Rockdelta

Stone wool mats that protect people, buildings and infrastructure from ground-borne vibration and noise caused by nearby railways.

The world needs rail

Railways are a vital part of critical infrastructure, and the world is moving towards a future in which 80% of the population will live in urban environments. Providing healthy, attractive, and comfortable living environments for these urban dwellers will raise many challenges. Although it’s not easy to predict how urban mass transit systems will develop, railways and trams will undoubtedly play a role increasing the need for protection.

Higher volumes of rail traffic present difficulties, with a substantial increase in vibration and noise people, city infrastructure, and track structures can all be impacted. Rockdelta stone wool mats offer a resilient and reliable solution with sustainable vibration control and structure protection, specifically engineered for demanding rail applications.

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Railway vibration and noise control

Railways, tramways and metros are essential for modern cities – but they also generate vibration and noise. Wheel–rail contact and the passage of wheels and bogies over joints and sleepers create low frequency vibrations (typically from 1 – 250 Hz) that travel through the ground and nearby buildings and can be reradiated as audible noise.

Without proper control, this can lead to:

Disturbance and reduced comfort for residents
Sleep disruption and increased stress levels
Damage risk for sensitive buildings, especially historic structures
Interference with precision equipment and critical infrastructure

Solving the vibration challenge with Rockdelta stone wool mats

Introducing resilient elements to create mass-spring-damper systems is a proven method of reducing ground-borne vibrations and extending rail track life. In these systems, the mass (track and train) interacts with a spring (resilient material) to isolate vibrations. The higher the mass, the better the isolation, which is why resilient mats placed at the base of the system are particularly effective for mitigating noise and vibration.

Rockdelta by ROCKWOOL applies this principle at the source. Our high performance under ballast mats and slab track mats, made from resilient stone wool, are designed specifically for railway, tram and metro lines. First used in the 1970s in Norway to protect city centres, stone wool mats are engineered to withstand the continuous pressure and friction of track systems while shielding cities and citizens from vibration.

Rockdelta resilient stone wool mats help you to:

Reduce ground borne vibration and structure borne noise
Improve comfort for people living and working near the tracks
Protect buildings and sensitive equipment close to rail infrastructure
Support sustainable, high-capacity rail operations in urban areas

By integrating Rockdelta mats into your track design, you combine reliable vibration and noise control with the durability, fire resilience and sustainability of ROCKWOOL stone wool – helping to create quieter, more livable cities without compromising on performance.

Rockdelta RB: Vibration control for ballasted tracks

Rockdelta RB mats deliver high-performance vibration mitigation for ballasted railway tracks, combining durability, efficiency, and ease of maintenance.

Their performance is verified through standardized testing in accordance with DIN 45673-5 and EN 17282, ensuring reliable results under real-world operating conditions.

Rockdelta RB Under Ballast Mats are a 2-component system:

Dual-density stone wool slab: A single, integrated element combining a resilient first layer for long-term vibration reduction under demanding loads with a second, higher-density layer that efficiently distributes forces, protecting the track structure and enhancing durability.
Geocomposite protection layer: A geocomposite with nonwoven geotextiles and a deformable core protects the mat during installation and operation, supports easier ballast maintenance/replacement, and provides optional drainage functionality.

The result is a robust, maintenance-friendly solution that enhances track performance, extends service life, and reduces environmental impact.

Key benefits of Rockdelta RB mats:

Excellent dynamic properties with inherent, first-rate volume compressibility
Outstanding functional performance under any climatic conditions, including at sub-zero temperatures
Exceptional lifespan with virtually no change in functional performance
Maintenance-free solution
Quick installation with no need for gluing

Rockdelta RX: Vibration control for Concrete Slab Tracks

With ultra-low sensitivity to environmental factors such as water, frost, and acid rain, Rockdelta RX mats exhibit outstanding efficiency and durability even after decades of operation under harsh climatic conditions. This has been verified by a Norwegian field study of the long-term functional performance of a track that had been vibration-isolated in 1978 using stone wool-based anti-vibration mats, as well as being documented by the Technical University of Munich in DIN 45673-5 testing.

