Handbook for Bridge Inspections - TSP2

9.1 ELEMENTS IN THE GROUND
101. Subsidence of Ground/Embarkments
Description
Vertical movements in the soil behind abutment, wing walls and infill etc. which do not affect the
bridge itself.
Degree of Damage
Error during the planning phase. The load capaci ty oflhe soi l has been overestimated .
• Incorrect material(s). Wrong compos ition of material has been used in the backfill.
'" Work incorrect ly exec uted - not as origina lly described.
* Loads. Traffic causes overloading.
'*' Damage caused by accidents, e.g. flooding
'" In-service damage, e.g. the results of erosion.
'" Relevant Measurement
* Levelling
'" Evenness
Degree of Damage/Consequences of the Damage
The degree of damage should be selected based on its scope and probable rale of development.
Basically subsidence can be of significance fo r traffic safety, maintenance costs and the environment.
In fact subsidence behind abutment piers can result in differences in the height of the road
surface where intill and pavement meet. This in turn has implications for traffic safety. Height diffe
rences can also lead to impact in the joints and consequent noise pollution for those living in the
vicin ity of the bridge.
Conditions Triggering Maintenance Measures
The inspector must assess each case indi vidua lly. If the lengthwise height difference for the carriageway
on a main road exceeds 20 mm (or 30 mm for other national roads) when measured with a
2m long straightedge, then the necessary maintenance measures should be set in motion.
Maintenance Measures
* Fill in with sui table material(s)
* Small differences in he igh t can be evened out with asphalt
• If the subsidence continues then consideration should be given to replacing the entire inti II
behind the abutment.