FLOATING SLAB TRACK - CHATSWOOD TRANSPORT INTERCHANGE Author: Adam Brunskill Academic Qualfications: B(hons) Civil Engineering Company of Affiliation: Laing O Rourke INTRODUCTION Chatswood Transport Interchange (CTI) is one of NSW s largest transport PPP project and particularly notable for all works taking place in the centre one of the largest CBD s in the state. Laing O Rourke is undertaking the design and construction of the new CTI-IW contract on behalf of the PPP developer. The contract value is approximately $165m. This paper will focus the difficulties and challenges faced by the design and construction team during the development of Floating Slab Track (FST) system. 1.0 PROJECT OUTLINE The CTI is a redevelopment of the existing Chatswood transport interchange and will serve as one of the terminating stations for the Epping to Chatswood Rail Link (ECRL previously known as PRL). The old interchange comprised of a single island platform and undercover bus interchange, refer to Figure 1. The new interchange will comprise of two island platforms and a partially undercover bus interchange. Figure 1. Cross Section of the North Track Slab showing the new bus interchange below. Also included in the CTI is a new underground concourse, three new levels of underground parking, two new rail bridges (on either side of the CTI) and new commercial / retail centre above. (see figure 2)
Figure 2 - Cross Section through the CTI Structure. In addition, provision has been made to construct three high rise apartment towers on the CTI footprint. The towers will share the same structural support columns as the remainder of the CTI building. The largest tower (41 stories) will be located directly above the commercial / retail area known as the podium (centre build). (see figure 3). The four tracks are located directly below the podium therefore there was a risk that noise and structure born vibration (known as regenerated noise) could be transmitted from the track to the lower levels of the towers> As a result of the concerns about regenerated noise the Ministers Condition of Consent limited structure borne noise levels inside apartments to 40dBa for 95% of train pass-bys.
Figure 3 - Cross Section through the CTI Structure and future tower 1.1 Structures There are five distinct structures within the CTI site. The track fixing for each area is as follows: 1. Help Street Bridge - Single span bridge (31m) with Direct Fixed Track and Egg type acoustical isolation rail fasteners spaced at 600mm 2. North Track Slab - Suspended Slab (122m) with Direct Fixed Track and Eggs Spaced at 700mm, plus a swing nose crossing on Delkor Eggs.
3. Centre Build - Suspended slab (150m) with Floating Slab Track and Eggs Spaced at 700mm 4. South Track Slab - Suspended slab (55m) with Direct Fixed Track and Eggs Spaced at 700mm 5. Albert Ave Bridge - Single span bridge (26m) with Direct Fixed Track and Eggs Spaced at 600mm 1 2 3 4 5 Figure 4 CTI Layout The trains will run through the CTI suspended slabs from bridge to bridge, approximately 350m in length each track. The track needed to be suspended to allow for the underground car parks / concourse in the centre build and south track slab and also to allow for the bus interchange on the north track slab. 2.0 DESIGN CONSIDERATIONS As mentioned previously the CTI development has made provision for the construction of three new high rise apartment towers. These towers are located on the CTI footprint and share the same structural members as the rest of the CTI structure. Therefore regenerated noise from trains was a major issue when designing the track and the design concentrated on isolating the CTI structure and towers from the rail corridor. The track support structure design was principally driven by the requirement to achieve the Ministers Condition of Consent for structure born noise inside the future apartment buildings. The structure born noise criteria imposed by the Ministers Conditions of Consent in different spaces within the development are presented in the table below. Space Noise Level Assessment Operating Conditions (dba) Parameter Station Concourse 60# LAmax (Fast) Regenerated train noise Ticket office and staff 60# LAmax (Fast) Regenerated train noise offices Bus terminal 60# LAmax (Fast) Regenerated train noise
Residential living 40# LAmax (Fast) Regenerated train noise and sleeping areas Commercial and retail AS 2107-2000 plus 5 dba# Regenerated train noise spaces # Must be designed such that at least 95% of train events comply with these criteria. Table 1. Design Criteria Structure Bourne Rail Noise Space AS 2670.2:1990 criterion curve Assessment Parameter Operating Conditions Station platforms Curve 30# Max 1 second RMS Trains Station concourse Curve 8# Max 1 second RMS Trains Ticket office and Curve 8# Max 1 second RMS Trains station staff offices Bus terminal Curve 8# Max 1 second RMS Trains and buses Station retail Curve 4# Max 1 second RMS Trains and buses outlets Residential living and sleeping areas Curve 1.4# Max 1 second RMS Trains and buses Other commercial Curve 4# Max 1 second RMS Trains and buses and retail spaces # Must be designed such that at least 95% of train events and 95% of bus events comply with these criteria. Table 2 Design Criteria Structure Bourne rail and bus vibrations 2.1 DESIGN CRITERIA A 50 year design life for track support systems, including noise and vibration mitigation measures RailCorp Standard C 3304 Specification for Vibration Isolated Rail Fasteners Operating axle-load 137kN & Unsprung mass 1340-2160kg (max 250kN @ 60km/hr) Max dynamic deflection (lateral and vertical) 4.5mm Noise testing was undertaken at North Sydney to gather vibration data from existing trains traveling on a suspended structure for use in structure born noise modeling. The north shore line south of North Sydney station is on a viaduct as it approaches the Sydney Harbour Bridge. Results of the testing are shown in the following table. Test Vehicle Near Track (SB) Far Track (NB) 1 2 3 Tangara 68 69 DDSU 65 59 Tangara 66 62 DDSU 62 61 Tangara 64 64 DDSU 63 60 Table 3 estimated noise levels Options
