Variable thickness fabric mat for railway track structure and method

A variable thickness fabric mat for use with railroad track right of way beneath the track structure. The mat has a central portion of predetermined thickness, and lateral shoulder portions of a reduced thickness as compared to said cental portion, with the central portion being of a predetermined width of adequate dimension to generally completely underlie the railroad track structure. The mat provides a method for transmission of force from a train on the railroad track structure to be spread over a greater area of the underlying earth bearing surface, and with the mat possessing the capability of passing water, and aiding in draining water from the soil beneath the mat, as well as from the top and sides of the track support.

This invention relates to general to a resilient mat adapted to underlie a 
railroad track structure along its right of way, for more uniformly 
distributing the loads from trains passing thereover to the underlying 
earth bearing area, and more particularly relates to a variable thickness, 
fabric mat adapted for underlying the railroad track structure along the 
right of way and wherein the thicker central portion thereof underlies the 
track structure, and thinner lateral shoulder portions of the mat extend 
laterally from such thicker portion. The mat in addition to more uniformly 
distributing the forces of a train moving on the track structure, to the 
underlying bearing soil areas, aids in drainage of water from the soil and 
from above the track support, and helps to stabilize poor support areas of 
soil. A method of utilizing the mat is also disclosed. 
BACKGROUND OF THE INVENTION 
Non-woven mats for use under roads and under railroad track structure along 
the right of way, are well known in the art. One such arrangement is 
disclosed in U.S. Pat. No. 3,670,506, dated June 20, 1972 and entitled 
"Process for Stabilizing Soils", and is directed to a method of utilizing 
non-woven fabric in poor support areas. Other prior publications include, 
for instance, an article entitled "Testing of Subgrade Stabilization 
Fabrics Moves Ahead" in the October 1976 publication of Railway Track and 
Structures. However, to applicant's knowledge, these prior art mats as 
used in the environments indicated are of generally uniform thickness 
throughout. Moreover, such prior art mats are generally one unitary member 
formed of a predetermined substantially uniform thickness of fabric 
material, and cut into predetermined lengths for use at the site. 
Also in a pending U.S. patent application of Robert Luebke, Ser. No. 
092,709, filed Nov. 9, 1979, now U.S. Pat. No. 4,265,398, there is 
disclosed a variable thickness fabric mat for use under railroad track 
crossings, switches and the like, which patent application is assigned to 
the assignee of the present application. Various prior publications 
including aforementioned U.S. Pat. No. 3,670,506 are identified in said 
Luebke application, and reference by incorporation is made thereto. 
The present invention provides a novel variable thickness mat, adapted for 
use along a railroad track right of way beneath the track structure, so as 
to more uniformly distribute the force loads from a train to the 
underlying bearing support soil, and which will not impede drainage. The 
mat comprises a thicker central portion which underlies the track 
structure proper, thereby locating the thicker portion where it is most 
beneficial to the applied loads, and lateral shoulder portions of reduced 
thickness, as compared to the central portion, with such lateral shoulder 
portions projecting laterally beyond the confines of the track structure, 
and adapted to be covered by the ballast bed supporting the track 
structure. 
Accordingly, an object of the invention is to provide a novel variable 
thickness mat for use along a railroad right of way beneath the track 
structure for more uniformly distributing the force loads applied to the 
track structure due to traffic thereover, to the underlying soil bearing 
areas, and which will not impede drainage, but instead will actually 
facilitate the latter. 
Another object of the invention is to provide a mat of the aforementioned 
type which is formed of non-woven fabric. 
A still further object of the invention is to provide a mat of the above 
described type which is comprised of a plurality of layers of fabric 
material, with means connecting the layers together, to form an integral 
mat member. 
A still further object of the invention is to provide a mat of the 
aforementioned type which includes layers of non-woven fabric combined 
with at least one layer of woven fabric, together with means connecting 
the layers together into an integral mat member. 
A further object of the invention is to provide a railroad track structure 
utilizing a mat of the aforediscussed type. 
A still further object of the invention is to provide a method in a 
railroad track environment of reducing the stresses thereto utilizing a 
fabric mat underlying the railroad track structure. 
Other objects and advantages of the invention will be apparent from the 
following description, taken in conjunction with the accompanying drawings 
wherein:

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now again to the drawings, there is illustrated in FIG. 1 a 
railroad right of way including track structure 10 comprising ties 12 
supported on and embedded in ballast bed 14, with the ties, in the 
embodiment illustrated, supporting thereon conventional tie plates 16, on 
which are supported spaced rails 18. Any suitable means can be provided 
for anchoring or securing the rails and/or tie plates to the ties. 
