VAN DEN BOS, Rene (Schippersmeen 165, CP Harderwijk, NL-3844, NL)
STRUKTON RAIL MATERIEEL B.V. (Veemarktweg 2a, AA 's-Hertogenbosch, NL-5223, NL)
BRAAKSMA, Egbert (Oranje Nassaulaan 60, GE Zeist, NL-3708, NL)
VAN DEN BOS, Rene (Schippersmeen 165, CP Harderwijk, NL-3844, NL)
| Claims 1. Railway construction comprising a substructure on which a superstructure is arranged, which superstructure comprises a ballast bed with a series of sleepers which are placed at at least substantially regular mutual distances and to which a pair of at least substantially parallel rails is connected, wherein a water-permeable stabilizing layer is provided between the superstructure and the substructure, characterized in that the stabilizing layer comprises over substantially a whole surface thereof an at least substantially continuous granular filter bed of a fluidal composition comprising a microfine mineral powder. 2. Railway construction as claimed in claim 1, characterized in that the composition comprises moderately fine sand chosen particularly from a group of quartz sand and silver sand. 3. Railway construction as claimed in claim 1 or 2, characterized in that the mineral powder is taken from a group of microfine quartz powder, ceramic powder and microfine pozzolan powder, particularly pozzolan powder taken from a group comprising fly ash, more particularly coal-dust fly ash, and microfine granulite powder. 4. Railway construction as claimed in claim 1, 2 or 3, characterized in that the filter bed comprises a minimum of 20-30% microfine mineral powder. 5. Railway construction as claimed in claim 4, characterized in that the filter bed is composed at least substantially wholly of fly ash, in particular coal-dust fly ash. 6. Railway construction as claimed in claim 4, characterized in that the filter bed comprises between 20% and 25% fly ash, in particular coal-dust fly ash, and for the rest is composed at least substantially of fine sand. 7. Railway construction as claimed in claim 4, characterized in that the filter bed comprises between 25% and 50% microfine quartz powder, in particular from a group comprising micro silica and millisil, and for the rest is composed at least substantially of fine sand. 8. Railway construction as claimed in claim 4, characterized in that the filter bed comprises between 10% and 15%, and in particular 13% microfine quartz powder, in particular from a group comprising micro silica and millisil, between 10% and 15%, and in particular 13% fly ash, in particular coal-dust fly ash, and for the rest is composed at least substantially of fine sand. 9. Railway construction as claimed in one or more of the foregoing claims, characterized in that the microfine mineral powder is at least substantially wholly no more than extremely fine, with a particle size of a maximum of 63 micrometres. 10. Railway construction as claimed in one or more of the foregoing claims, characterized in that the ballast bed is partially recessed into the filter bed. 11. Railway construction as claimed in one or more of the claims 1-9, characterized in that the filter bed lies enclosed between an underlying stabilized sand layer and an overlying stabilized sand layer. 12. Railway construction as claimed in one or more of the foregoing claims, characterized in that the filter bed has a thickness of a minimum of 5 to 15 centimetres, in particular between 8 and 15 centimetres. 13. Filter bed composition as can be applied in the railway construction as claimed in one or more of the foregoing claims. 14. Method for manufacturing a railway construction as claimed in one or more of the claims 1-12, characterized in that the composition is suspended with water in order to form a liquid slurry, that the slurry is spread onto the substructure and that a water fraction in the slurry is allowed to escape therefrom. 15. Method as claimed in claim 14, characterized in that the slurry comprises between about 20% and 30% water. 16. Method as claimed in claim 14 or 15, characterized in that the slurry is poured onto the substructure and that the ballast bed is arranged on the liquid slurry. 17. Method as claimed in claim 14, 15 or 16, characterized in that the slurry is injected under the ballast bed. |
The present invention relates to a railway construction comprising a substructure on which a superstructure is arranged, which superstructure comprises a ballast bed with a series of sleepers which are placed at at least substantially regular mutual distances and to which a pair of at least substantially parallel rails is connected, wherein a water- permeable stabilizing layer is provided between the superstructure and the substructure. The invention also relates to a method for manufacturing such a railway construction and to a fluidal filter bed composition.
