Conservation Objects – Southern Gasholder

The restoration of the ‘Southern Gasholder’ was part of the Macdonaldtown Gasworks Remediation, a contaminated soil remediation project in Sydney’s inner-west. The gasholder’s superstructure was temporarily braced in February 2015, disassembled in July 2015, and restored offsite while its steel bell was restored onsite. Dewatering of the gasholder’s annulus and excavation adjacent to the annulus was completed in December 2015. Backfilling, reinstatement of the clay puddle, and re-filling of the annulus was conducted in early 2016. The superstructure was reassembled above the restored steel bell in July 2016. Finials and column caps specially cast to replace the gasholder’s only missing components were placed atop its columns in February 2017, completing the restoration.

The ‘Southern Gasholder’, the only Victorian-era gasholder still standing in NSW, was restored by Ventia Utility Services (Ventia) for its client, Sydney Trains. The restoration of the heritage-listed gasholder was an important element of the Macdonaldtown Gasworks Remediation, a contaminated soil remediation project in Sydney’s inner-west.

Although this award entry concentrates on the protection and restoration of the Southern Gasholder, other heritage-related conditions were that:

• Archival recording and archaeological monitoring be completed for the former Northern Gasholder; and
• Interpretive signage be installed to document the heritage significance of the area.

The conservation and restoration of the gasholder aligns with Sydney Trains’ commitment to be a responsible custodian of heritage assets. As such, a number of heritage impact studies were completed to determine the potential impacts to the gasholder posed by the broader project’s soil remediation works.

A restoration methodology was developed that was approved and endorsed by the NSW Heritage Division, Office of Environment and Heritage.

Location
The location of the Southern Gasholder is within the site of the former Eveleigh Gasworks (also known as the Macdonaldtown Gasworks). This triangular-shaped site is located to the east of Burren Street, Erskineville, between the Macdonaldtown Stabling Yard and the railway tracks of the Illawarra Corridor.

Operation and features
In 1892, the Eveleigh Gasworks was established to produce gas for NSW railway operations, including those at the Eveleigh Railway Workshops. When most of the gasworks was demolished in 1958, the Southern Gasholder was retained. It was used to store gas from the Mortlake Gasworks until 1977.

The Eveleigh Gasworks consisted of two separate but parallel works. One works produced gas fuel from coal for lighting railway stations and signals primarily, and the other works produced a much richer gas fuel from shale for carriage lighting. The coal-derived gas was stored in the Southern Gasholder, while the shale-derived gas was stored in the Northern Gasholder (Figure 1).

Storing purified gas in a gasholder was the last step in gas manufacturing. Gasholders usually consisted of a steel bell storage tank contained within a steel frame and the Southern Gasholder reflects this. Its storage capacity was 100,000 cubic feet, or just over 2,800 cubic metres – twice the capacity of the Northern Gasholder. The Southern Gasholder’s steel bell weighs 18 to 20 tonnes but all that was needed to make it rise was the force of gas under pressure. As the stored gas was depleted, the steel bell would slowly descend.

The Southern Gasholder’s frame, or superstructure, measures 18 metres in diameter and 11.5 metres in height. It has eight cast iron columns, or stanchions, connected by bracing trusses at the top and centre sections, and tie rods across the top section. The superstructure sits on a brick annulus that encircles the gasholder’s steel bell below ground. The bell is separated from the annulus by a void filled with water. Throughout its operational life, the superstructure supported and guided the two-stage bell lift.

Heritage significance
The Southern Gasholder is listed on the State Heritage Register as part of the Eveleigh Railway Workshops (SHR No: 01140). It has heritage significance due to its rareness and the importance of the rail network in the development of NSW during the 19th and 20th centuries.

As stated in the Macdonaldtown Gasworks Remediation Project, Archival Recording – Southern Gasholder (ERM, January 2017): “The Macdonaldtown Gasworks site is an important component of the larger State heritage listed Eveleigh Railway Workshops site. The Southern Gasholder has some historical and scientific significance for its archaeological potential and as a contributory feature of the larger complex demonstrating the workings of a nineteenth century gasworks. The Southern Gasholder is a landmark in the locality, and is reported to be the last remaining example of its type in the State. It demonstrates the principal characteristics of its type including intact gas ring with cast iron stanchions, and substructure including brick annulus and tank.”

