Railway track structure
United States Patent [1 1 Uzuka m1. 3,878,987 [451 Apr. 22, 1975 RAILWAY TRACK STRUCTURE ABSTRACT An improved track structure which can hold the progress track irregularities under high-speed, high axle load and high-density train operation to a minimum, with the settling of conventional ballasted track structures due to the ballast being minimized. In the improved track structure, large panel sleepers or reinforced concrete including prestressed concrete or of steel are placed on the bottom ballast previously fully rolled to flatness with the gaps filled in with smaller crushed stones; the top-ballast is spread and rolled around the sleepers; rails are laid and fastened over the sleepers; the rail top is lifted to a specified height; a quick-hardening material is injected into the space between the base of the sleepers and the top surface of the bottom ballast to form an elastic hardened layer; a waterproof coat. made of .a quick-hardening waterproofing material is provided on the surface of the top ballast; and a gutter to drain the rainwater from the ballast is provided along the sides of ballast.  
 17 Claims, 7 Drawing Figures PATENTEDAPRZEIHTS SHEET 1 0F 5 FIG.I(a)  
 PMENTEBAFRZZiQFS SHEET 2 0F 5 Fl G.I(c)  
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 sumaq g FlG.l(e)  
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 PATENLEAPRZZEB SHEET u or 5 FIGQ 2(a) RAILWAY TRACK STRUCTURE BACKGROUND OF THE INVENTION The present invention relates to an improvement of the ballasted track structure. The present invention provides particularly an improved track structure which can hold the progress of track irregularitiesunder high-speed, high axle load and high-density train operation to a minimum, with the settling of the conventional ballasted track structure due to the ballast being minimized.  
  The commonly used railway track structure is a socalled ballasted track structure, wherein cross-ties are continuously laid on ballast, with rails fastened to the cross-ties by means of a rail-fastening device. Thus structure has been primarily designed for facilitating the correction of track irregularities caused by ballast settling under train load. In one of the known repair procedure, the ballast is vibrationally compacted by means of tie-tampers, etc. The width of the cross-ties is commonly set at 20-30 cm and the tie-to-tie distance set at least at 20 cm. These values have been chosen to permit effective work with the tie-tamper, etc. It is desirable, however, as mentioned hereinafter that, if possible, the width of the ties be increased to give a greater base and width. Meanwhile, it has been revealed that the vibrational compaction by tie-tampers or the like itself contributes to the settling of ballast.  
  In his basic survey before development of a track structure with minimum settling, the present inventor found the items listed in Table l to be the factors causing rail deflections in the ballast track structure of the prior art.  
 TABLE 1 beds. which have been in service under track for 20-30 years, the degree of such settling has been negligible. The conventional ballasted track structure, however, is inherently not free from the factors listed in Table I, i.e., the factors other than those mentioned above.  
  In addition to the above-mentioned ballasted track structure, recently a ballastless&#34; slab track structure has been proposed as an improvement. This proposal is fundamentally different from the ballasted one in that an elastic deformation of the track in the former absorbs energy of train and an artificial correction of track is not needed. But, if in this structure the heavy train load is to be borne through elastic deformation alone, special installation will be required for spreading the load and providing elastic elements. Thus, it would particularly be difficult to realize such a stucture through a short-term work on lines with ballasted track in existence.  
 SUMMARY OF THE INVENTION In view of the disadvantages of these conventional track structures for railways, an object of the present invention is to provide an improved ballasted track structure which is free from the major factors causing rail deflection inherent in the conventional ballasted track structure and the attendant maintenance practice, and which can minimize the progress of track irregularities under high-speed, [high axle load and high density train operation.  
  Another object of the present invention is to provide an improved ballasted track structure in which large panel sleepers with increased dimensions consistent with workability are placed on the elastic hardened Site of Deflection Description of Cause Phenomena Cutting of rail into wood Sleeper rail Compressive failure of sleeper, wood under Wear of P.C. tie bottom Insufficiency of contact area with ballast Ballast Ballast pumping Sinking of ballast into roadbed and mud-pumping (ballast pocket) Loss of gap between ballast stones due to compaction Pulverization of ballast and mud-pumping in ballast &#34;Sifting&#34; of ballast Dust from concrete tie and from ballast turned into mud after rainfall and cause mud-pumping under the train road.  
 Combination of three factors; bad bed. rainwater penetration and ballast pressure.  
