Carving out a Mexican mountain highway 02 Mar 2016

Sandvik jumbos are helping carve out a 3.2km highway tunnel that will help significantly reduce journey times in and around the iconic holiday resort of Acapulco, as well as helping avoid tourists falling prey to mountain bandits.

Acatunel workers inside the tunnel

Weekend visitors and residents in Acapulco Bay, Mexico, have long been frustrated by the long journey times they face; while tourists find the 12km journey from Juan Alvarez International Airport to the Acapulco Bay beaches and resorts heavily congested.

This will soon to change when Mexican construction company Acatunel SA, part of the internationally known Ingenieros Civiles Asociados (ICA) Group, completes a three-lane x 3.2km tunnel through the Cumbres de Llano Largo Mountain.

Tunneling runs from Cayaco on the south side of the mountain to Brisamar on the bay side. To complete excavation of what will be the country’s longest highway tunnel by the scheduled July 2016 completion date, the contractor is relying on Sandvik, DT820-SC and DT1131-SC tunneling jumbos.

Under the terms of the contract Acatunel will begin work on a parallel tunnel once traffic levels through the new tunnel reach a predicted saturation level of 13,500 vehicles a day.

Working two 12-hour shifts each day, and after more than four years of excavation, the contractor is now within six months of final breakthrough of the first heading. Advance rates have reached a much as 7.2m each working day, but a geology of mostly hard granite, quartz, mica and basalt has proven a tough challenge and progress rates have been correspondingly slow.

Sandvik DT1130 can cover an area 18m x 11m

Water ingress has also proved problematic, and the fractured nature of the hard granite has resulted in numerous collapses and landslides along the heading. “What happens is that the ceiling of the tunnel falls in, leaving a hollow upper part over the tunnel,” explained Miguel Angel Banuet Rodríguez, the project’s general supervisor. “This hollow space needs to be filled in with shotcrete or hydraulic concrete so as to make it safe. This causes delays.”

In addition to dealing with geological faults, the drilling crews are working on a downward slope, which exacerbates problems with water ingress and places a premium on the stability of the drilling equipment. The Sandvik DT1131-SC jumbo is 18m long from its rear overhang to the front of its fully-extended booms, but the fitting of SAHR fail-safe disc brakes securely lock the machine in place.

Weighing 44 tonne the electro-hydraulic tunneling jumbo unit carries three booms that can excavate an area 18m wide x 11m meters high. The four-wheel drive boom carrier is powered by a 148 HP diesel engine.

Carving out the top heading using a Sandvik DT1130 jumbo

Acatunel stresses that ensuring the safety of its 350 employees was one of the major reasons it selected Sandvik tunneling jumbos for the Acapulco project. Besides being stable in operation, and pairing a powerful engine with fail-safe braking systems, the DT1131-SC boasts a FOPS-certified cabin that insulates the operator against the noise and vibration that comes with drilling through rock. Large window areas surround the operator station so that the operator has full view of the 3,300kg booms, as well as any auxiliary personnel working nearby.

To meet the challenge where the drilling boom meets the rock, Acatunel is using Sandvik T38-Hex35-R32 16ft rods, T38-T38 couplings, and RD525 drifter shanks with 48mm bits. Miguel Angel Banuet Rodríguez says the durability of the Sandvik drilling components is helping his crew hammer its way through the mountain. Acatunel has also utilized Sandvik DX680 and DX700 drill rigs to open the tunnel, and create benching for water drainage within the tunnel.

“The booms are cleverly mounted, automatically fixed in parallel positions for accurate hole drilling, and engineered to provide the widest possible coverage on the face of the rock,” said Jair Gonzalez, Sales and Technical Support Representative for Sandvik Construction rock tools and parts. He added: “When you put Sandvik bits in front of all that, you can expect higher penetration rates, longer bit life, and straighter holes.”