The Third Mainland Bridge in Lagos is a vital artery of the network of Federal Highways and commands high patronage in Lagos Municipal Area, considering the importance of the city as the major commercial centre in Nigeria.
2. The Bridge is 11.8 km long and was constructed in two sections. The first section, from Lagos Island to Ebute Metta (Adeniji Adele Interchange – Adekunle Interchange) which has a box girder arrangement cantilevered from the pier to the mid-span was completed in 1979 by PGH, a consortium made up of Messrs Borini Prono, Messrs Girola and Messrs Hiconi. The second section from Ebute Metta to Oworonshoki which was later completed in 1990 by Messrs Julius Berger Nigeria Plc. (JBN) is a multi-span structure.
3. Following reports of oscillation and excessive vibrations of the bridge under traffic load, the Federal Ministry of Works in 2008 engaged the services of Messrs JBN Plc. to conduct preliminary investigations of the structure and later Dynamic tests were carried out by Messrs 4EMME, an internationally acclaimed Bridge Engineering Consulting firm. The reports of the investigations and tests at the time indicated that the bridge was structurally adequate but required the replacement of bad expansion joints and bearings.
4. Consequently, Messrs Borini Prono & Co. Nigeria Ltd. carried out the replacement of 4 No. critically affected expansion joints (Phase I) which drastically reduced the vibrations on the bridge to tolerable limits and allayed the fears of members of the public.
5. Following yet, another report of subsidence and oscillation of the bridge structure exceeding tolerable limits under minimal load stress, the Ministry’s engineers inspected the bridge and their Site Inspection Report indicated that:
i) excessive vibrations occurred at damaged expansion joints locations whenever heavy vehicles crossed over them;
ii) rubber accessories of the expansion joints at the Ebute Metta axis of the bridge had been damaged and were therefore not water-tight;
iii) significant horizontal displacement of a retaining wall at an intermediate abutment of the bridge was observed;
iv) dredging activities around the bridge piers from where large quantity of sand was being excavated on a daily basis might undermine the integrity of the bridge foundations.
The Site Inspection Report recommended the immediate replacement of more damaged expansion joints since the vibrations were still traced to them and also underwater inspection to ascertain the current state of the bridge substructure/foundation. Accordingly, and following the approval by the Federal Executive Council in October 2011, 8 No. Additional joints (Phase II) adjudged to be border line cases in 2008 were replaced by the same contractor in 2012.
6. In recognition of the importance of the bridge, the Ministry commissioned Messrs Nigerian Submarine Divers Limited (NSD) in December 2010 to undertake the underwater inspection of the Third Mainland bridge and Eko bridge in Lagos in order to ascertain the state of the underwater structural elements which had hitherto not been inspected since the bridges were constructed and opened to traffic some 35 and 25 years ago respectively for the two sections. An initial report of the underwater inspection presented by NSD in July 2011 showed “alarming” deterioration and serious damages on numerous pile foundations of the Third Mainland Bridge.
7. The Final Report submitted by NSD in November, 2011 indicated “extensive” deterioration of embedded steel reinforcement in piles, concrete degradation and appreciable loss of concrete material as well as discontinuities in some foundation piles which apparently has affected the load bearing capacity of the piles. They recommended the replacement of some piles, encapsulation of others, cleaning piles of marine growths using high pressure water jets and discontinuation of organic effluents discharge into the water. Hence, Advanced Integrity Assessment tests of the affected foundation piles and chemical analysis of the concrete samples were recommended.
8. Following further review of Messrs NSD Ltd’s Final Report, it was observed that not all piles were inspected due to various reasons advanced such as obstruction by human activities and inaccessibility. To ensure that their report was adequate and comprehensive in accordance with the contract’s Terms of Reference, the Ministry directed that all piles whether in water or on land should be duly investigated which culminated in the submission of an addendum to the Final Report in December, 2012.
9. It is pertinent to note that the Addendum to the Final Report submitted by Nigerian Submarine Divers Limited in December 2012 confirmed some deterioration and defects at the underwater sections of some of the foundation piles as follows:
i. Concrete degradation and appreciable loss of concrete infill materials
ii. Extensive deterioration of embedded steel reinforcement in piles
iii. Progressive deterioration of steel caisson of foundation
piles.
10. The findings of Messrs Nigerian Submarine Divers Ltd (NSD) were strictly based on visual inspection and under water photos. For this reason, and following meetings between officials of the ministry, Messrs NSD, Julius Berger and Borini Prono, it was decided that Advanced Integrity Assessment including high technology chemical analysis of concrete samples from piles was inevitable, and in order to authenticate the findings of NSD as contained in their reports. Moreover, since Messrs NSD Ltd is not a Civil Engineering Consultancy Firm, their capacity and professional competence to carry out such works was doubtful.
11. Therefore, in recognition of the fact that the required Integrity Test has not been exhaustively conducted on the entire bridge, even as various investigations had been concluded, the Ministry felt obliged to request Messrs Borini Prono & Co. (Nigeria) Limited, a member of the PGH Consortium that constructed the first section of the bridge to assess the condition of some foundation piles of the first section of the Third Mainland Bridge which was mostly impacted in the reports by studying the original designs, conducting site investigation in collaboration with Messrs Trevi Foundations Nigeria Limited, the foundation specialist that undertook the piling works in the first place. Messrs ICECON Nigeria Limited, specialist in Bridge Investigations, was also engaged by Messrs Borini Prono to independently confirm the results of their investigation. A Report was submitted in November 2012 and the major findings were:
· The visual underwater inspection, the Non Destructive Tests and coring campaign carried out on the Third Mainland Bridge in Lagos confirmed the adequacy of pile concrete quality;
· Some degradation was observed particularly in the first few meters of pile shaft, a consequence of 35 years of bridge life;
· Although Serious steel casing corrosion was noticeable, it was pointed out that the steel casing has no structural function regarding pile bearing capacity, as they simply served as formworks to the R.C. Piles;
· No cases of total loss of piles, clearance between the pile and pile cap or other major anomalies were reported on the tested piles;
· Based on the results of the investigations, there is no evidence of immediate threat of failure of the pilings;
· In their conclusion, they made recommendations that elaborate maintenance programme based on systemic assessment of all the piles should be put in place.
12. Therefore, to safeguard the integrity of the bridge, the Ministry has commenced in earnest the process of engaging a consultant to urgently carry out investigation/assessment on the entire bridge substructure so as to determine the extent of maintenance work required. The scope of works to be covered is as detailed below:
i) Echo metric test to check the structural integrity of the piles in water and selected piles on land (total of 988 No. piles), including coring on selected piles, testing and chemical analysis;
ii) Underwater Inspection of 658 No. piles;
iii) Submission of Report of the Inspection/Assessment of Foundation piles with appropriate Recommendations.
13. From the foregoing, it is obvious that the Ministry has taken proactive steps in line with its mandate to ensure that the Third Mainland Bridge, a very important infrastructure investment of Government, is protected and kept in an acceptable service state.
Engr. A. O. Effiong
Director Highways Design (Bridges)
Federal Ministry of Works.
08 February, 2013
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