Deformation of sand in plane strain and axisymmetric compression

• Main Author: Thornton, Colin
• Published: Aston University 1974
• Subjects: 624.15; Civil Engineering
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545119

Small scale laboratory exper:iJnent s, in which the spec:iJnen lS considered to represent an element of soil in the soil mass, are essential to the evolution of fundamental theories of mechanical behaviour. In this thesis, plane strain and axisymmetric compression test s, performed on a fine sand, are reported and the result s are compared with various theoretical predictions. A new apparatus is described in which cuboidal samples can be tested in either axisymmetric compression or plane strain. The plane strain condition is s:iJnulated either by rigid side platens, in the conventional manner, or by flexible side platens which also measure the intermediate principal stress. Close control of the initial porosity of the specimens is achieved by a vibratory method of sample preparation. 'llhe strength of sand is higher in plane strain than in axisymmetric compression, and the strains required to mobilize peak strength are much smaller. 'rhe difference between plant? strain and axisymmetric compre ssion behaviour is attributed to the restrictions on particle movement enforced by the plane strain condit ion; this result s in an increase in the frict ional component of shear strength. The stre ss condit ions at failure in plane strain, including the intermediate principal stress, are accurately predicted by a theory based on the stress-dilatancy interpretation of Mohr's circles. Detailed observations of rupture modes are presented and measured rupture plane inclinations are predicted by the stress-dtlatancy theory. Although good correlation with the stress-dilatancy theory is obtained during virgin loading, in both axisymmetric compression and plane strain, the stress-dilatancy rule is only obeyed during reloading if the spec:iJnen has been unloaded to approximate (C3IJ1bient)stress conditions. The shape of the stress-strain curves during pre-peak deformation, in both plane strain and axisymmetric compression, is accurately described bv a combined parabolic-hyperbolic specification.