Customer case

Tunnel centrale grossotto

Centrale grossotto repaired with automated concrete removal

Wan-Jet, in joint venture with fellow Swiss contractor Hydrodemolizione, removed the concrete lining from a water supply tunnel feeding the Centrale Grossotto hydroelectric power station in northern Italy.

The task involved about 550 m3 of damaged concrete and was included in the CHF 1.1 million renovation subcontract. The joint venture was for Vienna Construzioni, main contractor on the approximate 6.4 km long tunnel repair project, designed by consulting engineers Lombardi for client and power station owner Azienda Elettrica MunipaleMilano.

Water was channelled from the River Adda into the concrete lined tunnel, which, with a very shallow 0.007% gradient, closely follows the hillside contour of the Valtllina Valley above Sondrio near the Italian-Swiss border. The water flows through the lightly meandering tunnel at 2 m3/sec before plunging 250 meters down a 900 mm diameter steel pipeline and into one of the 3mW power station’s turbine generators for discharge back into the Adda. The tunnel is 1.1 m2 from the intake for about half its length, before a gradual transition into a narrow, 3.5 meter high elliptical egg shape where it discharges into the power station’s steel down pipe.

The solution

The contractors had to remove a minimum of 20 mm of concrete from the tunnel lining and the Conjet ACR™ robot accomplished this at a rate of about 20-21 m2/hour compared with around 4 m2/hour with a hand lance. The Conjet ACR™ robot produced a very accurate and uniform surface finish to the concrete left behind. It was also safer and less stressful than a hand lance for the operator.

Wan-Jet used the crawler mounted Conjet ACR™ robot to remove concrete from about 12,500 m2 of square section tunnel and just over 11,000 m2 from the egg shape. Conjet’s compact tunnel robot is ideal for working in these confined areas. The rubber tracks can be easily adjusted independently to follow the tunnel invert contours, making the maneuverable machine a very stable platform for the rotor cutter. And, because the robot is remotely controlled, the operator is well away from the hazardous cutting area.

How it works

Wan-Jet’s Conjet ACR™ robot carries a special hydraulically driven rotor complete with four high-pressure water jetting nozzles which deliver water at 2500 bar pressure and flow up to 40 liters/min. Water was fed to the robot through a flexible hose from a separate power pack (160 kW) outside the tunnel. The rotor, spinning between 300-1000 RPM, is mounted on a rotating and telescoping boom which allows the cutting head to constantly follow the tunnel wall profile and maintain the nozzle’s pre-set angle of attack to the concrete. Maximum concrete removal depth with the rotor cutter is 50 mm. However, much deeper cuts can be made when fitted with the optional single nozzle mounted on an oscillating cassette and 1 meter long feed beam.

All functions on the Conjet ACR™ robot are operated from a remote and separate CCU 176 data controlled, electrically powered hydraulic unit, which allows progress of the hydrodemolition process to be safely controlled and monitored away from the hazardous cutting area. The CCU 176, which can be located more than 50 meters from the Conjet ACR™ robot, incorporates an advanced computerized closed loop control, monitoring and display system. This system is extremely flexible and very easy for the operator to use and optimize production. It stores all the relevant parameters and machine performance data, which can be downloaded for future reference or used in estimating future hydrodemolition projects.

The operator chose one of several pre-loaded software programs to ensure that only the concrete set to a predetermined quality depth was selectively removed in a continuous, uniform and safe operation. Additional programs are available on request to suit customer’s individual requirements, and the operator can also easily adapt and program the remote onsite to match a specific operation or set it to memorize and save specific working settings for future use.


Wan-Jet preset the Conjet ACR™ robot to selectively remove a minimum of 20mm from the old, worn-out concrete lining. At the end of each shift the mixture of concrete spoil and water was removed from the invert prior to a thorough cleaning and spraying of a new synthetic fiber-reinforced concrete coating.

The small, lightweight, water resistant robot is exceptionally maneuverable and can pass through an 850 mm wide opening making it ideal for working in small tunnels, culverts, canals and inside concrete box girder bridge decks. The versatile robot can also be used as a very efficient industrial cleaning machine, especially for applications in small spaces and other areas of restricted access.

The simple and easy-to-use Conjet ACR™ robot, developed by Conjet in close cooperation with the major Swiss hydrodemolition contractor Wan-Jet, has proved to be between four to five times more productive than a high-pressure hand lance. The remotely operated robot is also much safer to use in the very confined tunnel and produces a far more accurate and uniform surface finish than the results obtained with a handheld water jetting lance.

Customer case



MISSION:  Remove damaged concrete
from a water supply tunnel


Robot 557 MPA

For restorations of tunnels, Conjet ACR™ hydrodemolition robot 557 MPA is recommended. The robot features the latest technology in hydrodemolition. Combining the reach of Robot 367, the flexibility of Robot 327 and the diesel engine of Robot 437, this robot has it all.

Find the right solution for your structure

Fill out the form and we will get back to you with a tailor-made offer to your specific needs.

Copyright © 2024 Conjet . All Right Reserved.