The restoration and onsite reassembly of the Southern Gasholder provides the local, NSW and Australian communities with a physical marker indicating the site’s previous use and acknowledges the gasholder’s heritage value. The gasholder’s worth as a restoration item was enhanced by its good condition and structural integrity. The restoration has enabled the gasholder to retain its heritage value into the future.

The restoration of the Southern Gasholder also demonstrated a commitment by Sydney Trains to social sustainability, as the gasholder provides a unique educational view of how our railways and cities were previously illuminated. In addition, since many parts of the Eveleigh Railway Workshops have been restored and repurposed to once again play a significant role in community life, it was fitting that a piece of infrastructure essential to their historical operations be restored.

Process
The main goal of the project was the conservation of the heritage-listed Southern Gasholder in a manner that minimised risks: risks to the structure, as well as risks to the surrounding community.

On mobilisation to the site, Ventia identified the need to protect the gasholder from potential collapse during other Macdonaldtown Gasworks Remediation works. Ventia engaged the specialist structural and conservation consultant, Bill Jordan and Associates, who recommended temporary bracing until the restoration works were implemented.

Sydney Trains had originally intended the restoration of the gasholder to be carried out in-situ; however during the bracing, Ventia recognised that restoring the gasholder’s superstructure offsite would achieve a better long-term conservation outcome. As such, it was decided to pursue offsite restoration despite the need for additional resources to prepare the Heritage Act application including a Statement of Heritage Impact. After achieving a restoration exemption under the Act, an engineered disassembly plan was developed. Subsequent offsite restoration of the superstructure minimised risks to the structure and allowed protective treatment of all metal-work and the reuse of many original fastenings during reassembly. In addition, the disassembly reduced the health risks to the adjacent community by allowing remnant lead paint to be removed in a controlled workshop environment.

All surfaces of the gasholder’s cast iron and steel frame, or superstructure, were treated to ensure durability, even the mated surfaces that were hidden upon its reassembly. This treatment has optimised the surface restoration as the mated surfaces at the joints are considered critical locations for moisture penetration and corrosion. Furthermore, such corrosion can be worse in older structures, like the gasholder, where the low-strength bolts are not tightened for a friction grip like they are in many modern structures. The protective treatment of all of the superstructure’s metal work even included treatment inside the hollow columns, which would not have been practicable had the columns been restored in-situ. Advice from coating manufacturers also suggested that protective treatment applied in a controlled, offsite environment would be more durable.

Prior to application of the protective coating and paint, it was determined that pitting found in the cast iron columns could not be filled with the original specification of coatings. Trials to measure the performance of different protective coatings were undertaken until one was selected that could successfully in-fill the pitting. Certain elements of the gasholder, including some of the columns and their base plates, showed evidence of cracking that had to be fixed because they were structural components. Due to the difficult nature of welding such thick and old cast iron, a welding procedure was developed, reviewed and implemented to successfully repair these cracks.

The gasholder’s steel bell was restored onsite as the structural risk was too great for disassembly. The same specification was applied to the bell as was applied to the superstructure. Although little paint remained on the bell, to protect the community a wet-blasting removal method was chosen instead of a dry-blasting method – eliminating the potential for airborne paint and rust particles.

Protective vibration monitoring
Continuous vibration monitoring was performed on the brick annulus of the Southern Gasholder and a few metres away on the site’s western boundary, adjacent to the Burren Estate Heritage Conservation Area. The monitoring program was designed to protect the Southern Gasholder during site excavations and back filling for the Macdonaldtown Gasworks Remediation.

Due to the gasholder’s heritage significance, a conservative particle velocity vibration limit of 3 mm/s was required by the Department of Planning and Environment for monitoring the structure. Going one step further, Ventia adopted a more conservative goal of 2 mm/s goal. If the vibration on the structure exceeded this 2 mm/s criterion, an email alert was sent instantaneously to the environmental officer through a 3G modem built into the vibration monitor. These alerts were reviewed in real-time through iPhone notifications.

The monitoring alert system allowed proactive management of tasks being conducted around the gasholder. It was particularly important during auguring to install the concrete pile retaining walls that protected the gasholder during remediation excavations (Figures 6 & 7). It was also important when the excavated site was backfilled and compacted. On the rare occasion that the vibration criteria were exceeded, works were immediately stopped for investigation. The community and other stakeholders were kept informed of the vibration monitoring results via the monthly Environmental Monitoring Summary posted on the Macdonaldtown Gasworks Remediation.

