Innovative Design at the Homebush Bay Rail Link

 

Doug Jenkins

Engineering Manager

Reinforced Earth Pty Ltd

Ian Cox

Design Manager

Connell Wagner Pty Ltd

Greg Fanning

Design Manager

Leighton Contractors Pty Ltd

 

Synopsis:  The rail link to the Sydney 2000 Olympic site at Homebush Bay is a landmark project which presented complex technical challenges to both designers and constructors. The project included the design and construction of a number of significant structures including a new station, a driven tunnel, cut and cover arch tunnels, four bridges and retaining walls including reinforced soil walls. Innovative design was required throughout the project to meet the demanding aesthetic and technical requirements of the project within very tight time constraints and project budgets. The design for the on-site civil works was jointly developed by Leighton Contractors, the Head Contractor and Connell Wagner, Leighton’s Lead Design Consultant. In this paper the main features and unique innovations of the project will be described with particular focus on the concrete structures including the cut and cover tunnels where the use of precast concrete arch units, designed and supplied by The Reinforced Earth Company, was adopted as a value engineered alternative.

 

Keywords:  Olympics, Rail, Tunnels, Bridges, Precast Arches, Reinforced Soil Walls

 

1.         Introduction

 

The main objective of the Homebush Bay Rail Link is to provide a rail service to Homebush Bay for the 1998 Royal Easter Show, for pre and post Olympic events and for the 2000 Olympic Games. The rail link is an important part of the infrastructure for the Sydney 2000 Olympics and will provide the primary means of travel for large crowds attending events at Homebush Bay.

 

The $90 million Homebush Bay Rail Link is a landmark project which presented complex technical challenges to both designers and constructors given the fast track nature of the project, the necessary integration of a number of civil and multi-discipline activities, and the need to achieve technical and aesthetic quality of the highest standard.

 

The rail link on-site works, north of the M4 Motorway, comprise a 3km long balloon loop within the Homebush Bay site which connects the new Olympic Park Railway Station to the metropolitan rail network between Lidcombe and Flemington stations through the disused Pippita rail corridor (refer Figure 1).

 

Figure 1. Site Location


2.                  Project Description

 

The Homebush Bay Rail Link has involved a significant integrated effort by a number of authorities, consultants and contractors to deliver this key element of the transport infrastructure for the 2000 Olympics. The key authorities involved were the Olympic Co-ordination Authority (OCA), Rail Access Corporation (RAC), and Department of Transport (DoT).

 

In July 1996, Leighton Contractors was awarded the design and construct contract by the Olympic Coordination Authority (OCA) to build the rail link, including the station. Leighton Contractors engaged Connell Wagner to undertake the tender design and the detailed design and documentation of all civil works for the on-site works, as well as the tunnel and station services. Leighton also engaged Reinforced Earth Pty Ltd to design and supply the cut and cover tunnel roof arch units and the reinforced soil walls.

 

In summary, the rail link on-site works comprise approximately 3km of trackwork and formation constrained by steep grades up to 3% and tight 180m radius curves to accommodate existing and future sporting and recreational facilities, a heritage precinct, buildings, roads and utilities established by the Homebush Bay Master Plan. This required the construction of significant sections of tunnel and a number of bridges. The station is located in a section of bifurcated track allowing a 200m long four-platform station to be constructed with a capacity of up to 50,000 passengers (or 30 trains) per hour in peak Olympic mode. It is the largest capacity and most impressive railway station in Australia. The main elements of the project are:

 

·         Four bridges: two rail underbridges, one road underbridge and one pedestrian bridge.

·         560m of cut and cover precast concrete arch tunnels.

·         300m of driven tunnel.

·         200m long Olympic Park railway station.

·         Cast in situ concrete and reinforced soil retaining walls.

·         Rock reinforced and shotcrete cutting wall stabilisation.

·         Tunnel and station mechanical, electrical, fire and hydraulic services.

·         Trackwork and other railway works.

·         Earthworks and stormwater drainage.

·         1.5km of roadworks.

·         Sewer and water utility adjustments.

