Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

Abstract

[1] The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by >3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60-70% smectites, 20-30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1-5 MPa normal stress, 2 × 10 −7 to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v < 5.0 × 10 −5 m/s to 0.12 at 1.31 m/s. Microstructural and mineralogical analyses of the gouge after experiments indicate that the dramatic weakening results from thermo-chemical pressurization of pore fluids (smectite decomposition to illite-type clays) and powder lubrication. In wet experiments, the coefficient of friction decreased from 0.17 at v < 1.0 × 10 −4 m/s to 0.0 at v > 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse.

Landslide Spreading, Impulse Water Waves and Modelling of the Vajont Rockslide

“…1a, b) and characterized by weak centimetre-to decimetre-thick smectitic clay levels (Hendron and Patton 1985), interlayered with thin micritic limestone of the Fonzaso Formation. Clay level strength was investigated under different degrees of saturations, total displacement and low to high slip rates (Skempton 1966; 16.67 lm s -1 , Hendron and Patton 1985; 0.24 lm s -1 to up to 0.08 m s -1 , Tika and Hutchinson 1999; 0.2 lm to 1.31 m s -1 , Ferri et al 2011). As a consequence, the determined friction coefficient varies within a relatively broad range from 4.4°to 22.3°(Tika and Hutchinson 1999), 5°to 16° (Hendron and Patton 1985), and finally from 1.7°to 37.2°and 0°to 36.7° (Ferri et al 2011) for peak and steady-state conditions, respectively.…”

Structure and lithology of the Japan Trench subduction plate boundary fault

“…Rock friction experiments show that smectite-rich materials are predominantly velocity-neutral or velocity-strengthening at low velocities [Saffer and Marone, 2003;Ikari et al, 2007;Faulkner et al, 2011;Ferri et al, 2011;Sawai et al, 2014;Ikari et al, 2015] and velocity-weakening at high velocities [Ferri et al, 2011;Faulkner et al, 2011;Ujiie et al, 2013;Sawai et al, 2014;French et al, 2014], with both characteristics promoted by water saturation. Distributed shearing has been associated with velocity-strengthening behavior in friction experiments [e.g., Beeler et al, 1996;Logan et al, 1992;Scruggs and Tullis, 1998].…”

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

“…More recently, CCAs have been recognized in the principal slip zones of the Chelungpu fault in Taiwan (Boullier et al, 2009) and the Tre Monti fault in Apennines, Italy . Based on high-velocity shear experiments, Boutareaud et al (2008Boutareaud et al ( , 2010 and Ferri et al (2010Ferri et al ( , 2011 suggest that CCAs could be a new textural indicator of large slip at co-seismic velocity with thermal pressurization. Boullier et al (2009) suppose that the presence of CCAs in TCDP samples indicate that the gouge was fluidized as a result of frictional heating and thermal pressurization.…”