Los Angeles County Sanitation Districts (LACSD) and contractor FlatironDragados have launched an investigation into the partial collapse of the under-construction Clearwater Tunnel last week.
Thirty-one people were rescued after the collapse, which occurred approximately 8-10km from the sole access portal.
The investigation will look at the safety, engineering and structural integrity of the tunnel. Clearwater Tunnel operations have been halted while the investigation takes place and LACSD said there was no timeframe for the process.
“Safety remains the highest priority of the Los Angeles County Sanitation Districts. We will continue to co-ordinate with all relevant agencies and provide updates as they become available,” the organisation said.
LACSD said preliminary information suggested the incident occurred under Western Avenue, approximately 113m below ground. Survey crews at the site verified there was no surface damage or discernible movement at the location, and the area was safe.
During construction, survey crews have been monitoring the road above the tunnel alignment before and after the TBM has passed through. The area had been monitored since September 2024 and as recently as April this year, with no discernible movement, LACSD said.
From July 10, the day after the partial collapse, survey crews will monitor the area daily, 90m either side of the site. Readings will be taken across the road in 15m increments.
The Clearwater Tunnel is designed to address concerns over the existing infrastructure. Currently wastewater is conveyed in two tunnels – one built in 1937 and the other in 1958. They are not built to modern seismic standards and rainstorms in recent years have nearly exceeded their capacity.
