Tunnel boring machines (TBMs) are very advanced equipment used as an alternative to drilling and blasting through rock and “conventional mechanical excavation” in soft ground. Mechanized tunneling has become more important with the rapid growth and expansion of underground construction in recent years. Sika provides a wide range of products designed specifically for use with a variety of TBMs, throughout the whole tunnel excavation and construction process.

Advantages of TBMs for Tunneling

Tunnel boring machine in tunnel construction

Tunnel boring machines reduce disturbance in the excavation area, which makes them ideal for use in heavily urbanized areas. They also produce a smooth tunnel wall that reduces the cost of the final lining. The total excavation time of long tunnels is significantly reduced with TBMs compared to conventional excavation methods.

A variety of TBMs have been introduced during the past decades - these include the Slurry and the Earth Pressure Balance (EPB) for soft ground, the Grippers for hard rock and the Single Shield TBM for tunneling through rock and other stable, non-groundwater-bearing grounds.  A smaller form of TBM called a microtunnel boring machine is used extensively for underground infrastructure tunneling, since it allows fast excavation without the need to disturb the surface.

Sika engineer standing next to tunnel boring machine in tunnel construction

Solutions for Tunnel Boring Machines

Watch the video below to learn about Sika's systems and products for TBM
Browse and click on the illustration below to see Sika's solutions for tunnel boring machines

1. Foams, Polymers and Additives

The injection of foams, polymers and other additives into the tunnel face can significantly modify the characteristics of soft ground, including its plasticity, texture and permeability, in order to make the work and progress of the TBM easier and faster. The selection of the best type and quantity of material for this ground conditioning is dependent on the specific geology and the equipment available with the TBM.

Sika Solutions for Foams, Polymers and Additives

As not all ground is ideal for excavation by TBMs, the use of ground conditioning
foams can allow EPB TBMs to achieve better advance rates, even in heterogeneous
grounds containing gravel, sand and water, or under other critical geological conditions.

Foaming agents from the range Sika® Stabilizer TBM are liquid conditioning foaming agents which have been formulated to be used with earth pressure balance machines (EPB) for modifying the properties of the excavated soil.

To fulfill specific increasing environmental expectations and try to reduce the ecological impact of soil conditioned and excavated by the TBM after its disposal, Sika is promoting an alternative range of foaming agents from the Sika® Stabilizer TBM family, which has an adapted formulation without glycol. Considering the tunnel geology and job site conditions, the use of these products may reflect a more positive environmental impact of foaming agents.



Typical Sika polymer applications in the TBM excavation process are for:

  • Reduction of “stickiness”
  • Reduction of adhesion to metal surfaces
  • Reduced segregation in the mixing chamber
  • Drying out the ground

Water absorbing polymers, viscosity modifiers or stabilizers for foams from the range Sika® Stabilizer TBM are specially formulated for the use in TBM tunneling.


Although foams are the most widely used materials, they are not the only type of products that can be considered. Additional products may be used to achieve different results during TBM excavation and progress.

The range Sika® Stabilizer TBM also counts with special liquid products such as cutter cleaners, defoaming agents or friction reducers.

Illustration rendering of TBM tunnel Sika foam polymers additives

2. Main Drive Sealant

One of the most important and expensive components of the TBM is probably the main bearing. In order to keep this in good condition, it has to be properly sealed and lubricated. Experience has shown that most failures of TBM main bearings are related to a loss of lubricant, or to the entry of contaminants from outside. For this reason, it is absolutely essential to have the system working with reliable products. Sika® Stabilizer TBM H protects the main bearing preventing it from contact with water, mud, dust and foam contamination.

Sika Solution for Main Drive Sealant
Main Drive Sealant

Sika sealants have been specifically designed and developed with a hydrocarbon-free, vegetable oil based formulation, which avoids any residual spoil contamination and are also resistant to water and ground pressure.

Sika® Stabilizer-2001 TBM is a bearing sealant for TBMs with a strong grab and adhesion to metal surfaces, with extremely high wash-off resistance. It also has good lubrication and pumping properties.

