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Successful story for Tseung Kwan O – Lam Tin Tunnel

By the Civil Engineering and Development Department with the coordination of the CV Division

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The Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) project is a dual two-lane carriageway that stretches 3.8 km in length (see figure 1a). The main tunnel, which runs for 2.2 km between the road interchanges at Lam Tin and Tseung Kwan O (TKO), is supplemented by a branch tunnel that provides a direct link between the westbound tunnel and the Eastern Harbour Crossing toll plaza. Additionally, the project includes the construction of an underpass, Road P2, which connects the TKO Interchange to town centre. The TKO-LTT connects further to the road network of the Cross Bay Link project, forming a comprehensive network serving the traffic between the southeastern part of the TKO and Lam Tin.

 

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Figure 1a: Overview of Tseung Kwan O – Lam Tin Tunnel

 

The project also provides two ventilation buildings at the east and west portal, and an administration building as the control centre for housing the electrical and mechanical equipment as well as that of the traffic control and surveillance system. There is also a storm water pumping station to discharge the surface runoff collected from the Tunnel and the Lam Tin Interchange (see figure 1b) as flood control measure of this low-lying area.

 

Besides, the iconic Southern Footbridge (see figure 1c), serving both pedestrians and cyclists, shapes the gateway of TKO-LTT to TKO South.

 

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Figure 1b: Lam Tin Interchange

 

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Figure 1c: Southern Footbridge

 

TKO-LTT was commissioned in 2022, along with the Cross Bay Link, providing a new route between TKO and Kwun Tong as well as the Eastern Harbour Crossing. This shortens the journey time between the LOHAS Park and Kwun Tong Town Centre by up to about 20 minutes during the morning peak hours. Apart from serving as an alternative traffic route to the existing TKO Tunnel, TKO-LTT creates an opportunity for waiving the toll of the TKO Tunnel, as well as additional traffic capacity for meeting the demand of the continual development in TKO. The TKO-LTT project is widely and favourably reported by the media, fully recognised by the industry, and well received in society.

 

An intact team was formed by the Civil Engineering and Development Department (CEDD) as the proponent of the project, AECOM Asia Company Ltd as the project consultants, and various contractors including Leighton – China State Joint Venture (Contract NE/2015/01), CRBC-Build King Joint Venture (Contract NE/2015/02), Wing Lee (SK) Construction Company Ltd (Contract NE/2015/03), Chun Wo – Shanghai Tunnel – China Metallurgical Joint Venture (Contract NE/2017/01), Zhen Hua Engineering Co Ltd (Contract NE/2017/02), as well as GTECH Services (Hong Kong) Ltd (Contract NE/2017/06). The team overcame various challenges in different key parts of the project and achieved timely commissioning of this traffic infrastructure project.

 

 

The team overcame various challenges in different key parts of the project

and achieved timely commissioning of this traffic infrastructure project.

 

 

Tunnelling

 

TKO-LTT was constructed by drill and blast method, involving over 1,000 times tunnel blasts, with stringent control on the tunnel blasting works. Various safety and environmental measures were also implemented, comprising installation of silencers, blast doors and multi-layer protective nets at tunnel portals, together with a comprehensive monitoring and notification mechanism. The project accomplished a significant achievement by tunnelling a branch tunnel with tunnel bifurcation (see figure 2a) — the first time for a road tunnel in Hong Kong — using drill and blast method. The 38-m excavation span at the turnout presented a major tunnelling challenge, and the 700-m branch tunnel required special consideration for fire safety. Cross passages at 100-m intervals for evacuation were provided at the main tunnel, while a protected evacuation corridor was required along the branch tunnel with doors at no more than 100-m intervals. To maintain positive pressure against possible smoke intrusion along the entire 700-m evacuation corridor, a pressurisation system was designed and constructed with minimal response time upon opening the corridor doors. Due to significant site constraints, there was insufficient land for a separate ventilation building for the branch tunnel, and, therefore, the Western Ventilation Building of the main tunnel at the Lam Tin Interchange was designed to cope with the air ventilation of this branch tunnel.

 

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Figure 2a: Tunnel bifurcation

 

To ensure cost-effectiveness, a ventilation adit (see figure 2b) was built to connect the main and branch tunnels. The adit was designed with a 45-degree inclination, which was more efficient than the conventional approach of a horizontal adit with a vertical shaft and a 90-degree bend, to reduce pressure loss as well as the energy consumption of the tunnel ventilation system. To overcome the construction difficulties of this inclined adit, a separate construction adit was constructed to intercept the ventilation adit at around the midpoint, which also served as early access for the excavation of the branch tunnel from the Lam Tin Interchange. Permanent sprayed concrete lining structure with spray-able waterproofing membrane was adopted at the ventilation adit to eliminate extensive falsework and formwork along this inclined adit, achieving safe working environment.