 Gap created between stones as result of ballast maintenance work Ballast maintenance work; pulverization due to acceleration of ballast vibration; and invasion of rainwater.  
 Increased acceleration of ballast vibrations (due to train speed up) Road bed Settling due to compaction Insufficiency of fillings; lnsufficiency of rolling work Natural ground Settling due to compression Poor geology Among the settling-causing factors enumerated above, the cutting of rail into wood is a phenomenon .peculiar to the wooden sleepers and never occurs in P.  
 C. ties. Meanwhile the compression settling of roadbed or natural ground is attributable to poor geology or a fresh roadbed. On elevated track, in tunnels or roadlayer formed in the ballast, thereby the flat area and weight being utilized to spread the train load and miti- 65 gate vibration.  
 jection material, thereby mitigating an excessive ballast vibration. I y I I I An additional object is to coat the top ballast surface with a waterproof layer to prevent the rainwater from invading the ballast or roadbed, thereby averting a rail deflection as far as possible. I  
  Still another object of the present invention is to provide an improved ballasted track structure which can be installed easily and with few materials and within limited train intervals by using a quick hardening material and which permits train operation immediately after installation.  
  The problems of the prior art are solved by the present invention which provides for a-railway track structure comprising a bottom ballast having a relatively flat uppersurface; at least one large panel sleeper of reinforced concrete including prestressed concrete or steel disposed over said bottom ballast; top ballast disposed around said large panel sleeper; a quick-hardening material injected between the base of said large panel sleeper andthe adjacent upper surface of said bottom ballast and a waterproof layer of a quick-hardening waterproofing material provided on the upper surface of said top ballast. Preferably, gutters with at least one through hole in .the wall adjoining the ballast are provided along, the longitudinal sides of the ballast. Advantag eously, the waterproof layer is provided with a drainage gradient. Crushed stones most suitably of a size smaller thanthat of the bottom ballast are disposed on the upper surface of the bottom ballast thereby controlling the depth of the injected material into the ballast. Preferabl y,&#39;:the injected, quick-hardening material is of a thermoplastic nature, such as asphalt, synthetic resin or combinations thereof, which fills adjacent voids in the ballast. Most preferably, the ballast around the large panel sleeper is consolidated with the injected material, thereby increasing the ballast resistance.  
  The present invention further relates to a method for making a railway track structure comprising rolling bottom ballast to substantial flatness; placing at least one large panel sleeper of reinforced concrete including prestressed concrete or steel on said bottom ballast; spreading and rolling top ballast around said large panel sleeper, lifting said large panel sleeper; injecting a quick-hardening injection material into the space created between the base of said large panel sleeper and the surface of said bottom ballast beneath said large panel sleeper and coating with a waterproof layer of a quick-hardening waterproofing material the exposed top surface of said top ballast. Preferably, gutters with at least one through hole in the wall adjoining the ballast are provided along the longitudinal sides of the ballast. Advantageously, the waterproof layer formed on the top surface of said top ballast is provided with a drainage gradient. Most suitably, crushed stones of a size smaller than that of said bottom ballast are spread on the rolled surface of said bottom ballast prior to placing said large panel sleeper thereby controlling the injected depth of the material into the ballast. Preferably, quick-hardening injection material is of a thermoplastic nature, such as asphalt, synthetic resin or mix- &#39;tures thereof, and is injected in a hot molten state and allowed to cool and harden whereby an extensive solid mass is formed with the voids in the ballast filled up..  
 Most preferably, the ballast around said large panel sleeperis consolidated with said injection material, thereby increasing the ballast resistance.  
 BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description taken in conjunction with the drawings wherein:  
  FIG. 1 (a) is a plan view of an embodiment of the present invention.  
  FIG. I (b) is a sectional view along the line lb 1b of FIG. 1 (a).  
  FIG. 1 (c) is a sectional view along the line 10 1c of FIG. 1 (a) FIG. 1 (d) is a sectional view, corresponding to FIG. 1 (c), of another embodiment of the present invention.  
  FIG. 1 (e) is a plan view illustrating a third embodiment of the present invention.  
  FIG. 2 (a) is a plan view illustrating a fourth embodiment of the present invention.  
  FIG. 2 (b) is a sectional view along the line 2b 2b of FIG. 2 (a).  
