Rock blast fear for buildings

City rail link diagram.

Auckland Council officers fear noise from blasting rock from the Mt Eden end of the city's underground rail project may seriously damage fragile buildings.

Council body Auckland Transport wants hearing commissioners to allow up to 150 decibels of noise around unoccupied buildings to blast away extensive basalt deposits near where it intends joining a pair of rail tunnels to the western line. That is similar to the noise of a jet on takeoff, which can rupture unprotected ear-drums.

A report by council principal planner Ross Cooper quoted a consultant's opinion that 150 decibels would create an unacceptably high risk "of windows and other fragile building elements being damaged or destroyed".

Although most of the 3.4km rail link can be tunnelled without need for blasting, Auckland Transport expects to have to bowl almost 70 properties. It wants a route designation for up to 20 years to provide flexibility in case growth projections calling for the link to be completed as early as 2021 prove too optimistic.

That is causing concern among some submitters, including Downtown shopping centre owner Precinct Properties, which wants to redevelop the site after it is demolished for the project but fears a loss of tenants of city buildings for too long could cause urban "blight".

But Auckland Transport's senior lawyer, Andrew Beatson, told the commissioners properties would be carefully managed between acquisition and construction, and kept occupied where possible.

He said about 90 per cent of 35 or so submitters due to appear at the hearing "do not oppose the project, subject to the control of effects".

Auckland Transport acknowledged the inevitability of significant disruption along Albert St over two years of trench and building the project's largest underground station but aimed to ensure "the most appropriate trade-off between maintaining access to properties and minimising construction duration".

Mr Beatson said the sequential closure of three Albert St intersections would cut six to 12 months off an earlier estimate by allowing more efficient construction.