Subsurface drainage Update on RMS standards and current issues

James AllenSupervising Pavement Engineer (flexible pavements)Engineering Technology Services BranchRoads and Maritime Services24 February 2014

Outline

• Moisture in rigid pavements• Update on technical documents• Highlight current issues

Moisture in rigid pavements

• Do I really need subsurface drainage?

• Is omitting subsurface drainage a wise decision?

• What happens if there is moisture in my pavement?

Moisture in rigid pavements

Moisture in rigid pavements

Purpose of pavement subsurface drains

Edge drains• Drain the base/subbase interface• Release hydraulic pressure• Prevent subgrade fines pumping• Prevent joint seal damage

Trench drains• Collect water from edge drains • Drain the pavement subgrade• Intercept ground water

Durability of pavement subsurface drains

Durability is important

• Precipitation occurs randomly throughout the pavements design life

Durability of pavement subsurface drains

Durability is important

• Precipitation occurs randomly throughout the pavements design life

• Construct to standards

Durability of pavement subsurface drains

Durability is important

• Precipitation occurs randomly throughout the pavements design life

• Construct to standards• Outlets must remain unblocked

What have we established?

• Yes moisture does get into our pavements• Yes we need subsurface drainage to extract the moisture• Yes we need to comply with our standards• Yes we need to provide effective outlets

New RMS technical documents

Information to assist in the design and construction process

Technical directions• Use of RMS standard pavement subsurface drainage drawings• Pavement subsurface drainage in embankments subject to

flooding

Technical Guide• Standard pavement subsurface drainage details

Use of RMS standard pavement subsurface drainage drawings

• Intention is for standard drawings to be applied to all pavements under typical conditions

• Some non-standard situations are identified• Non-standard situations require …..•Same drainage path•Equivalent capacity•Consider safety in design (construction and operation)•Similar or improved maintenance regime

Pavement subsurface drainage in embankments subject to flooding

Issues• Special case requires particular consideration• Inundation can saturate pavement and subgrade• Inundation leads to siltation• Flat grades reduce potential of SD to drain

Pavement subsurface drainage in embankments subject to flooding

Special conditions• Separate trench drains from high side of pavement• Include flushing points• Achieve minimum grades

Technical guide – Standard pavement subsurface drainage details

Technical guide – Standard pavement subsurface drainage details

• Provides instruction on applying the standard edge details• Specification information• Material information• Requirements for general conditions• Approach to non-standard conditions• Construction issues• Plan presentation requirements • Background to edge details and model drawings• Living document – reviewed in line with standard drawings

Current issues

• NFC pads under kerbs

Current issues

• NFC pads under kerbs• Daylighting SMZ

Current issues

• NFC pads under kerbs• Daylighting SMZ• Pavement interface drains

Current issues

• NFC pads under kerbs• Daylighting SMZ• Pavement interface drains• Bridge approach slabs

Current issues

• NFC pads under kerbs• Daylighting SMZ• Pavement interface drains• Bridge approach slabs• Achieving 0.5% grade at sags and

flat longitudinal grades

Current issues

• NFC pads under kerbs• Daylighting SMZ• Pavement interface drains• Bridge approach slabs• Achieving 0.5% grade at sags and

flat longitudinal grades• Rural details (no longitudinal

stormwater drains)

Current issues

• NFC pads under kerbs• Daylighting SMZ• Pavement interface drains• Bridge approach slabs• Achieving 0.5% grade at sags

and flat longitudinal grades• Rural details (no longitudinal

stormwater drains) • Clearance to WRSB post

footings AND anchor blocks

The way forward

• Release technical directions• Release technical guide• Review current edition of drawings

• Please raise any specific issues for consideration

Summary

• RMS requires subsurface drainage to be effective and durable• Compliance with standards and specifications is expected• New guidelines are expected to be released in the near future• We continue to work through the issues at hand