 

 

 


 


Figure 2. General Arrangement of Key Project Elements


3.         Project Requirements

 

The Olympic Coordination Authority (OCA) had a number of specific requirements to be met in the design and construction of the project.

 

The stated purpose of the works was to provide rail infrastructure to enable the operation of a reliable, high capacity heavy rail service to Homebush Bay for both major events and daily requirements. The rail infrastructure was required to satisfy a number of important stakeholders including:

 

·         The long-term owner, the NSW Government, in terms of design life, maintainability and safety.

·         The rail service operator, in terms of integration with the metropolitan rail system, operating cost and safety.

·         The OCA and the Department of Urban Affairs and Planning, by achieving a high standard of urban design consistent with the OCA’s Public Domain Strategy.

·         The neighbouring property owners (tenants and users), by minimising disturbance of and intrusion on their activities and amenities both during construction and operation.

·         The rail users, by providing for a safe and comfortable rail service.

 

Programming was also critical to the OCA. The rail link was to be open to passengers by 31st March 1998, i.e. in time for the first Royal Easter Show at Homebush Bay. This dictated a very tight design and construct programme (19 months) requiring a fast track design and documentation phase to keep construction proceeding for Leighton Contractors. Progressive delivery of design documentation was required primarily during an initial period of 4-5 months.

 

Given the high profile nature of the project and the site, the urban and landscape design was critical to the OCA. The design intent was to:

 

·         Provide a memorable rail journey experience for visitors to Homebush Bay.

·         Provide rail infrastructure works which are of outstanding design quality and appearance, complementary to the existing and proposed sports and recreation facilities.

·         Implement the urban design and landscape works within the OCA budget.

 

Connell Wagner worked closely with Leighton’s Urban Designers Hassell Pty Ltd in the design of a number of structural elements including the bridges, retaining walls and tunnel portals.

 

Environmental performance is a fundamental element in all developments and works undertaken by the OCA. Ecologically Sustainable Development is identified as underpinning the environmental philosophy of the Sydney 2000 Olympics and Homebush Bay Development. Environmentally sensitive design and environmental management were important requirements of the project. Connell Wagner designed and prepared the works in accordance with a Design Environmental Management Plan prepared by Connell Wagner specifically for the project.

 

Key technical criteria for the design of the rail link included:

 

·         Compliance with the design criteria nominated in the ACER Wargon Chapman Concept Design Report including standards and requirements of the SRA.

·         Fixed constraints included track horizontal alignment, kinematic envelope at cuttings and in tunnel, and vertical clearances at bridge structures.

·         Track vertical alignment was to be designed to accommodate normal train running speeds of up to 50km/hr.

·         Design life for the tunnels, bridges and retaining walls was 100 years.

·         The tunnel roof was required to be watertight.


4.         Innovative Features and Solutions

 

The main features and unique innovations on the project are outlined below:

 

·         The driven tunnel solution under the Aquatic Centre bus parking area limited the impacts on the amenity and operation of the popular Aquatic Centre during construction.

·         Precast concrete arches in the cut and cover tunnels provided a cost effective solution which enhanced speed of construction and provided flexibility for the variety of spans and varying finished surface levels along the route.

·         Rock bolting and screeded shotcrete were used to retain the cuttings in the ramps and tunnels in lieu of concrete pile and infill panel walls.

·         Avenue A and Avenue B rail underbridges incorporated girder continuity for the two-span structures and a curved arch girder profile for enhanced aesthetic appearance.

·         The urban design and aesthetic quality of the station, bridges, retaining walls, fencing and tunnel portals were developed to a high standard to minimise the visual impact of the rail infrastructure and to complement the existing and proposed high quality sports and recreation facilities.

·         Station design utilised extensive use of precast concrete structural elements to minimise the construction programme.

 

These and many other innovations were an outcome of the effective teamwork between contractor and designer and were carried out within the framework of Ecologically Sustainable Development (ESD) principles and the need to achieve a high standard of urban design. The extensive use of precast concrete elements in both the civil works and building works at the Homebush Bay Rail Link was highly successful in terms of quality and programme.

 

The main features and unique innovations of the project are described in further detail below.