Key benefits of Rockdelta RX mats:

Excellent dynamic properties with inherent, first-rate volume compressibility
Outstanding functional performance under any climatic conditions, including at sub-zero temperatures
Exceptional lifespan with virtually no change in functional performance
Maintenance-free solution
Quick installation with no need for gluing

Rockdelta RG: Track Structure Protection & Bridge Noise Control

A stable track foundation is critical to railway safety, performance, and lifecycle cost. In ballasted tracks, excessive loads, moisture ingress, and subgrade degradation can quickly lead to geometry defects and increased maintenance. Rockdelta RG high-strength stone wool mats are designed to protect the track support structure, improving load distribution and reducing stresses on the subgrade

Beyond structural protection, Rockdelta RG mats are highly effective in reducing bridge noise. On bridges, vibrations from wheel–rail contact can be amplified by the bridge deck, which acts like a vibrating membrane and radiates sound into the surrounding environment. By decoupling the track structure from the bridge deck, Rockdelta RG mats significantly dampen vibration transmission, reducing structure-borne noise by 5–15 dB. Performance is verified through standardized testing in accordance with DIN 45673-5, delivering a proven solution for quieter bridges, improved track durability, and lower maintenance costs.

This track support system keeps the rails and sleepers stable at the required position by resisting and dissipating the vertical, transverse, and longitudinal forces transmitted through the rails, the fastening system, and the sleepers. By distributing the loads to the layers below, it also protects the subgrade from excessive stresses, attenuates mechanical shocks, and provides efficient drainage. When this track support structure goes wrong, however, the impact is felt across safety, operational, and economic dimensions.

Key benefits of RockDelta RG products

Improve load distribution within the ballast layer and increase tamping intervals
Combine the benefits of sub-ballast and capping layers in a single layer
Prevent subgrade overstressing
Facilitate good drainage
Prevent mud pumping
Prevent intrusion of ballast into the subgrade
Decrease ballast height without compromising track stability
Minimise the risk of track heave
Combat bridge noise while maintaining high track superstructure stiffness

Case Studies

Creating peaceful living at the heart of Stockholm, Sweden

Stockholm City Line is a 6 km-long double-track commuter train tunnel beneath central Stockholm, Sweden. For the most part, the line passes through rock but, in the waters of Riddarfjärden between Riddarholmen and Söder Mälarstrand, it runs through a submerged concrete tunnel.

The Stockholm City Line was one of the biggest Rockdelta projects in Sweden. In the extensive tender phase, Rockdelta calculation and prediction tools proved extremely helpful in providing the necessary data and verifications. To ensure the comfort of those in and above the tunnel, attenuating ground-borne vibration was a high priority for the project, particularly as the granite through which much of the tunnel runs transmits more vibration than softer rock types and soil. The route also ran below a famous historic church, which had to be protected from ground-borne vibration.

The challenge

One of the first challenges was to balance the demands of the engineers for minimal deflection of the rails and those of the acousticians for vibration attenuation.

Conditions during construction also posed problems. The building site was situated in the busy center of Stockholm. All building materials had to be delivered to a storage site 50 km south of the city from where they were distributed further. Construction materials were often stored on this open-air site for months, undergoing the harsh Swedish weather conditions – including frost, heavy rain and snowstorms. Meanwhile, inside the tunnel, conditions could be extreme. In winter, temperatures sunk to well below zero. In view of the tight schedule, it was important to work with construction materials that could be installed under these conditions without special requirements.

Rockdelta experts visit construction sites regularly to advise on the installation of the mats and to be available to answer any questions that may arise during the process. On the Stockholm City Line, timing such visits was a challenge, amid the inevitable delays experienced by projects of this size.

The Rockdelta solution

In total, 60,000 m² of Rockdelta natural stone wool mats were installed during the project, achieving a vibration attenuation of 20 dB in the mean frequency between 63 and 125 Hz. In the main part of the tunnel, mats with a thickness of 50 mm were installed. In the section underneath the church, mats with a thickness of 85 mm were applied, providing additional protection.

Fire-safety was a major issue, especially in view of the use of dynamite to blast the tunnel. The non-flammable Rockdelta stone wool mats were safe to store and use inside the tunnel at any moment. The stone wool mats are also insensitive to weather conditions. During storage and installation, sub-zero or high ambient temperatures and moisture do not influence the intrinsic properties or the processability of the mats.

Lastly, Rockdelta mats are easy to handle and install: no special tools, welding, gluing, or taping are needed. This proved a big advantage in the confined tunnel space and sometimes difficult working conditions. Thanks to this ease of installation, the use of Rockdelta mats didn’t cause delays or put additional pressure on the tight schedule. In addition, the mats can be installed on uneven surfaces without the risk of punctures. Therefore, the granite bottom did not have to be flattened completely, saving much time and money.

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Smooth passenger flow in Gdansk, Poland

The historic Polish city of Gdansk, situated on the Baltic Sea coast, is home to an expanding population, as well as being a popular tourist destination. The Gdańsk Śródmieście railway station is one of the city’s major transport hubs. From 2014 an extensive renovation project was started to prepare the lines and station to meet the challenges of the rapidly increasing rail traffic.

