As reported in SN of March 26 and 27, the revetment under construction at the Kumaka waterfront in the North West District has started to tilt and slide into the Aruka River as the ragged alignment in your accompanying photo clearly indicates.
It is unfortunate that over 300 ft or so of revetment has already been completed and the Ministry of Public Works (MPW) did not recognize that something was amiss during its construction, although it was clearly evident to residents of the area that the design appeared to have serious flaws and the contractor was executing poor quality work as it progressed.
The misalignment of the revetment is indicative that a rotational and stability failure involving the piles, sheeting and anchorages has started. To exacerbate the situation the contractor has been backfilling using a Cat excavator, layers of weak soil to replenish displaced and settled material behind the revetment, and this has been placing additional lateral pressures on it and causing the structure to tilt and slide faster into the river.
Before the entire revetment collapses into the river, MPW needs to have its geotechnical and structural design calculation rechecked urgently to ensure that the revetment’s sheet piles were driven to firm soil below the compressible layer and river bed with adequate tie-back anchorage, and that the lateral soil and pore pressures on it are within the factor of safety for stability and rotational failures.
The contractor’s poor quality work should have been halted a long time ago since his performance has been evident to anyone in the business, and even the ordinary residents have been expressing their grave concerns as the work progressed, but unfortunately their cries were in the wilderness. Further, it seems that the site inspector who should have been responsible for quality control and assurance and alerted the MPW to stop the work because of the contractor’s poor project execution apparently fell asleep on the job.
There is an urgent need for the MPW to review the methods it uses in the selection of engineers, contractors and construction supervisors for MPW projects, with great emphasis being placed on their relevant qualifications and experience which ultimately determine the quality of their performance.
Nevertheless, the Minister of Public Works should hold an inquiry as to the soundness of the design of the Kumaka revetment and why his staff allowed the contractor to execute shoddy work for such a long time and paid him for it with no action being taken against him; it probably will only now take place after the media has reported on the matter. If MPW staff are also found wanting in the execution of their duties, appropriate disciplinary action should be taken against them.