The new Japanese screw piling system for metro rail piers has proved incompatible with metro rail piers.
Sources said screw piling, aimed at freeing the busy Farmgate-Karwanbazar corridor promptly, has been shelved as piers failed to bear the load.
According to the engineering school BUET, underground soil not suitable for screw piling.
A BUET test has found clay materials 40 to 50 metres deep into the ground as Dhaka city has been developed mostly on canal and water bodies.
Before any testing of the technology, Obaidul Quader inaugurated the system on February 25 last year.
At that time, the road transport and bridges minister claimed that it would help speed up the piling job from Agargaon to Motijheel.
Dhaka Mass Transit Company Limited (DMTCL) stopped the work after meeting one third of the target until August as the BUET found it unsuitable for underground soil.
According to an August 2019 progress report posted on DMTCL website, the Japan-Bangladesh joint-venture contractors did the piling of 27 out of the initially planned 104 screws by August.
The DMTCL is constructing the 20-kilometre Mass Rapid Transit line-06 (MRT-06) from Uttara to Motijheel via Agargaon, Farmgate and Shahbagh.
The first 10-kilometre track from Uttara to Agargaon has been developed with the conventional bore piling system and the rest is being done by two other joint-venture companies.
But the DMTCL inaugurated the screw piling job from Agargaon to Karwanbazar and declared so many good features of the system.
It claimed the new system would give 10 advantages, including high bearing capacity, minimum workspace, low noise and vibration and improved quality in piling and rapid construction.
DMTCL managing director MAN Siddique acknowledged the BUET findings and said a decision to stop screw piling was made to avert risks.
As Dhaka city has been developed mostly on canal and water bodies, he said, the test founds clay materials 40 to 50 metres depth.
"Though the test report found the load-bearing capacity more than average, we decided not to go for screw piling as we don't compromise with quality," Mr Siddique told the FE.
Sources said a panel of experts sat with the contractors to settle the issue.
They guided the builders to go for mixed boring, meaning bore piling on the site of screw piling.
The remaining piling was suggested under conventional boring. The experts accepted some screw piling.
Sumitomo Mitsui Construction Co Ltd, the lead partner of the joint venture, brought the new technology to carry 3.19-km track work and three stations after its contract in August 2018.
After a change of decision, the company completed 601 out of 621 bore piling, according to the January progress report posted on the website.
No comment on the impact after the rejection of screw piling could be gathered from the contractors' side.
But the DMTCL claimed there was no effect on the MRT line-06 work due to the changed decision. The progress in this package work is 38.2 per cent.
As screw piling is expensive, sources said, scope for financial loss is little after shifting to the conventional bore piling.
Under package 05, the DMTCL also brought a mock-up train for display outside the MRT-06 depot for making people aware of the new transport system.
smunima@yahoo.com