7 minute read
5. Management and Mitigation Measures
Potential impacts on built heritage in proximity to construction activities are also considered as part of the CNV DWP and the GSMCP for the Karangahape Station 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. The methods to be implemented during construction to avoid, manage and/or mitigate potential built heritage effects include:
Building Condition Surveys prior to the commencement of works; Investigations of building foundations prior to the commencement of works; Management, monitoring (of vibration and ground/building movement), 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 6 of this HC DWP).
Prior to construction, condition surveys of heritage buildings identified in the CNV DWP, GMSCP and/or HC DWP as being potentially impacted by the works (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: o Any information about the type of foundations; o Existing levels of damage (aesthetic, superficial, affecting levels of serviceability); o Whether observed damage is associated with structural damage; o Susceptibility of building or structure to further movement; and o Photographic evidence.
With respect to built heritage, the building condition surveys will generally 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. Consideration of the stability of any elements, including applied decorative elements or features, and any fragile elements.
Page 29
Karangahape Station Main Works
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 +/- 200mm. 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 pre-construction 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, as set out in the GSMCP, the Link Alliance shall carry out visual inspections of the surrounding ground and external building facades of buildings for which pre-construction condition surveys are required (in accordance with the CNV DWP) adjacent to the main works to monitor any deterioration or movement of any pre-existing cracks. In addition to visual inspections, the GSMCP 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 surveys 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 early 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.
Page 30
Karangahape Station Main Works
5.2 Monitoring and Management Measures 5.2.1. Monitoring Instrumentation
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, or nearby to, existing structures. In some instances, this will include instrumentation installed within the property as well as on the external surfaces of the building with the property owner’s consent.
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.
5.2.2. 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 Section 5.1) and monitoring prior to and during construction.
Site Specific Construction Noise and Vibration Management Plans will be prepared for buildings where vibration levels are predicted or measured to exceed the vibration limits set out in CRL designation Condition 33 (refer to Section 5.3 of the CNV DWP).
Regular monitoring and assessment of vibration levels will determine the process to be followed and any required action to mitigate and manage any potential effects, as set out in Section 8.2 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 will be prepared summarising the findings of the survey and recording.
Table 5-1 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 or historic streetscape elements.
Table 5-1: Overview of Protection Methodology
Built Heritage Feature
Exterior building fabric and surfaces
Protection Methodology
Where works will be undertaken immediately adjacent to these features, appropriate protection such as plywood sheets or temporary fencing to a minimum of 2 metres high will be required.
Page 31
Karangahape Station Main Works
Canopies and overhangs
Fragile exterior or interior building elements
Historic streetscape elements Establishing the operating requirements of equipment to be used in relation to the dimensions and structure of existing canopies and 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 stained glass and leadlight windows, chimneys, parapets, 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.
5.3.1. 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. The Karangahape Communications and Engagement team will arrange the process to manage maintenance works.
5.4 Rectification Methodology The building condition surveys, and assessments and monitoring/management methods outlined in Section 5 of this HC DWP will be the vehicle for any discussion around the need for rectification works. In addition, it is likely that rectification discussions will be undertaken on a case by case basis when the post-condition assessments are undertaken.
Page 32
Karangahape Station Main Works
