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Yohana Bako @lokojaboy
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How are Potholes formed?

The images below are of the recently tarred service lane at Oshodi, work here was completed barely 6 months ago.

So, apart from the obvious poor quality of work done, why & how exactly did the Potholes occur?

A thread ~…
The Wikipedia post basically outlines the issues as a failure in the fabric of the road due to moisture beneath the road surface & fatigue from vehicle load.

The article points more at snow as being the moisture enabling culprit but we obviously don't have snow in these parts.
'Snow' may therefore be substituted for another firm of precipitation - rain (and subsequently water).
There's a whole lot more to these in terms of the actual science to this occurrence, however, three major elements are clearly present,

1. Water

2. Constant heating up and cooling of the surface (which causes contractions in the asphalt).

3. Vehicles

The presence of water above & below the surface accelerates the damage.

When the water is above the road surface it aids the wearing out of the asphalt & loosening up of the stone aggregates that are a part of the asphalt layer.
The stones that come loose further aggravate the damage to the surface in a similar way to how sandpaper's abrasive quality wears down a surface.

So, basically water above the surface works its way below after having created cracks in the surface.
Water that finds its way below the surface of the asphalt layer makes the soil beneath soft.

This water may have seeped in from above via cracks on the surface or have risen from below from burst water pipes or a seasonal rise in the water table.
Constant heating of a road surface occurs with exposure to the Sun during the day while cooling occurs at night.

Heating & cooling cause a surface to expand & contract in turn.

Ordinarily, this is factored into the design of the road and is one reason asphalt is preferred.
Asphalt is elastic to a degree & easily accommodates the expansion & contraction brought on by weather.

However, asphalt is not infinitely elastic;

Once water is inordinately present in volumes beyond projected levels, wear from above or soft soil below will cause it to yield.
Vehicles, especially heavily loaded vehicles agitate the surface & deal what would be the final blow to the asphalt surface.

Tyres running over a spot already weakened by water either from soft soil substrate below or loose stones above further aids to defeat the asphalt layer
The weight of the vehicles depress the asphalt surface into the soft soil below hence the actual pothole.

This fatigue results in cumulative damage which in time widens and deepens the pothole.
The occurrence of water below the surface must be eliminated.

This is usually done during construction & accounts for the bulk of work done.

Suffice to say that the road we 'see' is not the actual road per se.
In like manner, water above the surface must be rapidly evacuated.

Stagnant water is a huge 'No-No'

This is achieved by introducing 'camber' across the width of the surface.

This means the surface slopes down towards the sides from the middle of the road. (Image via fotolibra)
This allows water run off from the road to the sides into DRAINS.

Unfortunately, in Nigeria there are hardly drains on the side of most roads.

Where drains occur, they are usually blocked with plastic bags and bottles which impede the flow of water.

When roads are commissioned, the cost of constructing drains is sometimes near to or as much as the cost of the road proper.

Guess which one your average Nigerian politician would rather spend money on?
Roads are more visible & score more political capital.

Ironically, the absence of drains mean that the lifespan of the road is drastically reduced.

More ironically & even macabre is that this serves the average politician's purpose quite well (more bloated contracts to award)
This thread only speaks to the why and how Potholes are formed or occur...

It does not address the proliferation of Potholes across Lagos and other towns or cities in Nigeria beyond the fact that an inordinately high incidence of Potholes implies in large extent to shoddy work.
Sorry, shoddy work in someway implies capacity to do but refusal to do well.

The instances observed relate more with the incapacity of the 'contractor' to perform to the required standard.
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