A traditional railway construction comprises a ballast layer in the form of a bed of broken stone poured onto the substructure. The substructure is the ground surface on which the railway track is constructed. This can for instance be a flat ground, but also a railway embankment, a bridge or a viaduct. Lying embedded in the bed of broken stone is a series of sleepers to which a parallel pair of rails is fixed. The sleepers are placed at a regular mutual distance and usually manufactured from concrete or wood. The ballast bed provides for stability, damping of the vibrations and the discharge of excess rainwater. In order to stabilize the ballast bed without adversely affecting the drainage of excess rainwater, a water-permeable stabilizing layer is provided between the ballast bed and the substructure. In a conventional railway construction this layer is formed from so- called geotextile. Geotextile is a permeable fabric which is suitable for use in combination with soil, in hydraulic engineering and road engineering works, and depending on the method of manufacture can be subdivided into woven, non-woven
(non-woven membrane) and knitted textile. The materials most frequently used for this purpose are polypropylene and polyester, although other plastics such as polyethylene, nylon and glass fibre can also be used. Because the textiles are water-permeable they are highly suitable as filtering, drainage and separating layer. Because such a textile layer also has a certain strength and can absorb forces, it additionally serves in a traditional railway construction as stabilizing layer for the ballast bed present thereon. A drawback of such a conventional railway construction is that the ballast bed must be cleaned from time to time, and must ultimately be replaced. The geotextile must also be replaced here, after which a fresh ballast bed is once again poured onto the new layer of geotextile. This is relatively laborious, time-consuming and therefore also expensive. This approach also causes problems because the textile can end up in the machine used here. Another drawback is that geotextile is on rolls of 20-50 metres. This means that the maintenance train must always be stopped after this distance in order to replace the roll. With the increasing speed of this type of train the production loss becomes increasingly greater. In addition, this has an adverse effect in terms of health and safety aspects. An existing track is moreover out of use for a long time during such maintenance. Finally, the commonly used geotextile material is relatively expensive.
The present invention therefore has for its object, among others, to provide a railway construction and method with a filtering stabilizing layer which does not have these drawbacks, or at least does so to considerably lesser extent.
In order to achieve the stated object a railway construction of the type stated in the preamble has the feature according to the invention that the stabilizing layer comprises over substantially a whole surface thereof an at least substantially continuous granular filter bed of a fluidal composition comprising a microfine mineral powder. Microfine mineral powder is understood here to mean a powder with a grain size distribution which is at most equal to that of extremely fine to very fine sand. These are powder grains or powder particles which are at least substantially wholly smaller than respectively about 63 and about 105 micrometres and which are present in fluidal manner, i.e. as separate, individual granules, in the filter bed.
Tests have shown that a fluidal filter bed with at least a fraction of such fine-grain material remains extremely stable once it has formed. In this composition the mineral powder has sufficient cohesion, i.e. form-retention, even when water is poured over it. This imparts stability to the superstructure with the ballast bed. It has moreover been found that such a filter bed has an excellent filtering action and is self-repairing. When small channels occur therein, so-called rat-holing, and (drainage) water flows more quickly therethrough, this results in turbulence in these channels, whereby material erodes from a wall thereof, is then deposited in and eventually recloses the channel. The filter bed then functions once again at this location as water-permeable filter.
A preferred embodiment of the railway construction has the feature according to the invention that the mineral powder is taken from a group of microfine quartz powder, ceramic powder and microfine pozzolan powder, particularly pozzolan powder taken from a group comprising fly ash, more particularly coal-dust fly ash, and microfine granulite powder. Microfine quartz powder is commercially available under the name Millisil or Micro Silica. In addition, microfine ceramic powders are also suitable within the scope of the invention. Use is thus made here of optionally natural materials which have been formed after heating, for instance in a furnace or as natural igneous rock, at high temperature and sometimes also high pressure, wherein a minimum of two elements are present.
One of these is non-metallic and the other may be either metallic or non-metallic.
Pozzolans are powders which can be used as aggregate material for mortar or concrete. A pozzolan behaves as a hydraulic binder. In reaction with water a solid substance is created which no longer dissolves in water. Natural pozzolans consist of ground stone or soil-like materials of volcanic origin, such as for instance granulite. An artificial pozzolan is for instance fly ash. Fly ash is ash which is entrained by the flue gases during the combustion of inter alia coal. The part of the ash which does not rise is referred to as bottom ash. Fly ash consists for the greater part of silicon dioxide, iron oxides and aluminium oxide. In addition, it contains among other substances a small proportion of heavy metals.
