Restoration of Traffic

After the necessary information has been collected, immediate and prompt action should be taken to restore traffic on the line. In the case of causeways, etc., it may be necessary to restore traffic by making temporary arrangements such as the insertion of a rail cluster or the provision of a temporary diversion. Arrangements should be made for adequate labour and permanent way material and the damaged track should be attended to as soon as possible.

It may be emphasized here that adequate labour is the most predominant requirement for the restoration of traffic. All engineers and inspectors should thoroughly acquaint themselves with all possible sources from where labour can be readily obtained in the event of a breach or a serious derailment in their section.

22.4.1 Diversions

Diversions are set up at those points in a track where there is some obstruction or where some reconstruction work is in progress. They may be classified into two main categories.

(a) Temporary diversions constructed around an obstruction to traffic, which are not likely to be used for more than 10 days.

(b) Semi-permanent diversions constructed for the special purpose of facilitating the reconstruction of lines, bridges, etc., which are likely to be used for a period of more than 10 days.

All trains must stop before entering a temporary diversion and proceed at highly minimized speeds. On a semi-permanent diversion, trains may proceed at a nonstop but reduced speed but only after an adequate period of construction.

Normally semi-permanent diversions are provided on Indian Railways with an initial speed requirement of zero, though this may be relaxed after the consolidation of the bank. A semi-permanent diversion should be laid according to the specifications presented in Table 22.4.

Table 22.4 Geometric elements for semi-permanent diversions

Item

BG

MG

NG

Radius of curve

Not less than 450 m

Not less than 300 m

Not less than 45 m

Gradient

Not steeper than 1 in 100

Not steeper than 1 in 80

Not steeper than 1 in 40

Superelevation

Normally there is no superelevation, but if it is provided, it should be limited to suit the speed permitted on the diversion and should run out at a rate not exceeding 12 mm (1/2") in 10 m (30 ft)

In difficult terrain, it may be necessary to lay curves of radius not less than 225 m on BG and 125 m on MG and adopt the steepest gradient on the section.

In addition to the standards specified in Table 22.4, it is desirable that a semipermanent diversion have the following features.

(a) The existing bank should not be cut to lay the diversion.

(b) The gradient should be suitably compensated for curvature in order to ensure that in spite of the curvature, the gradient does not exceed the limiting value specified in Table 22.4.

(c) If the diversion includes a bridge with cribs, a straight and level portion of 30 m (100 ft) should be provided on either approach to the bridge.

(d) To guard against the possible settling of the diversion a blanket of coal ash should be provided on the new embankment and rolled if possible.

Plan and longitudinal section of diversion

The plan laid to ensure that the diversion settles in its place is illustrated in Fig. 22.2.

The formulae used in connection with the same are the following:

where L is the length of half the diversion measured along the original alignment, D is the maximum distance of diversion from the original alignment, C is the straight line between the two reverse curves connecting the original alignment to the diversion, which is not less than 30 m (100 ft), S is the straight portion of the diversion that is parallel to the original alignment, R is the radius of the curve, and T is the length of tangent.

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