THE PUMPHOUSE MOVE
The Cornish Pumphouse is a relic of Waihi’s mining past. It is one of two pumphouse examples in New Zealand and was built in 1904 to house steam-driven pumps for dewatering the mine. It was used until electricity arrived in town in 1913, but kept in working order until 1929 as a contingency against electrical failure.
The pumphouse is a listed heritage building and is scheduled in the operative Hauraki District Plan.
In 2006 the structure was moved from its original position, adjacent to the old No. 5 shaft, because the shaft had subsided, and the structure was tilting into it. The pumphouse is currently sited about 280 m southwest of its original location, between the Waihi town centre and the open pit. It will require another relocation to allow for the proposed Martha Open Pit Phase 5 extension.
The relocation will be guided by an up-to-date condition assessment and detailed relocation methodology to ensure its structural integrity is maintained. An appropriate landscape design has also been developed for its new site. With these measures in place, it is considered the relocation of the building will not significantly affect its physical structure or its historic fabric, significance and amenity value.
The pumphouse is scheduled in the Hauraki District Plan and will need to be moved to accommodate for the Martha pit extension. Assessments of the structural integrity of the building and a visual assessment of the pumphouse in the proposed new site have indicated that the relocation of the building will not significantly affect its physical structure or its historic fabric, significance and amenity value.
As part of the Project Quattro proposal to enlarge the Martha pit, the pumphouse will again need to be relocated, and OceanaGold Waihi will be seeking community input to guide the final design.
PROPOSED RELOCATION SITE
The new site is on the southern side of the upper Seddon Street carpark, area near the replica headframe. This is currently the location of Hauraki District Council’s ‘housing for the elderly’ units. New, modern ‘housing for the elderly’ will be built in Gilmour Street prior to the pumphouse move commencing. OceanaGold Waihi will work along-side the residents and HDC to ensure a smooth transition between their homes.
Mining artefacts such as the pumphouse and replica headframe have become significant features within the township and waypoints visible from surrounding areas.
Relocation of the pumphouse will transform the immediate context and setting of this structure which is widely recognised by the community as a key local landmark. The pumphouse reaches a height of about 21 metres above the surrounding ground level and forms a prominent feature, visible from within the town centre.
The new location has been carefully considered so the building continues to be a prominent feature. It will remain a highly visible focal point when viewed from the town centre and from wider afield.
The new location will align the building more directly with Seddon Street and be about four metres lower in elevation. It will retain a relevant pit rim setting, drawing tourists up to Waihi’s visitor precinct. Other mining artefacts encountered along the pit rim walkway will continue to maintain a strong association with mining heritage in Waihi, albeit in a different pit rim configuration.
HERITAGE VALUE ASSESSMENT
The evaluation was undertaken according to the statutory criteria and with regard to the building’s identified heritage values for its historic and architectural significance.
The pumphouse has been on its present site since 2006. Due to the move from its original location, the site does not have its authentic historical context. Nevertheless, it is acknowledged that the relationship with Martha Hill and the pit is still discernible from its present location.
The new site is not a significant change from the present setting and is closer to its original site. With the pit expanded, the pumphouse will be at a similar distance from the pit rim as it is today.
STRUCTURAL AND ENGINEERING ASSESSMENT
Prior to the 2006 move, the pumphouse was seismically strengthened by the installation of steel bracing ‘diaphragms’. These took the form of beams at the first-floor level, and roof trusses at eaves level.
A visual condition survey was conducted in January 2019, followed by drone photography of the upper steelwork in February 2019. The appearance of the ‘ruin’ is not significantly different from what it was immediately following the 2006 move. The concrete structure and external render shows no significant deterioration and the steelwork is in excellent condition.
Sub-soil testing at the new site has indicated an increase in shaking hazard of about 25% compared to the current location. The structural assessment of the proposed relocation has therefore considered mitigation for the increased seismic hazard once in its new location. In order to mitigate this increased hazard, it is proposed that the building would be base-isolated on lead-rubber bearings.
Base-isolation is commonly regarded as the ‘gold-standard’ of seismic protection. It effectively isolates the superstructure from seismic lateral displacements of the ground during an earthquake. This greatly reduces the lateral accelerations experienced by the superstructure.
It is considered that the pumphouse would be very well suited to base-isolation, firstly because of its stiff superstructure, and secondly because the structure will be effectively isolated as part of the relocation methodology.
It would be a relatively straight forward and cost-effective procedure to replace the sliding bearings with lead-rubber base-isolation at the conclusion of the move.
Base-isolation is likely to reduce seismic accelerations by more than 50%, resulting in an overall reduced seismic hazard from its current location. This would give the pumphouse a level of seismic protection greater than that required by the New Zealand standard for a new building.
Investigation is ongoing, but the proposed method of relocation could be very similar to that used in 2006.
The above-ground structure will be separated from the below-ground foundation and will then be slid on greased Teflon-stainless steel bearings. The stainless steel strip is mounted on concrete ‘runway’ beams, which are laid on a compacted fill causeway built between the two sites.
The pumphouse will firstly move east along the original causeway route for about 80 m. At that point it would be pivoted around to align with a second 100 m long causeway.