Sleeper Cribs:-
Sleeper Cribs are required for supporting the rail clusters or Service spans at a particular height. Sleeper cribs are designed for a base loading of 1 Ton/Sq ft. If it is considered that soil is not fit for this loading, boulders must first be laid in such a manner as to spread the load until a safe bearing pressure is reached. The top surface of boulders is leveled with smaller stones to form an even surface for the first layer of sleepers. Single Cribs of wooden sleepers are made for height up to 3.05 meters (10ft),whereas double cribs are made for greater heights.
Following points require special attention during construction of cribs.
(i) Size of crib depends upon the type & span of temporary girder and nature of rail.
(ii) Cribs should be constructed of good sound sleepers of size 2750x250x130mm(9’x10’x5”).
(iii) Sizes of sleeper cribs ranging from 1.525m to 7.625m(5ft to 25 for height and above along with speed restriction generally being followed for each, are given below:
(iv) Rails in sleeper cribs should be introduced at more than 1.83m(6’) interval in height.
(v) A layer of kacha plaster 75mm(3inches) thick should be laid on all exposed surfaces o the crib after the track has been laid to prevent danger from fire.
(vi) Should the height of the crib exceed 1.5m(5’),the cribs should be suitably tied with through bolts.
(vii) A watchman, equipped with fire fighting appliances such as fire buckets etc. should be employed to deal with any fire that may break out on the cribs.
(viii) Cribs forming abutments have to take the side thrust due to earth pressure of the embankment, apart from the load of the Engine& the train, and therefore such cribs require special attention. Normally an auxiliary crib is used behind the main crib to lower the plane at which the live load is applied and reduce the horizontal earth pressure on the main crib.
(ix) The arrangement of sleepers directly below the girder seating should be so done that the concentrated load gets spread over the length & breadth of cribs 16.26.