 DETAILED DESCRIPTION Referring to FIGS. 1 (a) 1 (c), bottom ballast 3 has been elaborately rolled on a roadbed 8, with smaller crushed stones 32 filling the gaps therebetween. The height of the bottom ballast is usually set at about l5-25 cm. At a specified portion of the thus-formed ballast, usually at the center following the longitudinal axis of the ballast, are continuously placed, with a specified interval, large panel sleepers 2 and 2&#39; of the same size in two rows. The opposite sleepers 2 and 2, constituting the two rows, are arranged parallel with a specified spacing, ballast being spread and rolled around the sleepers to form top ballast 33. The height of the top ballast 33 is usually set at about l5-25 cm. Range of sizes of stones constituting top and bottom ballasts is usually IO- mm. Each large panel sleeper can be a prestressed concrete member with a profile as illustrated in FIGS. 1 (a) I (c) or a steel member of the prior art with art-cross section as illustrated by numeral 21 in FIG. 1 (d). The prestressed concrete sleepers 2 and 2&#39; illustrated in FIGS. 1 (a) (c) are approximately rectangular cubes, each with the top surfaces of the two end portions thereof in the axial direction of ballast being formed as downward inclined surfaces 24 (FIG. 1 (b)) at a certain angle and recess 31 being provided at the mid-point of the bottom surface. The large panel sleeper, however, can be a simple rectangular cube. Rails 1 are laid over these two rows of large panel sleepers and fixed thereto by rail-fastening devices 7 of the prior art provided at equal intervals in the longitudinal direction of the large panel sleepers.  
  In FIG. 1 (a) which illustrates the dimensions and layout of large panel sleepers and rail-fastening devices, the width W, of the large panel sleepers 2 and 2&#39; can be set at, e.g., cm for the narrow track gauge 1,067 mm and, say, cm for the standard track gauge of l,430 mm; while the length L can be set regardless of the track gauge, at from about 50 cm to 300 cm. To accomplish the purpose of the present invention, however, the valueof L is preferably over 50 cm. Desirable preferred values of the tie-to-tie distances g W can be as follows; g, 10 cm; W 18 cm for the narrow. gauge and about 20 cm for the standard gauge. The reason for selection of these values are as follows:  
  The value W has been selected tomake it possible to existing track in a limited time without dismantling the rails especially on so-called long-rail sections. The value of W, being set smaller than rail-to-rail distance RD permits easy insertionof a large panel sleeper between the rails and accordingly, the placement of the large panel sleepers in the position indicated in FIG. 1 (a) (&#39;e) can be made easily. The value of L, depends on the spacing of the rail fastening devices 7, the number of such devices to be provided on one large panel sleeper and tie-to-tie distance g Regardless, both design and handling restrictions make the value of over 50 cm desirable. Tieto-tie distance g,, for reasons of ballast resistance and working, is preferably about cm. W is automatically set from the relation between W and the track gauge. Two large panel sleepers laid in opposition to each other in the longitudinal direction of the ballast, when the ballast resistance is not large enough, may be linked together by say, turn buckle 23 of the prior art as illustrated in FIG. 1 (a), 1 (c) and 1 (d), thereby supplementing the ballast resistance.  
  FIGS. 2 (a) and 2 (b) illustrated another embodiment ofa large panel sleeper. In this case, large panel sleeper 22 can again be of reinforced concrete including prestressed concrete or of afi-shaped steel as in the embodiments of FIGS. 1 (a) l (e). However, large panel sleepers 22 are provided only inya single row with both rails being laid on the single row. An example of the desirable dimensions of a large panel sleeper in this embodiment, is as follows: L 73 cm; W 200 cm for the narrow gauge and 240 cm for the standard gauge; g about 10 cm. For the same reason as stated previously with respect to W, in FIGS. 1 (a) (c), it is desirablethat L be set smaller than the distance between the oppositely laid rails. When 12 rail-fastening devices are provided at equal spacing for every 10 m. of rail, the above condition will be brought about.  