Normally, the ballast bed rests directly on a bearing ground surface 20 
which has preferably been previously leveled, as by a bulldozer, track bed 
plow, undercutter, or the like, and which may or may not provide a good 
bearing surface. Many times tracks are laid through soft or wet soils 
which do not provide a good support for the track structure, and 
therefore, the forces applied to the track structure by the trains moving 
thereover can affect the track stability, cause undue wear and problems, 
fouled ballast, and including failure, in the track structure. 
Accordingly, in order to attempt to stabilize the ground bearing surfaces 
and to more uniformly apply the force from the vehicles moving over the 
track structure, to the underlying soil bearing areas, it is known in the 
railroad field to use fabric mats including non-woven fabric mats beneath 
a layer of ballast so as to more evenly distribute the force loads to the 
bearing areas. 
In accordance with this invention, the mat 22 underlying the track 
structure 100, comprises a thicker central or track portion 24 and thinner 
lateral shoulder portions 26 on both sides of the central portion. In the 
embodiment illustrated in FIG. 2 the mat 22 is formed of a plurality of 
layers of non-woven synthetic fabric material with the central portion 24 
being partially formed of one layer 24a of fabric and the remainder of the 
central portion and the lateral shoulder portions 26 being formed of a 
further layer 26a of fabric, which layer 26a extends laterally of both 
sides of the top layer 24a. In this connection for purposes of underlying 
conventional United States gauge railroad track structure, the top layer 
24a of the central portion may be approximately 90" to 110" in width, 
while the bottom layer 26a which includes the lateral shoulder portions, 
may be approximately 150" to 186" in width, with each of the lateral 
shoulder portions being in the range of from approximately two and 
one-half feet wide to a little over three feet in width. Means 28 (FIG. 2) 
is provided connecting or bonding the layers forming the mat 22, together. 
Such means comprises, in the embodiment illustrated, intertwined fibers of 
the various layers of fabric, which intertwined fibers are produced by 
needle punching of the layers, resulting in an integral mat member. 
These mechanically interlocked fibers 28 due to the needle punching, may be 
produced in the conventional manner on needle looms, with the layers of 
fabric making up the mat being passed into the loom, and being connected 
as the needle barbs pass downwardly through the layers, interlocking 
engaged fibers of the mat into individual groups. The end results is a 
flexible layered, liquid pervious mat of high stability, with the layers 
thereof secured together by the punched fiber groups as diagrammatically 
illustrated in FIG. 2 at 28. 
Chemical binders of suitable known type may also be utilized between the 
layers of the mat, for aiding in connecting the layers together. For most 
purposes, however, and for the purposes of underlying railroad track 
structure with which the present product is particularly applicable, 
needle connecting or bonding is adequate, and is preferred, and chemical 
binders for attaching the mat layers 24a, 26a together are not necessary 
or even desirable, since such chemical binders may adversely effect the 
permeability of the mat. 
Non-woven fabrics for use in the construction and railroad industries are 
well known, with such fabrics as aforementioned being utilized in the 
construction industry for the laying of the automotive roadways as well as 
in railroad track routes. These known fabrics which are made from a 
plurality of materials, such as for instance from polyesters, are 
available from a plurality of companies, including the assignee of the 
instant invention. 
The mats are expeditiously utilizable with poor load bearing soils and form 
an effective resilient support bed for the railroad track structure in 
such an environment, to help support and spread the forces from wheeled 
traffic over the track structure, to the underlying ground bearing area. 
The mats readily pass runoff water and facilitate the drainage of the 
water from the railway right of way without impeding drainage. Such 
drainage is facilitated by the mat 22 from the top of the ballast bed 14 
down through the bed, as well as laterally or horizontally through the 
mat. The lateral shoulder portions 26 of the mat 22 underlying the 
shoulders 14a of the ballast bed aid in anchoring the bed in place as well 
as facilitating drainage of ground water laterally through the mat and 
from the overlying ballast bed. The mats also actually facilitate by 
surface tension, the passage of ground water from the underlying bearing 
ground surface 20, and filter out fine soil particles that might otherwise 
contaminate the track ballast, thus aiding in maintaining good drainage in 
the ballast bed, and improved stability of the bearing ground surface. 
In the mat structure illustrated in FIGS. 1 and 2, the central track 
portion 24 is preferably of from about 125 mil to 200 mil thickness, and 
the lateral shoulder portions are preferably of about 60 to 100 mil 
thickness. As shown in FIG. 1, the ballast bed 14 preferably fully covers 
the lateral shoulder portions 26 of the mat. 
Layer 24a of the mat is preferably saturated by any suitable means, such as 
by dipping or spraying, with a synthetic resin-like binder, such as for 
instance a thermosetting self cross linking acrylic co-polymer emulsion 
(e.g. Nacryl No. 977 obtainable from Derby Chemical Company of Ashland, 
Mass.) Thereafter the layer 24a of needle punched non-woven material and 
binder is subjected to a blast of air operable to drive off the excess 
binder, and then is oven dried at suitable temperature, to set the 
resin-like material dispersed throughout the fibers of layer 24a. Such a 
resin-like impregnating treatment of the non-woven fabric layer 24a does 
not materially affect the permeability of the fabric to fluid flow, but 
does substantially increase the tensile strength of the fabric of the mat, 
as well as increasing the abrasion resistance of the layer 24a. 