 

Driven Tunnel

 

The driven tunnel was an innovative alternative, proposed at the time of tender and acknowledged by the OCA as being a major factor in Leighton’s successful tender. The driven tunnel limited the impacts on the amenity of the popular Aquatic Centre during construction and facilitated early construction of the Olympic Boulevard. The “horse-shoe shaped” tunnel was driven through weathered shale geology and relatively shallow cover up to a maximum of 12m. The northern end of the tunnel was particularly complicated, given the relatively large 9m width of the tunnel resulting from track bifurcation and 4-5m of relatively poor quality class IV and class V shale above the crown. Careful attention was paid to a major existing utilities services corridor above the tunnel in this location. Spiling bars were installed above the crown to assist in the support of the ground ahead of the face to reduce settlement, and to also allow grout filling of open joints in the rock mass. Tunnel support comprised a primary lining of shotcrete and temporary Swellex rockbolts followed by a permanent secondary steel fibre reinforced shotcrete arch lining of a minimum 150mm thickness. A waterproof membrane was installed in the crown of the tunnel to prevent any “drips or discernible flows” (as required by the contract), from entering the tunnel.

 

Cut and Cover Tunnels

 

The design and construction of the cut and cover tunnels was complicated by the variable cross section, variable cover, the proposal to build a hotel over part of the route, the substantial excavation required, and the provision for existing roads across the route. In the area of the Homebush Bay Hotel, the concrete pile and infill panel wall was retained to transfer the future building loads to competent rock, while the remainder of the cut and cover tunnel was constructed using precast arches manufactured by the Reinforced Earth Company. Precast arches were selected because of:

 

·         Speed of construction and cost.

·         Flexibility in handling a variety of spans and founding level.

·         Load carrying capacity, given the variable cover.

·         Ability to protect efficiently the tunnel from water ingress.

 

The design and installation of the cut and cover tunnel arches are described in further detail in Section 6 of this paper.

 

Cutting Wall Stabilisation

 

An assessment of the geotechnical investigation work undertaken by OCA prior to calling tenders indicated that Class I to Class III shales existed over most areas to be excavated. In tendering for the project, extensive use of rock nailing was made to support the cuttings in lieu of previously proposed, more expensive, solutions such as pile and infill panel walls. The foundation conditions were also suited to the use of high level sill beams for the cut and cover structure in lieu of piled foundations. This approach not only saved considerable cost on the project but also enabled ambitious time targets for the project to be achieved. The rock nailing proposal involved the use of permanent “CT” rockbolts with steel fibre reinforced shotcrete to maintain the integrity of the rock face. It had been proposed that precast concrete panels be used to face the piled walls. While this method proved to be appropriate in the station box, it was replaced with a combination of screeded shotcrete and cast in situ concrete L-walls in the cuttings. Again, this technique provided considerable savings in time and cost to the project.

 

The use of shotcrete and permanent rockbolts for the cutting wall stabilisation proved to be cost effective and provided the benefit of quickly developing several work fronts, thereby providing greater flexibility for this construction operation.

 

Bridges

 

The bridges over Avenue A (Australia Avenue) and Avenue B, along with the retained embankment on the approaches, presented a significant visual element of the Homebush Bay area. Connell Wagner, together with Leighton’s urban design consultant, Hassell Pty Ltd, developed a girder design for the bridges which reflects the significance of their position.

 

Both rail underbridges consist of two spans of concrete through girders with a ballast top deck which is continuous over the centre blade pier. Alternative steel superstructures were considered for the bridges, however concrete was preferred by the OCA in terms of appearance and long term maintenance.

 

Avenue A bridge carries a single track with equal spans of 22m and an onerous 36° skew. Avenue B bridge carries twin tracks with equal spans of 18m and a normal skew of 6°. The girders for both bridges are post tensioned longitudinally in three stages and the deck is post-tensioned in both directions. The girders for Avenue A were constructed as precast elements (manufactured in Queensland) while the shorter spanned Avenue B bridge was cast in situ. The urban design of the bridges was very important to the OCA given the significance of their position on the site, and the structural design of the bridges was to a great extent architecturally driven. The interesting and innovative features of the design of both bridges were the:

 

·         Curved arch facing profile of the external face of all girders designed to make the girders appear lighter, thereby reducing the apparent depth and enhancing the overall appearance.

