NL2004722C2 - RAILWAY CONSTRUCTION, METHOD AND FILTER BED COMPOSITION. - Google Patents

Description

Railway construction, method and filter bed composition

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 placed at at least substantially regular distances from each other, to which a set of at least substantially parallel rails is connected, the superstructure and the substructure a water-permeable stabilization layer is provided. The invention also relates to a method for manufacturing such a railway construction and to a filter bed composition.

A traditional railway construction comprises a ballast layer in the form of a rock bed that has been poured onto the substructure. The substructure is the substrate on which the railway line will be laid. This can for instance be a flat bottom, but also a railway embankment, a bridge or a viaduct. A series of sleepers is embedded in the rock bed on which a parallel set of rails (rails) is secured. The sleepers are placed at a regular mutual distance and are usually made of concrete or wood. In the latter case it is also called sleepers or sleepers. The ballast bed provides stability, dampens the vibrations and drains off 20 excess rainwater.

In order to stabilize the ballast bed without compromising the drainage of excess rainwater, a water-permeable stabilization layer is provided between the ballast bed and the substructure. In a conventional railway construction, this is formed from so-called geotextiles. Geotextile is a permeable cloth suitable for use in combination with soil, hydraulic engineering and road construction works and can be subdivided into woven, non-woven (non-woven non-woven) and knitted textile, depending on the method of manufacture. The materials that are usually used for this are polypropylene and polyester, but other plastics such as polyethylene, nylon and fiberglass can also be used. Because the textiles are water permeable, they are excellent as a filter, drainage and separation layer. Because such a textile layer also has a certain strength and can absorb forces, PA1598NL00.nl.wpd -2- in a traditional railway construction also serves as a stabilization layer for the ballast bed present thereon.

A drawback of such a conventional railway construction is that the ballast bed 5 needs to be cleaned and eventually renewed from time to time. The geotextile must also be replaced, after which a fresh ballast bed is returned to the new layer of geotextile. This is relatively time-consuming, time-consuming and partly because of that expensive. This approach also causes problems because the textile can end up in the machine used for this. Another disadvantage is that geotextiles are on rolls of 20 to 50 meters. This means that the maintenance train must always be stopped after that distance to replace the roller. With the increasing speed of this type of train, the production loss is increasing. In addition, this occupational health and safety has a negative effect. Moreover, an existing track is out of use for a long time during such maintenance. Finally, the commonly used geotextile material is relatively expensive.

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The present invention therefore has for its object, inter alia, to provide a railway construction and method with a filtering stabilization layer to which these drawbacks do not adhere, at least to a considerably lesser extent.

In order to achieve the intended purpose, a railway construction of the type mentioned in the preamble according to the invention is characterized in that the stabilizing layer comprises an at least substantially continuous, at least substantially homogeneous granular filter bed of a composition in which a microfine mineral powder is used. Microfine mineral powder is herein understood to mean a powder with a grain size distribution at most equal to that of extremely fine to very fine sand. These are powder grains or powder particles that are at least substantially completely smaller than approximately 63 and approximately 105 micrometres respectively. Tests have shown that filter bed with at least a fraction of such fine-grained material remains extremely stable after it has formed. The mineral powder has sufficient cohesion in this composition, that is to say, dimensional stability, even when it is topped with water. This gives stability to the superstructure with the ballast bed. Moreover, it has been found that such a filter bed has an excellent filtering effect and is self-repairing. When small channels arise therein, so-called rat-holing, and (drainage) water flows through it faster, this leads to turbulence in these channels, causing material from a wall thereof to erode and subsequently to precipitate in the channel and ultimately close it again. . The filter bed then functions as a water permeable filter on the spot.

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 puzzolane powder, in particular puzzolane powder taken from a group comprising fly ash, more in particular powder coal fly ash, and microfine granulite powder. . Microfine quartz powder is commercially available under the designation Millisil or Micro Silica. In addition, microfine ceramic powders also lend themselves within the scope of the invention. These are natural or non-natural materials that were formed after heating, for example in an oven or as a natural solidification rock, at high temperature and sometimes also high pressure, with at least two elements being present. One is non-metallic and the other may be both metallic and non-metallic. Puzzle lanes are powders that can be used as aggregate material for mortar or concrete. A puzzolane behaves like a hydraulic binder. A solid is formed in reaction with water, which no longer dissolves in water. Natural puzzolans consist of crushed stone or earthy materials that are of volcanic origin, such as granulite. An artificial puzzolan is, for example, fly ash. Fly ash is ash that goes with the flue gases when burning coal, among other things. The part of the shaft 25 that remains lying is referred to as bottom ash. Fly ash consists for the most part of silicon oxide, iron oxides and aluminum oxide. In addition, it also contains a small proportion of heavy metals.

