APPLICATION OF PRECAST CONCRETE IN EPPING TO CHATSWOOD RAIL LINE Cathy Han*, Parsons Brinckerhoff, Australia Jim Rozek, Parsons Brinckerhoff, Australia 32nd Conference on OUR WORLD IN CONCRETE & STRUCTURES: 28-29 August 2007, Singapore Article Online Id: 100032024 The online version of this article can be found at: http://cipremier.com/100032024 This article is brought to you with the support of Singapore Concrete Institute www.scinst.org.sg All Rights reserved for CI Premier PTE LTD You are not Allowed to re distribute or re sale the article in any format without written approval of CI Premier PTE LTD Visit Our Website for more information www.cipremier.com
32 nd Conference on OUR WORLD IN CONCRETE & STRUCTURES: 28 29 August 2007, Singapore APPLICATION OF PRECAST CONCRETE IN EPPING TO CHATSWOOD RAIL LINE Cathy Han*, Parsons Brinckerhoff, Australia Jim Rozek, Parsons Brinckerhoff, Australia Abstract Although the use of precast concrete in Australia has been common for many years, it was not widely used in the underground structures. This paper presents the advantages in the application of precast concrete in the new Epping to Chatswood Rail Line (ECRL), the largest publicly-funded infrastructure project underway in NSW, Australia. Its 12.5km of underground passenger rail line will link the Main North Line at Epping to the North Shore Line at Chatswood. The works involve twin underground rail tunnels with one track in each tunnel, three new underground stations at Macquarie University, Macquarie Park and North Ryde, one upgrade of Epping station and nine underground service buildings. Precast concrete has been extensively used at many locations throughout the project. Innovative use of precast concrete construction played a significant role in the success of the project. The ECRL project served as excellent examples to demonstrate that the use of precast concrete in underground structure can be technically feasible and cost effective. Keywords: Underground, Infrastructure, Innovation, connection, constructability 1. Introduction The Epping to Chatswood Rail Line (ECRL) is the largest publicly funded infrastructure project underway in NSW, Australia. The design and construction of ECRL was carried out by Thiess-Hochtief Joint Venture with Parsons Brinckerhoff as the structural designer of the running tunnels and stations, acting as sub-consultants to GHD. ECRL s 12.5km of underground passenger rail line will link the main North Line near Epping to the North Shore Line near Chatswood. When opened in 2008, the new line will be fully integrated into the City Rail network (Figure 1). This will create the capacity for an additional 12000 rail passengers a day and make public transport more attractive to a greater number of residents and visitors to Sydney. The ECRL project includes twin underground rail tunnels, three new underground cavern stations at Macquarie University, Macquarie Park and North Ryde and one upgraded station, Epping Station. Each station has two entry shafts between the ground and the underground concourse level. The stations have two service buildings at each end to accommodate the service equipment for the electricity and ventilation. The service buildings will also serve as escape passages. An additional service building was provided at Lady Game Drive to service the tunnel between North Ryde and Chatswood Stations. Other project works included dives, cut and cover structures and other civil works. Figure 2 shows the key elements of the project.
Figure 1-City Rail Network Figure 2-Location Plan Design Elements 2. Constraints and design criteria All underground stations and services buildings are located in built up urban areas, and presented significant challenges due to the restricted space within a defined road reserve, limited construction access and the need to maintain the existing traffic flow and capacity. The construction schedules were very tight. The external wall of service buildings and the structure of entry shafts were in contact with natural ground which meant the structures had to be designed for exposure category B2, in accordance to Australia standards [1]. The Australia standards and the design criteria set out in the DIR (Design Input Report) document also required that all underground structures including stations, entry shafts and services building designed for 100 years design life. The stations and entry shafts were designed to withstand a design fire of 20MW for 4 hours, while the service buildings were designed for 2 hour fire rating. The service buildings had to satisfy acoustic criteria, as well. Based on the site space restriction, tight schedules and design criteria, the design team together with construction team quickly realized that concrete was the most suitable construction material and that the maximum use of precast concrete would play a significant role in the success of the project to satisfy the requirements of economic, construction efficiency, durability, design innovation and aesthetics. 3. Application of precast concrete The first use of precast concrete was a house system in UK consisting of precast cladding panels fixed to a structural frame in 1875. The first documented use in Australia was in 1904 for Sydney Harbour s Bradleys Head Lighthouse, which is still in use today [2]. Precast concrete has become a very important material for many types of structure. The Sydney Opera House used precast concrete and probably could not have been constructed any other way. The wide application of the precast technique is based on the advantages of prefabrication such as the freedom of design, the reduction in construction time, accurate control of quantities of materials and manpower, the improvement of the accuracy and quality of the product. Construction with precast concrete can proceed almost independently of weather conditions and other project activities. All these eventually result in a better working conditions and reduction of costs. The concrete material itself satisfied the design criteria such as durability, fire resistance and acoustic requirement. Precast Concrete has been widely used in many locations throughout the ECRL project. In order to minimize costs, the use of market available products such as RTA standard prestressed bridge planks, prestressed hollowcore planks as well as Ultrafloor system became the preferred material selected. The custom made load bearing and non-load bearing wall panels were used for all nine of service buildings. The new stations and service buildings have similar layout and same floor to floor height. This arrangement enabled the designers to minimize the number of moulds and maximize the number of castings from each mould. The panel size was governed by the consideration for the capacity of lifting, handling and transportation as well as maximization of panel repetition. Underground stations and entry shafts design
