A road crossing flyover is a clever engineering solution to efficiently handle traffic flow by directing the main traffic through a bridge at a higher level. In contrast, the low traffic is diverted to travel below. With the ramps on both sides, vehicles can easily access the flyover, allowing for a smooth and safe journey. By dividing the traffic in this manner, the chances of accidents are minimised, making it a reliable and effective means of transportation. They can be built using various materials, such as concrete, steel, or composite materials.
The foundation of these bridge piers requires a serious geological investigation. The chief factors which govern the stability of flyover bridges are lateral forces, so, Piers should be found at a depth safe from scouring erosion and easy settlement.
However, in many cases, the location of a bridge is decided more by socio-economic factors than geological considerations. In big cities like Warri in Delta State Nigeria, roads are divided by streams and rivers, and a flyover bridge has to be places where necessary irrespective of subsurface geology. The niger Delta of Nigeria is covered by varying thicknesses of unconsolidated natural deposits of sand, gravel and boulders not safe for foundation of a bridge pier. The piers placed directly on them would be unstable. The depth of sound rock may vary from 5-20 m in some to more than 100 m in others.
FISAS Limited is making Drill holes carrying out Dynamic and Static Cone Penetration tests, DCP and CPT, all along the centre line of the proposed flyover bridge, in Warri Town. The height of individual piers may vary according to the depth of the sound bedrock below the surface as each them should be founded on the stable rock.
A decision to place the pier in a particular location at a particular depth is a matter of judgment and design requirement. Horizontal attitude and uniformly massive structure with depth are desirable characters on the foundation rocks as these offer resistance against failure.
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