BRITISH RAILWAYS 1920 - 1970

 

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TRACKWORK TERMS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TRACKWORK, TERMS 

 

 

 

 

Ballast: the aggregate on which the track is laid. Typically this material consists of two layers: a lower spread of hardcore which may cover the whole of the formation, depending on the drainage conditions, and an upper layer of angular rock chippings in which the track is set. This 'top ballast' prevents movement of the sleepers.

Blanketing: an intermediate layer, spread between the formation and the hardcore of the ballast, to prevent clay subsoil from working upwards into the ballast. The blanketing may consist of sharp gravel, sand-grade material or concrete.

Chair fastening: the method of fixing the track-chairs to the sleepers; the G.W.R. used bolts whereas other companies used large forms of coach screws.

Creep (of rails): the tendency of rails to move gradually in the direction of the traffic. In the case of keyed bull-head track the keys are inserted in the direction of traffic to counteract this effect.

Crossing vee (or frog): a component of pointwork (q.v.).

Formation: the surface of the ground on which the track road-bed is laid; the design of the road-bed is governed by the nature of the ground and its load-bearing properties. Weak soils may be stabilised by subsoil injection or surface dressing with cement, resin, bitumen or asphalt.

Key: a wooden or coiled metallic wedge used to hold rail correctly in the chair. See creep.

Loading gauge: Certain lines had reduced clearances but the passenger stock gauge for a typical free user coach (revised 1965) had the following maximum dimensions:

Coach body width: 9’0” (9’3” including handles and bottom hinges)

Coach height (rail level to roof): 12’41/2”

(rail level to top of roof projections: 12’10”)

Height to centre of buffing gear (from rail level): 3’51/2”

Width of centres of buffing gear: 5’81/2”

Height to footboards (from rail level): 3’8”

(platform heights typically 2’9” to 3’0”)

Packing: the maintenance of a well compacted ballast-fill against the sleepers, to provide a level and stable track-bed.

Plain line: simple trackwork, without pointwork.
 

Pointwork: simple points (or switches) provide a single bifurcation of the line and can be classed as 'facing' or 'trailing' according to the direction of traffic; the former are fitted with locks. The components of a simple point and other forms of more complex pointwork are shown in the figure above.

   Catch points are fitted in the trailing direction in order to deflect and derail runaway stock from the running line e.g. at the foot of gradients; these are spring-controlled and normally stand open. They may be fitted in other situations such as the throats of sidings, where special locking arrangements apply.

   Stub point (or switch): an early form of pointwork which consisted of a single length of rail which was displaced sideways to bring it into alignment with one of the two diverging tracks.

Rail: prior to nationalisation British trackwork used bull-head rail of rolled steel weighing 95 lb/yd, keyed in chairs. Rail lengths were variously 36, 60, 90 or 120ft long. Lengths of 39ft were imported from the U.S.A. during the war. In 1949 the Railway Executive adopted a new standard of flat-bottom rail at 109 lb/yd; this was superseded in 1960 by a new heavier British Standard 110A

   flat-bottom rail. The advent of continuous-welded rail, which had been introduced experimentally by the L.N.E.R., provided for rail lengths of up to 1500ft, from 60ft manufactured lengths of manganese/steel alloy.

   Check rail: an additional rail fitted on the inside of the inner rail on curves of less than 660ft radius and on pointwork, in order to take part of the side thrust. The gap between the rails (or flangeway) is 1Ύin.

   Closure, point, splice, stock, switch, wing rails: see figure above.

Running line classification: after 1948 all sections of line on British railways were classified in four main categories:

   A. Lines subject to speeds exceeding 60mph over which 12 or more express trains operate in winter timetables every 24 hours.

   B1. Lines subject to speeds of 60mph and over, but not classified as A.

   B2. Lines carrying intensive traffic, though the speed is less than 60mph

   C. Lines subject to maximum speeds of 60mph.

   D. Lines subject to speeds of less than 45mph.

   Category A and (some) B lines were laid with 110 lb/yd flat-bottom rail. Category C and D lines were generally laid with serviceable rail recovered from main line relaying or from redundant lines.

Run-round facilities: the most common form of trackwork which enables a train locomotive to run round its train at a terminal station in order to reverse direction is that of a loop, fed by trailing and facing points, and parallel to the platform road. Other methods of releasing the train locomotive include the use of station pilot locomotives at large termini. Less common systems involved the use of traversers (as at Birmingham Moor Street, G.W.R.), gravity shunting (as at Cowes, I.O.W.C.R., Maiden Newton, G.W.R., Wellington, Salop, L.N.W.R and Yelverton, G.W.R.), a sector table or 'turntable point' (as at Bembridge, I.O.W.R. and Ventnor, I.O.W.R.) or a turntable (as at Rothbury, N.B.R.)

Sleeper: a rail spacer of softwood (e.g. fir), hardwood (e.g. oak, jarrah, sal, teak), steel, pre-stressed concrete or post-stressed concrete. The use of steel sleepers on British railways was limited and none was installed since before 1939. Wooden sleepers are typically 8ft 6in long, 10in wide and 5in thick. A chaired and creosoted sleeper weighs 237lb; a pre-stressed concrete sleeper, as standardised by B.R., weighs 5Όcwt, complete with fastenings.

Sleepers are typically placed at 2112 per mile of track: spaced at 1ft 81/2in at joins, then 2ft 31/2in, then 2ft 71/4in nominal.

Switch: see pointwork.

Track gauge: the distance between the inner faces of the rails. After the Gauge Act of 1846, the standard gauge was defined as 4'81/2", later modified by B.R. to 1432mm.

Track maintenance typically required a team of five men who worked on a fixed section of track: a ganger, a sub-ganger and three lengthmen. Subsequently the gang system was revised and the introduction of mechanised systems has led to the increasing use of track recording vehicles, automatic tamping machines, ballast cleaning machines and automatic lining machines for correction of alignment.

Transition curve: track of increasing curvature to provide the transition from straight track to 'radius' track laid on a set curve; the super-elevation is increased proportionally to the degree of curvature.

Turntable: a rotating section of track, enabling rolling stock, particularly locomotives, to be turned and/or to be propelled on to a selection of radial exit roads. The early turntables were 'unbalanced', rigid, and with the centre of gravity over a bearing at the centre of the rotating span. 'Articulated', or centre-hinged, versions were vertically hinged in the centre and acted as two independent spans, but rotated as one unit. Continuous or three point systems consisted of a rigid span, whose load was spread on a circle of pit rails and on a centre bearing. Such turntables were moved manually or by vacuum or electric power. They were also classed as overgirder (rigid) or undergirder, according to the disposition of the supporting span.

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