Question – The tunnel design of the Central Kowloon Route and the impact of future construction works (Priscilla Leung)

Following is a question by Dr Hon Priscilla Leung Mei-fun and a written reply by the Secretary for Transport and Housing, Professor Anthony Cheung Bing-leung, in the Legislative Council today (June 19):


The Transport and Housing Bureau (THB) has pointed out earlier that the dual-3 lane tunnel design will be adopted for the proposed Central Kowloon Route (CKR). The distance between the top of the tunnel in CKR’s Ma Tau Wai section in To Kwa Wan (CKR tunnel) and the ground levels around some of the buildings in the area is approximately 50 metres. The authorities have indicated that the CKR tunnel will be constructed by the drill-and-blast method, and stressed that such method, being adopted for the construction of tunnels in Hong Kong for over four decades, will not affect the structural integrity of buildings along the tunnel alignment. However, in its paper submitted to a committee of the then Provisional Legislative Council in March 1998, the then Transport Bureau (TB) indicated that the dual-3 lane tunnel design was not recommended. One of the reasons was that such an option (irrespective of the “very deep” tunnel option at approximately 76 metres below ground or the “medium deep” tunnel option at approximately 51 metres below ground) would create problems and, in particular, the “medium deep” tunnel option would lead to problematic building settlement during construction in the To Kwa Wan area. In this connection, will the Government inform this Council:

(a) of the reasons for the completely different assessment results obtained by the then TB and the present THB respectively on the aforesaid design option;

(b) of the implementation details of the construction of tunnels by the aforesaid drill-and-blast method, and of the reasons for choosing such method to construct the CKR tunnel; given that the tunnel section will pass through densely populated urban areas, which is different from other tunnels in Hong Kong which were mainly constructed by hill cutting in the past, whether the authorities have assessed if the past experience is applicable to this project; if they have, of the assessment result; if not, the reasons for that;

(c) given that it has been pointed out in the environmental impact assessment report submitted by the authorities that, during the construction of CKR, a number of residential buildings, housing estates and schools (which are mainly located at Kansu Street, Yau Ma Tei in the western section of CKR; Chung Hau Street, Ho Man Tin in the central section; and San Ma Tau Street, Kowloon City in the eastern section) will be affected by noise, whether the authorities have, apart from using low-noise construction plant and noise control facilities, formulated other measures to mitigate the noise impact which will be brought about by the future construction works; if they have, of the details; if not, the reasons for that; and

(d) of the number of housing estates in Kowloon West under which the present alignment of the CKR tunnel will pass through, and of the names of those housing estates; given that the CKR tunnel will pass through the Maidstone Road area, To Kwa Wan, wherein vibrations with unknown cause were experienced at the same time in May this year in a number of buildings located near the construction site of the MTR Shatin to Central Link under construction, whether the authorities will re-assess if the future construction works of the CKR tunnel will affect the structures of buildings along the tunnel alignment; if they will not, of the reasons for that?



The proposed Central Kowloon Route (CKR) will provide an alternative express route enabling vehicles to bypass the congested road sections in Central Kowloon, thus reducing journey time significantly. Its importance lies in its functions of relieving congestion along the existing major east-west corridors and improving connectivity between different districts. The CKR is of vital importance in supporting various developments on the Kowloon side.

The proposed CKR is an approximately 4.7 kilometre (km) long dual three-lane trunk road, connecting Yau Ma Tei Interchange of West Kowloon Highway with the road network at Kai Tak Development (KTD) and Kowloon Bay in East Kowloon. It consists mainly of about 3.9 km of tunnel sections mostly constructed deep in rock stratum, without affecting the foundations of the buildings along the tunnel alignment, requiring no demolition of private developments and rehousing as well as preserving the historic building of the Yau Ma Tei Police Station. To ensure safety, the works departments will adopt appropriate measures during the course of construction to ensure compliance of all design requirements and legislative stipulations.

