Tunnel construction makes up a significant portion of Hong Kong’s civil engineering industry. This includes all the different tunnel types that enable roads, rail, cable, drainage and sewage and water supply to work effectively around Hong Kong. This article will detail the differing methods of tunnel construction and outline some examples of their use in major construction projects in Hong Kong. I will also offer some career advice to tunnel engineers and tunnelling professionals.
The Three Main Tunnelling Methods
There are 3 main methods of tunnel construction in Hong Kong These comprise:
1) Cut and Cover
2) Drill and Blast
3) Bored Tunnelling
There are advantages and disadvantages inherent in each method and of course, there are certain situations in which one method is clearly the best option, while in other situations the choice of method can be controversial from the start.
Cut and Cover is as simple and straightforward as the name suggests. A trench is excavated from above ground; the tunnel is constructed within this trench which is then backfilled with soil. This method is used mainly for shallow construction in soft ground conditions and actually executed a lot for stations – a current example being the early stage construction work on Whampoa Station on the Kwun Tong Extension Line.
Drill and Blast employs the use of explosives to break away rock and soil. Holes are drilled into the rock surface then explosives are installed into these holes. Upon timed detonation of the explosives, the broken up rock and soil is then transported out of the tunnel. Supports must then be installed in the newly formed space before further blasting takes place. The West Island Line tunnel between Sai Ying Pun and Kennedy Town is constructed with the Drill and Blast method.
Bored Tunnelling is a method used for long stretches of tunnel. A Tunnel Boring Machine (TBM) is used to drive and cut through the rock– the waste material is transported to the back of the TBM for disposal. The TBM is assembled by means of vertical shafts. Bored tunnelling is an efficient and faster way of constructing tunnels of a certain diameter and can handle a variety of ground conditions. The Diamond Hill tunnels are currently being constructed for the Shatin-Central Link using the TBM method.
Special Tunneling Circumstances
In special circumstances such as sub-sea tunnel construction, other techniques may be used. For example in Hong Kong, the 3 vehicular cross-harbour tunnels were all constructed using the Immersed Tube method – pre-constructed segments of the tunnel are sunk into the body of water and joined together once in place. This method is fast and efficient and more cost-effective than alternative options of boring into the seabed or constructing a bridge. Of course, immersed tubes are used in conjunction with bored tunnels or blasted tunnels to connect at either end. MTR will employ this method for the cross harbour section of the Shatin-Central Link project.
Tunnel Engineering and Expertise as Highly Valued Disciplines
The process of constructing a tunnel for any given purpose is lengthy and complex and will always have unique considerations and circumstances. To achieve the best outcome, specialised tunnelling professionals at every level are needed for this sort of specialist work. Currently, the construction market in Hong Kong has an ongoing shortage and need for tunnel engineers, geotechnical engineers, blasting engineers, shotfirers, TBM pilots, shaft supervisors etc. As new tunnel contracts are being awarded, older projects are either still on-going and retaining workers who are skilled in tunnel construction, underground structures and working in confined spaces or workers are often transferring to other projects with their existing employer.
From a recruiter’s perspective, I have come to understand that companies show a keen interest in candidates who have diverse tunnel experience and have not just exclusively worked within one method of tunnelling. This appears to be because they value experience, flexibility, and the ability to bring critical thinking and problem solving to a situation.
An obvious example of this would be the Tuen Mun Chek Lap Kok Northern Link, which is the largest design-build contract ever to be awarded in Hong Kong. It incorporates a combination of cut and cover tunnelling as well as bored tunnelling to construct the approach tunnels and sub-sea tunnels (4.2km!) respectively. Candidates with prior experience in both sorts of tunnel projects have a distinct advantage during the recruitment and selection process. Moreover, marine engineering and environmental engineering skills will also be favoured in site specific jobs such as this involving water quality, marine ecology, waste management and acoustical impact.
Reviewing Your Career in the Tunneling Industry
As a part of our service to our construction customers, we offer a chance to review career and project opportunities with engineers, quantity surveyors, project managers and other construction industry professionals. Hong Kong offers great opportunities in tunnelling and infrastructure as do a number of other international locations. Please get in touch if we can be of assistance.
Hong Kong and Asia Region