In order to meet the required criteria for noise and vibration the following options were considered. 1. Isolation under the Podium using a Floating Track Slab + smaller sections using column isolators 2. Isolation under the Podium and beyond using a floating track slab 3. Isolating the future Apartment Tower 1 on resilient supports at the Residential Amenity Level, possibly in combination with a floating track slab 4. Separating the Rail Track Slab from building and isolating on column isolators 2.2 PROCESS Extensive co-operation between stakeholders and engineers, including a 4 day workshop. Key stakeholders were: o RailCorp o TIDC o CRI Schematic vibration isolation design accomplished through detailed option development and discussion for achieving the regenerated rail noise criterion to select the option that best integrated with the existing architectural and structural design for further analysis. 2.3 THE SYSTEM CONCEPT The agreed option was Option 2, which involved isolation under the podium using a floating track slab. There were however two different types of FST system that was considered. 1. Large cast in-situ concrete slabs measuring 14m in length on Gerb Springs. This system was considered relative easy to install however presented issues regarding replacement. 2. Small FST units on rubber pads which would allow only 4 Delkor eggs per block. This system was considered relatively easy to install. The blocks could be removed if required for maintenance and replacement of the bearings. The design consultant and the construction team both favouring the smaller rubber supported FST units. The detailed design progressed with the smaller FST units, however in order to ensure that right system had been chosen the team looked overseas to confirm the decision. 3.0 THE HONG KONG EXPERIENCE Laing O Rourke senior management decided to send a fact finding team to Hong Kong. The team consisted of the Laing O Rourke Design Manager, Civil Construction Engineer responsible for the FST installation and the Track Engineer responsible for the track construction. The purpose of the trip was to meet with the two rail authorities in Hong Kong (KCR and MTR) and gain from their vast experience using this type of track form. Facts from the meeting with KCR Similar Slab unit size and mass (compared to smaller units proposed by Laing O Rourke) Similar pad design and configuration Pads manufactured by Trelleborg Queensland Rubber Delkor resilient fixings used on KCR Axle loads comparable to NSW loadings Higher line speed FST proven to be best performing slab isolation system on KCR (test data taken) Design being refined with each project Upstand kerbs on either side of slab used for derailment containment. Unable to use central upstand due to signalling equipment.
Image 1 KCR Floating Track Slab Units Facts from the meeting with MTR Slab design is more complex than CTI IW and KCR. Bottom up rail construction has been used previously Axle loads comparable to NSW loadings Similar slab size and mass Higher line speed (especially Airport link) MTR use Low Vibration Track (LVT), Isolated Slab Track (IST), and Floating Slab Track (FST) on network FST proven to be best performing slab isolation system on MTR (test data taken). MTR have FST which has been in service since 1981 with no maintenance problems. The experience gained from visiting the authorities in Hong Kong confirmed the decision to continue with the smaller units. It proved that the design was consistent with other FST in use. Small changes were made to the fixing arrangements of the side pads and to the construction methodology as a result of the trip. The final agreed CTI FST system was individual FST precast concrete blocks measuring 1.35m width x 2.7m in length, similar to KCR in Hong Kong. The height of the FST block would vary between 320mm on the sides to 570mm in the centre. This step up in the centre was a result of increasing the mass of the unit. Due to the height restrictions in the floors below and the fixed RL for the track, the FST block was narrower than preferred by the design consultant 320mm. The mass of the FST unit was increased to compensate for the reduction in width by increasing the thickness of the centre of the FST unit 570mm. The additional concrete in the centre of the track also acted as a guard rail. Details of the FST unit are shown below.
The FST system would comprise of the following: The precast concrete FST block 4 rubber support bearings below in each corner for each block 4 rubber side pads for each block, ie 2 either side 2 longitudinal pads for each block, ie 1 either side 4 Delkor Eggs per FST block. Based on this system the design consultant predicted noise levels in the future apartments would be as follows: Predicted Highest Noise Level in Apartments, L Amax db(a) 95% of Trains on Near 95% of Trains on Far Tracks Tracks 36-40 32-38 Table 4 - Predicted Noise Levels In order to achieve the required acoustic performance, the side and longitudinal bearings had to be installed under compression, adding a new level of difficulty to the construction. The installation of the FST and the pre-compression would require a construction solution that would be quick, simple and cost effective.