  For all of the above embodiments elastic hardened layer 6 made of a quick-hardening injection material is formed in the space between the base of large panel sleepers 2, 2&#39; 21 and 22 and the surface of the bottom ballast beneath said large panel sleepers. The injection material can be a l 1 mixture, heated and molten, of a straight asphalt (penetration less than l0) and bronze asphalt (penetration l0 or an asphalt mixed with a small amount of a substance which is thermoplastic at low temperatures such as polyethylene. This injection material is injected into the large panel sleeper through injection holes 25. The injection material is necessarily heated before injection to improve fluidity to thereby fill up voids in the ballast. After passing through the voids in the ballast, the hot injectionmaterial goes also into the adjacent ballast. After cooling and hardening, the material consolidates the adjacent portion of the ballast into integral ballast cohesion 61. When cohesion takes place to the desired depth, it is possible to minimize vibrational deflection of ballast in the track structure of the invention. For accomplishment of this purpose, it is desirable to form different depths of the cohesion, depending on the site of (the track structure. If the siteis on a stable roadbed, cohesion 61 should extend through the total depth to the bottom of the bottom ballast 3. When the site is on.an  
 elevated track, where the rail expansion&#39;and contractiondue to the temperature variationtakes place separately from that of the bridge, it is desirable that the depth of cohesion 61 be set smaller than the ballast thicknesiso that the rail and bridge may bemutually insulated at. ballast layer. &#39;The depth of ballast cohesion 61 depends on the type of the injection material, the heating temperature forinjection and particle size of ballast including smaller crushed stones 32. In an experiment conducted by the inventor, when said asphalt preparation was injected in a hot state at 170C into a ballast of small crushed stones 32, 5 30 mm in diameter spread at 0.05 m m over&#39;bottom ballast 3 of stones l0 mm in diameter, cohesion 61 could be made to a uniform depth of about. 10 cm.  
  The vibrational acceleration of ballast differs depending on the train speed. According to the result of practically measuring a train running at over 200 km/hr., 25 cm thick ballast having a 10 cm thick top ballast developed 1 g in the top ballast and in the bottom ballast developed less than I g. Thus, it is learned that cohesion of the ballast to at least 10 cm from the top can effectively prevent the ballast deflection. It is known, meanwhile, that the depth of ballast cohesion is practically governed by spread amount of small crushed stones 32 and preferable range of thickness of small crushed stone layer is l-4 cm.  
  Quick hardening injection material penetrates not only downwardly into the lower portion of bottom ballast 3, but also, sideways reaching a height of several cm. above the top surface of the bottom ballast, causing a cohesion of the ballast. Consequently, the ballast resistance to the sleeper (resistance to longitudinal and transverse displacement of the sleeper in the horizontal direction) can be increased. If necessary, an, additional amount of the injection materialmay be spread over the ballast provided around the large panel sleeper, thereby creating a wider area of .ballastcohesion 61 On the surface of the ballast except. the area on which said large panel sleeper is laid there is provided waterproof layer 4 made of a quick-hardening waterproofing material. As the waterproofing material for this purpose a quick-hardening waterproofing material-of prior art such as cutback asphalt or filler bitumen may be employed. When waterproof layer 4 is constituted as an inclined surface with a progressively decreasing height toward both sides of the center of the sleeper in the axial direction of the ballast, a good drainage effect is obtained.  
  Meanwhile, along both sides of the ballast, gutters 5 with a U-shaped section are installed with the walls of gutters 5 contacting the ballast including more than one throughhole 51, to permit the egress of rainwater from the ballast. i  
  The track structure of this invention can be executed, for instance, in accordance with the following procedure.  
  In the case of a line of conventional track structure, the conventional cross-ties are first dismantled by a method of the prior art. Next a pair of the ballast is removed, thereafter the ballast is elaborately rolled to flatness by a roller of prior art, for instance, Vibroplate B PN 1,000, for form bottom ballast 3 of, e.g., l5-25 cm high. In this case, the finishing accuracy of the surface roughness of bottom ballast 3 may be, say, 1 cm. If necessary,- on the surface of the bottom ballast, smaller crushed stones, of, say, 5 20 mm diameter may be spread at a rate of 0.05 m/ m to fill existing gaps. A large panel sleeper (2 and 2&#39;, 21 or 22) is then disposed on bottom ballast 3, with the positional adjustment made&#39;by a method of the prior art. Ballast is then spread around the large panel sleepers and rolled by. for intance, a hand capacitor of the prior art to form top ballast layer 33 of l-25 cm high. Thereafter, rails l are fastened with rail-fastening devices 7 of the prior art to the large panel sleeper. A track skeleton thuscomposed of a plurality of large panel sleeper groups with a definite length of rails fastened thereto is lifted to a specified height by a jack of the prior art; and after fine lateral adjustment and adjustment of alignment and cross-level, is held in the lifted position. The standard amount oflift is about 20 mm on the average and the tolerance of the adjustments of alignment and cross-level is preferably less than 5 mm.  
