8. Blasting

Blasting is proposed as an effective method to remove basalt from the worksites between Dominion Road and Mount Eden Road.

The work will be done by a blasting contractor. It is their responsibility to design and carry out the blasting programme so that vibration and air overpressure comply with the limits in CRL designation condition 32.

The blasting contractor has prepared a Blasting Management Plan (BMP) refer document CRL-MTEERW-LKA-CWP-800000. It identifies the geology, drill and blast methodology, safety control measures, compliance limits and other management protocols for the blasting programme. It will be kept up to date by the blasting contractor.

The blasting area is shown in the ‘Drill and Blast Methodology’ section of the BMP. The BMP states that “all blasts will be designed to be fully compliant with all applicable standards. Particular attention will be given to the local residence and Media Works NZ to minimise effects and disruption”. Despite predicted compliance, it states: “A Dilapidation Report will be commissioned by Link Alliance covering the following affected buildings”:

Residential properties on Shaddock street, Nikau street, Ruru street, Ngahura street, Akiraho street, Mount Eden road Media works NZ Commercial properties Shaddock street, Nikau street, Ruru street, Ngahura street Akiraho street Mt Eden train station platform and lines

8.1 Trial Blasts

Trial blasts were carried out by Red Bull Powder Company Ltd on 5 February 2020 in order to measure the way vibration propagates through the basalt in the Mt Eden works area. The findings are summarised in Red Bull’s report ‘Link Alliance –97 Mt Eden Rd Seed Hole Analysis’, dated February 2020.

This was the first stage in the blasting process, and small amounts of explosive (charge weights) were used to minimise vibration and noise. The blasting contractor uses this data to calculate the maximum instantaneous charge weight (MIC) for each blast –the maximum amount of explosive that can be used while still achieving compliance.

The trial blasts showed that compliance with the building damage limits is predicted within:

50 metres for an MIC of 0.6kg 70 metres for an MIC of 1.2kg 100 metres for an MIC of 2.5kg

Subsequent production blasts in June 2020 were compliant with the building damage limits. Vibration levels remain the controlling factor. Blasting overpressure can be sufficiently suppressed through use of blast mats and overburden.

Specific mitigation and management recommendations for blasting are listed in Section 9.9, and in the BMP.

Page 29 Mt Eden Main Works CNV DWP