Breakthrough at the Ritom inclined shaft
Breakthrough at the Ritom inclined shaft

Breakthrough at the Ritom inclined shaft

The Ritom power plant in Ticino, which was built in 1920 and is located only a few kilo­meters from the Gotthard Tunnel, is in need of re­newal. Since 2018, a number of con­tract­ors from the Marti Group have been working on this over­all complex re­novation on behalf of Ritom SA. In February 2022, Marti will pass an important mile­stone with the break­through of the inclined shaft to Lake Ritom.

It is Wednesday, February 23, 2022, shortly before half past ten in the morning. The miners from Marti Tunnel are anxiously waiting for the rotating drill head of the tunnel boring machine (TBM) to stop. Just a few minutes earlier, the TBM broke through the shaft wall of the slide cavern in Piora at the top. The valve cavern structure is located 40 m under­ground and only a few meters from Lake Ritom. Some 800 m further down in altitude, the invited guests at the Piotta portal in the start cavern are en­thralled by the moment as it un­folds via live­stream. The time has now come; the machine is stopped and the first member of the tunneling crew climbs through the narrow manhole. With cheers and applause, he hands over the statue of St. Barbara to his colleague, who is already waiting for him on a ladder, in keeping with the old tradition. One by one, the remaining crew members climb out of the machine. They are received by their com­rades, who are visibly moved and highly emotional. After all, the journey they have come on has not been an easy one.

Pressure Gallery from Piotta to Piora

Work on the pressure gallery for the re­novation of the Ritom power plant in Piotta started with the ex­cavation of the lower pressure gallery in 2019. Here, some 600 m were ex­cavated at a gradient of approx. 0.5 % using under­ground blasting. After about 450 m, the tunneling crew came across a massive water inrush, with up to 200 l/second entering the gallery. This forced them to stop driving operations temporarily. They employed an in­jection campaign that spanned several months to combat the water and seal the tunnel so that it could be ex­cavated again. At the end of 2020, the start and assembly cavern at the end of this pressure gallery was completed. There, the TBM was assembled and pre­pared for driving on a starting ramp. The gripper TBM, with a dia­meter of 3.2 m, was de­veloped by Herrenknecht AG in collaboration with Marti specialists specifically for the construction of this sloped shaft. Thanks to the back­loading drill head and a double, mechanically self-locking back­loading system, it meets the highest safety standards. Ventilation installations were also added to the greatest extent possible and the work­stations were optimized for the slope.

In March 2020, the TBM started driving operations toward Lake Ritom. The slope started at 42 % (just under 23°) and after about 800 m, the slope was increased to 90 % (42°) within a radius of 150. 451 m after the start cavern, the machine drove into a rough fault, a cleft with loose rock. The ex­perienced crew assessed the situation with exploratory drilling and stabilized the cavities with spiles and cement in­jections. Once this had been secured, it was possible to pass through the fault zone. Steel liner plates ensured that the machine was securely braced during the critical phase. Alarmed by this in­cident, the company carried out ex­ploratory surveys on the rest of the route to check for ex­pected fault zones and to secure them in advance. Although this led to delays, it also prevented pro­longed down­times.

“I am ex­tremely proud of what our people are ac­complish­ing here.”
Sergio Massignani,
Project Manager, Marti Tunnel

The Diversity of the Marti Group

While digging takes place in the mountain, various other operations for the over­all project are running at the same time. At the portal in Piora near Lake Ritom, Marti Tunnel constructed the valve cavern with a 40 m deep shaft leading to it. This part of the con­struc­tion site is difficult to access in winter. Due to the danger of ava­lanches, the access road is partially closed and the team is flown in by helicopter. The supply of con­struc­tion materials and equipment is, however, ensured at all times via the material rope­way.
The Marti Basel metal­working facility produced structural steel­work and infiltration elements for the portal in Piora. Marti Technics Ltd. also particip­ated in fitting out the start tube and ramp and provided the conveyor belt and silo for the ex­cavated material. In the start cavern, a se­paration system from Simatec separates the excavated material from the water and Alwatec then en­sures optimum waste­water treat­ment. Stump BTE carried out the ex­ploratory drilling in the gallery leading to the start cavern, which allowed the geo­logy from the water infil­tration to be invest­igated in greater detail. The professionals from Marti Geotechnik GmbH (Renesco) used these exploratory surveys as the basis to plan and carry out the necessary injection work. Last but not least, Mancini & Marti is in charge of the inner lining of the new power plant control center and the civil engineering work on the equalizing basin together with a construction consortium partner in the outer area.

Thanks to the diversity of the Marti Group, the response times through­out the project were and are short and efficient. It was possible to solve virtually all difficulties quickly and without un­necessary red tape, thanks to the internal ex­pertise and with the ex­perience and know­ledge of the seasoned professionals. The work in the sloped shaft in particular requires tremendous physical per­formance by the tunneling crew. Sergio Massignani, project manager at Marti Tunnel, is naturally exceedingly proud of his team. After all, building a sloped shaft at this inclination is a very particular challenge that does not arise every day. During his short speech, he praises and thanks the team ex­tensively before the TBM breaks through the last few meters.

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