More in particular, a further preferred embodiment of the railway construction according to the invention has the feature that the microfine mineral powder is at least substantially completely at most extremely fine with a -4-particle size of at most 63 micrometres. It has been found that, particularly with such an extremely fine powder size, demixing occurs and an extremely stable filter bed is formed that remains intact even after repeated action of (drainage) water. On the other hand, if coarse material such as fine sand is exclusively assumed, the layer remains water-rich and gel-like, so that no stabilizing and filtering effect can be expected from it.

A method for manufacturing a railway structure, as set out above, has the feature according to the invention that the composition is suspended with water in water to form a liquid slurry thereof, that the slurry is spread on the substructure and that a water fraction is the slurry is allowed to evade from it. The composition with at least one micro-fine mineral powder and water is mixed in a certain ratio so that a good liquid slurry is formed that spreads easily and evenly over the ground surface. A special embodiment of the method in this connection according to the invention has the feature that the processed slurry comprises between approximately 20% and 30% water.

The consistency is such that even on a slope of 10 degrees with the horizontal, the slurry is evenly distributed. On a dry surface, the slurry "dries up" within a few 20 seconds. The excess water migrates to the substrate. The slurry flows further out on a wet surface, but forms an even filter bed. There is no migration of excess water from the slurry to the substrate so that the slurry only dries out by evaporation. Once the filter bed has formed, the shape remains stable. The granular composition has sufficient cohesion, ie dimensional stability, even when the filter bed is again topped with water. The dried up slurry layer always retains a certain percentage of physically bound water; this can only be removed thermally. The percentage of residual water in the slurry layer is related to the granulometry of the mineral powder composition. The dried up slurry layer has an excellent filtering effect and is "self-repairing". When rat holing takes place and the water flows through it more rapidly, turbulence arises in a formed channel through which the slurry material itself "closes" again and thus continues to function as a filter cake.

Such a slurry header, provided with a number of spouts, can be mounted at the same location where a geotextile roll hangs in a conventional railway construction. A particularly preferred embodiment of the method for this purpose is characterized in that the slurry is poured onto the subsurface and that the ballast bed is applied to the liquid slurry. At the back of a working train a wagon is coupled to a weighing, mixing and pumping installation and a storage for the dry matter and water from which the slurry will be formed. The ballast material can be deposited on the slurry immediately after flowing out, whereby the bottom layer of ballast is immediately enclosed in the filter cake. Without binder, the filter bed formed from the slurry, while maintaining sufficient water, remains deformable and can therefore move with the environment within limits.

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The slurry can be perfectly pumped and injected. 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. As a result, in an existing situation the filter bed can first be applied or repaired without the ballast bed having to be lifted or removed for this purpose. This provides a considerable cost saving compared to a conventional approach where a geotextile can only be applied or exchanged on an exposed substructure.

The invention will be further elucidated and particular embodiments thereof treated with reference to the following exemplary embodiments and an associated 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.

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The figures are purely schematic and not to scale. In particular, for the sake of clarity, some dimensions may be exaggerated to a greater or lesser extent. Corresponding parts are designated as far as possible with the same reference numeral.

5

Figure 1 shows an exemplary embodiment of a railway construction. The railway construction is based on a sub-structure 10 in the form of a flat soil, railway embankment or other suitable surface. A superstructure 20 of a set of parallel rails 21, 22 is located thereon and is fixed at regular distances to one another on sleepers 23. The sleepers 23 in this example comprise wooden sleepers, but can for instance also be made of concrete.

To stabilize the whole and for adequate dewatering, the sleepers 23 are embedded in a ballast bed 24 of crushed stone, for example coarsely milled or crushed granulite or basalt. Between the superstructure 20 and the substructure 10, according to the invention, there is a water-permeable stabilization layer 25 in the form of a filter bed which is formed at least partly from microfine mineral powder.

Embodiment example 1: 20 To this end, in this example, a filter bed is assumed that consists at least substantially entirely of microfine powdered coal fly ash. To obtain this, pulverized coal fly ash with a maximum particle size of approximately 63 micrometres and water was mixed in a ratio of 70-80% fly ash to 30-20% water, so that a good liquid slurry is formed that spreads easily and evenly over the ground surface. The consistency is such that even on a slope of 10 degrees with the horizontal, the slurry is evenly distributed.

