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5. Management and Mitigation Measures
Potential impacts on built heritage in proximity to construction activities are considered as part of the CNV DWP and the GSMCP for the Aotea main works. The performance standards for construction induced settlement specified in the Consent Conditions will be met through the specific design aspects of the main works, along with management, monitoring, mitigation and contingency measures set out in the GSMCP. Methods to be implemented during construction to avoid, manage or mitigate potential impacts on built heritage include: • Building Condition Surveys prior to the commencement of works; • Investigations of building foundations prior to the commencement of works; • Monitoring of vibration and ground/building movement, and mitigation and contingency measures as set out in the CNV DWP and GSMCP; • Built heritage protection where appropriate; and • Building record and salvage strategy (with respect to the removal of any built heritage items) (refer to Section 5.1.1 and 6 of this HC DWP (Built Heritage)).
5.1 Building Condition Surveys
5.1.1. Pre-Construction Surveys
Prior to construction, condition surveys of identified built heritage (refer
Table 3-1) (inclusive of those buildings listed in Appendix 2 of the CRL designation conditions) will be undertaken. These condition surveys will ascertain any pre-existing damage to a building, existing structural distress, and any potential weakness of the structure’s foundations or structural elements, as well as non-structural damage. The condition surveys will form the basis for recording buildings and recording baseline information prior to works commencing.
The building condition surveys will generally be undertaken as follows (in accordance with CRL designation condition 46):
The building surveys will be undertaken by an independent senior qualified person. The survey shall include:
Any information about the type of foundations; Existing levels of damage (aesthetic, superficial, affecting levels of serviceability); Whether observed damage is associated with structural damage; Susceptibility of building or structure to further movement; and Photographic evidence.
With respect to built heritage, the pre-construction condition surveys will include:
A survey of the exterior and interior of heritage buildings. A record of the condition of buildings using photographs, annotated drawings and written records, noting any existing signs of structural distress and damage or deterioration of a non-structural nature.
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Consideration of the stability of any elements, including applied decorative elements or features, and any fragile elements. Any recommended remediation to secure or mitigate potential problems prior to the commencement of construction based on consideration of the heritage character and detail of the building. The location of all cracks greater than 2 mm in aperture width, which shall be recorded with a positional accuracy of +/- 200 mm. Installation of grid crack monitors may be required on selected readily accessible cracks with an aperture width greater than 2 mm discussed above and as determined in consultation with the Built Heritage Specialist.
The condition surveys shall generally include:
An introduction with overview of the premises, record of when the inspection was made, orientation notes for viewing photos and captions, summary of the scope of inspection, purpose of report and any limitations, any areas not accessed; A description of the property construction, based on a visual inspection and review of available architectural drawings and property information obtained from Council; A summary of existing damage and susceptibility to future damage; Site plan; Annotated plans, elevations and sections that relate to the photographic record; Floor plans if available; Burland building damage classification matrix; Pre-Construction Condition Schedule, with description, visible damage evident, damage category recorded and photograph reference; and Annotated photographs recording building condition. This should include general exterior and interior views as well as photographs of specific defects.
The building condition surveys will be reviewed by the Project Built Heritage Specialist, prior to works commencing.
5.1.2. Surveys during Construction
As set out in the CNV DWP, building condition surveys may be undertaken during the construction works in the event that complaints in relation to building damage are received or if the vibration criteria set out in the CRL designation conditions are exceeded.
In addition, the Link Alliance shall carry out visual inspections of the surrounding ground and external facades of buildings for which pre-constriction condition surveys are required adjacent to the early works to monitor any deterioration or movement of any pre-existing cracks, as described in the GSMCP. The GSMCP also requires continuous measurement of any ground surface or building movement during construction (refer Section 5.2.1 below).
5.1.3. Post Construction Surveys
Post-construction survey shall comprise a repeat of the required elements of the pre-construction survey so that a direct comparison can be made. In accordance with CRL designation Condition 46.4, building condition surveys of those buildings or structures that were subject to a pre-construction building condition survey may be undertaken post-construction of the works. Where a postconstruction building condition survey confirms a building has deteriorated as a result of the works, the damage shall be rectified by the Link Alliance.
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5.2 Building Record Strategy
Where heritage buildings or structures are directly affected by the works, a comprehensive record will be made before, during and after construction works. This section describes the building record methodology that will be implemented in any locations of built heritage directly affected. Refer Section 5.1 of this HC DWP (Built Heritage) for further detail regarding pre - and post-construction surveys of built heritage. Buildings and structures that are directly affected by the Aotea main works include the Bluestone Wall and Toilets and heritage and special character buildings where canopies must be removed.
Refer Section 6 for matters regarding the Bluestone Wall and Toilets.
5.2.1. Building record
The following recording level will be undertaken for identified built heritage adjacent to the main works in any locations directly affected:
a)
b) c) d)
e) Prior to any works an archival photographic record should be made of buildings or structures directly affected. Existing drawings should be assembled (if held in public records). Measured drawings relevant to elements directly affected by the works. Written records, including recording of changes/alterations, composition and finish of materials. Research and collate existing archival photography where this exists.
5.2.2. Measured Drawings
Measured drawings should be prepared for all relevant elements and record materials, detail and finishes, to suitable scale as indicated in Table 5-1.
