1 INTRODUCTION 1.1 THE COLLAPSE At approximately 1:40am on Wednesday 2nd November 2005 a section of the roof of the Lane Cove Tunnel collapsed, an unravelling failure ensued and the collapse propagated through a height of 17m to the surface forming a sinkhole that undermined the front section of Kerslake Apartments (Figure 1). The collapse occurred during the final excavation stages of the intersection of a ventilation tunnel and the exit ramp to the Pacific Highway.

AUSTRALIAN GEOMECHANICS VOLUME 53: NO.4 DECEMBER 201822 LANE COVE TUNNEL COLLAPSE AND SINKHOLE, A FORENSIC REVIEW – 1: THE COLLAPSE BURMAN ET AL By about 2:00am the sinkhole was observed in front of Kerslake Apartments and by 5:30am it had expanded in size to be around 8 to 9 m in diameter. At about 6:00am a secondary collapse occurred involving a number of retaining wall piles and the decision was made to fill the hole with mass concrete to mitigate any further collapse. The spoil from the collapse buried the road header and a Caterpiller loader (Figure 2) but fortunately the 4 members of the tunneling crew retreated from the area without suffering physical injury.

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