On a dry surface 10 the fly ash "dries up" within a few seconds. The excess water mainly migrates to the subsurface. On a wet substrate, the fly ash slurry flows further out, but forms a smooth fly ash bed 25. There is now virtually no migration of excess water from the slurry to the substrate, so that the fly ash only dries out by evaporation. Once the fly ash bed 25 has formed, the shape remains stable. In this composition, the fly ash has sufficient cohesion (dimensional stability), even when the fly ash bed 25 is once again topped with water. However, the water easily penetrates through it, but solid components are effectively filtered out of it.

The dried up slurry layer 25 always retains a certain percentage of physically bound water, this can only be removed thermally. The percentage of water in the slurry layer is related to the granulometry of the powdered coal fly ash used. The slurry layer 10 has an excellent filtering effect and is "self-repairing". When rat holing takes place and the water flows through it more rapidly, turbulence and deposition of wall material eroded as a result into molded channel is created, as a result of which the fly ash layer 25 continues to "close" itself and thus function as a filter cake.

A fly ash slurry header, provided with a number of spouts, can be applied to the substructure prior to the ballast bed 24. At the back of a work train a wagon is coupled with a weighing, mixing and pumping installation as well as storage of fly ash and water. The fly ash slurry can be excellently pumped and poured over the substructure at the intended location to a layer thickness of typically a minimum of 5 to 15 centimeters, in this example approximately 8-10 centimeters. The ballast material 25 is preferably poured onto the fly ash slurry immediately after flowing out, whereby the bottom layer of ballast sinks immediately and is enclosed in the filter bed 25.

Instead, the filter bed 25 can also be injected under an existing ballast bed. To this end, the fly ash slurry is pumped and brought to a depth under the ballast bed with the aid of an injection tube or nozzle where it will flow out slightly. This operation is repeated with a suitable pitch to thus form an at least substantially continuous filter bed under the ballast bed. A charcoal fly ash slurry without binder remains deformable while retaining sufficient water and can therefore move with the environment (within limits). The filter bed 25 according to the invention therefore offers, in addition to an excellent filtering effect, also an adequate stabilization of the entire construction.

However, such a slurry that was completely formed from fly ash must take into account a certain environmental impact. Table 1 gives the result of a leaching analysis that was performed on a 100% fly ash slurry. This shows that an emission standard in force here applies to the shares of chromium, molybdenum, selenium, chloride and sulphate. In the case of 25% admixture, it is an option to select a fly ash that has a low molybdenum and selenium content.

Leaching analyzes of non-shaped materials

Mixing percentage: 100%

Parameter flight bait maximum L / S = 10 emission ___ [yyg / l] [mg / kgds] [mg / kgds] [mg / kgds] antimony exceedance Sb 6__0.06 0.06 0.16_ arsenic Ash 20 0.2 0.2 0.9 barium__Ba 770 7.7 7J 22_ cadmium Cd 4__0.04 0.04 0.04_

chrome Cr 180 1.8 1.8 0.63 YES

cobalt Co 5 0.05 0.05 0.54 copper Cu 7 0.07 0.07 0.9 mercury Hg 0.4 0.004 0.004 0.02 lead__Pb 20__0.2 02 2.3_

molybdenum Mo 800-8 8 1 YES

nickel__Ni__10 0.1 Ol ^ 0.44_

selenium__Se 180__1.8 18 0.15 YES

fin__Sn 1 0.01 0.01 04_ vanadium V 70__0.7 07 18_ zinc__Zn 50__0.5 05 43_ bromide Br 730 7.3 73 20_

chloride Ct 92000 920 920 616 YES

fluoride F 1400 14 14 55_

sulfate SO 4 308000 3080 3080 1730 JA

TABLE 1 -9-

Embodiment example 2:

A second exemplary embodiment of a railway construction according to the invention is shown in Figure 2. The substructure and superstructure of this construction are substantially identical to those of the previous example, to which reference is therefore made in this respect for the sake of brevity. In this case, unlike in the previous example, the filter bed 25 is enclosed between an underlying stabilized sand layer 26 and an upper stabilized sand layer 27. The composition of the filter bed 25 is based on the same slurry formed from at least substantially pure powder fly ash as in the first example was applied.

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Embodiment example 3:

During the breaking of granite, fine parts are released that are (wet) caught and kept separate from the crushed stone. Granulite is the trade name of the fraction with a particle size of less than 63 µm that is released after dehydrating the wash water stream by mechanical means of a filter chamber press. In addition to the Granulite, Bestone micro sand is also released, which is captured by cyclones.