Thereafter layer 24a is passed through the loom together with 
aforementioned layer 26a, and is needle punched by the needle barbs of the 
loom, to mechanically bond or connect layers 24a, 26a together into an 
integral mat. While layer 26a of the mat could also be impregnated with a 
resin-like binder material, the latter is not required, and the economics 
of the situation generally dictates that such not be done. 
The finished mat may be provided in any desired lengths. For ease of 
handling and storage and ease of applying the mat to the railway track, 
lengths of approximately 300 feet have been found to be convenient and can 
be rolled, and dropped off at the site of use (FIG. 6) for expeditious 
handling in laying on the bearing ground surface that has been prepared, 
such as for instance by leveling, prior to the placing of a layer or bed 
14 of ballast thereover. Also such mats can be inserted under existing 
track structure by the use of the aforementioned undercutter and track bed 
plow devices, by undercutting an existing track bed and track and 
inserting the fabric material under the track structure, while the latter 
is in raised condition, and then redepositing the ballast bed thereon and 
then lowering the track structure. Such undercutting and ballast 
redepositing procedures are known in the railway track art. 
The choice of the denier per filament or fiber used in the non-woven fabric 
is governed primarily by the requirements of the end product. However, a 
denier in the range of 3-9 is preferred for use in the FIG. 2 mat of the 
invention. In the embodiment of mat illustrated, the fibers from which the 
mat is formed are of non-continuous or cut type, preferably possessing a 
length of approximately 3-4 inches. However continuous fibers could also 
be utilized in formation of the fabric from which the mats are formed. In 
any event, in the mat of FIG. 2, layer 24a thereof defining in part center 
portion 24, preferably possesses a weight of approximately 8 to 12 oz. per 
square yard (this includes the weight of the resin-like binder), while 
layer 26a which defines shoulder portions 26 preferably possesses a weight 
of approximately 4 to 6 oz. per square yard. 
The following is a table which lists various typical physical 
characteristics of a polyester fabric mat of the FIG. 2 type embodiment. 
______________________________________ 
TEST 
PROPERTY VALUE METHOD 
______________________________________ 
Composition 
100% of Polyester Fiber 
Construction 
Needle Punch Bonding, Variable Thickness Fabric 
(Binder Impregnation of 
Track Section of Mat) 
Shoulder 
Track 
Grab Tensile, lbs 
80 175 ASTM D-1682 
(American 
Society of 
Testing Mat'ls.) 
Grab Elongation, % 
125 100 ASTM D-1682 
@ 10 lbs, % 40 5 
@ 25 lbs, % 70 20 
Trapezoid Tear, lbs 
50 100 ASTM D-2263 
Mullen Burst, lbs 
175 +300 Mullen Test 
Thickness, mils 
100 125 ASTM D-1777 
Width, inches 
30- 90 
30 
Abrasion Resistance 
50 75 Tabor Test 
(CS 17 Wheel, % ASTM D-1175 
Grab Strength 
Retained - 1000 gm 
weight, 1000 gm 
weight, 1000 cycles) 
Puncture Resist. lbs 
50 140 ASTM D-751 
EOS.sub.D50 U.S. Std. 
70 mesh 140 mesh Corps. of E. 
Sieve Sizes Test 
Air Perm. cfm 
250 150 ASTM D-737 
______________________________________ 
The non-woven synthetic fabrics used in the mat are preferably resistant to 
attacks by the components normally found in soils and in ground water, and 
aid in maintaining the ballast layer 14 free of fluids and well drained, 
any such fluid readily draining both laterally and vertically through the 
mat. The various layers of the mats may be formed of a polyester which is 
a stable, long-lived polymer, and preferably is of such porosity that the 
mat will hold back particles larger than about 70 microns, while generally 
permitting smaller water born fines to pass through without clogging or 
binding the fabric. 
Referring now to FIG. 3, there is illustrated another embodiment of pad or 
mat for use beneath railroad track structure. In this embodiment, a 
plurality of stacked fabric layers 30, 32, 34, 36 are provided, with the 
bottommost layer 30 comprising the shouldered portions 26 of the mat. In 
this embodiment, layers 30, 32 and 36 are formed of non-woven synthetic 
fabric material such as for instance from the aforementioned polyester, 
while layer 34 may be a relatively heavy denier monofilament synthetic 
fabric layer, providing a relatively large void section in the mat, 
thereby facilitating greater drainage of ground water laterally or 
horizontally through the mat. The heavy denier could be of the order of 10 
to 20 denier for the monofilament fiber. 
