How to read box culvert drawing plan at site

From section B-B, Let us consider a box culvert of size 4x4 m.
A = clear span. Clear span is the discharge volume.
Clear span width is based on inflow and outflow of water. Based on factor of safety and H.F.L clear span volume will be decided. In factor of safety for load calculation we have to consider 2.5 times ( according to code book ) more than actual load.
F = wall thickness, B = height of vent.
The above figure is the single vent.
If there is heavy flow, then provide another vent beside the existing vent.
Here you can increase the size of vent when it is heavy flow, but because of heavy flow there will be damage in the outside discharge d/s side. The damage occurs because heavy flow occuring in the same place continuously.
Due to this reason, when there is heavy discharge another vent will be provided beside the existing vent.
In previous days culvert size will be taken as 2.5 m. After letter issued by forest department then size of culvert is minimum 4 m clear span and vent size is considered.
C = offset of raft foundation. Offset is provided for getting more strength.
In previous years box culvert is used to design only up to wall end portions. But in present designs engineers are providing offset also to get more strength.
D = slab.
PCC = profile correction course. Consider 100 mm. For PCC minimum M10 grade of concrete used or best grade.

From the section A-A, The width of the culvert can be taken according to the road width but 0.5 extra must be taken on both sides of road to provide crash barrier.
Road median will be provide on the center of proposed road.
the expansion joints will be provided in the 20 mm gap on road in L.H.S and R.H.S sides.

civil engineering