Formation width
The final surface of the ground, excluding any side slopes, after completion of earthworks. Formation width includes pavement + shoulders + verges.
Pavement
That portion of a road surface, normally excluding shoulders, placed above the sub-grade for the support of vehicles.
Grade
The slope of a carriageway centreline with respect to the horizontal, expressed as a ratio or percentage, e.g. 3%, 1:150 etc.
Crown
The highest point on the cross section of a carriageway with a two-way crossfall. On one lane roads this will usually be the centreline.
Boxing
The space formed above the level of the subgrade to receive the paving material.
Course
Any one of the different layers of which a pavement may be constructed.
Culvert
One or more adjacent pipes or enclosed channels for conveying a watercourse or stream below the formation level.
Recovery peg
Pegs placed with known relationship in level and horizontal position to other survey marks (control) within the construction area, to enable those stations to re-established after disturbance.
Crossfall
The slope of the carriageway surface measured at right angles to the road centreline.
Why do we need crossfall?
Crossfall provides drainage for the pavement on straights and curves and provides super elevation on horizontal curves.
Standard pavement crossfall:
Earth, loam?
Gravel surface?
Bitumen surface?
Earth, loam: 0.05m/m (5%)
Gravel surface: 0.04m/m (4%)
Bitumen surface: 0.03m/m (3%)
Road shoulders are necessary for:
- Safety in cases of breakdowns or emergencies as vehicles can be cleared of traffic flow.
- Improved sight distances on cuttings.
- Room for placement of road signs, barriers, etc.
- Increased driver comfort and road attraction as wider roads appear more open, safer and more attractive.
Shoulder Crossfall:
- Earth, loam?
- Gravel surface?
- Bitumen surface?
On straights crossfall on shoulders can be up to 2% steeper than on the traffic lanes.
- Earth, loam 0.06m/m (6%)
- Gravel surface 0.04 to 0.05m/m (4-5%)
- Bitumen surface 0.03 to 0.04m/m (3-4%)
Table Drains
- Located on the outside of shoulders in cuttings.
- Unsealed table drains need invert levels below pavement level of the subgrade for effective drainage.
- Collect water from the pavement to discharge it away from the road.
- Grades steeper than 5% or less than 0.5% need lining (by grass, rocks or concrete) to prevent scouring or siltation.
Catch Drains
- Placed on the high side of cuttings, to prevent excess run-off into tables, drains and scouring of batter faces.
- Should be at least 2m from the edge of the cutting to minimise possible undercutting of the top of the batter.
Batters
- Expressed as 1 vertical to n horizontal
- ‘n’ varies according to the material (soil, rock, etc).
Slope Benches
- On batters > 10m in height or where the material is unstable, 3-5m wide benches may be required.
- Benches should slope away from the road and also longitudinally, to discharge water towards the end of the bench to natural ground where possible.
Advantages of Benches:
- Minimising of rock falls onto the road carriageways.
- Reduced scour on the batter face.
- Reduced volume of water in cuttings to be carried in table drains.
- Improved appearance of the cuttings.
- Assisting in re-establishing vegetation.
- Eliminate the need to flatten the batter slopes in the interests of stability.
- Provide easier access for maintenance of the batter face.
Name 6 types of road construction equipment
DOZER SCRAPER LOADER GRADER TRUCK ROAD ROLLER
Dozers main uses
Clearing: Main use
Winning: Main use
Loading: With open bowl scrapers, Transporting: Very short hauls
Spreading: Possible use
Scraper main uses
Winning: Main use Loading: Main use Transporting: Main use Spreading: Main use Compacting: Assists during travel Finishing: Possible use
Loader Main uses
Winning: For easy in-bank digging
Loading: Main use
Transporting: Very short hauls
Spreading: Possible use
Grader main uses
Winning: Possible use
Spreading: Main use
Finishing: Main use
Truck main uses
Transporting: Main use
Spreading: Possible use
