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Cleanup operations at the portal of the 160-meter-long cable duct tunnel of the Trishuli–3A Hydropower Project in Rasuwa have been intensified following the devastating Bhotekoshi flood on August 26.

More than 20,000 cubic meters of mud, sand, rocks and other debris have been removed from the tunnel’s portal area in just five days, while more than two dozen large boulders have been blasted and cleared, according to engineers involved in the search and rescue operation.

Engineer Shriram Neupane, who is involved in the rescue operation, said two excavators have been operating continuously since September 13 to clear the massive deposits of mud and debris.

The material removed so far includes mud, sand, rocks, concrete slabs, beams, pillars and extremely large boulders - some reportedly as large as houses.

Breakers and controlled explosives are being used as required, with cleanup operations continuing around the clock.

Around 50 meters of portal area cleared

According to Neupane, approximately 50 meters of the portal area has now been cleared up to around 2.5 meters below the top face or crown of the tunnel.

However, workers have not yet started removing the mud deposited deeper inside the tunnel.

The 5.5-meter-high tunnel requires construction of an access and drainage system to a depth of approximately three meters before workers can safely begin removing the accumulated mud from inside the tunnel, Neupane said.

“The work inside the tunnel will begin only after the access and drainage arrangements are completed,” he said.

Initial signs indicate no water accumulation inside tunnel

Preliminary observations have provided some encouraging indications regarding conditions inside the cable duct tunnel.

Neupane said an initial inspection found that the section extending approximately one meter inward from the tunnel entrance was completely filled with mud.

However, water is reportedly flowing out of the tunnel at a rate of approximately two liters per second, without any noticeable pressure.

This suggests that there may not be a significant volume of trapped or accumulated water inside the tunnel.

At the outer section of the portal, workers have also found obstructions including a gate slab, two large pieces of timber and large boulders.

Based on the initial assessment, Neupane said it appears that large rocks may not have entered deep into the tunnel and that the major material inside could be limited to water and mud.

However, he cautioned that the actual internal condition of the tunnel has not yet been fully confirmed.

Tunnel structure believed to be intact

The 160-meter-long cable duct has a bend at approximately the 60-meter point. The tunnel also rises toward the powerhouse, creating an upward gradient.

According to Neupane, these structural characteristics have led engineers to make an initial assessment that the inner section of the tunnel may remain relatively normal and structurally intact.

A full assessment, however, will only be possible once the accumulated debris is removed and the rescue team gains safe access to the tunnel interior.

Lack of road access complicates operation

The cleanup and rescue operation is also facing logistical challenges because there is currently no road access to the site.

Machinery, spare parts and other equipment required for maintenance and operation must be transported to the area by helicopter.

Neupane said the lack of direct road access has caused delays in transporting some materials and equipment, but the rescue and cleanup operations are continuing without interruption.

The immediate priority remains clearing the portal, establishing safe access and drainage, and then gaining entry into the cable duct to determine the actual condition of the tunnel and any people or equipment that may remain inside.

The progress made over the past five days has increased expectations that the rescue and assessment operation can move into the tunnel once the remaining access work is completed.