The reply to the four parts of Dr Hon Priscilla Leung Mei-fun’s question is as follows:

(a) The Administration commenced the study of the CKR project and its suitable alignments as early as in the 1990s. Taking into account the then South East Kowloon Development (SEKD), the Administration proposed in 1998 to build the CKR as a dual two-lane tunnel to connect the existing Yau Ma Tei Interchange and the planned road network of SEKD. Subsequently, the SEKD project was revised, including a reduction in the scale of reclamation. The Administration therefore reviewed the alignment of the section of the CKR to the east of Ho Man Tin in August 1999. At the meeting of the Legislative Council Panel on Transport in April 2002, reports were made on the revised alignment option and the proposed design of a dual three-lane tunnel. This alignment option proposed in 2002 forms the basis of the present alignment of CKR.

The latest alignment of the CKR runs through Ma Tau Wai and Ma Tau Kok, crosses Kowloon Bay and surfaces again in KTD. It differs from the alignments under the medium depth tunnel option or the “deep tunnel” option mentioned in 1998 (as shown in Annex 1) in that they pass different parts of To Kwa Wan with different geological conditions.

Under the “medium depth tunnel” option of 1998, the alignment would pass Chi Kiang Street and Bailey Street in To Kwa Wan, with the bottom of the tunnel located at about 51 metres underground. Since the tunnel would run through reclaimed land, the bedrock would be at a relatively deep level from the road surface. At such a depth, the tunnel would have to be built in mixed ground. The geological conditions there would make construction very difficult and pose greater impact on adjacent buildings. Hence, this option was not adopted.

The alignment under the “deep tunnel” option, also discussed in 1998, would run under Bailey Street. To avoid impact on the buildings in the district, the floor slap of the tunnel would have to be situated at about 76 metres below ground level to allow the tunnel to remain in rock stratum. Located deeper underground, the tunnel would have to travel a much longer distance to rise back up to the ground level, thus would be unable to connect with the proposed road network at the desired location. As such, this option was eventually dropped.

Instead of passing Chi Kiang Street and Bailey Street of To Kwa Wan, the latest proposed alignment of the CKR turns northward to the Kowloon City Ferry Pier Public Transport Interchange and links up with Kowloon Bay via areas within the original shoreline of Kowloon Peninsula (as shown in Annex 1). With the solid bedrock being only a few metres to 40 metres away from the ground level, these areas are of better geological conditions than the unadopted alignments under the “medium depth tunnel” option and “deep tunnel” option of 1998, enabling the tunnel to be built at about 26 to 62 metres underground deep in solid rock. Given the relatively long distance maintained between the tunnel and the building foundations, it is appropriate to adopt the drill-and-blast construction method. Also, the current tunnel alignment ties in with the design of KTD and connects with the proposed and existing road networks at appropriate locations.

In conclusion, the tunnel sections of the current alignment will be constructed mainly in rock stratum deep underground. As such, the alignment will not affect the structural integrity of the buildings along it.

(b) When examining tunnel construction methods, the Administration will make different considerations with regard to the length and size of the tunnel sections as well as the underground geological conditions encountered.

The drill-and-blast method is generally adopted for tunnel construction in rock stratum in Hong Kong and around the world. Having been adopted in Hong Kong for over 40 years, the drill-and-blast method has been confirmed to be a safe and effective construction method. Examples of its application in road construction include the Lion Rock Tunnel, Aberdeen Tunnel, Tseung Kwan O Tunnel, Shing Mun Tunnels, Tate’s Cairn Tunnel, Tai Lam Tunnel, Cheung Tsing Tunnel, Eagle’s Nest Tunnel, Sha Tin Heights Tunnel and Nam Wan Tunnel. As for railway construction, examples of completed works are the section of East Rail Line between Kowloon Tong and Tai Wai, the section of Tung Chung Line and Airport Express between Lai King and Tsing Yi, Tseung Kwan O Line, the Tai Lam section of West Rail Line, Disneyland Line and Island Line; while examples of works in progress are the section of West Island Line (between Sai Ying Pun and Kennedy Town), Nam Fung Road Tunnel of South Island Line (East), the South Horizons section of Ap Lei Chau Tunnel and Lee Wing Street Tunnel. Some of these works, including the Island Line and South Island Line (Sai Ying Pun section), pass under existing buildings in densely populated urban areas. Thus, the experience so gained is also applicable to the CKR project.

