SRT governor Prapat Chongsanguan also said he was confident the number of train passengers between Bangkok and Chiang Mai _ about 2,000 per day _ would not decrease during the repair work, despite the fact they have to switch to a bus when they reach Uttaradit.
The SRT plans to suspend services along a 300km stretch from Sila-art station in Uttaradit to Chiang Mai from Monday until Oct 31.
Railway tracks and sleepers will be fortified while the earthen and rock foundations of certain parts of the railway would be replaced to make them stronger, Mr Prapat said.
Many wooden railway sleepers would be replaced with concrete sleepers, he said.
As a result, the height of rail tracks will probably increase slightly, he said, adding that the height of tracks running through tunnels would be adjusted carefully.
The maintenance will be divided into two phases, he said. Starting Monday, the first phase will take 15 days to finish.
Under this first phase, sharp curves will be corrected, and old sleepers and ageing rail tracks will be replaced, he said.
In the second phase, the earthen and rock foundations of the railway in four tunnels, including the 1km Khun Tan tunnel, will be replaced and fortified with new sleepers.
During the maintenance, 10 buses a day will be put into service to transfer passengers from Uttaradit to Chiang Mai.
Two trains from Bangkok will be suspended during the railway maintenance. They are the 6pm service due at Sila-art station at 1.57am and the 7.35pm service due at Sila-art at 3.27am.
Their arrival times were inconvenient, Mr Prapat said.