The subject matter of the invention is a positive railway under sleeper pad intended for use under railway sleepers on a ballasted track.

Under sleeper pads are used predominantly in high-speed rail to reduce the impact generated by rail vehicles and transmitted from wheels through rails, the mounting system and sleepers to the crushed stone ballast. They are especially used where: - for justified reasons, sufficient thickness of ballast under sleepers cannot be obtained, - due to special operating conditions, the railway surface needs protection against early degradation (preventing deformation of the track), - there is a need to adjust stiffness of the railway surface, mainly in transition zones between surfaces of different stiffness.

Under sleeper pads are typically made of elastic polyurethanes or composite materials of natural or synthetic rubber. Mounted under sleepers and switch sleepers, standard pads have a flat working surface.

The American patent US2018127922A1 describes an under sleeper pad to be fastened to at least one surface of a sleeper, facing the ballast. The pad has at least one damping layer with a side suitable for direct contact with the ballast, of an EPM within the range of 10-25%, where the EPM is determined in a stress test performed on a test bench comprising a damping layer of a surface area of 300 mm x 300 mm.

The European patent DE 102009038414A1 describes an elastic pad mounted at the bottom of a concrete sleeper and covering the entire surface of the sleeper base, composed of several parts made of materials of various parameters. The bearing areas are designed in such a way that under wheel loads symmetrical to the middle of the sleeper, the elastic sleeper depressions in the middle of the sleeper and at the sleeper ends are of the same size, while under wheel loads asymmetrical to the middle of the sleeper, the mentioned sleeper depressions are different in size.

Solution WO2019157540A1 describes an elastic footing fastened to the underside of a sleeper, which has at least one elastic layer containing cork particles (cork granulate) spread over the entire surface. Moreover, the elastic layer has at least one synthetic closed cell elastomer material.

Utility model Ru-63872 describes an under rail pad in the form of an elastic plate, whose top surface is flat and faces the rail foot, and the bottom surface has a depression and faces the rail support. The depression on the bottom surface has longitudinal projections of various heights and lengths, distributed in multitude rows, each of which has several successive projections, where each projection is limited by two sloping sides and a cylindrical top surface convex towards the rail support. The pad shows little permanent deformation in the operation of railways, so the increase in its stiffness is small.

The purpose of this invention is to design a positive under sleeper pad which mitigates to the transverse and longitudinal impact relative to the track’s centre line, causing desynchronization of vibrations generated by the passage of a rail vehicle. The positive under sleeper pad according to the invention has the form of a plate of a shape and size substantially corresponding to the shape and size of the sleeper. It is made of an elastic synthetic material and has profiled working surfaces. The top surface of the pad, facing the sleeper, has grooved sections repeated at equal intervals, transverse to its longer sides.

The surface of the pad facing the ballast has regular, alternating, spherical bulges and depressions, which ease into one another in a wavy manner; in a cross section, the bulges and depressions form a sinusoidal pattern.

The alternating bulges and depressions are arranged in rows, diagonally in relation to the longer centre line of the pad, and individual rows are shifted in relation to one another by a half of the a wave length.

The bottom surface of the pad, facing the ballast, has regular alternating spherical bulges and depressions, arranged in rows, diagonally in relation to the longer centre line of the pad, where the rows are shifted in relation to one another by a half of the a wave length. The positive under sleeper pad according to the invention is characterised by an a wave length at least equal to the mean value of the mean ballast grain size, and a b amplitude at least equal to the mean value of the minimum ballast grain size but not bigger than the mean value of the mean ballast grain size. Preferably, the (a) wave length is 80 mm and the (b) amplitude — 15 mm.

The texture of the pad top surface makes it possible to spread the binder evenly, and thus ensure that the pad sticks to the sleeper regardless of the type of fastening used.

The wavy surface of the pad bottom surface reduces the stability of the pad’s static stiffness under load and thus the pad changes its thickness. Reduced stress on the contact surface between the sleeper and the ballast is achieved through smaller changes in stiffness along the track, and thus a more even load distribution.

An advantage of the solution according to the invention is that owing to the profiled bottom working surface, the effective area of impact on the contact surface between the ballast and the sleeper is expanded. The pad mitigates the movement of ballast grains thus reducing vibrations and increasing resistance to the impact, longitudinal and transverse, along the centre line of the track. It causes desynchronization of vibrations generated by the passage of a rail vehicle. Additionally, less prone to shifting in the ballast, sleepers provide a greater stability of the track. The positive under sleeper pad according to the invention has a higher elasticity than the existing pads used in the construction of railway tracks, and shows variable parameters of stiffness under load. In comparison to standard under sleeper pads, the pad according to the invention reduces the level of vibrations in the vicinity of the railway by 10-20%. An additional advantage of the solution according to the invention is the fact that the pads can be made from an easily accessible raw material — granulate from recycled rubber tyres.

A version of the subject matter of the invention is shown in the figures and Figure 1 shows the top working surface of the positive under sleeper pad in an orthographic projection, Figure 2 shows the bottom working surface of the positive under sleeper pad in an orthographic projection, with the a wave length marked and Figure 3 shows a cross section B-B of the positive under sleeper pad with a detail, Figure 4 shows a detail view — the sinusoidal shape of the bottom working surface.

This version of the positive under sleeper pad according to the invention has the form of a plate of a shape and size substantially corresponding to the shape and size of the sleeper. It is made of an elastic synthetic material made from granulate from recycled rubber tyres. It has two working surfaces — the top one, facing the sleeper, and the bottom one, facing the ballast.

The top working surface has grooved sections repeated at equal intervals, transverse to the longer sides of the pad.

The bottom working surface has regular, alternating, spherical bulges 2 and depressions 3. Bulges 2 and depressions 3 ease one into another in a wavy manner, in a cross section, the bulges and depressions form a substantially sinusoidal pattern. The parameters of the sinusoid are as follows: the a wave length and the b amplitude have been determined in such a way, that (the a wave length) is equal to the mean value of the mean ballast grain size, and the b amplitude is equal to the mean value of the minimum ballast grain size. The bulges 2 and depressions 3 are arranged in rows, diagonally in relation to the side surfaces of the pad, where the rows are shifted in relation to one another by a half of the a wave length.