CDM - Rail Noise and Vibration Isolation

Since 1951, CDM has specialized in the design, production and implementation of noise and vibration isolation systems.

With ten regional CDM sales offices and even more international partnerships, CDM is active worldwide in the segments building, industry and railway infrastructure (track and light rail, tram, metro, subway).

A multifunctional engineering team - searching for the most economical way to isolate noise and vibrations with respect to the local requirements and related budgets - offers continuous support to guide you through the project.

VIBRATION ISOLATION SYSTEMS

Tracks for train, tramway and subway traffic always ask for an isolation cut or elastic decoupling at the source itself. The performance of the vibration isolation system must be optimized in function of the loads (permanent and variable), in order to obtain an optimized mass-spring system, related to a certain (low) resonance frequency. For track isolation it is also very important to consider the consequences of a decoupling with respect to track stability as well as re-radiated noise.

Tracks for train, tramway and subway traffic can be isolated at different levels, depending on the required performance and related budget.

LEVEL 1 - RAILPAD AND RAILSTRIP VIBRATION ISOLATORS

The simplest way of isolation consists of the introduction of a railpad situated directly under the rail, at the intersection with the sleepers.

In case of a slabtrack, this can also be a continuous railstrip. Since there is not much dead load available in this setup, the thickness of such a railpad or strip must be small (up to 10mm) in order to limit the static deformation of the rail.

LEVEL 2 - UNDER SLEEPER MATS AND UNDER BASEPLATE MATS

Higher performances can be obtained through the use of under-sleeper-mats or under-baseplate-pads (in case of slabtracks). Because of the ballast stones, under-sleeper-mats must be protected, for instance via a geotextile. As the dead load is yet significantly bigger (in case of under-sleeper-mats), the thickness of the isolation layer (always in CDM-SOLIDS) can be made higher as well (up to 20mm).

LEVEL 3 - BALLAST MATS AND FLOATING TRACKBED SYSTEMS

The best performance is obtained with ballast mats or floating trackbed systems, since here the dead load is very big and acts as an inertia mass. In case of floating trackbeds, discrete isolator systems can be used, possibly even with steel springs, allowing for high flexibilities and possibilities (easy adaptation of the stiffness for instance at track curves and at borders with non-isolated tracks).

RESILIENT PRE-LOADED RAIL FIXATION SYSTEM

The CDM-2L-DF fastener is a modular system, which allows components to be tailored to specific needs. The rail base plate can be designed to accommodate a variety of rail types and clips (Pandrol, Vossloh, Stedef Nabla …) and the stiffness of the under baseplate pad is selected in function of specific project parameters (axle loads, fastener spacing, clearance restrictions, desired degree of vibration isolation).

The compression springs are specified for the selected under baseplate pad to limit the vertical deflection of the rail to 3mm or less. Suitable for installation on concrete, on wooden ties or assembled as a unit on a flat steel base.

CHARACTERISTICS AND BENEFITS

The CDM-2L-DF fastener is made of very soft vibration damping material, down to 5kN/mm: It has a low resonance frequency of about 20 Hz, and excellent vibration isolation – 20dB between 25Hz and 120 Hz. Low track stiffness eliminates corrugation growth.

Its heavy pre-load – up to 18 kN – and minimum rail deflection to less than 3mm reduces airborne noise radiated from the rail and stresses in the rail clips. The combination of high resiliency and minimal deflection minimises stresses in the rail and eliminates rail breaks.

De-coupling of the compression springs during wheel passage completely eliminates the pre-load of the compression springs and prevents the transmission of structure borne noise from the base plate through the springs into the tunnel invert. Smaller springs generate a nominal, pre-load to maintain system stability.

A life expectancy of >30 years is assured by the under baseplate pad operations within its linear elastic range and is selected for its longevity and stability against creep, ageing and absorption. Springs operate at a fraction of their design limits.

Higher resiliency prevents rail breaks and thus reduces maintenance, increasing track availability and reducing costs. Elimination of corrugation growth eliminates the need for rail grinding, and installation on ties on ballast eliminates the need for ballast maintenance.

EMBEDDED RAIL VIBRATION ISOLATION SOLUTIONS

For embedded rail setups, CDM has been developing many different decoupling systems, of which the selection depends on the situation and available budget. An important advantage of embedded setups is that the re-radiated noise by the rail stays limited. This re-radiated noise can become important when isolating the rails via intervention levels 1 or 2. To reduce this noise, a damper system was developed, called CDM-ABSO-RAIL, which is acting at the first and second rail movement mode in case of tracks on sleepers.

CDM PREFARAILS PREFABRICATED CROSSROAD SYSTEMS

Installing and renovation an entire crossroads is now possible with the CDM MODULIX® system that consists of prefabricated reinforced concrete modules, containing all necessary elements (rails, slab, traffic separation, platform edge, road paving/covering, eventual transition stiffness elements, etc.).

The system has been designed to cross vital points in an urban environment (crossings in heavy traffic, access to strategic locations etc.) in a minimum of time.