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Title: Fast shearing of cohesive soils using ring shear apparatus
Author: Taylor, Paul
ISNI:       0000 0001 2409 2462
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1998
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Residual shear strength is a fundamental property of cohesive soils and is the governing parameter in many slope stability problems, particularly the reactivation of landslides. Traditionally, residual strengths are determined in the laboratory at slow drained rates of shearing using either shear boxes with reversals or ring shear apparatus. Many catastrophic landslides have been triggered by seismic loading inducing fast rates of shear. Interest has therefore developed in laboratory shear testing at faster rates and over greater displacements to establish fast residual shear strengths. This thesis presents results from testing using the Imperial College-Norwegian Geotechnical Institute Ring Shear Apparatus modified to conduct shearing at velocities up to 1 m/min. The variation of residual strengths as shear rate increases is investigated in association with soil grading and plasticity and also with the morphology of the shear zone. A novel set of undulating interfaces are used to investigate the influence of shear zone waviness. The research concludes that as shear rate is increased three types of fast residual shear strength variation may occur: (i) little variation from the slow residual shear strength, (ii) a continuous increase above the slow residual shear strength or (iii) an initial increase followed by a decrease to levels significantly below the slow residual shear strength. Increases in fast strength are attributed to particle disorientation and viscous effects. Falls in fast residual shear strength are attributed to the generation of positive pore water pressure in the shear zone, as a result of a pumping effect induced by wavy or inclined shear zones. Computational modelling of this pumping effect is undertaken using consolidation theory. Fast peak strengths and slow peak strengths after fast shearing are also investigated. Finally, the influence on slow residual shear strength of shear zones with undulations parallel to the shear direction are studied both mathematically, and using the Bromhead Ring Shear Apparatus.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)