Transcribed from the June 1922 edition by David Price, email
ccx074@pglaf.org

(1,000—W. 192-7-22).

                          Great Western Railway.

                                * * * * *





                              INSTRUCTIONS.


                                * * * * *

                        SUPERELEVATION OR “CANT.”

                           EXPANSION OF RAILS.

                      GAUGE AND CHECKING OF CURVES.

                                * * * * *

                                                           W. W. GRIERSON,
                                                         _Chief Engineer_.

PADDINGTON,
         _June_, _1922_.




SUPERELEVATION OR “CANT.”


  _To be given to the Outer Rail in Curves ranging from 6 to 200 Chains
                                 Radius_.

  Offset      Radius       MINIMUM “CANT.”         MAXIMUM “CANT.”
 (Length        of
    of        Curve.
 Cord 66
   ft.)
                          Outer       For a       Outer       For a
                           rail      maximum     rail to     maximum
                          to be      speed of       be       speed of
                         raised.                 raised.
 Inches.     Chains.     Inches.    miles per    Inches.    miles per
                                       hr.                     hr.
       16½           6          3¾          20           6          25
        10          10          3½          25          5⅛          30
        6⅝          15          3⅜          30          4⅝          35
         5          20          3½          35          5¾          45
         4          25          2¾          35          4⅝          45
        3¼          30           3          40          4¾          50
        2¾          35          2⅝          40           4          50
        2½          40          2¼          40          5⅛          60
        2¼          45          2½          45          4½          60
         2          50          2¼          45          5⅝          70
        1⅝          60          1⅞          45          4⅝          70
        1⅜          70          1⅝          45           4          70
        1¼          80          1¾          50          3½          70
        1⅛          90          1½          50          3⅛          70
         1         100          1⅜          50          2¾          70
         ⅞         120          1⅛          50          2⅜          70
         ¾         140           1          50           2          70
         ⅝         160           ⅞          50          1¾          70
         ½         200           ¾          50          1⅜          70

The amount of “cant” to be given to a curve is governed by the speed at
which trains run over it, and in no case must the raising of the outer
rail in Running Lines be less than is given in the column headed “Minimum
Cant,” except where necessary to meet special cases, as at switches,
crossings and junctions.  In curves on falling gradients where high
speeds are run, the outer rail must be kept well up, while on rising
gradients a lesser “cant,” but within the limits of the latter, must be
given.  On gradients on single lines the outer rail of curves must, as a
rule, be raised to suit the speed of descending trains.

The superelevation must be gradually attained at the rate of 1 inch in
each 66 feet length as the curve is approached, maintained uniformly over
the whole length of the curve, and run out after passing the curve in the
same way.

On reverse curves, or curves with very short pieces of straight between
them, the “cant” must be made gradually on the curves commencing at the
middle of the short piece of straight in the latter case.



EXPLANATION.


Stretch a cord measuring exactly a chain (66 feet) across the inner side
of the curve, and measure the distance (C D) between the inner edge of
the rail and the cord, as shewn in sketch below.

Look for this measurement in the column headed “Offset,” opposite to
which, in the column headed “Radius of Curve,” will be found the radius
of the curve in chains; and in the columns headed “Minimum Cant” or
“Maximum Cant” will be found how much the outer rail is to be raised
above the inner one, according to the speed of trains.

         [Picture: Diagram showing the above curve, offset etc.]



EXAMPLE.


Suppose the distance between the inner edge of the rail and the cord at C
D is found to be 2½ inches, the column headed “Radius of Curve,” shews it
to have a curve of 40 chains radius; and those headed “Minimum Cant” or
“Maximum Cant” will shew that the outer rail must be raised 2¼ inches
higher than the inner one for a speed of 40 miles an hour, or 5⅛ inches
for a speed of 60 miles an hour.




EXPANSION OF RAILS.


In laying the 45 ft., 44 ft. 6 in., 39 ft. 5 in., 32 ft., 29 ft. and 26
ft. lengths of rails, the following spaces must be left at the joints,
according to the temperature for the expansion and contraction of the
metal, viz.:—

      Air            NATURE OF               Length of Rail.
  Temperature.        WEATHER.
    (Degrees
  Fahrenheit.)
                                         45′ 0″            32′ 0″
                                         44′ 6″            29′ 0″
                                         39′ 5″            26′ 0″
       80         In hot Summer          5/32″             3/32″
                  weather
       60         In moderately            ¼″              3/16″
                  cool weather
       30         In cold Winter         13/32″            9/32″
                  weather

For laying down new permanent way iron expansion gauges, equal in
thickness to the respective spaces given, to be used.

Wooden gauges must on no account be allowed.

The expansion granges must, as far as possible, be allowed to remain in
the joints until they are properly fished up, and the road slewed into
its proper line and “topped.”




GAUGE AND CHECKING OF CURVES.


When laying new lines, or relaying in curves of 10 chains radius and
above in plain line work, the gauge of the road must be laid to the
standard width of 4 ft. 8½ in., but in curves of less than 10 chains
radius, worked over by Passenger and Goods Trains, the gauge may be
slightly eased according to the radius of the curve and other
circumstances.

The check rail in plain road is to be second-hand bull-head rail, and all
curves of Passenger lines of 10 chains radius, and under, must be
continuously checked; the check rail in all cases to extend, where
possible, for a length of 50 feet or thereabouts outside the commencing
and terminating points of the curve to be checked.

Continuous check chairs for plain road, are of two patterns, one allowing
a clearance of 1¾ in. to be used in curves of 10 chains radius, and the
other allowing a clearance of 2 in. to be used in curves under 10 chains,
both rails in each, case being level on top.

In sharp reverse or “S” curves in plain line work where a piece of
straight line cannot be given, the junction of the two curves must be
laid with check rails on both sides, each check to be laid to cover the
other for a safe distance.