A composition of 75% of this micro sand with 25% powdered fly ash gives a stable slurry that does not settle quickly. The moisture content of the slurry is approximately 23.3% of the total. After pouring on a sandy substrate, it dries quickly comparable to a 100% fly ash slurry. After pouring over with a fixed amount of water, the first water comes through after approximately 3 minutes. All the water has gone through within 1 hour.

Technically this is a good option. From an environmental health point of view, this option has the drawback that molybdenum and selenium leaches and could exceed a prevailing emission standard at this percentage of fly ash, as the result of a leaching analysis carried out on it suggests in Table 2. By starting from a selenium and / or molybdenum-low fly ash as starting material, this could be brought within the norm.

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Leaching analyzes of non-shaped materials

Mixer rate: 25% fly ash

Parameter fly ash maximum L / S = 10 emission [µg / i] [mg / kgds] [mg / kgds] [mg / kgds] antimony exceeded Sb 6 0.06 0.015 0.16 arsenic Ash 20 0.2 0.05 0.9 barium Ba 770 7.7 1.925 22_ cadmium Cd 4 0.04 0.01 0.04_ chrome Cr 180 1.8 0.45 0.63_ cobalt Co 5 0.05 0.0125 0.54 copper__Cu 7 0.07 0.0175 03_ mercury__Hg 0.4 0.004 0.001 0.02_ lead Pb 20 0.2 0.05 23_

molybdenum Mo 8Q0__8 _2 _1 JA

nickel__Ni 10 0.1 0.025 0.44_

selenium Se 180 1.8 0.45 0.15 YES

tin__Sn 1 0.01 0.0025 _0A_ vanadium V 70 0.7 0.175 1.8_ ank__Zn 50 0.5 0.125 43_ bromide Br 730 7.3 1.825 20_ chloride Cl 92000 920 230 616_ fluoride F 1400 14 33 55_ sulfate S04 308000 ~ 308Q 77p | 1730 | TABLE 2

Embodiment example 4:

Granulite is first mixed with water and dissolves with difficulty, after which Bestone microsand with a mixing percentage of 75% is added. The moisture content of the slurry is 27.7% on total. After pouring on a sandy substrate, the slurry dries up fairly quickly, but it remains slightly sludge-like. After pouring with a fixed amount of water, the first water comes through within half an hour. Technically this is a reasonable option. From an environmental health point of view this is a good option due to the lack of heavy metals in the slurry.

10 -11-

Embodiment example 5:

A composition of 45% microfine quartz powder (Millisil® M6), 45% microsand and 10% fly ash is diluted with water to 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 (SiO 2) higher than 99% is the basic raw material for this.

The mixture remains well in solution and dries out reasonably quickly after pouring. After pouring over with a fixed amount of water, the first water comes through after 10 minutes.

10 Technically this is a reasonably good solution. This is also a reasonable alternative from an environmental point of view. Selenium emissions are just at the limit of a current emission standard, see Table 3.

Leaching analyzes of non-shaped materials

Mixing percentage: 10% fly ash

Parameter fly ash maximum L / S = 1Ö emission ___ [pg / l] [mg / kgds] [mg / kgds] [mg / kgds] antimony exceedance Sb__6 ___ 0.06 0.006 0.16_ arsenic Ash 20 02 0.02 09_ barium__Ba 770__7.7 0.77 22_ cadmium Cd__4__0.04 0.004 0.04_ chrome__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 Z3_ moiybdenum Mo 800__8 05 \ _ nickel__Ni 10 0.1 0.01 0.44 0.44

selenium__Se 180__1.8 0.18 0.15 YES

tin__Sn 1__0.01 0.001 04_ vanadium V__70__0.7 0.07 18_ ank__Zn 50__0.5 0.05 45 bromide Br 730 7.3 0.73 20 chloride Cl 92000 920 92 616 fluoride F 14Q 14 14 55 sulphate S04 308000 3080 308 | 1730 | TABLE 3 -12-

Embodiment example 6:

Micro-silica is quartz powder with a quartz content greater than 85% in addition to some other natural minerals. A composition of 75% micro sand with 25% micro silica remains well in suspension at a moisture content between 20% and 30%, despite the fact that the slurry is reasonably thin in liquid. This makes the slurry particularly suitable for pumping and (sub-surface) injection.

After pouring the slurry dries quickly and after pouring with a fixed amount of water the first water comes through within 10 minutes. From a technical point of view this is a good alternative and also environmentally sound, because it is based on a naturally pure, uncontaminated starting material.