The underground stations included three new cavern stations at Macquarie Park, Macquarie University and North Ryde Stations, and the upgrade of the Epping Station. The three new stations have similar layouts, broadly. Each station consisted of 170 m long suspended concourse floor linked to back ofstation, 170 m long platform and two entry shafts. For simplicity, only one station is described in this paper. Figure 3 is a schematic plan view of a typical station. Figure 4 shows a section through a service building. Figure 3-Schematic plan view of typical station, entry shafts and service building Figure 4-Section through service building Concourse floor The suspended concourse floor structure primarily consists of prestressed precast hollow core floor planks spanning between concrete in-situ beams located on 6m spaced grids. 6m grids were selected to suit 1.2m standard width of the hollowcore planks. The beams either cantilever from the excavated rock face of the platform cavern or span from the excavated face to a supporting column on the centerline of the platform. The mass of the beams and the roughness of the excavated rock face prevented the use of precast beam units. Therefore these beams were cast in situ on conventional formwork. A structural topping placed over the floor acts compositely with the floor planks to form the structural floor system. The dynamic behavior of the suspended concourse floor has been analyzed to maintain natural frequency of the floor within a range of 6-8 Hertz which is larger than the suggested threshold levels of 5 Hertz for floors with crowd loads. The lightweight of the hollow core planks enable the support beams to be designed for no cracks under selfweight therefore they played an important role to increase the natural frequency of the floor. Stairs between platform and concourse were cast as in situ reinforced concrete. The size of stair units prohibits use of large precast components for the stairs due to the limited underground space. Figure 5 shows the cavern stations at Macquarie Park under construction. Platform deck The original design for the platform deck and under structure consists of two rows of single cell precast crown culvert type units. Each row is located over each of the exhaust air ducts. The typical 2m long precast units incorporate cantilever structural decks at the trackside and at the other side for partial bridging over the fresh air supply duct. These two rows of units are jointed by 500mm cast in situ infill slab to form the roof of the fresh air supply duct. This also provides structural integrity against for train impact loading. However, after cost comparison and the modification of the construction schedule, it is found that
reinforced block wall incorporating cast in situ slab on bondek as lost formworks was the most economic solution for these typical area and this scheme was adopted. Back-of-station floor Back-of-Station is the area between end of station and service building at both ends of the station. The elements includes a primary flooring system which includes hollowcore precast planks and in situ structural topping; precast reinforced concrete support girders bridging over the running track to enable continuation of the excavation and construction works and equipment to pass under; support framing including reinforced concrete station air supply/exhaust ducts and pockets excavated into sandstone; and a reinforced concrete end of platform wall supported off the concourse level. Figure 5-Station under construction Figure 6-Image of entry shaft Entrance shafts The station has two entrance shafts (declines) at each end. Due to the different geology at each location, the depth of the shafts varied depending on the level of concourse. The permanent shaft support structures were designed to support in the first 10m soft ground. The shaft support structures comprised of 600 mm concrete piles around shaft with 2 or 3 layers of horizontal concrete wall beams. The concrete wall beams were lateral supported by several internal precast struts. The shaft structures were constructed by using top-down method so that the temporary support of piles could be eliminated and the concrete wall beams could be cast against ground. To speed up the excavation, the roof slab was left open until the completion of the excavation to the intermediate landing level, about 8m below the surface. As soon as excavation was completed to this level, the roof slab was installed to minimize the disruption of existing surface services. The composite slab of prestressed bridge planks with cast in situ topping was used for roof slab for the larger span and loads from the heavy mass of soil from landscaping. The circular precast concrete struts with high standard of finish satisfied both architectural and engineering requirements. Figure 6 is the architect s image of station entry shaft. Underground service building The station has two service buildings, one at each end. The layout of each service building is similar in general. The use of precast components where possible is the preferred structural system given the constructability and safety issues associated with construction of a building within a vertical shaft excavation. The structural system for the service building consists of suspended slab and beam floor system spanning to load bearing precast walls founded on rock at the base of the excavation. Lateral stability was achieved through a combination of the shear wall action and diaphragm action of floors, with floors locally strutted to the excavation where necessary for additional stability. Upper floor levels were used in the permanent arrangement to strut the soft ground retention system. The load bearing walls were generally precast concrete panels fabricated off site and lifted into position. Openings were incorporated within the panels to accommodate site fixed door frames and the requirements for penetrations for mechanical and electrical equipment particularly cabling, ventilation ducts, and hydraulic services located in a services zone in the ceiling space. At the interface with the escape corridor to the station, an insitu concrete transfer beam and column were incorporated into the wall line of the shaft. Wall thickness varies between 150mm to 250mm thick depending on applied loads and floor-to-floor height. Walls will be tied into the floor diaphragms at each level.
