Soil-Steel structure : inspection and rehabilitation methods

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1 Pierre GILLES Soil-Steel structure : inspection and rehabilitation methods Public service of Wallonia General Inspector Pierre.gilles@spw.wallonie.be

2 Soil-steel structures Thin corrugated steel plates Wave profile Surrounded with well-compacted soil Vertical load on the culvert => deformation of the culvert => horizontal passive soil reaction

bridge stock 40-50 years Design life time :

3 Challenge Our challenge in Wallonia (South of Belgium) About 500 steel culverts 10 % bridge stock years Design life time : years Real life time may be shorter!

4 Goal of this presentation Small structures as soil-steel structures, need also to be managed Soil-steel structures Innovative aspects Inspection methods Rehabilitation methods

5 Different shape and size Circular profile Opening : 0 to 15 m Length : up to several hundreds m Ellipse profile Ømax. 8 m Pipe arch Max span 13 m Arch Max Span 12 m Opening >>

6 Use of soil-steel structures Cross an embankment River Rural road Forestry road Low or high soil cover

7 Main problems Water infiltration Corrosion From external face Water tabel From internal face River

8 Main problems Deformation Where : Local or Global Why : Overloading Initial bad compaction Lose of compaction due to erosion Steel thickness reduction due to corrosion

tolerance was often high => may be difficult to know Thickness may varies over length

9 Investigation : Corrosion Thickness measurement Ultrasonic measurement Wave profile => need small sensor Initial thickness Initial documents => nominal value Production tolerance was often high => may be difficult to know Thickness may varies over length (if cover height varies) Measurement following different generatrix Focus on Tidal zone

10 Investigation : Corrosion Core sampling : outer face examination Water aggressiveness ph Resistivity Cl - / SO4 -- content

11 Dimensions (Cm) (cm) Investigation deformation What to measure? Local and global deformation Change over time How? Previously : Visual inspection (bad precision) Convergence measurement (slow) Blue Red Actually : Use of a 3D model N Section profils Largeur H Hauteur V

12 3D model How to obtain a 3D model? 3D scanner => direct Photos + software to assemble the photos

13 3D for soil-steel structures Analyse the 3D model to detect the outer and inner waves 5-8 cm

14 3D for soil-steel structures Detection of each wave Outer wave Inner wave

15 3D for soil-steel structures Evolution over time : Compare different measurements Not really usefull Too much information Select several sections Regular distance Thin section with only 1 wave

16 3D for soil-steel structures Several section to compare Over time => evolution Over length => deformation detection

Rehabilitation How to rehabilitate? Local reinforcement What else? Replacement : difficult Insert a new tube inside Different materials PVC, HDPE, : limited diameter about 1.

17 Rehabilitation How to rehabilitate? Local reinforcement What else? Replacement : difficult Insert a new tube inside Different materials PVC, HDPE, : limited diameter about 1.2 m GRP : Glass fiber reinforced plastics : up to 4 m diameter Reinforcement Shotcrete Concrete basement combine with cathodic protection! Thickness (section reduction)! Durability

soil-steel structure Need a good knowledge of

18 GRP New tube able to accept full load transfert Prefabricated elements Section based on existing soil-steel structure Need a good knowledge of existing geometry (3D model can help) Section may change over length

19 GRP Void between soil-steel structure and GRP tube injected by cement grouting Advantages : Customized section High durability Allow section variation Few case in Wallonia with masonery culverts 2 new cases in 2018 with soil-steel structures

20 Basement and Cathodic protection Tidal zone Medium corrosion

21 Basement and Cathodic protection Bottom : Very severe corrosion Complete dissolution Corrosion from both side : water table River Acid water : ph 5.8 Structural problem Durability problem

22 Basement and Cathodic protection Structural : Reinforcement Reinforced concrete Internal tube Manage water during works Accept small river flow => manage the water level upstream of the culvert Durability : Cathodic protection External electrode Surrounding soil : 8 Silicon-Iron electrode at 1.2 m depth Internal electrode Concrete basement : 2 titane wires Imposed current system

23 Conclusion Small is also important! A steel culvert may also collapse => accident, fatalities, flooding, Soil-steel structures need To be inspected Deformation Corrosion To be rehabilitate Not easy Innovative methods may be used

24 Pay attention on steel culvert Questions?

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