A further preferred embodiment of the railway construction according to the invention more particularly has the feature that the microfine mineral powder is at least substantially wholly no more than extremely fine, with a particle size of a maximum of 63 micrometres. It has been found that, particularly in the case of such an extremely fine powder size, separation occurs and an extremely stable filter bed is created which remains intact even after repeated action of (drainage) water. If on the other hand use is made solely of coarser material, such as fine sand, the layer remains rich in water and gel-like, whereby no stabilizing and filtering action is to be expected therefrom.
A method for manufacturing a railway construction as set forth above has the feature according to the invention that the composition with water is suspended in water in order to form a liquid slurry therefrom, that the slurry is spread onto the substructure and that a water fraction in the slurry is allowed to escape therefrom. The composition with at least a microfine mineral powder and water is mixed in a determined ratio so that a properly liquid slurry is created which spreads easily and evenly over the ground surface. A particular embodiment of the method has in this respect the feature according to the invention that the processed slurry comprises between about 20% and 30% water. The consistency is such that the slurry also spreads evenly on a slope of 10 degrees to the horizontal. On a dry ground surface the slurry "dries" within several seconds. The surplus water migrates to the ground. On a wet ground surface the slurry flows out further, but does form an even filter bed. No migration of excess water takes place from the slurry to the ground, so the slurry dries only through evaporation. Once the filter bed has been formed, the form remains stable. The granular composition has sufficient cohesion, i.e. form-retention, even when water is poured onto the filter bed again. The dried layer of slurry always retains a determined percentage of physically bound water; this can only be removed thermally. The percentage of residual water in the layer of slurry is related to the granulometry of the mineral powder composition. The dried layer of slurry has an excellent filtering action and is "self-repairing". When rat-holing occurs and the water flows through it more quickly, turbulence is created in a formed channel, whereby the slurry material "seals" itself again and so continues to function as a filter cake. Such a slurry header, provided with a number of outlets, can be mounted in the same location as where a geotextile roll hangs in a conventional railway construction. A particular preferred embodiment of the method has for this purpose the feature that the slurry is poured onto the substructure and that the ballast bed is arranged on the liquid slurry. Coupled to the end of a work train is a wagon with a weighing, mixing and pumping installation and a storage for the dry substance and water from which the slurry will be formed. The ballast material can be poured onto the slurry immediately after outflow thereof, whereby the bottom layer of ballast is immediately enclosed in the filter cake. Without binder the filter bed formed from the slurry remains deformable when sufficient water is retained, and can thereby co-displace within limits with the surrounding area.
The slurry can be pumped and injected extremely well. In a further particular preferred embodiment the method according to the invention therefore has the feature that the slurry is injected under the ballast bed. In an existing situation the filter bed can hereby only be arranged or repaired later, without the ballast bed having to be lifted or removed for this purpose. This results in a considerable cost-saving compared to a conventional approach, in which a geotextile can only be arranged or replaced on an exposed substructure.
The invention will be further elucidated, and particular embodiments thereof discussed, on the basis of the following exemplary embodiments and an accompanying drawing. In the drawing:
figure 1 shows a first embodiment of a railway construction according to the invention; and
figure 2 shows a second embodiment of a railway construction according to the invention.
The figures are otherwise purely schematic and not drawn to scale. Some dimensions in particular may be exaggerated to greater or lesser extent for the sake of clarity.
Corresponding parts are designated as far as possible with the same reference numeral. Figure 1 shows an exemplary embodiment of a railway construction. The railway construction makes use of a substructure 10 in the form of a flat ground, railway embankment or other suitable ground surface. Situated thereon is a superstructure 20 of a pair of parallel rails 21, 22 fixed at regular mutual distances to sleepers 23. In this embodiment the sleepers 23 comprise wooden sleepers, but can for instance also be manufactured from concrete.
In order to stabilize the whole and for the purpose of an adequate drainage, sleepers 23 are embedded in a ballast bed 24 of broken stone, for instance coarsely ground or broken granulite or basalt. Situated according to the invention between superstructure 20 and substructure 10 is a water-permeable stabilizing layer 25 in the form of a fluidal, fine-grained filter bed consisting at least partially of microfine mineral powder.
