By Walter Ononuju Nnadi
Few days ago, the Zuckervile and other social media platforms was awash with pictures of the drainage tunnels at the Imo state House Of Assembly and Concorde junction undergoing demolition; polemics were targeted at the state government and her agencies. I was also amazed that some respected scholars were among those playing in the mud and making some unfounded statements to whip up emotions that were capable of causing unrest.
Firstly, Tunnel is an “artificial underground passage, especially one built through a hill or under a building, road, or river”. It is used to ease traffic congestion off some roads, or make way for an alternative route to destination without causing some discomfort on the users and the ecosystem.
The Tunnels built by the Owelle Rochas Okorocha’s Administration served the first purpose but failed on the later.
Let’s now discuss further on the processes and procedures of Tunnel construction.
Note, The method of Tunnel construction adopted for a project depends on various factors. Tunnel construction and Tunnel Engineering is considered to be one of the most sophisticated and specialized art in the field of Civil Engineering. Unpredictable ground conditions, environmental requirements and geological factors makes tunneling a challenging job.
Below are the civil/construction engineering methods of Tunneling;
√Cut and cover method.
√Bored tunnel method.
√Clay kicking method.
√Shaft method.
√Pipe jacking method.
√Box jacking method.
√Underwater tunnels.
The type of tunnel and method used depends on various factors, which are listed below.
Geometrical configuration;
Geology
Ground condition;
Type of crossing;
Project Requirement;
Environmental requirements.
In view of the above Explanations, let’s discuss the first method of TUNNEL CONSTRUCTION as stated above which was used by Owelle Rochas’ administration in building the now demolished Tunnels.
√ Cut And Cover Method
In this type of tunnels, the tunnel structure is cast-in-situ or precast on an excavation. After construction, the structure is back-filled with new or excavated soil. Cut and cover construction is adopted when the depth of tunnel is shallow and the safe excavation is possible from the surface with out collapsing the walls of excavation and when it is economical and acceptable. This method is usually used for the construction of underpasses, approach sections of other tunnels and tunnels in flat terrain or shallow depth.
The tunnels may be constructed in place or by using precast sections. There are two types of cut and cover construction process, namely;
√Bottom-up
√Top-down.
It is instructive to note that there are many studies that are carried out before embarking on the design and construction of tunnel as enumerated above.
Owelle Tunnels:-
Poor designs and Construction
From the above explanations on the processes and methods of tunneling, it is glaring that many steps as stated was not followed thus their failure.
The carcass seen during the demolition exercise clearly showed that the grade of reinforcements used in building the tunnels were below the approved standard thus the vibrations one usually feels when plying the upper part (roof) of the tunnels.
The influence line of the moving loads on the roof are felt by the users of the tunnels thus the noise one notices when there is a movement on top of the tunnels.The tunnels are bedeviled with poor drainage system which makes it impassable when it rains because the runoffs were not properly channeled to the main drain.
It could be noticed that the tunnels is always dark which is very dangerous and poses great security risk to the users, remember many terror activities have been carried out in dark tunnels In some cities globally due to dark tunnels.
The ministry of works could not find the structural designs of the tunnels thus leaving them in doubts of how and what was used in the construction process. No project of that magnitude is embarked without complete and approved designs.
Note; Designs serves as guide to the Engineers on construction processes, materials to be used and their grades, all to specifications as it relates to the project and also it serves as a check for the client and consultants, (if any) for compliance sake.
The now demolished Tunnels can best be described as a source of worry and discomfort to the commuters because many ended up in the mechanic workshops for repairs as a result of damages they incurred plying the tunnel.
Ndi IMO, the state government is coming up with a unique, properly designed, and state of the art edifice in place of the tunnels. Just wait for it because it will surely come.