Minimum surcharge height design

Road surcharge definition:

Vertical spacing between the pipe head and design road level incl. structural pavement layers.

Culvert facilitiesRailway surcharge definition:

Vertical spacing between the pipe head and slippers bottom incl. groundwork layers.

The largest of the calculation data below should be considered as a minimum road/railway surcharge height.
Minimum road surcharge height is obtained as:

H=B/6 [m], H=B/8+0,2 [m], H≥0,6 m

Minimum railway surcharge height is obtained as:

H=B/4[m], H≥0,6 m

where:
H – surcharge height [m]
B – pipe diameter or span [m]

Culvert facilitiesShould pavement layers height exceed recommended minimum surcharge, aggregate backfill top must be 0.10-0.15 m over pipe level.

For special culverts, i.e. under main road ramps, min. surcharge height may be 0.3 m.

Static analysis must be performed whenever a culvert requires lesser surcharge or steel thickness is below standard value.

If traffic is required over a culvert, a minimum height of properly compacted surcharge layers or min. 1.2 of loose surcharge must be observed.

Concrete slabs over the structure are recommended for temporary pavement.Culvert facilities

In particularly demanding applications (pavement layers compaction or foundation underpinning with heavy equipment, soil jacking etc.), never compact soil with vibration rollers or stop heavy machinery/equipment over the culvert.

Culvert overhead soil should be jacked with cement and imported premix.