·         Continuity of the girders over the centre support to eliminate the conventional headstock at the centre pier and avoid the need for a significant and highly visible centre joint.

·         2.1m depth adopted on all bridges for consistency.

 

These features are indicated in Figure 3.

 



 


Figure 3. Avenue A Bridge

 

Urban Design

 

Leighton engaged Hassell Pty Ltd to undertake the urban design for the project to achieve OCA’s objectives. In the design development, Hassell’s approach was to:

 

·         Recognise the rail corridor’s monumental scale.

·         Express structures with simplicity and clarity of architectural expression.

·         Use a family of elements unified by consistent materials and colours.

 

This had a particularly significant effect on areas such as:

 

·         Retaining walls and joint locations - form, finish, panel sizes and joint locations in all wall forms to be compatible (dark grey colour was adopted for all major walls).

·         Use of reinforced earth walls with similar panel sizes to the major walls and at all portals.

·         Bridges - use of curved profiles on major girders and detailing of the reinforced earth wall abutments.

 

Olympic Park Station

 

The award winning Olympic Park railway station is a very innovative, world-class facility. It is the central element of the Rail Link project. The innovations embodied in the project are the outcome of significant work from many contributors, including the OCA, Leighton, Hassell, Tierney and Partners and Connell Wagner.

 

The significant concrete elements adopted for the railway station were:

 

·         Use of precast concrete wall panels for the station box, manufactured to a high level of finish quality.

·         Precast concrete columns from platform level to support the large span steel roof structure .

·         Post tensioned mezzanine level suspended concrete slab to provide the primary means of egress from the platforms.


5.         Environmental Achievements

 

The OCA required the contractor to:

 

·         Recognise environmental performance as a fundamental element of the project in line with the NSW Government’s environmental commitments for the Olympics.

·         Incorporate the principles of Ecologically Sustainable Development (ESD).

·         Comply with the Homebush Bay Environmental Strategy.

 

Connell Wagner developed all aspects of the design in accordance with the Design Environmental Management Plan which it developed for this project. Leighton Contractors carried out a critical review of the Plan with an emphasis on cost, programme and buildability aspects.

 

Connell Wagner’s environmental assessment process for the Homebush Bay Rail Link included an evaluation of potential environmental impacts associated with a product from its virgin material extraction through the stages of refining, manufacture, distribution, use, maintenance and waste disposal. The assessment process was project specific and used ESD analysis to ensure that the design not only addressed the relative impacts of alternative materials, but also included features which minimised the environmental impacts associated with material selection and construction. Connell Wagner’s assessment process offered a systematic approach to decision making based upon understanding of the environmental attributes associated with a product. Key criteria evaluated included life cycle cost, resource depletion, embodied energy, inherent pollution, suitability and availability.

 

The significant benefits derived from this process were:

 

·         Confirmation that many proposed products achieved the required outcomes.

·         The recycling of excavated shale within the site for use as backfill behind retaining walls and over cut and cover tunnels.

·         The use of materials which are manufactured using recycled or natural raw materials, eg recycled concrete for sub-base and HDPE in subsoil drains and strip drains

·         Incorporation of waste by-products such as flyash to reduce cement content in concrete.

·         Adoption of local technology and manufacture to promote Australian products and to reduce energy in transport.

·         Separate track and non-track drainage systems to reduce demand on pumps and rising mains.

·         Maximum use of gravity drainage to reduce energy demand and life cycle cost.

·         The use of oil / grease separators and silt fencing to control sedimentation and contamination of receiving waters.

 

Leighton Contractors extensive experience in environmental management enabled this project to be carried out in an environmentally responsible manner. The establishment and maintenance of environmental protection devices was afforded a high priority in order to satisfy the OCA’s environmental objectives.

 

Environmental monitoring and reporting provided OCA with a high level of confidence in Leighton’s ability to carry out the works without compromising their environmental responsibilities.

 


6.         Design and Supply Works by The Reinforced Earth Company

 

The Reinforced Earth Company was initially involved with the Homebush Bay Rail Link Project through the design and supply of Reinforced Earth® retaining walls and bridge abutments. In all, six bridge abutments and 6,500m2 of retaining walls were supplied by Reinforced Earth for the on-site works.

