performance Corner was first used in 2015. Customer requirements for the corner design in segmental tunnel construction have increased enormously in recent years, both in terms of material and components as well as the degree of individualization and costs involved.

In Saint Joseph, Missouri, at Blacksnake Creek, a tunnel construction project is currently underway which will significantly improve the quality of the drinking water.

Currently, Blacksnake Creek and stormwater runoff from streets, roofs, and other areas is piped along with wastewater in a large, 100-year-old pipe known as the Blacksnake Creek Combined Sewer.

The existing pipe is not large enough to carry all the stormwater runoff and sewage to the Water Protection Facility (wastewater treatment plant) and it overflows to the Missouri River after most rain storms. The new Blacksnake Creek tunnel project uses a combination of new pipes, tunnels, stream channels, and other methods to convey the stormwater flow directly to the River.

This will reduce the quantity of water in the existing sewer during storms and the quantity of combined stormwater and wastewater that overflows to the river.

Since the tunnel construction presents special challenges here, particularly in terms of geographical location, high water pressure and soil conditions, the design was adjusted to precisely these requirements and customer-specific solutions are demanded.

Datwyler’s Performance Corner is being used for the newly constructed tunnel pipe. By using this system, the goal is to significantly reduce the number of overflows and avoid waste water running directly into the river. The pipe will catch the rainwater directly, separate it from the sewage system, and redirect it right into the Missouri River.

Tunnel Characteristics

The Blacksnake Creek tunnel project includes the repair of concrete and brick cracks in the Blacksnake Combined Sewer pipeline, the removal of encrustation and deposits at select lateral connection locations, the surface repair of plugged lateral connections and of existing missing brick junctions as well as the construction of the new tunnel.

The project comprises a 2.32km-long tunnel with 2.3m inner diameter of segmental concrete lining and an around 38m-long crossing of the railroad with 2.3m-diameter auger boring.

Altogether, five shafts including launch and target shaft will be built. The construction includes also a 11.3m-diameter baffle drop shaft, an around 15m reinforced concrete box culvert which is close to the surface, a ventilation shaft with 61cm diameter, more than 51m open cut steel pipe installation with 2.3m diameter, a more than 38m-long jacked steel pipe with 2.3m diameter, an energy dissipation structure, site restoration and further various job site works.

That means that the new project uses a combination of new pipes, tunnels, stream channels and other methods to separate wastewater and stormwater and to convey the rainwater flow directly to the Missouri River, which will reduce the quantity of water in the existing sewer during storms and the quantity of combined storm- and wastewater that overflows to the river.

The TBM is delivered by the Canadian- Chinese Lovsuns Tunneling Canada. It is the first China-Built TBM of the North American market. The double shield rock TBM has a diameter of 3.3m and will dig the tunnel for the USD 27M Blacksnake Creek Stormwater Separation Improvement Project.

The machine is designed and engineered by the Canadian Lovsuns team and built by its parent company Liaoning Censcience Industry Co. (LNSS) at its Liaoyang facilities in China.

The TBM is equipped with a main drive power cutterhead with two electric water cooled motors with 300kW each. The machine is prepared to operate in double shield mode with a primary conveyor belt and can be converted to operate in an EPB environment under pressure up to 4 bar. With a view on the soil profile, mixed geology is expected with soft ground to hard rock as well as some mixed face conditions. Due to the expected ground conditions, the following soil and rock engineering units were classified:

  • Soil Engineering Unit 1 (Coarse-Grained Soils): Fine to coarse sand and gravel, silty sand and sub-angular to angular rock fragments in varying proportions with less than 50 per cent passing the 200mm-sieve.
  • Soil Engineering Unit 2 (Fine-Grained Soils): Silts and clays in varying proportions with more than 50 per cent passing the 200mm-sieve.
  • Rock Engineering Unit 1: Designed as shale with Iatan limestone formation present in seams. Unconfined Compressive Strength 2,000 PSI.

The tunnel will transit soft ground and rock along each end of the tunnel alignment and mixed face conditions shall be anticipated for reaches along these subsurface transitions with the expected proportions of 23 per cent of soil engineering units 1 and 2, 63 per cent of the rock engineering unit and 14 per cent of mixed ground.

Gasket Requirements

The properties of the Performance Corner are designed to ensure that the tunnel is leak-tight throughout the various geologies, the soil conditions and to withstand the water pressure. It is critical here that the right adjustment is made for the corner geometry which is derived from the specific segment design. This guarantees the perfect fit of the gasket on the segment. The custom fit results from the combination of the right cutting angle and the right adjustments to the opening and torsion angles, which are taken from the ring design for the segments. The adjusted angle of torsion prevents the corner from tilting and the formation of an additional offset to the adjacent gaskets which could result in possible leaks.

One deciding feature of the corner is whether it possesses very high flexibility. This means reviewing very closely the specifications for each project with focus to the required tightness of the gasket and its spalling behavior. The resulting corner geometry is determined based on this. This includes the exact evaluation of the position of the gasket groove to the outer edge of the segment. In doing so, a decision is made on which chamfer angle to choose at the end of the section with resulting injected volumes, and to what extent the opening angle and/or torsion angle need to be adjusted. The section can be cut at 30°, 50°, or 90° in order to control the injected volumes.

In the case of the new tunnel for the Blacksnake Creek project, there is a 50° cutting angle in accordance with the specified corner geometry. The torsion angle had to be adjusted to 8° and the opening angle to 71° and 109°.

The manufacturing process for the Performance Corner allows for variable corner length and varying degrees of elasticity. The opening angle of the corner connection can be adjusted individually, preventing deformation of the gasket corner in the installed position. The result is custom-fit gasket frame for the corresponding segment design angles.

The injection molding process is used for manufacturing the Performance Corner, which allows significantly higher retaining forces to be generated in the corner area. These retaining forces within the gasket corner are absolutely necessary so that the high compression force between the concrete segments, that occurs while erecting them, does not result in tearing or moving the corner during the installation process.

The injection molding process starts with warming up the rubber compound in an extruder unit to 80-100°C. This plasticized EPDM compound will be fed via channels into the heated corner mold.

There the mixture is cured under high pressure and at high temperature. Thus the individual gasket pieces are connected to a complete and closed gasket frame.

These individually adjusted corners provide the necessary seal in the tunnel later on. In addition, only as much material is used as is actually needed for the relevant corner.

The use of a film butt joint, already well-known in the market for its use in manufacturing O-rings for concrete pipes and soft corners, is not suitable, because the required retaining force cannot be created due to the lack of volume.

The risk of potential leaks cannot be ruled out. In a worst case scenario, the gasket frame can tear when installing segments with film butt joints due to the low retaining force in the connection.

The Performance Corner consists of EPDM, which is also the basic material of the extruded gasket. EPDM has demonstrated excellent characteristics: it allows for a good connection to the injection corner, which guarantees the required tear resistance for the frame corner during the assembly of the gasket frames and the installation of the segments.

With regard to the long-term relaxation, EPDM ensures a gasket system that is leak-tight throughout its entire service life and has very good ozone, aging, and weather resistance.

For special requirements, for example soil contaminated with hydrocarbons, the Performance Center can also be made of chloroprene rubber.

Materials with an antibacterial effect can also be used in the construction of tunnels for drinking water and waste water drainage.