Regarding construction, the works departments will confirm the geological conditions of the tunnel section ahead before each excavation. Conditions of the buildings in the vicinity will be investigated, reviewed and recorded to identify the most suitable and proper construction arrangements. The contractors have to submit to the Mines Division of the Civil Engineering and Development Department the details of every blasting and apply for blasting permits from the Division. The quantity of explosives for each blasting is subject to stringent control for safeguarding the structural integrity of nearby buildings. Blasting operations have to be performed by qualified contractors and engineering personnel. Monitoring points will be installed by the works department to monitor the impact on surrounding buildings.

Other feasible construction alternatives have been considered. The tunnel section of the CKR between Shanghai Street and Ma Tau Wai has to be built deep in the solid rock stratum. As each tube of the tunnel measures about 18 metres in width, even the most advanced tunnel-boring machines currently available cannot drill a tube with such width. Ordinary mechanical drilling in rock stratum yields very low efficiency, and poses prolonged impact on nearby residents and traffic.

Given the shorter construction time, the smaller impact on the community and the fact that the structural integrity of the buildings along the alignment will not be affected as the tunnel has a relatively long distance from the building foundations, the drill-and-blast method is considered the most suitable and effective method to construct the tunnel section concerned.

(c) Along the entire length of 4.7 km of the CKR, the drill-and-blast tunnel sections measure about 2.8 km. The works concerned will be carried out in an almost concealed underground environment, reducing significantly the noises so generated. For the part of the CKR works to be implemented on the ground level nearer to residential buildings, we will adopt a series of mitigation measures as required by the Technical Memorandum of the Environmental Impact Assessment Ordinance to minimise the noise impact of the works to nearby residents. Apart from general alleviation measures such as low-noise machinery, noise insulation equipment, good site management, site hoardings and optimised procedures, the works departments will also erect full noise enclosures at all mucking-out points to reduce the noise during construction. For the tunnel section between Kansu Street and Kowloon City Ferry Pier Public Transport Interchange, the cut-and-cover method will be used. The works departments will arrange to have the works carried out under temporary decking or beneath the tunnel top decking to alleviate construction noise.

(d) The selected CKR alignment does not involve resumption and demolition of any private buildings. That said, as it passes highly developed areas, some tunnel sections have to go through the stratum of certain existing residential buildings. Locations of these residential buildings are at Annex 2.

The Administration has been investigating the cause of vibration at the buildings along Maidstone Road reported in mid-May this year. It has been known that the works for diaphragm walls and foundations of the Shatin to Central Link (SCL) were being carried out at the time. After the incident, the MTR Corporation Limited (MTRCL) has suspended some works procedures and installed additional monitoring devices in the buildings near Ma Tau Wai Station of the SCL to strengthen surveillance of the impact of the works on nearby buildings. With the consent of the Buildings Department, the impact of each construction procedure on the buildings has been gradually tested since May 28. No anomaly has been identified so far. On the basis of the test results, the MTRCL will submit investigation reports to the Buildings Department and Highways Department. Before allowing resumption of the foundation works, the Administration will study the reports to look into the cause of the incident, as well as to vet the construction methods submitted by MTRCL so as to ensure that the structural integrity of the buildings is not affected by the works.

Similarly, the Administration will formulate proper design and construction methods to ensure that no impact on the structural integrity of existing buildings along the alignment will be created by the construction of the CKR project.