Road construction

Question 1

Formation width

Answer 1

The final surface of the ground, excluding any side slopes, after completion of earthworks. Formation width includes pavement + shoulders + verges.

Question 2

Pavement

Answer 2

That portion of a road surface, normally excluding shoulders, placed above the sub-grade for the support of vehicles.

Question 3

Grade

Answer 3

The slope of a carriageway centreline with respect to the horizontal, expressed as a ratio or percentage, e.g. 3%, 1:150 etc.

Question 4

Crown

Answer 4

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.

Question 5

Boxing

Answer 5

The space formed above the level of the subgrade to receive the paving material.

Question 6

Course

Answer 6

Any one of the different layers of which a pavement may be constructed.

Question 7

Culvert

Answer 7

One or more adjacent pipes or enclosed channels for conveying a watercourse or stream below the formation level.

Question 8

Recovery peg

Answer 8

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.

Question 9

Crossfall

Answer 9

The slope of the carriageway surface measured at right angles to the road centreline.

Question 10

Why do we need crossfall?

Answer 10

Crossfall provides drainage for the pavement on straights and curves and provides super elevation on horizontal curves.

Question 11

Standard pavement crossfall:
Earth, loam?
Gravel surface?
Bitumen surface?

Answer 11

Earth, loam: 0.05m/m (5%)
Gravel surface: 0.04m/m (4%)
Bitumen surface: 0.03m/m (3%)

Question 12

Road shoulders are necessary for:

Answer 12

• 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.

Question 13

Shoulder Crossfall:

• Earth, loam?
• Gravel surface?
• Bitumen surface?

Answer 13

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%)

Question 14

Table Drains

Answer 14

• 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.

Question 15

Catch Drains

Answer 15

• 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.

Question 16

Batters

Answer 16

• Expressed as 1 vertical to n horizontal

- ‘n’ varies according to the material (soil, rock, etc).

Question 17

Slope Benches

Answer 17

• 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.

Question 18

Advantages of Benches:

Answer 18

• 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.

Question 19

Name 6 types of road construction equipment

Answer 19

DOZER
SCRAPER
LOADER
GRADER
TRUCK
ROAD ROLLER

Question 20

Dozers main uses

Answer 20

Clearing: Main use
Winning: Main use
Loading: With open bowl scrapers, Transporting: Very short hauls
Spreading: Possible use

Question 21

Scraper main uses

Answer 21

Winning: Main use
Loading: Main use
Transporting: Main use
Spreading: Main use
Compacting: Assists during travel
Finishing: Possible use

Question 22

Loader Main uses

Answer 22

Winning: For easy in-bank digging
Loading: Main use
Transporting: Very short hauls
Spreading: Possible use

Question 23

Grader main uses

Answer 23

Winning: Possible use
Spreading: Main use
Finishing: Main use

Question 24

Truck main uses

Answer 24

Transporting: Main use
Spreading: Possible use

Question 25

Road roller main uses

Answer 25

Compacting: Main use
Finishing: Main use

Question 26

The use of flexible pavements lends itself to stage construction. The process of stage construction involves the following 6 steps:-

Answer 26

1. Provision of low-cost access track
2. Improvement of formation
3. Extensive earthworks and drainage construction
4. Gravel sheeting
5. Pavement construction
6. Bituminous surfacing.

Question 27

Winning

Answer 27

Winning or “pushing up” is normally carried out by a bulldozer.
The laterite deposits are normally only about 600 mm thick and are underlain by a deposit of clayey gravel which needs to be mixed with the laterite to provide a material of the required grading and consistency. Stockpiling is carried out only just in advance of loading, unless the weather is fine, avoiding the possibility of the loose material becoming saturated by rain.

Question 28

Pavement preparation consists of a number of operations:
7 in order?
(Read the book for further information on the process of each step)

Answer 28

1. Mixing
2. Watering
3. Spreading
4. Shaping
5. Compaction
6. Final trimming
7. Sweeping.