Archival recording legacy
The archival recording that was conducted in relation to the Southern Gasholder and the former gasworks provides a body of knowledge that will benefit the broader community, particularly those interested in the history of NSW from personal or professional perspectives. Prior to the disassembly of the gasholder’s superstructure, the activities were undertaken by Environmental Resources Management (ERM) in accordance with national best-practice guidelines for heritage management and recording.

Commitment to heritage principles
The restoration of the Southern Gasholder conformed to the principles of the Australia ICOMOS Charter for Places of Cultural Significance, The Burra Charter, 2013 (the Burra Charter). The process of understanding the gasholder’s place, purpose and cultural significance started early with investigations by structural and conservation consultant, Bill Jordan and Associates, on behalf of Sydney Trains.

Ventia then conformed to the principles of the Burra Charter through the following practical approaches:

• The cultural significance of the gasholder was protected from vulnerability and risk when its frail structural condition was recognised at the start of the project and the specialist Bill Jordan and Associates was engaged for advice.
• Retention of the existing fabric and associations of the gasholder’s structure was sought. A restoration specification was developed that included guidelines for the reuse of elements that were deemed structurally sound. The result was no major elements were replaced and only minor additional fastenings were used to replace corroded fastenings.
• Each element of the gasholder’s superstructure was placed back in its original location upon reassembly due to a comprehensive labelling procedure implemented during the disassembly process. As each element was carefully dismantled, metal tags were attached to it to ensure the security of the piece throughout the restoration works.
• Heritage interpretation signage about the former Macdonaldtown Gasworks that includes information about the Southern Gasholder is currently being designed. The signage will be located near the site of the restored gasholder and in locations such as Macdonaldtown Station and Carriageworks. The Heritage Interpretation Strategy aligns with the general NSW Historical Themes of Interpretation endorsed by the Heritage Council of NSW. The adopted themes are Industry, Science, Technology, Transport, Utilities and Labour, which should ensure that the signage has broad appeal (Figures 33a & 33b).

Challenges overcome
The ‘Process’ section above documents how the challenges of the potential collapse of the Southern gasholder, the change from in-situ to offsite restoration for some elements, and the health risks posed by lead paint removal were overcome. The ‘Protective Vibration Monitoring’ section documents how vibration impacts on the gasholder were managed. Other challenges that were overcome to achieve the restoration are outlined below.

Disassembly of the Gasholder’s Superstructure
An engineered disassembly plan was developed for the removal of the gasholder’s superstructure to ensure no damage to the superstructure or the below-ground annulus during the process. The plan considered geotechnical advice from Coffey Geotechnics and structural analysis by Bill Jordan and Associates. The advice included an assessment of the possible impacts to the annulus during the mobilisation of a 90T crane required to disassemble the superstructure. No damages were sustained due to the process (Figures 9 – 11).

Protection of the Gasholder during Remediation Excavations
The gasholder’s substructure was kept intact during remediation excavations by dewatering its brick annulus and steel bell.

In addition, a series of piled retaining walls were designed and installed to achieve the excavation profile and to protect adjacent infrastructure including the gasholder. Piles up to 900mm in diameter with maximum pile depths of 15m were installed. The ‘continuous flight auger’ method was chosen to minimise vibration and noise impacts. The design of the retaining walls adjacent to the gasholder and the western boundary was based on maximum lateral movement criteria of 10mm. Coupled with ground settlement modelling, this achieved the best outcome for the gasholder as well as nearby residents, services and rail infrastructure. Particular planning was required to use a 60T piling rig to construct the retaining wall adjacent to the gasholder.

A 3D Building Information Model (BIM) informed the remediation design and guided the excavations, which were 9m deep in some areas of the site. The BIM protected the gasholder by incorporating the gasholder’s location and dimensions within the 3D model, enabling ‘clash detection’ when designing the piling and anchoring of the retaining walls.

