Question & Answer - What is the specification of blanketing material and how arrest the failure of railway embankment?

Qus.. What is the specification of blanketing material and how arrest the failure of railway embankment.

Ans:- The blanketing material should cover the entire width of formation from shoulder to shoulder except that in case of sent or similar erodible material. The depth of blanket should normally be about 30 cm ordinary clay soil. However if formation soil is week, a thickness layer up to 60 cm may be necessary depending upon the shear properties of the formation soil. Blanket material should have the following properties .

a. For sand, query, grit, gravel and other non cohesive material.

i. The blanket material should be coarse & granular.

ii. If the material the material contain plastic fine, the %age of fines should not exceed 5%. If fines are non plastic there can be allowed up to maximum of 12%

iii. The material should be properly graded to its particle size distribution.

b. For Mooram.

i. The liquid limit should not exceed 35% and plasticity index should be below 10.

ii. The uniformity coefficient should be above for and preferable about 7. Coefficient of curvature should be within 1&3.

iii. When mooram is used as blanketing material, should be compacted in layers at OMC so as to obtain optimum dry density.

iv. If erodible material is used as blanket. It should be conformed in a trench and sand drains should be provided across the cess to drain the track & blanket mechanical compaction of earth work are recommended for adoption. 

 These may require some modification to suit local condition.

i. Sub Grade compaction:- After site clearance all pockets and depression. Left in soil should be made good & compacted suitably.

ii. Method of compaction:- Earth work should be done in layer not exceeding 300mm to 600 mm thick. In the loose state with the static and vibratory rollers respectively. These layers should be compacted properly at or near the OMC to achieve the maximum den sity as per

15:2720(Pt-viii)-1983.

The cracks in the embankment can be avoided by adopting following methods.

1. Drainage of blanketing material should be kept adequate so as to avoid stagnation of

water in the formation.

2. Grass pitching should be done on side cess of embankment so as to restrict the propagation of cracks.