The various layers 30, 32, 34 and 36 are connected together into an 
integral mat, such as for instance by means of the aforementioned needle 
punching, as illustrated diagrammatically at 28, and in a similar manner 
as in the fabrication and connecting of juxtaposed layers of the mat of 
FIG. 2. 
The layers 32, 34 and 36 of the FIG. 3 mat may be impregnated with a 
resinous binder in the same manner as aforedescribed in connection with 
layer 24a of the FIG. 2 mat, which provides considerable abrasion 
resistance to the impregnated mat material, as well as increased tensile 
strength. Such resin-like binder material is preferably applied to the 
respective mat layer subsequent to the needle punching thereof to form the 
layer, but prior to the needle punching of the various layers to form the 
integral mat structure. 
The mat embodiment of FIG. 3 may be particularly useable where the ground 
support areas encompass considerable surface water, so that the water can 
more rapidly flow through the mat with reduced obstruction, and especially 
through the monofilament layer 34. The porosity of the other layers and 
denier of the filaments thereof may be generally similar to that 
aforedescribed in connection with the layers of the FIG. 2 mat embodiment. 
Referring now to FIG. 4, there is illustrated a further embodiment of mat 
structure. In this embodiment, the non-woven fabric layers 30', 32', 34' 
and 36' are of variable denier. For instance, layer 30' could be of 
between 1 to 3 denier per filament while layer 32' could be of between 
approximately 3 to 5 denier per filament, thus providing a greater 
strength to layer 32' as compared to layer 30'. Layer 34' could be of 5 to 
10 denier per filament, while layer 36' could likewise be of 5 to 10 
denier per filament, all of such layers being formed for instance from 
polyester filament. Also in this embodiment, the various layers 32', 34' 
and 36' may be impregnated with a resin-like binder as aforedescribed for 
FIGS. 2 and 3 providing improved tensile strength and abrasion resistance 
to the central portion of the mat during its use beneath railroad track 
structure. 
Referring to FIG. 5, there is illustrated a further embodiment of mat 
structure. In this embodiment, layers 30", 32" and 36" may be generally 
similar to the correspondingly numbered layers (except for the suffix 
prime) in the FIG. 3 embodiment. However, layer 34" in this embodiment 
comprises a woven synthetic fabric (as opposed to a non-woven synthetic 
fabric). Such woven layer may be formed of any suitable synthetic 
material, including polyester, and provides for strength reinforcement of 
the mat, and also increases its resistance to puncture. Also in this 
embodiment, the top surface of the uppermost layer 36" may be coated with 
an abrasion resistance non-apertured coating 40, such as for instance 
rubber, or plastic, or any other suitable material. Such a coating is 
adapted to resist wear and/or puncturing by the overlying ballast bed, and 
may be applied by spraying or by suitable adhesive means, or any other 
suitable means to provide a good attachment to the underlying confronting 
top surface of layer 36" of the mat. While coating 40 will substantially 
prevent the passage of water vertically down through the mat, it has 
practically no effect on water passage horizontally through the mat, 
and/or upwardly into the mat from the underlying ground surface 20. 
In all of these various embodiments of mats, it will be seen that they 
provide a generally resilient support for the railroad track structure, 
and more uniformly distribute the forces applied to the track structure by 
vehicles moving thereover, to the underlying ground support surfaces thus 
aiding in equalizing and reducing the stresses applied to the track 
structure itself. Moreover, these various mat structures actually increase 
the elimination of water from the underlying and adjacent ground bearing 
surfaces and the ballast bed, to thereby aid in stabilizing the ground 
bearing surfaces, and thereby further aiding in reducing stresses applied 
to the track structure by traffic moving thereover. 
From the foregoing discussion and accompanying drawings it will be seen 
that the invention provides a novel variable thickness mat adapted for use 
beneath a railroad track structure, for distributing the load on the track 
structure over increased area, and a mat structure which includes a 
thicker central portion adapted to underlie the railroad track structure 
per se, and lateral shoulder portions of reduced thickness, which are 
adapted to project laterally outwardly from the thicker central portion, 
and to underlie the ballast bed. 
The invention also provides a mat of the above type in conjunction with 
railroad track structure, for alleviating stresses applied to the track 
structure and for improving the condition of the ground bearing surfaces 
areas which support the track structure, and particularly being operable 
to improve poor bearing surfaces which have water problems associated 
therewith. 
The invention also provides a novel method of utilizing the mat and more 
evenly distributing the load from a railroad track and its associated 
ballast bed, along the railroad track right of way. 
The terms and expressions which have been used are used as terms of 
description, and not of limitation, and there is no intention in the use 
of such terms and expressions of excluding any equivalents of any of the 
features shown, or described, or portions thereof, and it is recognized 
that various modifications are possible within the scope of the invention 
claimed.