 

The successful tender design prepared by Leighton Contractors and Connell Wagner for the cut and cover sections of the tunnels proposed construction of bored reinforced concrete piled walls with a precast prestressed concrete plank roof. This was consistent with the design brief issued with the tender documents which suggested that a precast concrete arch was an unsuitable solution for the tunnels because:

 

·         There would not be enough cover over the crown of the arch.

·         The volume of excavation would be significantly greater than for a rectangular section.

 

The Reinforced Earth Company proposed the use of TechSpan® arches for all the cut and cover tunnels during tender negotiations for the retaining wall contracts. In addition to the issues raised in the tender design report the following concerns needed to be addressed before an arch solution could be accepted:

 

·         Stability of the arches under train impact loading in the twin tunnel sections.

·         The ability of precast arches to deal with the complex geometry.

·         Waterproofing of the precast joints to comply with the specification requirements.

 

These issues were successfully resolved and final design work on the arch structures started in November 1996.

 

Retaining Walls and Bridge Abutments

 

The first contract awarded was for the design, manufacture and supply of Reinforced Earth retaining walls for the bridge abutments and ramp walls of the Homebush Bay Rail Link on-site works. This contract was later extended to include the tunnel arch collar walls at the portals.

 

The Reinforced Earth walls for these areas of the project are unique in that a 3m long by 1.5m high rectangular panel was used and the joints are in a stretcher bond arrangement. The panels all have a black oxide added to the concrete with the ramp walls having a false vertical joint down the centre of the panels and the abutment panels having a number of horizontal grooves (refer Figures 4 and 5).

 

At a later stage, The Reinforced Earth Company was awarded a contract for the design, manufacture and supply of three Reinforced Earth structures for the connection between the Homebush Bay Rail Link and the existing main western rail line at Flemington, known as the Pippita Corridor.

 

The two rail bridges were constructed using the Terraset® precast concrete panel system. Terraset is a rectangular panel, 2.1 metres high by 1.7 metres wide. Both structures had the same finish as used on the walls of the new Homebush Bay Drive Overpass, also designed by Connell Wagner. Both structures had a maximum height of 6.0 metres and were designed to support full rail loadings and the stresses induced by the overhead wire structures. The third bridge, road over rail, was constructed using the traditional cruciform precast concrete panels.



 

Figure 4. 3m x 1.5m rectangular precast concrete panels, constructed in a stretcher bond configuration

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5. TerraSet abutment walls


 

TechSpan Arches.

 

Following award of the contract for design and supply of the TechSpan arches the arch profiles were optimised to suit the shale founding levels and track clearance envelopes. A single track enters the tunnel, splits into 2 at the station and returns to a single track before exiting the tunnel.

 

In total 9 arch profiles were adopted varying in span from 8m up to 19m. An insitu reinforced concrete infill was required at the interface of the different arch sections.

 

In all, there were three areas of cut and cover tunnel adopted on the project. Cut and cover tunnel 1 is located before the driven tunnel and cut and cover tunnels 2 and 3 are either side of the station. The design and construction of the cut and cover tunnels were complicated by the changing cross sectional geometry due to track bifurcation either side of the station. The arches were typically supported on cast insitu concrete footings founded on rock. Where the arches were founded at a high level such as in cut and cover tunnel 1, the walls of the tunnel were stabilised with rock bolts and shotcrete.

 

The key advantages of the TechSpan arch solution were:

 

·         Reduced supply cost.

·         Rapid erection.

·         Project specific arch profiles provided the required track clearances with no additional earthworks.

·         Minimal on site concrete works.

·         No obstruction to the track alignment during construction.

 

 


 

Figure 6. Installation of the 19 x 8 arches. Twin 10 x 3 arches can be seen behind.

 

 

Figure 7. Finite Element Analysis of the twin arches under impact load


 

Figure 8. Typical cross sections compared to the profile of the contiguous pile and plank solution

 

The TechSpan design process has two unique features, which enhance the efficiency of the arch design:

 

·         The arch profiles are designed on a project specific basis, taking account of the actual clearance requirements and vertical and horizontal loads, to provide an optimised arch shape with minimum bending moments in the finished structure.