Table 5-1: Recommended Scale
Overall site layout
Floor plans Roof and ceiling plans Elevations (interior/ exterior) Sections Joinery details Other significant details Moulding profiles 1:500 or 1:200 (showing overall layout, boundaries and topographic features in relation to main buildings) 1:50 or 1:20 1:50 or 1:20 (showing disposition of roof/ ceiling timbers) 1:50 or 1:20 1:50 or 1:20 (across and along structure) 1:20 or 1:10 or 1:5 1:20 or 1:10 or 1:5 1:2 or 1:1
5.2.3. Photographic Technical Requirements
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General Images - conventional (digital) photography will be used with appropriate professional lenses capable of producing high resolution 1- 2Mb JPEG images 5 .
Archival images - For archival images the camera should be set to record using a raw file format. This raw file should not be modified - it should be considered to be the ‘digital negative’. It is recommended that these images be converted to uncompressed baseline v.6 TIFF for archiving. All images should have accompanying metadata specifying: photo ID, capture device, converting software, colour space, bit depth, resolution, date of capture, photographer, caption and any alterations made to the image.
Video equipment shall be high-resolution (broadcast quality), with low light capabilities although additional lighting may also be required.
Photographic recording should include:
Context: Views showing relationship to the surrounding setting, other buildings and streetscape.
Exterior: Elevations, roof where practicable, typical elements (chimneys, windows, doors, parapets, details, fixtures).
Interior: General views of interior layout, individual rooms/spaces, interior elevations, typical elements (windows, doors, details, fixtures and fittings), features such as staircases, evidence of use, wear and changes made, chattels and artefacts).
5.3 Monitoring and Management Measures
Based on the results of the pre-construction building condition surveys, and in accordance with the GSMCP, geotechnical and structural monitoring instrumentation will be installed on surfaces of, and nearby to, existing structures. This will include ground and building survey monitoring marks installed along the areas affected by the main works. The location and number of monitoring marks will take into account the building type/size, accessibility and risk of damage from ground settlement.
This will allow any actual building movement to be monitored and compared with the estimated potential effects.
The purpose of this instrumentation will be to measure/monitor any movement, settlement, tilt, strain and induced vibrations as a result of the works which may have the potential to adversely affect the structure. The instrumentation will be installed prior to starting the construction works. Should monitoring indicate the exceedance of specified movement trigger levels, then the GSMCP also sets out an appropriate intervention and mitigation strategy.
5.3.2. Vibration monitoring and management
Vibration mitigation and management, based on a Best Practicable Option (BPO) approach will be implemented during the works as outlined in the CNV DWP, including undertaking building condition surveys (refer to Table 9 in Section 5.2) and monitoring prior to and during construction.
5 Heritage New Zealand Pouhere Taonga; AGS1 Guidelines for investigation and recording of buildings and standing
structures, November 2018.
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Regular monitoring and assessment of the vibration measurements will determine the process to be followed and any required action to mitigate and manage any potential effects, as set out in Section 8 of the CNV DWP. If vibration monitoring demonstrates non-compliance with the vibration building damage limits the construction activity responsible for the exceedance shall cease as soon as safe and practicable to do so, construction methodology, mitigation and management strategies will be reviewed, advice will be sought from a structural engineer and a detailed building condition survey shall be undertaken by a suitably qualified engineer.
Any damage to buildings or structures shall be recorded as set out in Section 9.3 of the CNV DWP. Recording shall include photographs and relevant annotated plans, sections and elevations to show the major features of the buildings including location, type, construction, age and present condition, including defects (cracks). A report shall be prepared summarising the findings of the survey and recording.
Table 5-2 outlines the methodology to be implemented to protect key features of historic (and other) buildings against construction activities undertaken adjacent to, or in close proximity to these buildings.
Table 5-2: Overview of Protection Methodology
Built Heritage Feature Exterior fabric and surfaces of buildings and structures (including the Bluestone Wall)
Canopies and overhangs
Fragile exterior or interior building elements
Historic streetscape elements Protection Methodology Where works will be undertaken immediately adjacent to exterior fabric and surfaces of buildings and structures (including the Bluestone Wall), appropriate protection such as plywood sheets or temporary fencing to a minimum of 2 metres high will be required. Avoiding impact from machinery movement through use of appropriate equipment and observation while works undertaken under or adjacent to canopies. Appropriate bracing or protection for features such as parapets, chimneys, stained glass and leadlight windows, if vibration or ground settlement will be likely to put these at risk. Elements, such as basalt kerbs, or basalt blocks inset into the footpaths shall be carefully removed if required, prior to or during the works and stored for reinstatement at an appropriate time following the completion of works. Cellar lightwells should be retained and protected with plywood as required during the works.
Protection measures shall be reviewed by the Project Built Heritage Specialist prior to works commencing and periodically during the works.
5.4.1. Managing Maintenance Works to Heritage Buildings during the Construction Works
The construction team will work with building owners to facilitate necessary building maintenance and repair works during construction should monitoring/inspections confirm this is needed. The Link Alliance Communications team will arrange the process to manage maintenance works.
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5.5 Rectification Methodology
The building condition surveys and assessments and monitoring/management methods outlined in Section 5 of this HC DWP (Built Heritage) will be the vehicle for any discussion around the need for rectification works on a case by case basis.
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