 

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Figure 2b: Ventilation adit

 

Site formation

 

Construction of the Lam Tin Interchange involved large-scale site formation works requiring over 1,000 times of open blasting. At critical locations, the open blasting works were to be carried out underground across the existing MTR Kwun Tong line and TKO line with only 12-m vertical separation, and also at surface ground overlooking the existing MTR ventilation building and open track (see figure 3). The open blasting works were also to be carried out adjacent to the Eastern Harbour Crossing (EHC), Cha Kwo Ling Village squatters and the restored landfill at Sai Tso Wan.

 

State-of-the-art blast design and technology, including the use of 3D and 2D finite element model and high precision electronic detonators to minimise the occurrence of concurrent detonation, were used to effectively control the ground vibration. A roof-over system, composing of blast cages, vertical screens, top screens and rubber tires, were used to prevent flyrock, resulting in the safe and timely breaking and removal of 2,000,000 m3 of excavated rock following a compacted construction programme. For some critical zones, a special “holding train” procedure was implemented to uphold the commuters’ safety. A real-time automatic deformation monitoring system and vibration sensors were installed within the MTR tunnel tubes with full coverage of the influence zone, and an algorithm was developed to collect monitoring data instantaneously, enabling the resumption of normal MTR operations as early as possible after the blasting.

 

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Figure 3: Open blasting works in the vicinity of MTR and EHC

 

Mined tunnelling

 

The project accomplished a remarkable achievement by mining a 16-m tunnel under the six-lane Lei Yue Mun Road (LYMR) in challenging mixed ground conditions with highly variable rockhead. The merely 3-m ground cover, extensive but indivertible underground utilities, and the significant traffic flow to be maintained at this working location, were some of the significant constraints met on the selection of a construction methodology that suits the planned programme. The mined tunnel approach (see figure 4) presented itself, an approach which required precise pipe roofing between the tunnel and the water/ gas mains, supported by lattice girders during the excavation. To ensure the safety of the works and those running traffic at LYMR and prevent unexpected ground loss, a traffic deck was constructed over the entire mined tunnel underneath LYMR. This was in addition to the excavation support system, which already took into consideration the busy traffic condition at LYMR.

 

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Figure 4: Mined tunnelling

 

Innovative semi-cavern

 

The project was the first road tunnel project in Hong Kong to construct its ventilation building in a cavern (see figure 5). This innovative approach significantly reduced the extent of site formation of the tunnel portal area, thereby minimising the generation of construction and demolition materials and the respective visual impacts. The semi-cavern structure allowed the majority of the fan and plant rooms to be placed underground. The exposed part of the building occupied a smaller footprint area, which, in effect, significantly reduced the excavation and soil nail works at the steep terrain of the TKO portal. This led to a 43% and 68% reduction in excavation volume and in soil nailing works respectively. Moreover, the slope cutting area was reduced by 46%, which helps preserve the valuable green belt habitat.

 

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Figure 5: Semi-cavern structure of the ventilation building

 

At the TKO portal, two caverns were excavated in highly fractured volcanic tuff, which was geologically complicated, for the construction of a semi-cavern ventilation building. This was an ambitious design that requires a thorough study during the design stage to ascertain its constructability. Extensive ground investigation works were carried out to form a three-dimensional (3D) geological model. The Norwegian Geotechnical Institute design approach has been verified with finite element analysis to ascertain its constructability before the semi-cavern ventilation building scheme was further developed.

 

During construction, 3D finite element analysis was carried out for design review and optimisation. The excavation was supported temporarily by a combination of steel canopy, lattice girder, rock bolting, fibre-reinforced shotcrete; and the rock pillar was reinforced by steel bars. The caverns were excavated by mechanical means, top-down synchronising with site formation works; the progressive nature of mechanical excavation made it possible to closely monitor ground movement throughout the excavation, enabling timely strengthening works to uphold the stability of the caverns under the challenging working conditions.

 

Hybrid reclamation

 

To construct the underpass Road P2 at TKO, a hybrid reclamation scheme involving partial dredging was employed. A steel cofferdam around the marine site, enclosing the dredging and reclamation works, was constructed under the project. TKO-LTT was the first project to install a double water-gate (see figure 6) for reclamation works in Hong Kong, allowing working barges to pass through the cofferdam without affecting the quality of the adjacent water. This innovative solution has considered both the feasibility of the works and the importance of water quality around the site.

 

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Figure 6: Reclamation works

 

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Enlarged section (L); Typical section (R)

Figure 7a: Tunnel with various excavation profiles

 

Sustainability

 

In addition to its innovative semi-cavern ventilation building, fully enclosed reclamation works, and inclined ventilation adit, which prioritised sustainability, the project had also thoroughly examined various tunnel schemes to ensure safety and sustainability in its design.

