soil-steel structure : inspection and rehabilitation...
TRANSCRIPT
Soil-Steel structure : inspection and rehabilitation methods
Pierre GILLES
• Public service of Wallonia
• General Inspector
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
Challenge
• Our challenge in Wallonia (South of Belgium)• About 500 steel culverts
• 10 % bridge stock
• 40-50 years
• Design life time : • 35 … 50 … 70 years
• Real life time may beshorter !
Goal of this presentation
• Small structures as soil-steel structures, need also to be managed
• Soil-steel structures
• Innovative aspects• Inspection methods
• Rehabilitation methods
Different shape and size
Circular profile Ellipse profile
Pipe arch
Arch
Ømax. ≤ 8 m
Max span ≤ 13 m
Max Span ≤ 12 m Opening >>
Opening : 0 to 15 m
Length : up to severalhundreds m
Use of soil-steel structures
• Cross an embankment• River
• Rural road
• Forestry road
• Low or high soil cover
Main problems
• Water infiltration
• Corrosion• From external face
• Water tabel
• From internal face• River
Main problems
• Deformation• Where :
• Local or Global
• Why :• Overloading
• Initial bad compaction
• Lose of compaction due to erosion
• Steel thickness reductiondue to corrosion
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
Investigation : Corrosion
• Core sampling : • outer face examination
• Water aggressiveness • pH
• Resistivity
• Cl- / SO4-- content
• What to measure ?• Local and global deformation
• Change over time
• How ?• Previously :
• Visual inspection (bad precision)
• Convergence measurement (slow)
• Actually :• Use of a 3D model
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Investigation deformation
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3D model
• How to obtain a 3D model ?• 3D scanner => direct
• Photos + software to assemble the photos
3D for soil-steel structures
• Analyse the 3D model to detect the outer and innerwaves
5-8 cm
3D for soil-steel structures
• Detection of each wave
Outer wave
Inner wave
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
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 1.2 m
• GRP : Glass fiber reinforced plastics : up to 4 m diameter
• Reinforcement• Shotcrete
• Concrete basement combine with cathodic protection
• ! Thickness (section reduction)
• ! Durability
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
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 masoneryculverts
• 2 new cases in 2018 with soil-steel structures
Basement and Cathodic protection
• Tidal zone• Medium corrosion
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
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
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
Pay attention on steel culvert
Questions ?