·         The arch analysis is carried out using a non-linear finite element analysis program, which models the loading sequence on the arch during erection and backfill.

 

To accommodate the diverging track clearance envelope the arch spans were increased in approximately two metre steps up to a maximum of 19 metres. Twin arches were adopted when the single spans became too large approximately 90m from either side of the station. The 19 metre span arch connected with a twin arch of two ten metre spans, with a central headstock and column support. The central support, which was designed by Connell Wagner, was required to carry a train impact load of 1000 kN. In order to verify that the arches would provide adequate restraint to the top of the column, without excessive deflection, Reinforced Earth carried out a finite element analysis of the full system, which showed minimal deflection under the design impact load (Figure 7)


Figure 9. Typical section through the twin arches

TechSpan Construction

 

Construction of the TechSpan arches started early in 1997 and was completed by June 1997. The system is designed to allow erection of arch units to proceed using only one crane after the first four units have been erected. For the rail link project Leighton chose to use two cranes for the whole project to provide additional flexibility and faster erection rates, allowing them to place up to 40 arch units a day (about 30 metres length of arch). For program reasons construction to the east of the station started at two separate locations, and proceeded on four fronts, requiring careful monitoring of joint thicknesses to ensure that the final closing precast elements could be placed without difficulty.

 


Figure 10. Three arch profiles, twin 10 x 3, 19 x 8 and 17 x 8. The arch in the foreground is 15 x 7

 

Figure 11. The completed twin tunnel


 

TerraTrel ® Faced Reinforced Earth.

 

For a 50 metre section of the twin arches where the shale foundation level dropped down vertically by 3 metres, two TerraTrel faced Reinforced Earth walls were constructed to form the arch foundation in lieu of modifying the arch profile. The TerraTrel walls are designed to support the full loads applied by the arch structure. To provide a full 100 year service life, the facing was sprayed with 100mm thick shotcrete.

 

TerraTrel was also used for two other applications on this project. It was used to form the TechSpan arch collar walls at the station and to form basement walls for the hotel development that crosses one section of the tunnel.

 

 

Figure 12. Typical section through the TerraTrel arch foundation


Innovations at the Homebush Rail Project, And Their Development

 

The Homebush Bay Rail Link saw a number of innovations from The Reinforced Earth Company:

 

·         Use of the TechSpan system for rail tunnels.

·         Stepped arch profiles, and twin arches supported on a central column.

·         Single piece arches for small span and height.

·         Large span arches with shallow cover.

·         TechSpan arches supported on Terratrel walls.

·         First large scale use of Terraset facing in Australia.

·         Use of large rectangular panels in vertical walls.

 

Since the introduction of the TechSpan system in Australia in 1990 it has gained increasing acceptance for use in large projects requiring a significant design input from the arch supplier. The system will find increasing use both in road and rail tunnels, and with extended range of spans at both the lower and upper end of the scale.

 

Whilst the Reinforced Earth systems are widely known and accepted in the construction industry, it is becoming increasingly necessary to provide project specific surface finishes and panel shapes. The Reinforced Earth Company will continue working with its clients and their consultants to provide new products that satisfy the aesthetic needs of the project whilst maintaining the traditional virtues of economy, speed of erection, and durability.

 

7.         Conclusions

 

In summary the completed project presented complex technical challenges to both designers and constructors which required the implementation of a number of innovative solutions to enable aesthetic and technical requirements to be achieved within very tight time constraints and project budgets.

 

The project included significant concrete structures including tunnels, bridges and retaining walls all of which have been designed and constructed to achieve the OCA’s requirements, presenting a high standard of urban design whilst achieving the technical and functional requirements of a reliable, high capacity heavy rail service to Homebush Bay.

 

The completed project passed its first major test with the hugely successful transport operation during the 1998 Royal Easter Show, during which more than 1.8 million passengers passed through the new station.

 

The authors wish to acknowledge the support of the Olympic Coordination Authority for this submission to the CIA Concrete 99 Conference.