Exemplary embodiment 1 :
Use is made for this purpose in this embodiment of a filter bed consisting at least substantially wholly of microfine coal-dust fly ash. In order to obtain this, coal-dust fly ash with a maximum particle size of about 63 micrometres and water is mixed in a ratio of 70-80% fly ash to 30-20% water so that a properly liquid slurry is created which spreads easily and evenly over the ground surface. The consistency is such that the slurry also spreads evenly on a slope of 10 degrees to the horizontal. On a dry ground 10 the fly ash "dries" within several seconds. The surplus water migrates here predominantly to the ground. On a wet ground the fly ash slurry flows out further, but does still form a level fly ash bed 25. There is now hardly any migration of surplus water from the slurry to the ground, so that the fly ash dries only through evaporation. Once the fly ash bed 25 has formed, the form remains stable. In this composition the fly ash has sufficient cohesion (form-retention), even when water is poured over fly ash bed 25 again. The water does however permeate through it easily, although solid constituents are here filtered effectively therefrom.
The dried layer of slurry 25 always retains a determined percentage of physically bound water, and this can only be removed thermally. The percentage of water in the layer of slurry is related to the granulometry of the coal-dust fly ash applied. The layer of slurry has an excellent filtering action and is "self-repairing". When rat-holing occurs and the water flows through it more quickly, turbulence is created and deposition of wall material eroded as a result thereof occurs in a formed channel, whereby fly ash layer 25 "seals" itself again and so continues to function as a filter cake.
A fly ash slurry header provided with a number of outlets can be arranged on the substructure before ballast bed 24. A wagon with a weighing, mixing and pumping installation, as well as a store of fly ash and water, is coupled to the end of a work train. The fly ash slurry can be pumped extremely well and poured over the substructure at the intended location up to a layer thickness of typically a minimum of 5 to 15 centimetres, in this embodiment about 8-10 centimetres. Ballast material 25 is preferably poured immediately after outflow thereof onto the fly ash slurry, whereby the bottom layer of ballast sinks down immediately and is enclosed in filter bed 25. Filter bed 25 can instead also be injected under a ballast bed that is present. For this purpose the fly ash slurry is pumped and arranged at a depth below the ballast bed using an injection pipe or nozzle, where it will spread to some extent. This process is repeated at a suitable pitch in order to thus form an at least substantially continuous filter bed below the ballast bed. When it retains a sufficient quantity of water a coal-dust fly ash slurry without binder remains deformable, and can thereby co-displace (within limits) with the surrounding area. In addition to an excellent filtering action, filter bed 25 according to the invention hereby also provides for an adequate stabilization of the whole construction. A certain environmental impact must however be taken into account in the case of such a slurry formed entirely from fly ash. Table 1 shows the result of a leaching analysis performed on a 100% fly ash slurry. This shows that an emission norm applicable in this country in respect of the proportions of chromium, molybdenum, selenium, chloride and sulphate is exceeded. In the case of 25% admixture it is an option to select a fly ash having a low proportion of molybdenum and selenium. Leaching analyses non-shaped materials
Mixing percentage: 100%
TABLE 1
Exemplary embodiment 2:
A second exemplary embodiment of a railway construction according to the invention shown in figure 2. The substructure and superstructure of this construction are wholly identical to those of the previous embodiment, to which brief reference is therefore made in this respect. Other than in the previous embodiment, filter bed 25 in this case lies enclosed between an underlying, stabilized sand layer 26 and an overlying, stabilized sand layer 27. The composition of filter bed 25 is based on the same slurry formed from at least substantially only coal-dust fly ash as applied in the first embodiment
Exemplary embodiment 3:
When granite is broken fine particles are released, which are collected (wet) and kept separate from the broken stone. Granulite is the trade name of the fraction with a particle size smaller than 63 um, which is released after the water is removed mechanically from the washing water flow by means of a filter chamber press. In addition to Granulite, Bestone microsand is also released, which is collected by means of cyclones.
A composition of 75% of this micro-sand with 25% coal-dust fly ash produces a stable slurry which does not subside quickly. The moisture content of the slurry is about 23.3% of the total. After being poured onto a sand substrate it dries quickly, similarly to a 100% fly ash slurry. After a fixed quantity of water is poured over it, the first water already comes through after about 3 minutes. All the water has passed through within 1 hour.
This is technically a good option. In terms of environmental protection this option has the drawback that molybdenum and selenium leach and, at this percentage of fly ash, could exceed an applicable emission norm, as suggested by the result of a leaching analysis performed thereon as shown in table 2. This could be brought within the norm by making use of a low-selenium and or low-molybdenum fly ash as starting material.