 

The project stood out for its adoption of a tunnel scheme without a toll plaza, which resulted in a reduction of reclamation works from 12 hectares to 3 hectares, and a shorter tunnel length of 2.2 km as compared with the original 4.8 km. This reduced not only the carbon footprint of the construction works but also the long-term energy consumption of the tunnel operation. The vertical tunnel profile was designed to ensure maximum separation at the MTR tunnel crossing points at Lam Tin and Tiu Keng Leng while still maintaining a high-speed road design standard. This resulted in minimum impact on the safe operation of the MTR. Overall, the project adopted a holistic tunnel alignment design to enhance both the safety and sustainability aspects of the tunnel.

 

The drill and blast tunnelling method employed in the project offered greater flexibility in the excavation profile, minimising over-excavation with less disposal material. Because of this flexibility, various excavation profiles suited the specific location requirements, such as directional sign gantries within the road tunnel and the bifurcation for the branch tunnel turnout (see figure 7a). It was estimated that this project achieved a 24% reduction in excavation volume as compared to others adopting only one standard profile. This approach optimised the excavation process and contributed to the sustainability goals.

 

A commitment to sustainability led to the implementation, in the project, of innovative solutions for the management of excavated rock. The project provided two fully enclosed crushers within the site, enabling the reuse of excavated rock for drainage layers and rock backfill at the tunnel invert. Additionally, a fully enclosed temporary vehicular bridge (see figure 7b) and barging point with tipping hall were built to transport the excavated material directly onto barges for off-site disposal, thereby minimising the disruption to local traffic because of the substantial reduction in the truck trips needed for material disposal.

 

In addition to the re-use of excavated rock, the re-use of excavated marine sediment also contributed greatly to the sustainability of the project. The excavated marine sediment was treated with cement solidification or stabilisation process. The treated material was re-used as filling material within the site. Over 75,000 m3 of excavated marine sediment was treated and re-used for backfilling. This was an effective way to manage marine waste materials in an environmentally friendly manner.

 

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Figure 7b: Conveyor bridge

 

Successful project delivery

 

The works progress of the TKO-LTT project was hit hard by the COVID-19 pandemic. The site was forced to shut down three times due to pandemic outbreak. Also, the workforce dwindled by more than 50% at the worst times and the restrictions in cross-border transportation also limited the delivery of construction materials and prefabricated assemblies. To meet the challenging commissioning target, weekly steering group meetings (see figure 8) with attendance of the top management of the project proponent, the consultants and the contractors were held with full support by frontline teams for purposes of daily supervision and works progress monitoring. The entire project team, with various parties, was united, fostering team spirit, brainstorming together and implementing various plans to speed up the progress of the projects.

 

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Figure 8: Project steering group

 

The construction of the tunnel and cavern involved several high-risk activities: drill and blast tunnelling, excavation of two large caverns with a small rock pillar in a highly fractured geology, open blasting at high ground for portal formation, and the mining of a large-span tunnel in mixed ground with extremely small ground cover beneath a busy LYMR. Despite the risks inherit in these activities, the tunnel and cavern were completed without any serious accident impacting the workers. Moreover, the project was carried out in an urbanised area surrounded by highly sensitive facilities, including MTR lines and the Eastern Harbour Crossing, with no reported incident affecting the operation of these critical infrastructure assets.

 

Despite the challenging nature of the project, the project team maintained the highest possible quality standards. This was demonstrated best by the completion of the fire service installations acceptance inspection for the road tunnel in less than two months, a record-breaking time. The achievement was the result of the team's unwavering commitment to quality assurance and precise planning in managing complex interfacing issues.

 

 

The project team maintained the highest possible quality standards

despite the challenging nature of the project.

 

Single site, multiple use

 

A section of the Tseung Lam Highway was designed as a depressed road in the form of an underpass, with a landscape deck on top to reduce the noise impact on the residents in the road’s vicinity. It was taken into consideration that this landscape deck could be a passive open space for leisure use by the public. This followed the “single site, multiple use” initiative, making the most of the created space to act as a highway functionally, as a noise mitigation measure and as an open space for leisure purpose. The open space was about 0.7 hectares and was connected to the 5.0-km cycle track opened after the commissioning of the TKO landmark, Cross Bay Link (see figure 9a). The landscape deck, with selected trees and shrubs, provided the public with a space to enjoy different sceneries at different seasons. To mark the opening of this new leisure facility, named the Tseung Lam Highway Garden (see figure 9b), local stakeholders in the TKO community were invited to attend a memorable tree planting event on 29 September 2023.

 

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Figure 9a: Cross Bay Link

 

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Figure 9b: Landscape deck

 

 

Concluding remarks

 

The project achieves its commissioning target, and the operation of the tunnel is successful in alleviating traffic congestion in the TKO area, existing TKO tunnel and eastern Kowloon major roads approaching the Eastern Harbour Crossing. So far, the project has received positive feedback from the public, and its full potential is yet to be realised with the completion of the Road T2 and Central Kowloon Route. The success of the project can be attributed to the team's dedication to planning, supervision and execution, as well as their commitment to quality assurance and safety of the works throughout every stage of the project delivery.

 

 

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