Embodiment example 7:

A composition of 50% micro sand, 43% millisil® M6 and 7% micro silica is mixed with water in a ratio of 75:25. The solid fraction remains well in solution and dries quickly after pouring. After pouring with a fixed amount of water, the first water comes through after 4 minutes. Technically this is a good option and the same applies from an environmental health perspective.

20 Embodiment Example 8:

A composition of 13% micro silica, 13% fly ash and the other microsand, is moistened with between 20% and 30% water. The solid fraction remains well in suspension and dries quickly after pouring. After pouring over with a fixed amount of water, the first water comes through after 3 minutes. Technically this is a good alternative.

25 This is a reasonable alternative from an environmental health point of view; selenium is just at the limit of the emission standard, see table 3.

The conclusion is that although powdered fly ash bed shows an excellent stabilization ring and filter action, sufficient mixtures can be assembled that have comparable properties and that, based on the origin of the material, fall within the emission requirements of the Soil Quality Decree or other criteria. -13- a current environmental regulation will fall. Moreover, an environmental choice can also be limited by a selective choice with regard to the fly ash used or a reduction of its share in the starting composition. Although the invention has been further elucidated above on the basis of only a few exemplary embodiments, it should therefore be clear that the invention is by no means limited thereto.

On the contrary, many variations and manifestations are still possible for the average person skilled in the art within the scope of the invention.

Claims (18)

1. Railway construction comprising a substructure on which a superstructure is arranged, which superstructure comprises a ballast bed with a series of sleepers placed at at least substantially regular distances from each other, to which a set of at least substantially parallel rails is connected, wherein between the superstructure and the substructure water-permeable stabilization layer is provided, characterized in that the stabilization layer comprises an at least substantially continuous, at least substantially homogeneous granular filter bed of a composition in which a microfine mineral powder is applied. 2. Railway construction as claimed in claim 1, characterized in that the stabilization layer comprises over an entire surface thereof an at least substantially contiguous granular filter bed of a fluid composition which comprises a microfine mineral powder. Railway construction according to claim 1 or 2, characterized in that the composition comprises moderately fine sand, in particular selected from a group of quartz sand and silver sand. 20 4. Railway construction as claimed in claim 1, 2 or 3, characterized in that the mineral powder is taken from a group of microfine quartz powder, ceramic powder and microfine puzzolane powder, in particular puzzolane powder taken from a group comprising fly ash, more in particular powder coal fly ash, and microfine granulite powder. Railway structure according to claim 1, 2, 3 or 4, characterized in that the filter bed comprises at least 20-30% microfine mineral powder. 2004722 Railroad construction according to claim 5, characterized in that the filter bed is at least almost completely composed of fly ash, in particular powdered coal fly ash. 7. Railway construction as claimed in claim 5, characterized in that the filter bed contains between 20% and 25% fly ash, in particular pulverized coal fly ash, and for the rest is at least substantially composed of fine sand. 8. Railway construction as claimed in claim 5, 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 otherwise at least substantially composed of fine sand. 9. Railway construction as claimed in claim 5, characterized in that the filter bed comprises between 10% and 15%, in particular approximately 13%, microfine quartz powder, in particular from a group comprising micro silica and millisil, between 10% and 15%, in particular approximately 13%, fly ash, in particular pulverized coal fly ash, and for the rest at least substantially composed of fine sand. 10. Railway construction as claimed in one or more of the foregoing claims, characterized in that the microfine mineral powder is at least almost completely at most extremely fine with a particle size of at most 63 micrometres. Railway construction according to one or more of the preceding claims, characterized in that the ballast bed is partially sunk in the filter bed. 25 Railroad construction according to one or more of claims 1 to 10, characterized in that the filter bed is enclosed between an underlying stabilized sand layer and an upper stabilized sand layer. Railway construction as claimed in one or more of the foregoing claims, characterized in that the filter bed has a thickness of at least 5 to 15 centimeters, in particular between 8 and 15 centimeters. A filter bed composition as applicable in the railway construction according to one or more of the preceding claims. A method for manufacturing a railway structure according to one or more of claims 1 to 12, characterized in that the composition is suspended with water to form a liquid slurry, that the slurry is spread on the subsurface and that a water fraction in the slurry is allowed to evade from it. 16. Method according to claim 15, characterized in that the slurry comprises between approximately 20% and 30% water. A method according to claim 15 or 16, characterized in that the slurry is poured onto the subsurface and the ballast bed is applied to the liquid slurry. 20 Method according to claim 15, 16 or 17, characterized in that the slurry is injected under the ballast bed. 2004722