Limited heights of vertical cliffs and mountain walls linked to fracturing in deep tunnels – An unconventional exploration of failure modes in rock masses
- Date: Friday 7 February 2020, 13:00 – 14:30
- Location: Roger Stevens LT 05 (7.05)
- Type: Seminars, Earth and Environment, Institute of Applied Geoscience
- Cost: £0.00
Dr Nick Barton will give a seminar on "Limited heights of vertical cliffs and mountain walls linked to fracturing in deep tunnels – An unconventional exploration of failure modes in rock masses".
Geoscience Seminar Title: Limited heights of vertical cliffs and mountain walls linked to fracturing in deep tunnels – An unconventional exploration of failure modes in rock masses.
Abstract: Intact brittle rock can fail in tension even when all principal stresses are compressive. This is due to lateral expansion and extension strain when near to a free surface, caused by Poisson’s ratio. Exceeding tensile strength due to stress anisotropy and Poisson’s ratio are the fracture-initiating conditions around deep tunnels, not the increasing mobilization of compressive strength, commonly beyond 0.4 x UCS. In a related discovery, the limiting height of vertical cliffs and near-vertical mountain walls can also be explained using extension strain theory. The range of limiting heights of approximately 20m for cliffs in porous tuff to record 1,300m high mountain walls in granite are thereby explained. Tensile strength is the weakest link behind cliffs and ultra-steep mountain walls. Sheeting joints can also be explained by extension strain theory. Maximum shear strength is the weakest link when stress levels are ultra-high, or when there is jointing and maximum slope angles is the issue. Rock masses do not fail by overcoming the addition of c and σn tan φ. There are multiple, displacement-dependent components of shear strength. The world’s highest mountains are limited to 8 to 9km. This is due to non-linear critical state rock mechanics. It is not due to UCS.
Bio: Nick Barton was born in England in 1944. He was educated in the University of London from 1963 to 1970: with B.Sc.(hons) in civil engineering from King’s College, and a Ph.D. in rock slope stability from Imperial College. He worked in NGI, Oslo from 1971-1980, and from 1984-2000, when he was a division director for 5 years and Technical Advisor for 10 years. From 1981-1984 he was manager of Geomechanics at TerraTek in Utah, USA. He was a visiting professor in the University of Luleå in Sweden, and in São Paulo Polytechnic University in Brazil in the nineteen-nineties. In 2000 he established the international consultancy Nick Barton & Associates in Norway. He is author or co-author of 330 papers, and has written two books. The first in 2000 was to develop the QTBM prognosis, the other in 2006 was to link rock quality and seismic attributes of rock masses. In 1973 he developed the Barton shear strength criterion linking joint roughness JRC and joint wall strength JCS, subsequently incorporating the gravity tilt test for calculating JRC. He is co-developer of the Barton-Bandis criterion for modelling coupled rock joint behaviour, published in 1985. In 1974 he developed the Q-system for characterizing rock masses and for selecting single-shell tunnel and cavern support. This was updated in 1993 with Grimstad to incorporate S(fr). He has consulted on several hundred rock engineering projects in 40 countries during almost 50 years, involving hydropower and metro tunnels and caverns, large dams, nuclear waste research and rock mass characterization, rock stress measurement, and jointed reservoir behaviour. He has thirteen international awards, including the 6th Müller Lecture in 2011. He is an honorary doctor of University of Cordoba, Argentina, and a Fellow of ISRM.