To address the requirement for 6m deep excavations around the gasholder’s annulus without damaging it, a well-researched solution was needed. Ventia engaged Coffey Geotechnics and Bill Jordan and Associates to develop an excavation sequence that would not have any adverse impacts. Comprehensive modelling of the earth and hydrostatic forces on the substructure brickwork was undertaken to assess a staged excavation and dewatering sequence that allowed Ventia to remove contaminated material to the depths needed to remediate the adjacent area. This sequence was then reversed during the re-instatement of the clay puddle around the annulus and the backfilling of soil.

Waterproofing of the gasholder’s substructure brickwork originally used a clay puddle material. As part of the remediation excavations this clay puddle, which was external to the brick walls of the annulus, needed to be removed. Geotechnical testing was conducted to characterise the permeability and material properties of the clay puddle and Ventia successfully sourced clay material from the site with matching properties. This material was used to reinstate the clay puddle during back filling activities, ensuring that the brickwork was sealed correctly and waterproof.

Casting of Finials
A creative solution can be seen in how the problem of the gasholder’s missing finials was addressed. The finials could not be found, despite a search by Sydney Trains and a request for information made via the project’s community newsletter. One clear photo of these original elements existed however, and they looked to be identical to those from the disassembled gasholder that once stood at Molong, NSW. As such, replicas were cast from these finials and installed, adding aesthetic value to the gasholder and enhancing its recognisability as a Victorian-era structure. Note: Some column caps were also missing but replacements were cast using the column caps that remained.

Community engagement pre and post-restoration
The Erskineville community and other stakeholders were engaged before, during and after the Southern Gasholder’s restoration, as recommended in the Burra Charter process.

A variety of mediums were used to educate the community about the heritage values of the gasholder and the former gasworks. For example, Sydney Trains and Ventia distributed 28 newsletters about the Macdonaldtown Gasworks Remediation to 1,600 local residences and businesses. A number of these newsletters included information and photos about the restoration of the gasholder and other heritage-related works such as archival recording. The community was also engaged through doorknocks, briefings, surveys, notifications, noticeboard signage, and a website. The Community Relations Manager for the project found that the educational process fostered an ongoing interest by community members in the site’s history and a frequent topic of conversation raised by people was the restoration of the Southern Gasholder. The project website, www.macdonaldtownremediation.com.au , contains a ‘Heritage’ webpage as well as a ‘Heritage-Listed Gasholder Restoration’ webpage. This website has been retained as an educational resource despite the completion of the remediation project and gasholder restoration.

In addition, the project sponsored ‘Greening Australia’ workshops at two local primary schools to promote sustainability awareness for students. Later in the project, the students visited the remediated gasholder site where the Community Relations Manager spoke to the students about the operations of the former gasworks. The students then planted native tube stock in the area surrounding the restored gasholder.

Note: Although the Southern Gasholder is situated on land that is operationally valuable to Sydney Trains, allowing the general public occasional access to the site is under consideration. Currently, the gasholder can be seen at a distance from the platform of Macdonaldtown Station and Burren St, Erskineville.

Heritage interpretation of the Northern Gasholder and other heritage features
The remnants of the Northern Gasholder that used to sit beside the Southern Gasholder were excavated during the remediation of the Macdonaldtown site. Archival monitoring and recording of the remnants was undertaken during the process. To preserve the heritage significance of the Northern Gasholder, three courses of bricks have been placed in the original location of its annulus.

The heritage assessment of the Macdonaldtown site also involved an archaeological excavation in the area of the gasworks’ former retort house and in the area containing the footprint of the superintendent’s residence. All works were undertaken to the standards of Sydney Trains’ Heritage Branch.
In addition, the various items found during remediation excavations, some of which may be of heritage value, were carefully photographed and catalogued for retention by Sydney Trains. These included glass and ceramic bottles, coins, horse-shoes and even well preserved newspapers from the 1960s.

Worked on the project:
Site and Heritage Item Owner: Rail Corporation NSW (RailCorp)
Principal Contractor: Ventia Utility Services Pty Ltd (Ventia)

Subcontractors:
Bill Jordan and Associates (heritage and structural), Coffey Geotechnics (geotechnical), Environmental Resources Management (ERM) (heritage investigation), Jacobs (structural dilapidation), Central Coast Metal Protectives (blasting and painting), Gillespies Cranes (disassembly and reassembly).

What the Judges said:

“What a delight to have a result like this out of a remediation project. The judges were particularly taken by this project. “