Why can limited road crossfalls experience hurt Bosaso jobs?

Road crossfalls experience gaps in Bosaso show up when a surface is set too flat or built the wrong way and water stands on the carriageway. Crossfall is the slope built across a road so rainwater runs to the edge or channel. Paving crews can set it correctly, but a crossfall gap on a Bosaso road means there is no record that the fall was checked before the surface was finished.

Why does the road crossfalls experience gap appear on a Bosaso job?

The gap comes from how crews are selected, not from the fall itself. A contractor can be strong on earthworks or kerbs and still have no one who has set and verified crossfalls on a road of this width. A bid may be priced on the basis of a similar-looking job rather than the same one. The person who signs the setting-out sheet may never have checked the fall on a finished carriageway.

You can probe this before award. Ask the bidder for the roads and drainage jobs the named foreman and surveyor have actually set out, and what the finished fall was on those jobs. Ask whether the firm owns or hires a straightedge long enough to span the road, and an engineer's level. Ask the municipal engineer's office what records it holds for road work in the area, and whether it inspects setting-out. The answers show whether the crew has set and verified crossfalls on comparable work.

What does a wrong crossfall do to the work?

A fall that is too flat, or built the wrong way, leaves standing water after heavy rain. Water that does not reach the channel, edge drain or soakaway soaks into the shoulder and the subgrade, softens the base, and starts the potholes and edge breaks that appear in the first wet season. On a crowned road, part of the surface can shed to the wrong side. Ponding also hides the defect until loading has already done the damage.

General practice is a single fall, or a crown with fall to both sides, so water leaves the carriageway quickly to the drain. Roads with a kerb and channel may take a different detail from those with a flat shoulder. Treat any number for the rate of fall as general practice, not a rule, and confirm it against the project's specification and drawings, and with the design engineer who set the drainage. Confirm the expected rainfall, local ground, exposure and salt conditions with that engineer as well, since these vary across the site and change how fast water drains and how it attacks kerbs and joints.

How do you check crossfall before paving?

The check is made before the surface is sealed or laid, while the base is still open. Ask for the setting-out sheet and the level book, then run the checks below with the supervisor present.

• Stretch a stringline or straightedge across the road at right angles to the centreline. Measure the gap at the edge against the design fall. Repeat at intervals along the length, not at one spot.
• Take levels on both edges and at the centre at each chainage and compare them with the drawing.
• Check the edge drain or channel is lower than the road edge, and that it runs to an outlet that actually takes the water away.
• Wet the base or wait for rain and mark any standing patches.
• Test the subgrade and base compaction first. Compaction testing keeps a poorly compacted layer from hiding under a correct-looking fall. Confirm the test method and how often to test against the project's specification and with the engineer.
• Record each check and the correction in the site file, signed by the person who took the levels.

If the base is already sealed and water stands, the client can ask for cores or levels on the finished surface and for a written proposal to correct the fall before more surface is placed.

What to do next

Ask the contractor for the setting-out sheet and the level book for the section about to be paved. Then walk that section together, wet it if you can, and mark any water that does not reach the edge. Do this before the final surface is laid, and keep the marked record signed by both sides.