  The space created, as the result of the track skeleton being lifted, between the base of the large panel sleepers 2-22 and the surface of the bottom ballast is filled with a quick-hardening material injected through through-hole 25 bored in the large panel sleeper 2-22, thereby forming an elastic hardened layer 6. As the quick-hardening material, for instance a l 1 mixture, heated and molten, of a straight asphalt (penetration less than and a bronze asphalt (penetration l0 is injected at about 170 180C, the quickhardening material may be spread also around the large panel sleeper. Meanwhile it is desirable that for instance a lime solution be preliminarily spread as a mold releasing agent over the base and sides of the sleeper and on the inside of the through-hole for injection. A wire stopper-removing provided at the through-hole 25 is also useful.  
  When the temperature of the injected material drops, say. below 50C, the lifted sleeper is lowered by removal of the jack, and, consequently, rails l are set into position. Next, the ballast surface except the area where the large panel sleepers lie is paved with a quickhardening waterproofing material with a drainage gradient, thereby forming waterproof layer 4. Waterproof layer 4 is desirably mm thick with a drainage gradient desirably of 2/l00 3/100. Thereafter, again using a method in the prior art the alignment and crosslevel are adjusted by means of rail-fastening devices 7 of the prior art and then the rails are prefectly fastened.  
  On both sides of the ballast are installed gutters 5 with a U-shaped cross section.  
  In the case of a fresh roadbed, ballast is spread and elaborately rolled to flatness to a specified height, to form the bottom ballast 3.  
  Thereafter the procedure as described above relating to a line of conventional track structure is followed. The same procedures as above are followed, whether it is the case, as illustrated in FIGS. 1 (a) (e), of large panel sleepers being arranged in two rows, or the case, as illustrated in FIGS. 2 (a) (b), of sleepers being arranged in a single row.  
  Through successive applications of the above procedures, a track structure of any desired length according to the present invention can be constructed.  
  In the track structure of the present invention, fine adjustments for track irregularities can be done with a method of prior art by means of rail-fastening devices 7, while a heavy settling of the track can be corrected by lifting the track skeleton to a definite height by means of a jack or the like and then injecting through injection hole 25 a quick-hardening material.  
 EXPERIMENT To confirm the beneficial effects of the present invention, the following tests were carried out to yield the indicated results: 1. Test conditions Ballast was spread and elaborately rolled to flatness to form a bottom ballast l5-25 cm high. The ballast was then filled with small crushed stones of 5 20 mm in diameter in an amount of 0.04 m -0.06 m m with thereon large panel prestressedconcrete sleepers, as illustrated in FIGS. 1 (a) (c) (2 m. long X 0.6 m. wide X 0.2 m. thick) were arranged. In this case, the thick-&#39; ness of small crushed stones layer was l-4 cm. Rails were laid and fastened thereon. Thereafter, ballast was spread and rolled around the large panel sleepers to form top ballast l5-25 cm high, and the track skeleton thus formed with lifted by a jack of the prior art. Thereupon, a 1 1 mixture, preliminarily heated and molton, of a straight asphalt (penetration less than 10) and a bronze (penetration l0 20) was amply poured through the injection hole 25 at a temperature of C. After the temperature of the injected mixture dropped below 50C, the lifted large panel sleepers were lowered through removal of the jack and the surface of top ballast 33 was paved with a quick-hardening waterproof material like cutback asphalt.  
  Using a cyclic vibration tester of the prior art, i.e., Vibrogir, the rate of track settling and the longitudinal and traverse resistance of the invented track structure and the traditional P.C. sleeper-crushed stone ballast were measured.  
 2. Test results (a) Measured results of track settling are as follows:  
  I. Effect of rainwater was not investigated in the present test. I  
  2. In the traditional P.C. sleeper-crushed stone ballast initial settling occurs every time maintenance is executed using a multiple tie-tamper, but in the track structure of the present invention the initial settling occurs only once. I  
  b. Results of ballast resistance measurements are as follows:  
  Longitudinal Transverse resistance y t/m resistance g t/m Traditional about l.0 about 1.0 RC sleeper crushed stone ballast Track strucabout 3.0 about 2.0 ture of present invention From the test data it is apparent with the track struc- I ture of the present invention that:  
  l. The train load-bearing area of large panel sleepers is more than 2.5 times as wide as that of the traditional PC sleeper and, correspondingly, the ballast pressure can be reduced.  
