Concerns over the blasts follow frustrations over shrinking tunnel depths, construction noise, vibrations, ruined sports venues and cracking damage felt by residents along earlier stages of the 33-kilometre project.
Three “small-scale controlled blasts” will be conducted beneath Reserve Street in Annandale to test whether the method should be used along the tunnelling route from Annandale Street to Catherine Street in Leichhardt.
Rosemarie Gates lives on Emma Street in Leichhardt, which lies within that section of the route. She is worried blasting parts of the tunnel bound for 24 metres beneath her property would damage the 100-year-old house.
“Tunnelling is bad enough, but to have rock blasting is insult to injury,” she said.
A WestConnex project update says the method involves “pre-drilling a series of small diameter holes in the rock face, loading the holes with small charges and detonating them to break the rock into removable pieces”.
The trial blast has been designed by industry experts “so as to not exceed vibration levels that could cause damage to property or heritage items”, the update says.
Mr Carmichael, who lives on Annandale Street, said residents were also worried about the lack of consultation, and noise disturbance, particularly given many people were working from home due to COVID-19 restrictions.
“The really distressing thing is they don’t have to blast. It’s an incredibly primitive way of building a tunnel.”
A WestConnex spokeswoman said the trial blasts on Monday would take place about 37 metres beneath the surface of Reserve Street and not directly below any homes. She said “no damage to properties is expected”.
“It is expected that up to 30 properties near the work area will experience some noise and vibration for a very short period of time (likely in the order of a fraction of a second) for each of the three short blasts, however, most residents in the area are unlikely to feel any impact.”
She said controlled blasting was “a common tunnel excavation method” used in areas of hard rock and it “may reduce the duration of noise and vibration impacts for local communities”.
It would potentially “reduce construction time in this location compared to using rock-breakers and roadheaders alone”.
“If the trial is successful, further detailed consultation will be carried out with local community members regarding the possibility of future controlled blasts.”
Balmain Greens MP Jamie Parker said residents in the densely populated area were already “shattered by constant noise and vibrations” from tunnelling and felt they’d been kept in the dark about the blasting and any safety precautions.
“Residents are rightly alarmed and anxious that the government is proposing to detonate explosives in some cases just 30 metres below their homes,” he said.
Civil engineer Philip Pells, who has worked on some of Sydney’s biggest tunnelling projects, said the vibration data should be made publicly available for residents who lived close to the test site.
“It’s got to be properly monitored and properly assessed before ongoing tunnelling is allowed.”
The WestConnex spokeswoman said vibration levels would be monitored at numerous locations during the trial to ensure they did not exceed the upper limit of 10 millimetres per second.
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Megan Gorrey is the Urban Affairs reporter at The Sydney Morning Herald.