Lateral stability of the whole structure was achieved via intermittent insitu concrete strutting beams cast into each floor level which bear directly onto the excavated shaft rock face or in the upper soft soil conditions by the support piling. The majority of suspended floors utilized an Ultrafloor system. Ultrafloor comprises precast pretensioned concrete inverted T-beams, spaced apart with infill cement sheeting spanning between the flanges of the beams. This assembly provided the strength to support the weight of the wet insitu concrete topping slab. After the concrete hardens, the topping slab and beams act compositely to support the applied loads. Perimeter waler beams were provided in areas of soft-ground retention tied into floor diaphragms or strutting beams. At edges of large voids and in areas of heavier loading, additional floor beams were utilized. These beams support the Ultrafloor beams prior to placement of the structural topping. Precast floor units were also utilized in areas of the fan and duct penetrations which will be tied into supporting beams or walls. Egress stairs within a fire-rated shaft will be composite precast concrete and steel framed construction. Stair elements include landings to be precast concrete panels with steel fixings to precast walls and stair stringers. Lady Game Drive Service Facility Building (LGDSF) Lady Game Drive Service Facility includes an underground service building, an above ground electrical building and the open roof transformer enclosure. The layout plan is shown on figure 7. The underground service buildings generally followed the layout and structural form of the typical station service building. This included load bearing precast concrete walls supporting precast Ultrafloor type intermittent beams with topping insitu concrete deck. Figure 7-Plan of LGDSF Figure 8-Sections The tight construction schedule required the construction of the service building before the excavation of the lower benches by the tunnel boring machine (TBM). This required consideration for a staged building system that could span across the width of the shaft excavation without structures coming within the cutting envelope of the TBM. The lowest service floor (Basement Level 2) was designed as a transfer floor designed to bridge across the TBM running tunnel to be excavated. The floor consists of large span reinforced concrete beams supported off bored piles and recessed niches cut into the vertical faces of the shaft rock profile. Both the recess niches and piles were excavated from the upper bench level. Piles were located outside the cutter area of the TBM and were later exposed by the late stage excavation of the Platform Level cavern. Figure 8 is the section through the service building. Figure 9 and 10 show the service building at different construction stages.
Figure 9-Construction of basement B2 Figure 10-Construction of basement B1 The above ground electrical building was been designed to meet the Urban Design and functional objectives of the Facility. It generally consisted of a precast wall system supported off either spread footings or the shaft structure. Lateral support of the walling and roof support was achieved through a conventional steel framing and sheeted system. Figure 11-Construction of ground floor Figure 12-LGDSF in completion Although the precast wall panels function, in part, as the façade of the building, the design of these wall was intends to create the impression that they were free standing elements merging into the landscape rather than being part of the building behind. This was achieved through the walls extending past the corners of the building, and above the roof level. Three different panel types were provided. Each panel type had a different width and had a different pattern of grooves on the surface. These arrangements provide a rich texture, emulating the jointed and bedded texture of the natural sandstone which responding to the colour and form of the existing sandstone rock formations on and around the site. The front transformer yard is an unroofed area of slabs and cable trenches on ground with precast architectural finished concrete walls and precast internal separation walls. Figure 11 is the above ground structures under construction and figure 12 is the structures of Lady Game Drive Service Facility after completion. Tunnel Invert Beam Invert beams were required to support TBM tracks during construction. They also serve as formwork for the invert slab. In the final service stage, the invert beams are the support beams of rail tracks. The total length of 25 km (total two sets of tracks) rail line would require total number of 4200 invert beams. The high level of repetition and standardization of these beams made the precast concrete construction the preferred option.
Figure 13-Tunnel invert beam 4. Conclusion The design of ECRL project is an excellent example of using precast concrete construction in underground infrastructure. The extensive use of precast concrete has proven successful in meeting the design criteria requirements. Incorporating the construction method and programs and operational requirement early in the design and working closely with the construction planning team had a significant impact on the final structural form. The integration of design, construction and operation was an essential part of achieving a successful project outcome. The benefit for using precast construction includes: o Brings significant quantifiable benefits to the owners. o Ability to construct in a congested environment. o Reduce construction time so that the disruption to existing traffic is minimised. o Improve aesthetics with coloured and textured face panel. o Increase quality by manufacture structural elements off site in factory conditions. The precast concrete solution presented in this paper for ECRL project is an example of the ongoing influence of precast concrete construction in transport infrastructure in Australia. 5. Acknowledgement The successful design outcome depended on teamwork and cooperation between the designers and construction team as well as the fabricators. The designers acknowledge the support with the TJH construction and RTA/IV team. The authors would also like to thank Mr. Bill So for providing a final review of the paper and Mr. Jim Nelson for his ongoing support. The valued contributions by all Parsons Brinckerhoff project design team members are also acknowledged by the authors. References: [1] AS5100:2004. Bridge design code, Standards Australia, all part. [2] Precast Concrete Handbook (2002), National Precast Concrete Association Australia and Concrete Institute of Australia, Section 1-1, pp1-2.