4.0 CONSTRUCTION The construction of FST was new to Australia for heavy rail applications and to the Laing O Rourke civil and track crews. As mentioned above the specified compression in the side and longitudinal pads introduced a problem which had not been experienced before by our crews. In order to resolve this issue our civil construction team (lead by Engineer, Andy Thompson, Engineer responsible for FST installation) constructed a mock up of the FST, which include the FST units and a base slab with side walls, as per the invert slab which the FST would sit. The size of the mock up was large enough to fit 3 FST units. The track team spent 2 weeks using various installation methods that had been proposed. The biggest issue was holding the compression in the pads. Finally a system using temporary supports between the FST units was developed that allowed the FST units to be installed under compression and that did not allow the compression to be lost during installation. Using this system, the installation of 150 linm of FST units (150m each track) would take five days, which included final QA checks. The positioning of the FST blocks for each track, were undertaken during a weekend (one weekend for each track). All the precast blocks were transported to site and lifted into the track-well using the site tower crane. The blocks had the bearings already pre-fitted by the precaster therefore the site crew only needed to level up each location (on the invert slab) to ensure that the blocks would not rock. A frame was constructed that would replicate the bearing locations of the blocks. The frame would be placed into position (relevant to the location of each FST block) and tested by rocking side to side to ensure that the location was level. Packing was placed prior to placing the block in its final position if the frame rocked. A forklift was used to transport the blocks in the trackwell. The side pads were designed to specified thickness. Installation of these side pads also required a specified compressive force however the side walls they would bear upon could vary between +/- 20mm due to construction tolerances. Based on the Hong Kong experience the side pad design was changed to allow the insertion of HDPE packers. These packers were used to make up the difference between construction tolerance and design. This took the onus off the civil crew to meet unreasonable construction tolerances. This system proved to be quick and simple to install and remove (if required) the side pads. Image 2 Positioning of rail onto FST. Jacking of slab to install side pads. Once the FST was in place the track could be installed.
The track construction methodology for the entire CTI was based upon a top down construction system. This system was successfully used by Laing O Rourke (formerly Barclay Mowlem) for the direct fixed track construction on the Bondi Junction Turnback Project. It was also noted that KCR in Hong Kong used Top Down Construction methodology and MTR agreed that Top Down Construction was the fastest of the two methods to construction direct fixed or FST track (where both top down and bottom up were used). The advantage of the Top Down method is that the finish level of the concrete invert can vary (ie. allowing for construction tolerance) therefore the track construction is not totally based on getting the exact level on the invert to therefore get the correct rail level. This system was proven to be fast and effective in getting the track geometry within the specified +/- 4mm for level, line and superelevation. Iron Horse track supports were used to suspend the rail at the correct level, alignment, gauge and superelevation. After final survey checks the track supports (in this case Delkor nd Eggs) could be concreted or grouted into position either within a 2 stage slab or onto grout pads. This system worked successfully on the North and South Track Slabs as well as both Help St and Albert Ave bridges. Image 3 Track construction using Iron Horse Track Supports on South Track Slab. ` The concrete guard rail on the FST units made it impossible to use the Iron Horses. The Iron Horse track support works by holding the rail from the underside which means there needs to be a clear space between the rail. This meant that the construction of the track on the FST would have to be done one rail at a time. Another issue that complicated the construction of the track on the FST was that the Down NSL track was on a curve with 35mm superelevation. The construction of the track on the FST was undertaken (as mentioned above) one rail at a time. The low rail was constructed first. Using a 1 in 4 construction sequence, the baseplates were fixed into position. The rail was adjusted using a digital inclinometer to ensure that the 1 in 20 cant was achieved. Once all the 1 in 4 baseplates were fixed and checked the remaining baseplates were grouted into position using a grout pump. The construction of the high rail was then done using the low rail as a guide. Again the same method was used to level and line the rail. A gauge stick was used to measure gauge and the superelevation before final grouting. This system of track fixing was slower and more tedious than the track constructed using the Iron Horse track support. More time was taken on QA checks and was more labour intensive to construct. Total construction time for each length of track (150m) on the FST was
3 weeks however the results achieved for accuracy to design alignment were equivalent to that of the direct fixed track. Image 4 Completed installation of Floating Track 5.0 CONCLUSION Initial monitoring has shown compliance with the design requirements set down by the Minister and Key Stakeholders, However final validation of the Floating Track Slab success will come with completion of the Eastern portion of the project. The Chatswood Transport Interchange has provided an opportunity to take an internationally used track system and adapt it to the Australian market. The Floating Track system used at Chatswood has enabled the interaction of a transport interchange encompassing Rail and road within close proximity of a multi tower high rise development.