Illustration rendering of TBM Sika main drive sealants in tunnel construction

3. Tail Seal Sealants

Tail seal sealants are injected between the rows of brushes in the gap between the tailskin and the lining segments to prevent water, soil and the backfilling grout from entering the TBM. Sika® Stabilizers are specifically designed to be safe for use in urban areas and elsewhere that the ground water could be in contact with TBM excavations, in order to prevent pollution of the environment.

Sika Solutions for Tail Seal Sealants
Tail Seal Sealants

Sika sealants have been specifically designed and developed with a special formulation which avoids residual spoil contamination and are also resistant to water and ground pressure.

In the range of Sika® Stabilizer TBM, Sika counts with different tail seal sealants for first filling and to be used during the advance of shielded tunnel boring machines. The sealants are used to fill the gap between the machine and the precast segments.

Illustration rendering of TBM Sika tail seal sealants in tunnel construction

4. Injections

Sika provides a wide range of injection products which are used with TBMs for different applications, including soil consolidation, rock stabilization, stopping water ingress, permanent sealing and waterproofing, plus the filling of voids and cavities and more.

Sika Solutions for Injections

Water ingress and wash-out with the development of uncontrolled cavities presents a security risk and potentially major costs for hard rock and gripper TBMs. SikaFix® injection technologies are highly efficient in solving such problems, as the cured material is easily cut by the TBM. The performance is not changed in the presence of water.

SikaFix® 301 This is an acrylate based, 3-component injection resin, specially developed to penetrate and consolidate low permeability structures. SikaFix®-301 has almost water-like consistence and therefore penetrates rock and sand filled structures quickly and very efficiently. Reaction time of the resin can be adjusted from 2 – 15 minutes depending on the application and penetration distances required.

SikaFix® 501 This is a 2-component, silicate resin with a high foaming factor of around 30 times (reaction time is around 15 sec.). The product foams with- or without the presence of water. Another important advantage for TBMs with this product is the cuttable nature of the cured foam, as a PU-foam would adhere to the cutter-head of the TBM. SikaFix®-501 also shows excellent cost performance in comparison to other TBM pre-injection products, and is widely used to stabilize fractured geology with a high void or cavity content.

SikaFix® 601 This is a 2-component, silicate resin with a short reaction time (around 40 sec.), which cures to a high strength solid resin, without the development of any foam. It also has excellent adhesion, even on damp surfaces, therefore SikaFix®-601 is frequently used for demanding rock consolidation and for controlling over-blasting in the tunnels. The product is also available as a thixotropic grade for use in overhead applications and self-drilling bolt injection.

Illustration rendering of TBM Sika injections made by worker

5. Conveyor Belt Repair and Bonding

The tunneling and mining industries are amongst the largest industrial sectors in the world where rubber conveyor belt systems are widely used. Sika’s expertise can provide superior cost-performance options for the bonding and repair of rubber belts and components for many applications.

Sika Solutions for Conveyor Belt Repair and Bonding
Belt Repair

SikaBond® R&B-100 is ideal for fast repairs with a rapid return to service of the conveyor belts.

SikaBond® R&B-100 This 2-component, high-performance elastomeric, synthetic resin based system is specially designed for the repair of textile and steel reinforced rubber conveyor belts. The material is primarily used to fix the commonly occurring, non-structural damage such as holes, cuts and ripped edges caused by the rocks. This significantly extends the service-life of the conveyor belt. When applied, it cures and develops outstanding mechanical properties on a well-prepared substrate.

Rubber Bonding

The vulcanization of rubber is time-consuming and can also be an expensive business with a lot of hardware and special know-how involved. Sika is one of the few companies with patented knowledge in this field, plus a global reach to supply outstanding rubber-bonding adhesives.

SikaBond® R&B-200/210 are fast curing, flexible adhesive systems designed to replace mechanical fixings or fastenings, such as rivets, screws or welding as well as hot vulcanizing itself. They are also suitable for bonding to and/or between many other materials as well as rubber, including metals, hard plastics, glass and wood etc.

Illustration rendering of TBM conveyor belt repair in tunnel construction

6. Backfilling Grouts

Sika is actively involved around the world in many tunneling projects, providing a wide range of products for TBM backfilling according to each project's specific requirements.

