Evaluation of full scale shear performance of tension anchor foundations: Load displacement curves and failure criteria

Abstract One of the biggest challenges faced by the offshore wave and tidal energy industry is the high cost of constructing and installing offshore foundations. Foundations based on post tensioned pile anchors can be effectively proposed to tackle this issue. A series of full-scale direct shear tests were performed on-shore to evaluate the shear resistance of post-tensioned pile anchor foundations designed for securing tidal turbine devices to a rock seabed. We focused, in particular, on the primary shear resistance mechanism of post-tensioned anchors, by applying a vertical force which mobilizes, a frictional force able to resist horizontal thrusts. Different load paths, involving monotonic or cyclic loading, were applied; several configurations for the footing of the foundation were tested. The footing stress-displacement behavior and the stress conditions at sliding failure from a number of different testing configurations were compared and analyzed. A marked consistency with the shear performance of natural rock joints was identified. This allows the behavior of tension pile foundations subjected to substantial horizontal loads to be modeled using relationships developed for rock joints, widely available in the literature. Additionally, the results obtained from different tests were also collated considering the various configurations adopted for the foundation-rock system and the applied load paths, to identify the factors that affect the shear resistance of the foundation.

[1]  E. T. Brown,et al.  EMPIRICAL STRENGTH CRITERION FOR ROCK MASSES , 1980 .

[2]  Subhamoy Bhattacharya,et al.  Dynamics of offshore wind turbines supported on two foundations , 2013 .

[3]  Michael E. Plesha,et al.  An investigation of the mechanics of rock joints—Part I. Laboratory investigation , 1993 .

[4]  Ralf Starzmann,et al.  Field measurements of a full scale tidal turbine , 2015 .

[5]  Friction of rocks , 1978 .

[6]  Roger Frank,et al.  Eurocode 7: Geotechnical design , 2011 .

[7]  Ali Pak,et al.  Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition , 2006 .

[8]  A. Serrano,et al.  Shaft resistance of piles in rock: Comparison between in situ test data and theory using the Hoek and Brown failure criterion , 2006 .

[9]  Subhamoy Bhattacharya,et al.  Vibrations of wind-turbines considering soil-structure interaction , 2011 .

[10]  Fred H. Kulhawy,et al.  Geomechanical Model for Rock Foundation Settlement , 2013 .

[11]  Ian W. Johnston,et al.  Shear Behavior of Regular Triangular Concrete/Rock Joints—Analysis , 1989 .

[12]  Marc Boulon,et al.  Experimental Study of Mechanical Behaviour of Rock Joints Under Cyclic Loading , 2004 .

[13]  Fred H. Kulhawy,et al.  Stress deformation properties of rock and rock discontinuities , 1975 .

[14]  Nick Barton,et al.  Review of a new shear-strength criterion for rock joints , 1973 .

[15]  C. Haberfield,et al.  Laboratory investigation of shaft resistance for piles socketed in basalt , 2004 .

[16]  J. C. Jaeger.  Friction of Rocks and Stability of Rock Slopes , 1971 .

[17]  N. Barton,et al.  The shear strength of rock joints in theory and practice , 1977 .

[18]  F. Patton.  Multiple Modes of Shear Failure In Rock , 1966 .

[19]  N. Barton,et al.  FUNDAMENTALS OF ROCK JOINT DEFORMATION , 1983 .

[20]  Stavros Bandis.  Experimental studies of scale effects on shear strength, and deformation of rock joints , 1980 .

[21]  Shane Donohue,et al.  Assessing the full scale performance of tension pile foundations under monotonic and cyclic shearing using direct shear tests , 2016 .

[22]  E. Alonso,et al.  Considerations of the dilatancy angle in rocks and rock masses , 2005 .

[23]  Abhijeet Shinde,et al.  Effect Of Salt Water On Compressive Strength Of Concrete , 2014 .

[24]  Robert Taylor,et al.  Marine micropile anchor systems for marine renewable energy applications , 2013, 2013 OCEANS - San Diego.

[25]  F. D. Blasio,et al.  Introduction to the Physics of Landslides , 2011 .

[26]  Xiangjun Qiu,et al.  A Theory for Dry Wear Based on Energy , 1991 .

[27]  J. C. Jaeger,et al.  Fundamentals of rock mechanics , 1969 .

[28]  D. F. Coates,et al.  Deformability of joints and its relation to rock foundation settlements , 1978 .

[29]  Nilanjan Saha,et al.  Coupled hydrodynamic and geotechnical analysis of jacket offshore wind turbine , 2015 .

[30]  G. Houlsby,et al.  Foundations for offshore wind turbines , 2003, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[31]  Marc Boulon,et al.  Evaluation of shear strength of rock joints subjected to cyclic loading , 2003 .

[32]  I. Owen,et al.  The effects of wave–current interaction on the performance of a model horizontal axis tidal turbine , 2014 .

[33]  A. Henry,et al.  The development of Oyster - a shallow water surging wave energy converter , 2007 .

[34]  A. Serrano,et al.  Shaft resistance of a pile embedded in rock , 2004 .

[35]  J. Chick,et al.  European Wave and Tidal Energy Conference , 2009 .