Contents

  • Cover
  • Front matter
  • Introduction
  • Identifying and managing risk
    • Risk overview
    • Working smart and efficiently
    • Starting the job – be prepared
    • The job is not finished until it is signed-off
  • Basics
    • Roading terms
    • Basics about soil
  • Good construction
    • A well-constructed road
    • A well-constructed landing
  • Earthworks
    • The right machine for the task
    • Clearing and stripping
    • Cut and side cast construction
    • Cut and bench fill construction
    • Full bench construction with end-haul
    • Earthworks compaction
    • Landing construction
    • Forming road corners and in-bends
    • Final grading before metalling
    • Stabilising cut/fill slopes
  • Water control
    • Water control overview
    • Ditches
    • Road drainage culverts
    • Berms and cut-outs
    • Flumes
    • Silt traps and soak holes
    • Silt fences
    • Single culvert river crossings
    • Ford crossings
    • Bridges
  • Applying aggregate (metalling)
  • Repairs and maintenance
    • R&M overview
    • R&M common to new construction
    • R&M of road formation
    • R&M during harvesting operations
    • R&M of river crossings
  • Assisting loggers and harvesting rehab
    • Installing deadmen
    • Installing debris traps
    • Harvesting track rehabilitation (rehab)
    • Harvesting track rehabilitation – cut-outs
    • Landing rehab
  • Want to learn more?
  • Glossary

NZ Forest Road Engineering Manual: Operators Guide

  1.  ›
  2. Earthworks ›
  3. Earthworks compaction
 

Earthworks compaction

Compaction is an important task in building a road and landing. How you compact depends on what material you are working in. All compaction needs moisture, but not too much or too little.

Why compact?

  • Compaction strengthens the fill and the road. It reduces the risk of fill movement or settlement on steep or unstable slopes
  • It reduces the amount of road metal needed as road subgrade is stronger
  • It helps protect or ‘seal off’ earthworks from water penetration
  • It can reduce repair and maintenance costs

Which compactor for the job?

Step 1: Is the soil a clay – try to roll a worm!

  • Moisten the soil and try and roll it into a thin worm 3-5 mm thick
  • If the soil feels sticky and turns into a snake without cracking, you have clay
  • A clay with sand – you will feel the sand particles

Step 2: Is the soil silty – try the tap test!

  • Roll a wet soil sample into a 20 mm ball and flatten it
  • Now tap the hand to see if water arises. If so, it is a silt
Table 5: Compactor and soil type

Step 3: Look at the table above

  • Sheep or wedge foot rollers are the most useful in formation
  • Vibrating drum rollers (smooth) are useful for sealing aggregate
  • Heavy compactors work better
  • Loaded metal truck wheels compact

How much moisture is enough?

Step 1: Do the squeeze test

  • Squeeze some material in your hand, then take off the pressure
  • If it just holds together, and the content doesn’t stick to your fingers, the moisture is about right
  • More granular materials are less likely to hold too much water

Step 2: Plan your next steps

Table 6: Earthworks compaction

How thick can a layer be compacted?

Limit layer thickness, so compaction goes the full depth of each layer.

Table 7: Earthworks compaction
  • The correct compactor − a vibrating sheep-foot − has been used
  • The right moisture content ensured good compaction
  • Compaction had been done in the right layer thickness for the material
  • The material has not been over-compacted
  • Dozers and excavators are not compactors
  • Wide tracked machines apply low ground pressure even though they are heavy
  • Track rolling only gives minor compaction, however, it tightens the fill by breaking down larger material
  • The metal is being compacted with the correct compactor − a vibrating steel drum
  • The aggregate is compacted in layers less than 150 mm
  • Excessive vibrating rolling has brought moisture to the surface and hasn’t improved the result
  • Do not try to compact wet or very dry materials, as these may become liquid
  • Penetrometers are useful for identifying subgrade weaknesses
  • They also show that the subgrade has met compaction standards
  • Lack of compaction, or too much moisture in the fill, led to this major road failure
  • Water will enter the tension cracks and make the fill even less stable

Compaction must be done right. Check the soil type, moisture content, and the thickness being compacted

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