It is widespread practice to support civil engineering structures such as railway tracks on beds of ballast which are built as flat topped ridges of small stones or large gravel on a graded sub-surface. The ballast is usually composed of crushed rock with sharp edges and facets which encourage the stones to rest with considerable void space within the ballast. This enables the ballast structure to react resiliently to vibrations caused by the passing of trains. The ballast also serves to spread the load of passing trains as the base of the ballast is wider than the spacing of the rails and sleepers, and provides more consistent running as variations in the ground structure have reduced effect on the support given to the track. For example, earth embankments, rock floored cuttings, and clay sub soils and bridge decks all have very different running characteristics.

During repeated loading the ballast reaches a resilient state with good interlocking properties. During this period the ballast settles leading to track misalignment. Ballast maintenance, usually through tamping and/or stone blowing is required to reinstate track alignment. Repeated loading of the ballast can result in the filling of the void spaces with dirt and/or dust, and oil-coating of the ballast due to leakage of train lubricating and propellant oil.

It has more recently been proposed, in order to prolong the useful life of ballast, using a polymer to coat the stones from which the ballast is made, which has the effect of tending to stabilize the stones in their initial positions so that there is increased resistance to relative permanent

displacement of the stones and thus compaction due to loading and repeated vibration.

In order to determine the required properties of the polymer, which may be single or multi-component in nature, such as strength, stiffness, damping etc. a design based approach is required to determine polymer composition and application methods and extent.

Also, whilst in general a method comprising binding ballast with a polymer achieves an overall improvement in the durability and performance of track support structures, this method cannot optimize the track support in every set of circumstances.

Ballast reinforcement has also been achieved through the use of geogrids, which are typically polymer based meshes located within the ballast matrix. These meshes tend to require large strains before improving ballast tensile properties, but can help prevent ballast penetration into the subgrade.

It is an object of the invention to provide a railway track support structure comprising a combination of components which can allow flexibility in the design of the structure to meet a range of conditions.

In accordance with the invention a civil engineering support structure for example in a railway track is provided which comprises a matrix of particles, one or more reinforcing elements within said matrix of particles, and a polymer binder applied to at least part of said matrix.

The invention also provides a method of preparing a civil engineering support structure for example in a railway track, comprising forming a matrix of particles, locating one or more reinforcing elements within said matrix of particles and applying a polymer binder to at least part of said matrix to

stabilize and reinforce said reinforcing elements and said particles into said matrix.

Preferably, the particles comprise ballast made up of crushed stone having a mean particle size in the order of 30-70 mm.

The polymer binder is preferably a polyurethane resin, but can be any one or more of a polyurethane resin, an epoxy resin, an unsaturated polyester, or an acrylate or methacrylate single or multi-component curing systems.

The reinforcing elements may be selected as appropriate from one, two or three dimensional parts: rods, tubes, channel sections and bars of any profile, chains, straps, strips, geo-grids, geo-mattresses, woven, non-woven, knitted, or felted fabrics, or membranes made from polymeric material or steel or other structural materials, such as reinforced concrete (pre-cast or cast in-situ), and wood (timber) all such elements being perforated or unperforated. Suitable polymeric materials include polypropylene, polyester, combined polypropylene and polyester, polypropylene or high density polyethylene or any blend thereof. Nylon (polyamide) or Keviar (Aramid) materials may alternatively be used particularly for yarns or fibres.

Yarns or fibres may also be used as reinforcing elements in place of woven, non-woven, knitted or felted textiles, or in the form of ropes.

Polymers may also be used in the form of strips, rods or tapes and geogrids. Steel or other material reinforcement members may be in the form of steel meshes or nets, rods or ropes and chains, extensible and non- extensible strips and tapes. Other materials which may be used particularly include aluminium, alloys for example magnesium alloy or aluminium alloy, rubber and carbon fibre reinforcement. Steel when used may be galvanized or non-galvanised or polymer coated.

Timber may be used in the form of lattices, panels or horizontal, vertical, lateral or longitudinal timber baulks.

Any or all of the above may be used separately or together in any combination of materials and form of reinforcement as required, and it is possible by selecting from the range of possible materials and forms to design and construct an appropriate support structure for any set of circumstances present, for example a combination of variations in ground type, ballast, designed polymer location and engineering/chemical properties, track bed condition, presence of track components and geometry, train speeds, train ladings properties and required track longevity and engineering behaviour will all have relevance to the details of the type of stabilization adopted. The multi-composite'reinforced systems may be formed in a mould prior to track installation to form a prefabricated reinforced ballast track segment.