Sika Solutions for Backfilling Grouts
Backfilling Grout

Excavation with shield TBMs means that precast concrete segments are installed to form the tunnel, and an annular gap remains between these segments and the ground. The filling of this annulus is a very important requirement, as this ensures homogeneous contact with the ground, transfers load from the TBM back-up and also can help to waterproof the tunnel.

Different types of filling materials have been developed: hydraulically-setting mortar and two-component grout. Sika offers a complete range of stabilizers and retarders to prepare the backfilling grout:


Sika® ViscoCrete®



Two-Component Grout

Two-component injection grout is prepared by mixing a blend of water/cement, bentonite and retarder (component A) with an accelerator (component B). These get mixed just before the component A is injected through the tailskin and transforms itself from a creamy liquid to a gel in around 10 – 20 seconds. The final mix has comparable compressive strength to that of the surrounding ground and can fill every gap and void before it sets and hardens.

For the required flow and retarded set effects, Sika’s Sika-Tard® and Plastiment® products are used.

SikaSet® or Sigunit® accelerators are then used to control the set and hardening time and process.

Illustration rendering of TBM Sika backfilling grouts in tunnel construction

7. Admixtures for Shotcrete or Concrete Segments

One of the most important ingredients in high performance, long-lasting, durable and beautiful concrete produced today are concrete admixtures. Concrete admixtures are natural or manufactured chemicals or additives added during concrete mixing to enhance specific properties of the fresh or hardened concrete, such as workability, durability, or early and final strength.

Sika Solutions for Shotcrete or Concrete Segments

Modern sprayed concrete units use modern materials handling technology as well as concrete technologies such as admixture chemistry. Increasing demands on cost-effectiveness, the protection of health and the environment have meant that sprayed concrete has been in continuous flux for recent years.

Sika® ViscoCrete® Products used to reduce the water demand of the concrete, control the workability and increase the durability of sprayed concrete. Strength development is positively influenced by the dual actions of the superplasticizer and the acceleration effect.

SikaTard® Admixtures developed to regulate the hydration of sprayed concrete which enable an extended workability time, so that continuous spraying with fresh mixes can continue without difficulty for defined periods of time as required.

Sika® Shot Accelerators are used in sprayed concrete applications such as waterproofing, repair works or fire protection for example. These can be produced as ready-to use mortars that give flexibility on site as the materials can be stored for relatively long periods and sprayed with comparatively small machines.

Sigunit® A complete range of alkali-free and alkaline accelerators for shotcrete providing fast strength development according to the required J1, J2 and J3 curves.

Concrete Segments

In modern tunnel-boring machine construction, the permanent tunnel lining is produced with precast concrete segments. This type of concrete often requires innovative solutions for the mix design.

Concrete for inner linings
The concrete volume that is required for the inner lining of tunnels is very large cost effectiveness is therefore a significant aspect. The concrete must flow easily so that it can be cast in the molds, it must not bleed or segregate and in order to ensure rapid production and mold turnaround, it must provide high early strength.

The requirements of consistence, stability and early strength are controlled by the use of Sika® ViscoCrete® technology. Additional Sika admixtures are also added and used to meet specific demands such as Sikament® and SikaPlast®. If retardation is necessary – SikaTard®, for air entraining – Sika®Aer. SikaFume® Micro Silica increases the density of the mix leading to higher compressive strength and even higher durability.

Concrete segments
During the production of concrete segments for tunnels, it is important that the concrete can be placed without the formation of hollows or voids. The mix must also have a high early strength to reduce the curing time and de-mold the segments as fast as possible. With a high plasticizing effect, a low water/cement ratio can be achieved that will result in increased early strengths and increased durability. After just a few hours the concrete should have sufficient strength.

To meet these requirements, special admixtures have been developed using Sika® ViscoCrete® technology. Sika® Separol® release agents are used to ensure easy demolding and improved concrete surfaces. In some conditions, the segments forming the permanent lining can be exposed to aggressive influences in the ground water for example, Sikagard®-65 WN, is a water dispersed epoxy coating, designed to provide a high level of protection.

Illustration rendering of TBM tunnel concrete segments

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