Technical visit of I3C to HATS Stage 2A  

 

 

 

 

On 19th September 2012, the NTU-JTC Industrial Infrastructure Innovation Centre (I3C) successfully organized a technical site visit to HATS Stage 2A project in Hong Kong special administrative regions of the People's Republic of China. The site is under the Works Contract No. DC/2007/23 - Construction of Sewage Conveyance System from North Point to Stonecutters Island, which involves the construction of many vertical shafts and the deepest and longest tunnel among the three conveyance systems to be constructed. The visit was kindly arranged with the informative presentations by the representatives of AECOM and Gammon.

AECOM Resident engineer Ms Mandy Fu firstly introduced the delegation with a brief background of the overall project. This was followed by a detailed presentation by Mr. Colin Foster of Gammon on the topic of “Mucking Out System for Shaft Sinking and Tunnel Construction”. The project involves the construction of drop shafts, temporary production shaft, riser shafts and junction shafts. The temporary production shaft is constructed as the main access for mucking out excavated material from the shaft and tunnels. Apart from the shafts, tunnels namely Tunnel K, J and L will be constructed under this Contract. The mucking out system used for North Point production shaft is a common use system for both shaft sinking and tunnel excavation. This system is widely used for mining, which has 3 means of access, restricted sites and enclosed operations, overhead protection/protection from falling objects and prevention of falls, real time load cells for double deck platform etc. The system can minimize the noise impact on the nearby sensitive receivers and enhance the capability of mucking out.

 

The final key topic of “Ground Water Control in Shaft Sinking” was given by Mr. Finn Garshol. This topic is critical for Singapore shaft construction and was proposed by Professor Lu Ming before this visit. Due to deep shafts and tunnels (70m, 120m and 160m bsl) excavated and reclaimed land on marine deposits located, too high water ingress to shafts and tunnels may cause settlement damage on surface. The ingress targets of HATS 2A are generally 15~30 or 50 L/min per 100 m tunnel/shaft. In some most critical sections the targets are 2.5 or 5 L/min per 100m tunnel/shaft. To achieve these goals, Pre-Excavation Grouting (PEG) method is used. The PEG is implemented through ingress in control holes to determine if subsequent grouting is required. The grout holes should have a minimum overlap of 5 m.

 

The activity came to the end with a lively Q&A session. Professor Lu Ming and Professor Zhao Zhiye briefly introduced the shaft construction of JRC project in Singapore. Mr. Finn Garshol suggested the ingress targets should be set in contract before construction based on working condition in the shaft or potential for surface damage. Then PEG method should be implemented carefully.

 

After the presentation, Ms Mandy Fu, Mr. Colin Foster, Mr. Finn Garshol kindly introduced I3C attendees to the construction works on site at the production shaft at North Point. The production shaft is constructed with ELS using diaphragm wall and ring beam at toe.

 

I3C would like to thank again for their generous invitation, informative presentations and warm hospitality.


 

By Zhang Xiaoping