Selected areas or volumes of the matrix of particles may be bonded by application of the polymer binder, other areas or volumes of the matrix being left unattended.

The matrix of particles may comprise a bed of ballast below and extending beyond each side of a railway track comprising two spaced rails supported on sleepers spaced apart along the length of the track, wherein, the polymer binder is or has been applied to bond the particles in the selected areas.

The selected areas may comprise the areas between the sleepers and/or the areas beyond each side of the railway track. Where both areas are selected, the reinforcing element may comprise at least one planar element such as a mesh, extending horizontally within the matrix. Where only the side areas are selected the reinforcing elements may comprise rods

of high stiffness extending through the bed of ballast below the rail track and between the bonded parts of the bed of ballast.

Two or more reinforcing elements may be used, which may be of the same or different kinds, for example one or more meshes, or a mesh and stiff tie rods used in combination.

The support structure may be prefabricated or prepared in-situ.

Examples of some civil engineering support structures according to the invention as used in railway tracks, will now be described with reference to the accompanying drawings, wherein:- Fig. 1 is a transverse cross-sectional view of a first embodiment of the invention; Fig. 2 is a plan view of a short section of railway embodying a second embodiment of the invention; Fig. 3 is a sectional view across the track on line III-III of Fig. 2; Fig. 4 is a longitudinal sectional view of the track on line IV-IV of Fig. 2; Fig. 5 is a view similar to Fig. 1 of a third embodiment of the invention; Fig. 6 is a sectional view of a track including a fourth embodiment of the invention on line V1-V1 of Fig. 7; and Fig. 7 is a plan view of a section of the track of Fig. 6.

Example 1: Fig. 1 is a simple embodiment of civil engineering support structure according to the invention such as may be adopted for supporting railway track under poor or normal conditions. This type of arrangement leads to a complete multi-component polymer/reinforced ballasted track railway structure.

Fig. 1 shows a track and track support in transverse cross section.

Rails 1 and 2 are carried on sleepers 3 of timber or concrete which are at least partially embedded in a ballast bed 4.

The ballast bed 4 is comprised of a matrix of stones consisting of crushed rock having a particle size of from 40-70 mm. The upper part of the ballast bed 4 is bonded with a polyurethane resin binder shown by line shading which binds the stones into the matrix and penetrates down to the level of the line 6 as shown by the cross-hatching. A reinforcing element 7 is incorporated into the matrix and comprises a mesh of galvanised steel, laid horizontally across the width and length of the ballast bed 4 above the lower limit 6 of penetration of resin into the ballast bed and is thus bonded by means of the resin into the matrix of resin and ballast stones, the depth of 5, 6 and/or 7 being a function of the design and track geometry.

This construction provides a reinforced ballast structure for supporting the tracks 1,2, and 3 with good resilience and enhanced durability and strength as compared with simply adding a polymer bonding to the ballast or just a galvanised steel mesh. The resin is applied in both crib area (the area between the sleepers) and underneath the sleepers to bond the ballast particulates and the additional reinforcing elements into a continuous resin stabilized reinforced track structure.

Example 2 : Figs. 2 to 4 show an embodiment of civil engineering support structure according to the invention in a railway track such as may be adopted for supporting track under normal conditions. This type of arrangement leads to, a partial multi-composite polymer/reinforced ballasted track railway structure.

The ballast bed 4 is comprised of a matrix of stones consisting of crushed rock having a particle size of from 40-70 mm. The upper part of the track bed 4 (ballast) is bonded with a polyurethane resin binder 5 which binds the stones into the matrix and penetrates down to the level of the formation and/or subballast layer line 6 as shown by the cross-hatching. A reinforcing element 7 is incorporated into the matrix and comprises a mesh of polymeric material, such as polypropylene e. g. an SS40 polypropylene tensar geogrid, laid horizontally across the width and length of the ballast bed 4 above the lower limit 6 of penetration of resin into the ballast bed e. g. at about 50mm above the formation and is thus bonded by means of the resin into the matrix of resin and ballast stones. The geogrid 7 has a tensile strength of 40KN/m in both its longitudinal and transverse directions. The resin is however only applied in the shoulder area 9 and crib areas 11 and not directly under the sleeper 10. This allows the reinforcing element 7 to be located during renewal work, during the layering and compaction of the ballast. Once initial settlement of the ballast has occurred the track is realigned and the resin either applied from the track or sleeper bottom surface level. The resin bonded sections provide an anchoring point 8 for the reinforcing element under the sleeper. The polymer used may have a stiffness of 1 GPa and the polymer/ballast mass ratio of 12%.

