The Nasarawa urban roads project delivered five bridges, all with 30 m spans. ICCO rehabilitated and widened three existing bridges and built two new ones, so that every crossing on the corridor matches the six-lane dual carriageway. Bridges are often the most technically demanding part of a road project, and these five went through a full cycle of investigation, design, construction and load testing.
Key facts
- Bridges: 5 in total, all with 30 m spans
- Scope: 3 existing bridges rehabilitated and widened, 2 new bridges
- Boreholes: 20, four per bridge to 30 m depth
- Bored piles: Ø1200, 1,120 m in total
- Beams: 23 precast prestressed 30 m beams
- Testing: All five bridges load tested before handover
Investigation and design
Ground conditions were tested before any design was finalised. ICCO drilled geotechnical boreholes at the bridge sites, four per bridge to a depth of 30 m, giving 20 boreholes in total. The soil and rock samples from these boreholes tell engineers how deep the foundations need to go to reach ground strong enough to carry the bridge.
The three existing bridges each received a condition assessment, followed by a rehabilitation and widening design. The two new bridges received full structural designs. Assessing the existing structures first meant the widened sections could be designed to work with the parts that were kept.
Foundations: Ø1200 bored piles
The bridges stand on Ø1200 bored piles, 1.2 m in diameter. These totalled 480 m for the existing bridge widening and 640 m for the new bridges, or 1,120 m overall. Bored piles carry loads deep into firm ground, which keeps the bridges stable over time.
A bored pile is made by drilling a hole into the ground, placing a steel reinforcement cage inside it and filling it with concrete. Because each pile is cast in place, it can be taken down to the depth where the borehole results show firm material.
Precast prestressed 30 m beams
The decks are supported by 23 precast prestressed 30 m bridge beams. Nine went into the widened bridges and 14 into the new ones. Precasting the beams lets them be made under controlled conditions and lifted into place, which helps with quality and speed.
Prestressing puts the concrete into compression before the beam carries any traffic. When vehicles cross, that built-in compression offsets the bending forces, letting a beam span 30 m while staying slim and resisting cracks.
Concrete and steel
| Item | Existing bridge widening | New bridges | Total |
|---|---|---|---|
| Structural concrete C35 | 450 m³ | 760 m³ | 1,210 m³ |
| Structural concrete C40 (deck works) | 141.12 m³ | 268.8 m³ | 409.92 m³ |
| High-yield reinforcement | 94.5792 t | 164.608 t | 259.1872 t |
The C35 and C40 labels refer to concrete strength classes: the higher the number, the stronger the concrete. The deck works used C40, the stronger of the two mixes, because the deck takes traffic loads directly.
Bearings and expansion joints
| Item | Widened bridges | New bridges |
|---|---|---|
| Existing bridge bearings replaced | 30 | – |
| Elastomeric bearings installed | 18 | 28 |
| Expansion joints | 96 m | 64 m |
Bearings and expansion joints let the decks move as temperatures change and vehicles pass. Concrete expands in the heat of the day and contracts at night; without bearings to allow that movement and joints to close the gap at the deck ends, the stresses would crack the structure.
Load tested before handover
Before handover, all five bridges, three existing and two new, underwent load testing. A load test places a known, heavy load on the deck and measures how the structure responds, confirming that it behaves as the design predicted.
The completed bridges now carry the six-lane dual carriageway across the corridor's waterways.
More on the Nasarawa 75 km urban roads
This article is part of a five-part series on the project:
- ICCO Completes Nasarawa's 75 km Six-Lane Urban Road Project – the scope, value, timeline and completion of the project.
- From Earthworks to Asphalt: Engineering Nasarawa's 75 km Road – the design studies, earthworks and layered pavement.
- How Drainage and Erosion Control Protect Nasarawa's New Roads – the drains, culverts and erosion control that keep water off the road.
- 1,878 LED Lights and More: Road Safety on Nasarawa's 75 km Road – street lighting, road markings, guardrails and pedestrian facilities.
Frequently asked questions
How many bridges are on the Nasarawa 75 km urban road?
There are five bridges, all with 30 m spans. Three existing bridges were rehabilitated and widened, and two new bridges were built.
What foundations do the bridges use?
The bridges stand on Ø1200 bored piles: 480 m for the existing bridge widening and 640 m for the new bridges, or 1,120 m in total.
How many precast beams were used?
23 precast prestressed 30 m bridge beams were used: nine in the widened bridges and 14 in the new bridges.
Were the bridges tested?
Yes. All five bridges, three existing and two new, underwent load testing before handover.
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