  2. The large panel sleeper used in the present invention is about three times as heavy as the traditional P.C. sleeper. The large panel sleeper and an elastic hardened layer formed thereunder work together as an integral supporting mass that can as a whole absorb train vibration.  
  3. Since there is established a plane contact between large panel sleeper and ballast through the injection material, there is no likelihood of mutual breaking and settling.  
  4. Since the part of ballast where the vibrational acceleration exceeds 1 g has been consolidated with the injection material, no vibrational deflection can take place.  
  5. Since the ballast surface is waterproofed, settling of ballast or roadbed caused by mud-pumping due to rainwater can be minimized, the resistance to the horizontal displacement of track can be increased, and the aggravation of track irregularities under high speed, high axle load and high-density train load can be minimized.  
  6. In the present invention, unlike the conventional ballasted track structure, is not intended for repairs to be made through vibrational compaction by means of a tie-tamper or the like. Accordingly, there can be no repetition of the initial deflection nor any pulverization of ballast by a tie-tamper.  
  7. Further, since a quick-hardening material is employed to form an elastic hardened layer and waterproof layer, the track structure of this invention can be installed even during short train intervals and the train operation can be resumed immediately after installation.  
  Thus this track structure is found economically advantageous in applications to the lines already in existence, since it saves manpower in track maintenance. Even in conjunction with a new line, it would be particularly effective where the compression settling of the roadbed is negligible or when the site is elevated or in a tunnel.  
 What is claimed is:  
  l. A railway track structure comprising a bottom ballast having a relatively flat upper surface, at least one large panel sleeper disposed over said bottom ballast; top ballast disposed around said large panel sleeper; a quick-hardening material injected between the base of said large panel sleeper and the adjacent upper surface of said bottom ballast and a waterproof layer of a quick-hardening waterproofing material /provided on the upper surface of said top ballast.  
  2. A railway track structure of claim 1 wherein gutters with at least one through hole in the wall adjoining the ballast are provided along the longitudinal sides of the ballast.  
 3. A railway track structure of claim 1 wherein the waterproof layer is provided with a drainage gradient,  
  4. A railway track structure of claim 1 wherein crushed stones of a size smaller than that of the bottom ballast are disposed on the upper surface of the bottom ballast thereby controlling the depth of the injected material into the ballast.  
  5. A railway track structure of claim 1 wherein the injected, quick-hardening material is of a thermoplastic nature which fills adjacent voids in the ballast.  
  6. A railway track structure of claim 5 wherein the injected quick-hardening material is asphalt.  
  7. A railway track structure of claim 5 wherein the injected quick-hardening material is a synthetic resin.  
  8. A railway track structure: of claim 5 wherein the injected quick hardening material is a mixture of asphalt and synthetic resin.  
  9. A railway track structure of claim 1, wherein the ballast around the large panel sleeper is consolidated with the injected material, thereby increasing the ballast resistance.  
  10. A railway track structure of claim 1 wherein said large panel sleeper is reinforced concrete.  
  11. The railway track structure of claim 1 wherein said large panel is steel.  
  12. A method for making a. railway track structure comprising rolling bottom ballast to substantial flatness placing at least one large panel. sleeper on said bottom ballast; spreading and rolling top ballast around said large panel sleeper; lifting said large panel sleeper; injecting a quick-hardening injection material into the space created between the base of said large panel sleeper and the surface of said bottom ballast beneath said large panel sleeper and coating with a waterproof layer of a quick-hardening waterproofing material the exposed top surface of said top ballast 13. A method of claim 12 wherein gutters with at leastone through hole in the wall adjoining the ballast are provided along the longitudinal sides of the ballast.  
  14. A method of claim 12 wherein the waterproof layerformed on the top surface of said top ballast is provided with a drainage gradient.  
  15. A method of claim 12 wherein crushed stones of a size smaller than that of said bottom ballast are spread on the rolled surface of said bottom ballast prior to placing said large panel sleeper thereby controlling the injected depth of the material into the ballast.  
 tion material, thereby increasing the ballast resistance.