Leaching analyses non-shaped materials Mixing percentage: 25%
TABLE 2
Exemplary embodiment 4:
Granulite is first mixed with water and dissolves with difficulty, after which Bestone microsand is added at a mixing percentage of 75%. The moisture content of the slurry is 27.7% of the total. After being poured onto a sand substrate the slurry dries reasonably quickly, although it remains a little sludge-like. After a fixed quantity of water is poured over it, the first water comes through within half an hour. This is technically a reasonable option. In terms of environmental protection this is a good option due to the absence of heavy metals in the slurry.
Exemplary embodiment 5:
A composition of 45% microfine quartz powder (Millisil® M6), 45% micro-sand and 10% fly ash is diluted with water to form a slurry with a moisture content between 20 and 30%. Millisil® is produced by iron-free grinding and accurate sieving by means of air separators. Selected quartz sand with a quartz content (Si0 2 ) above 99% is the basic raw material herefor.
The mixture remains in solution well and dries reasonably quickly after being poured. After a fixed quantity of water is poured over it, the first water comes through after 10 minutes. This is technically a reasonably good solution, this is also a reasonable alternative in terms of environmental protection. An emission of selenium is precisely at the limit of an applicable emission norm, see table 3. Leaching analyses non-shaped materials
Mixing percentage: 10%
Parameter fl: ash maxiri ium
L/S=10 emiss ion
[μ≠] [mg/kgds] [mgkgds] [mgkgds] exceeded antimony Sb 6 0.06 0.006 0.16
arsenic As 20 0.2 0.02 0.9
barium Ba 770 7.7 0.77 22
cadmium Cd 4 0.04 0.004 0.04
chromium Cr 180 1.8 0.18 0.63 cobalt Co 5 0.05 0.005 0.54
copper Cu 7 0.07 0.007 0.9
mercury Hg 0.4 0.004 0.0004 0.02
lead Pb 20 0.2 0.02 2.3
molybdenum Mo 800 8 0.8 1
nickel Ni 10 0.1 0.01 0.44
selenium Se 180 1.8 0.18 0.15 YES tin Sn 1 0.01 0.001 0.4
vanadium V 70 0.7 0.07 1.8
zinc Zn 50 0.5 0.05 4.5
bromide Br 730 7.3 0.73 20
chloride CI 92000 920 92 616
fluoride F 1400 14 1.4 55
sulphate so 4 308000 3080 308 1730
TABLE 3
Exemplary embodiment 6:
Microsilica is quartz powder with a quartz content of more than 85%, in addition to several other natural minerals. A composition of 75% micro-sand with 25% microsilica remains in suspension well at a moisture content between 20% and 30%, despite the slurry being relatively thinly liquid. This makes the slurry particularly suitable for pumping and (subsurface) injection.
After being poured the slurry dries quickly, and after a fixed quantity of water is poured over it the first water comes through within 10 minutes. Technically this is a good alternative, and likewise in terms of environmental protection because use is made of a natural, non-contaminated starting material.
Exemplary embodiment 7:
A composition of 50% micro-sand, 43% Millisil® M6 and 7% microsilica is mixed with water in a ratio of 75:25. The solid fraction remains in suspension well and dries quickly after being poured. After a fixed quantity of water is poured over it the first water comes through after 4 minutes. Technically this is a good option, and the same is true in terms of environmental protection.
Exemplary embodiment 8:
A composition of 13% microsilica, 13% fly ash and for the rest micro-sand is wetted with between 20% and 30% water. The solid fraction remains in suspension well and dries quickly after being poured. After a fixed quantity of water is poured over it, the first water comes through after 3 minutes. This is technically a good alternative. In terms of environmental protection this forms a reasonable alternative; selenium is precisely at the limit of the emission norm, see table 3.
The conclusion is that, while a coal-dust fly ash bed provides an excellent stabilizing and filtering action, sufficient mixtures can be composed which have similar properties and which, considering the origin of the material, will fall within the emission requirements of the Soil Quality Decree or other applicable environmental regulations. An environmental impact can moreover also be limited by a selective choice in respect of the fly ash applied or a reduction of the proportion thereof in the starting
composition. Although the invention has been further elucidated above on the basis of only several exemplary embodiments, it will be apparent that the invention is by no means limited thereto. On the contrary, many variations and embodiments are still possible within the scope of the invention for a person with ordinary skill in the art.