80 platform areas to be drilled in MTR steel probeTop News | Phoenix Un 6 Dec 2018
The MTR Corp has proposed drilling open 80 sites at Hung Hom Station to check the safety of steel bars, which would take at least 16 weeks.
The rail operator's managing director, Jacob Kam Chak-pui, said it is too early to say whether the tests will delay the launch of the Sha Tin to Central Rail Link, but the government has asked MTRCL to consider a part launch of the link.
The steel bar controversy at Hung Hom Station broke out in May when media reported that couplers embedded in the diaphragm walls of platform slabs were cut short.
It is not known how many couplers are problematic - only several dozens according to some sources, thousands according to others.
The MTRCL has come up with a plan to verify the safety of platforms at the station. It submitted the proposal to the Highways Department on Tuesday after an earlier proposal in October was rejected.
The October plan proposed merely opening up the East-West Line slabs. But the government found that insufficient.
The new proposal, accepted by the government, suggested a three-stage study.
The first stage will be a desktop exercise on verifying records, while the second stage will involve physical examination, including opening up slabs to check the couplers inside.
After that the MTR would conduct structural assessment based on verification findings in the previous stages, and would design remedial works if required.
Kam said there were two reasons to open up walls: to ensure that couplers were installed in accordance with the latest design drawings, and to inspect the workmanship of the steel bar-couplers.
For the first purpose, 24 locations on the East West Line platform would be opened up.
For the second purpose, 28 locations on the East West Line slab would be opened, with another 28 on the North South Line slab. A minimum of 168 steel bars/coupler connections would be examined.
That would mean there would be a total of 52 openings on the 400-meter-long East West Line slab.
Kam said this would mean one opening in about eight meters.
For the North South Line slab of the same length, there would be one opening every 14 meters.
It would take at least 16 weeks to complete. Kam said the MTR had already begun preparatory work such as tearing down rails and other areas so the walls could be opened. The first opening will be made on December 10.
He estimated there would be at least 23,000 coupler connections on the two slabs. Kam and Director of Highways Jimmy Chan Pai-ming stressed that the sampling size was scientific.
"The key is that the sampling is totally random, both the location and the depth of opening, and this sampling size calculation is accepted internationally, not just in our case, but also in engineering and science researches," Kam said.
Besides opening up walls, Kam also said non-destructive tests of ultrasonic scanning and ground penetration radar would be carried out.
Michael Tien Puk-sun, former chairman of the Legislative Council Subcommittee in Matters Relating to Railways, said the number of couplers covered in random tests constitutes only about 0.6 percent of the total number of 26,000.
The sampling percentage should be increased to five percent, he said.
China Technology Corporation Limited, subcontractor of the station responsible for concrete processing, suggested opening up 194 locations instead.