The one-day rock blasting trial involved three"small-scale controlled blasts"beneath Reserve Street to test whether the method should be used to tunnel between Annandale Street and Catherine Street in Leichhardt.
It raised concerns the blasting method would lead to construction vibrations,noise and cracking damage to properties experienced by residents living above earlier sections of the 33-kilometre motorway route.
A WestConnex spokeswoman said after analysing the results of the blasts"of approximately one second each"under Annandale,the contractor had determined the controlled blasting method was not viable at that location. The decision is not expected to impact on the timing of the project.
Rockbreakers and roadheaders would continue to dig the tunnels,she said,adding that the community would be consulted beforehand if blasting were to be carried out again.
The tunnelling decision on the M4-M5 Link comes as the state government awaits more concrete advice on the planned opening of NorthConnex,which has hit delays in its final commissioning stage.
Transurbanlast month indicated the nine-kilometre tunnel might be pushed back past the end of September due to the coronavirus'impact on supplies and overseas expert consultants.