This type of arrangement allows complete maintenance of the ballast under the sleeper within a significantly enhanced polymer stabilized railway track structure if polymer is applied below the sleeper base and not at the surface.

This construction provides a cost-efficient reinforced ballast structure for supporting the track 1, 2, and 3 with good resilience and enhanced durability as compared with simply adding a polymer bonding to the ballast

or just a polypropylene mesh. Since resin application is applied after track construction it does not interfere with, for example, normal track renewal procedures. This is especially beneficial for example, in the renewal of switch and crossings on railway tracks.

Example 3 : Fig. 5 is a sectional view similar to Figs. 1 and 3 of a further embodiment of civil engineering support structure according to the invention in a rail track. A bed of ballast 4 supports a track comprising longitudinally extending parallel rails 1 and 2 and transverse sleepers 3 of wood or concrete.

In order to correct overstressed subgrade formations, which may be characterized by subsidence pockets 5, below the rails. The voids or pockets 5 may be filled with resin bonded ballast and the ballast bed 4 prepared over the zone in which pockets of subsidence 5 occur. One or more beams 6 of resin bonded ballast are formed transversely of the ballast bed, extending over most of the width of the ballast bed 4, and incorporating a steel mesh or steel bar reinforcing element 7. A 100mm layer of ballast overlies the beam 6. The linear extent of the beam 6 lengthwise of the track may be such as to fully overlie the subsidence zone, or separate parallel beams 6 may be provided over each subsidence pocket 5. The beam 6 may be about 200mm high by 300mm wide, and for a 25T axle load freight train at 70mph, an estimated tensile load is exerted at the beam base of 3. 87N/mm2 for an assumed open bottom drainage condition. The polymer used may have a stiffness of 2GPa and the polymer/ballast mass ratio of 25%. The tensile strength of the reinforced geocomposite is 12. 07N/mm' which attains the required safety factor of 3. Separate beams may be

prefabricated off-track and lowered into position, thus saving on-track construction time.

Ample 4 : Figs. 6 and 7 show an embodiment of civil engineering support structure according to the invention in a railway track such as may be adopted for laterally supporting track under high lateral loading conditions.

The ballast bed 4 is comprised of a matrix of stones consisting of crushed rock having a particle size of from 40-70 mm. The ballast shoulders of the track are bonded to form beams 400mm deep by 400mm wide with a polyurethane resin binder 5,6 of stiffness of 1.5GPa at a polymer/ballast mass ratio of 14% which binds the stones into the matrix and penetrates down to a predetermined level to form longitudinal shoulder beams. This provides lateral resistance to temperature buckling of 10.7 KN/m, as compared to 4KN/m for ballast without shoulder beams. A reinforcing element 7 is incorporated into the ballast/resin shoulder matrix and comprises a longitudinal rod 8 of high stiffness material, such as galvanised steel, laid horizontally and lengthwise of each ballast shoulder, and transverse rods 9 extending across the width of the crib ballast 10 at a depth of 30mm below the sleeper underside and bonded into the opposite shoulder beam. This reinforcement increases the lateral resistance of the ballast to 15KN/m. The resin is not applied in the crib area or underneath the sleepers. The rods 9 ensure that the two reinforced shoulder beams act together in restraining the sleepers 3 and/or track against lateral movement significantly reducing lateral track misalignment problems. Full vertical maintenance of the track is still possible using conventional maintenance equipment. The shoulder beams may also contain additional reinforcing

elements, such as steel and/or polymer rods or meshes, to help prevent bending fatigue during very high lateral loading of curves.

This construction provides a cost-efficient reinforced ballast structure for laterally supporting the tracks 1, 2, and 3 against large lateral forces on for example, high-speed curves and transitions on railway tracks, and makes possible a design-based approach to the planning and carrying out of the fabrication in situ, or offsite prefabrication of civil engineering, especially railway track support structures.