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4. Overview of potential effects on Built Heritage during the Aotea main works

Unreinforced masonry buildings, including the historic heritage and special character buildings and structures in proximity to the Aotea main works are likely to be at higher risk from the potential effects of vibration or ground movement associated with the works. These buildings may have soft mortar joints, simple foundations and connections of structural members or limited bracing. It is important to understand the specific building structure, including foundations, fabric and detailing, in order to inform the likely built heritage effects and the methods that shall be implemented during the works to avoid, remedy or mitigate these effects (outlined in Section 5 of this HC DWP (Built Heritage)).

4.1 Vibration

Vibration can affect nearby buildings and their foundations, with consequential damage to building fabric and services. Potential damage from vibration can range from cosmetic to minor or major damage. Potential effects on historic structures as a result of ground movement due to vibration include cosmetic or aesthetic effects such as hairline cracks to surfaces or to mortar joints that might affect appearance, through to changes to building fabric that might affect weather tightness, alignment of windows and doors, or damage to services. Major damage could place buildings at risk in terms of structural stability. For built heritage places, even aesthetic damage may impact on heritage values, for example if original details or finishes are cracked or damaged, and potentially if inappropriate repairs to such defects are undertaken.

A Construction Noise and Vibration Delivery Work Plan (CNV DWP) (Appendix L of the CEMP) has been prepared to address the effects of the Aotea main works. Some construction activities are predicted to generate high levels of vibration including sheet piling, excavation, compaction and breaking.

Construction activities required for the Aotea main works will need to be carefully managed through this DWP, and the CNV DWP in accordance with relevant Conditions.

4.2 Ground Movement

Excavation and foundation work can also cause ground displacement and movement of an adjacent historic structure. Excavation deeper than the foundations of neighbouring historic buildings has the potential risk of such movements occurring. A historic structure, with a shallow masonry footing, may experience corresponding displacement that can result in major structural damage. Managing the risk and potential effects of ground movement or settlement is addressed in the Groundwater and Settlement Monitoring and Contingency Plan (GSMCP).

The GSMCP forms part of the CEMP for the Aotea main works, and addresses the relevant matters specified in the conditions of Water Permit R/REG/2016/1892 (groundwater diversion and discharge) (‘the Consent’).

As described in the GSMCP, Building Condition Surveys will be carried out for all structures listed in Appendix 2 of the Consent, including those buildings in the Aotea Station area. The surveys will be undertaken to establish a baseline building condition against which any subsequent surveys can be compared. Buildings will be assessed according to foundation type, construction and sensitivity to ground movement. The outcome of the investigations and monitoring will determine any mitigation measures to be implemented to control settlement to the building foundations.

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4.3 Stormwater Drainage

Maintaining a well-functioning stormwater drainage system is essential to the protection of any historic structure. This system can easily be rendered ineffective by construction or demolition work if debris originating at the construction site finds its way to the rainwater disposal system or drains of an adjacent building, with potential to adversely impact on heritage fabric through flooding.

4.4 Impact Damage

Construction activities have potential to cause accidental damage to building fabric through direct impact from machinery. Appropriate protection and management are required to avoid this.

4.5 Built heritage Potentially Impacted by the Aotea main works

Table 8 in Section 5.2 of the CNV DWP identifies the buildings in proximity to the Aotea main works including heritage buildings that may be at risk of receiving vibration which exceeds the building damage vibration limits.

Section 6.2 of the Groundwater and Settlement Monitoring and Contingency Plan (GSMCP) identifies the buildings for which Building Condition Surveys are required, including heritage and special character buildings.

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