Claims of faulty piling work at a block of flats above the Airport Express' Kowloon Station have prompted officials to demand checks by the contractor. Without revealing details of an anonymous letter sent to his office, Director of Buildings Leung Chin-man said there was sufficient evidence in the letter to merit an inquiry. 'We are taking this letter very seriously. You don't get a letter like that very often,' said Mr Leung. He said engineers visited the construction site hours after he received the letter on Monday, but the initial check provided no evidence to support the allegation about the project, called the Waterfront. But the contractor's foundation subcontractor, Chun Wo Building Construction, has been asked to inspect the piles for loose gravel. Developer Hang Lung said last night it had not been contacted by the department. But all work on foundation piles had been conducted in accordance with the contracts and had been approved by on-site engineers. The development was the biggest of 16 building plans approved by the department in January. While the site has 30 piles, another 70 needed for the building of three 70-storey residential towers have yet to be placed, the department said. Under normal procedures, department engineers inspect the structure and foundation works after construction is completed. Since the 'end-bearing' piling method used at the site was different from the typical 'H steel pile' or concrete pile, the piles must be firmly secured at one to five metres beneath the surface of the bed-rock, legislator and engineer Raymond Ho Chung-tai said. 'Depending on the amount of loose gravel found - by looking into a plastic tube previously inserted into the middle of the pile - it could affect the wind resistance of the building above,' said Mr Ho. An anonymous letter received by the department in 1998 led to the discovery of faulty piling works at a different phase of the Waterfront and 14 other sites. Remedial work had to be carried out and completion was delayed. A number of engineers and supervisors were arrested by the ICAC.