Bentonite in Microtunneling – Consortium Le Vertiaz

Introduction

Bentonite slurry in no dig excavation technologies plays a fundamental role in soil conditioning and in the lubrication of jacking pipes.

Its correct management therefore allows to obtain multiple benefits:

• Extend the excavation life of the mud itself by reducing the additions with fresh mud;
• Reduction of friction during the pushing phases;
• Properly condition the soil in the excavation chamber;
• Support the face under pressure, waterproofing the walls.

The Project

The project we are partnering with is the Swissgrid Tunnel in Martigny, canton of Valais in Switzerland.

The client is Swissgrid SA, and sees Pini Group – a Swiss Engineering company involved in the planning and supervision of the works and for the technical and commercial management CSC – Webuild participates as a partner of the consortium.

The Road and Civil Construction company S.A. – CSC SA – was founded in 1960 in Lugano and has always been part of the Webuild group.

Pini Group is a civil engineering firm leader in the sector of underground works, with more than 70 years of experience

Project details

The project concerns the undergrounding of the 380kV cables that cross the Rhone plain in the Martigny area. This involves connecting the new La Bâtiaz substation to the 380 kV Chamoson – Romanel overhead line at the height of pylon 51 in Le Verney.

Construction Technology

The excavation of the approximately 1,200 m long tunnel is carried out by means of a pipe pusher with AVN Machine of Ø 3.0 m. The route includes the passage of some critical points such as the motorway, the CFF railway line, the discharge channel of the Emosson plant, the cantonal road and the TMR railway line.

The project area is characterized by loose material from the plain consisting mainly of fluvial-glacial sediments (torrential, morainic, fluvial, lake and flood deposits). The project aquifer is located one meter below the ground level.

Laviosa

Laviosa is present as a partner on the construction site for the supply of T-LINE bentonite products and additives for excavation, both for the TBM head and for lubrication.

The product used is the BENTOSUND 120E TM, natural sodium bentonite free of any extension in polymer.

Laviosa is also present on the construction site with its portfolio of products for dewatering bentonite slurry, with its DEWATERING LINE, a range of coagulating and flocculating products.