The challenge

As part of the modernization and refurbishment of the Śródmieście railway station, a new tunnel with an underground platform was built. The new platform section is constructed in the direct vicinity of the old station infrastructure. The tracks are used by various train types, generating their own frequencies and causing ground-borne vibration in different ranges. The refurbished track system had to attenuate all of these vibrations, so passengers and station workers could enjoy an agreeable environment, despite the intensive train traffic.

In addition, heavy rain and cold weather are not uncommon in Gdansk but could not be allowed to cause delays. The construction site was located next to historic city architecture and a very busy road, so strict planning was of the utmost importance. The heavy traffic in the area also brought about logistic challenges. It was important that construction materials could be stored outside, close to the installation site and without need for weather protection.

The Rockdelta solution

The choice of Rockdelta resilient stone wool mats in combination with the Rheda 2000 slab track system developed by Rail One proved the optimal solution for this project, guaranteeing the required vibration attenuation. The fact that Rockdelta mats could be installed quickly and easily, without special tools and in sub-zero temperatures, was also a great advantage in this case, while the mats could be stored and installed in any weather conditions without degrading.

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Bridge Umbeluzi, Mozambique: structure protection for the long haul

On the Goba Line, which links the port of Maputo in Mozambique with landlocked Swaziland, an old bridge over the Umbeluzi river was showing serious signs of decay and had to be replaced by a new 362-metre-long bridge. Made of steel and concrete, it meets the increased carrying capacity needs of both nations and supports a load of 27 tonnes per axle. Trains of over 100 wagons can pass along the new bridge. As befits its strategic position, the new bridge will be intensively used over the years, so durability and low maintenance were a priority.

The challenge

The bridge is equipped with a ballasted track system. To ensure its durability, the bridge had to be protected against micro-cracks caused by ballast hitting the concrete structure on the sides. The vibrations caused by passing trains might also degrade the concrete and mirror back to the passing train, affecting the rolling stock. Lastly, the dynamic loads of passing trains can result in ballast attrition, causing track deflection and an extra need for maintenance.

The Rockdelta solution

Rockdelta resilient stone wool mats installed between the ballast and the concrete offered the following advantages:

High-performance protection, protecting the bridge from damage by ballast hitting the concrete sides.
Vibration attenuation, preventing micro-cracks that weaken the bridge structure.
Reduced ballast attrition and, thus, the need for maintenance.
Easy installation, without special equipment, gluing, taping, or welding.
Reliable quality, produced by ROCKWOOL, the market leader in stone wool technology.
Sophisticated calculation and prediction tools, allowing prompt and accurate responses to the project owner’s and engineer’s questions.
Onsite support with installation and logistics.

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Comfortable public transport in Lund, Sweden

Opened in 2020, the Lund Tramway is a 5.5km-long, double-track tramway, connecting Lund Central Station to the hospital, university, science park, and the multidisciplinary research facility Science Village/ESS in Brunnshög. This so-called ‘Science Road’ is the busiest commuter route in Lund.

The challenge

Building a new tramway in a lively city centre with narrow streets is challenging in many ways. “You have a large construction site,” says Pernilla von Strokirch, Lund Municipality's project manager, “and still people should be able to pass and not be hindered.”

In two locations specific challenges had to be overcome concerning ground-borne vibrations. “The beginning of the line is situated in the medieval city centre,” explains von Strokirch. “The closest buildings there had to be protected from ground-borne vibration translating into sound in the buildings. At the other end of the line, we have the Max IV research facility, including a circular particle accelerator that obviously are extremely sensitive to ground-borne vibration. In these two areas, we have applied Rockdelta stone wool mats for the attenuation of the vibration.”

The Rockdelta solution

The project was managed in cooperation with Skanska, who were responsible for detailing the construction and procurement of the materials used. Skanska opted for Rockdelta after a lengthy period of calculations and comparisons of possible solutions for the vibration issues. The experts from Max IV were also involved for their end of the line. This cooperation eventually led to the use of literally all available Rockdelta product thicknesses. In some areas, specific requirements even necessitated several layers of mats. “They tuned that track like a piano,” as one of the constructors observed.

“In the choice of the Rockdelta system, Skanska evaluated a lot of factors including performance, pricing, sustainability, longevity, and also the logistics and working conditions on the construction site.” says Pernilla von Strokirch, Lund Municipality's project manager.

The tramway infrastructure is designed to withstand the low temperatures and harsh weather conditions in Sweden. In addition, Rockdelta mats can be installed on surfaces that are not completely even and do not have to be glued or welded together. This was a definite advantage in this project, where one of the requirements was that no water should stay in the tracks. The small gaps between the mats function effectively as natural drainage system.

“For this project, with a track system with longitudinal beams and ballast, we found Rockdelta mats to be the best solution,” concludes von Strokirch.