In normal case, railway track is laid on ballast at formation level over blanket layer which rests on embankment. Strengthening layer of any cohesive material is provided on side slopes of embankment. Between blanket and embankment, there can be embankment sub-grade that would be of defined thickness and follows the required cross slope.
A drainage layer is laid first on the bare ground so that the water seepage is encountered effectively. When the ground is not of good quality, it needs to be treated. That can be done by excavating the ground and filling it with sand or any other material as per design.
Lined or unlined drain is provided at the ends where side slopes meet the ground.
At places where formation level is very high because of design requirement that results in very high embankment. High embankment is achieved at site by providing side slope berms of specific widths at regular depth intervals say around 3 to 6 mts. When strengthening layer/layers are provided, those should follow the side slopes with berms.
At places like yard area, sleepers are laid over layers of different material like WBM, stone soling, sub-grade that can be over or below the existing ground.
In case of doubling, center line of the proposed track will be outside the construction area, hence there can be challenges in relating the exact location of the cross section with reference to the existing track’s center line. Moreover, the offset distance between the center line to new line could be changing chainage to chainage.