GFRP Concrete Reinforcement

Reinforcement composed of fiberglass bars and brackets, capable of replacing traditional steel cages, both temporarily and permanently. In tunnel construction using TBMs, the unique mechanical and physical characteristics of these products (high tensile strength and low shear strength) allow the concrete reinforcement of temporary diaphragm walls to be maintained while maintaining high performance, without creating obstacles for the cutterhead.

The diaphragm wall can be penetrated quickly, without changing equipment, and is completely safe. The corrosion and chemical resistance of FRP profiles increases their durability, making them ideal for permanent structures built in aggressive conditions.

The reinforcing bar is made up of a multitude of continuous fibers, oriented in the direction of the load, bonded by a polyester or vinyl ester resin matrix. The surface is characterized by a ribbing that increases its resistance to pulling out. GFRP brackets are made by bending a bundle of continuous fibers impregnated with resin and then heat-cured. This process allows for a high fiber content and nearly parallel fiber alignment, thus providing high strength.
  • Corrosion resistant
  • High tensile strength
  • Lightness
  • Ease of cutting
  • Piles and diaphragms
  • Foundation
  • Soft-eye
  • Maritime works
  • Structures subject to corrosion
  • Design
  • Assembling

No preparatory work is required for TBM breakthrough

No preparatory work is required for TBM breakthrough. TBMs have been used for tunnel construction for several decades. Depending on the local situation, the TBM can be positioned at the beginning or end of its path, for example, in a precut in open ground, or lowered into an excavation shaft up to the level of the tunnel. The latter technique is used primarily in congested urban areas. A few years ago, starting and arriving at a TBM in an excavation shaft required measures such as breaking through the reinforced concrete walls of the shaft. This preparatory work was time-consuming and expensive. In recent years, however, the use of soft-eyes in these areas has become increasingly popular. A soft-eye can be made, for example, with diaphragm walls or bored piles reinforced with fiberglass-reinforced plastic (GFRP) bars instead of steel. Furthermore, a tunnel face anchored with GFRP anchors will not impede the passage of the TBM head. The use of GFRP products for tunnel construction is now commonly used in infrastructure and underground works.

No obstruction of the TBM cutter head passing through the diaphragm

Soft-Eyes typically consist of bored piles or diaphragm walls, locally reinforced with GFRP bars. The sections below and above the tunnel are reinforced conventionally. Depending on the designer and contractor’s preferences, solid rectangular sections are constructed with GFRP bars, and the fiber reinforcement more closely follows the tunnel cross-section, resulting in a rectangular arrangement of the GFRP connections, or a circular cross-section. Both options have their advantages. A rectangular arrangement saves time during cage design and assembly by more closely following the tunnel cross-section, thus reducing material costs for the GFRP bars. A compromise is often applied, in which the vertical bars span a rectangular cross-section, while the shear connections follow the circular arrangement. Experience shows that this approach reduces GFRP material costs by less than 5%, while maintaining detailed design and managing cage assembly efficiently. Constructing the corresponding reinforcing cages using GFRP bars on site requires the same work procedures as a similar steel cage. The required bars are custom-made and delivered to the site, even assembled. The bars are secured together with tying wire, plastic ties, or similar products. U-bolts are used to secure the bars together to ensure continuous strength. This is a connection between the vertical GFRP bars and the corresponding steel bars, which must support the dead load of the reinforcing cage during the lifting and application process. Welding, as is commonly done with steel reinforcing bars, is not possible with GFRP bars.