Experimental Study on Behavior of Saturated Loose Sands Under Complex Shear Loading

摘要

Various stress-controlled monotonic and cyclic shear tests of loose sandrnunder various complex initial consolidation conditions and differentrnvariation pattern of shear stress are conducted by using the soil staticrnand dynamic universal triaxial and torsional shear apparatus. Influencesrnof such factors as coefficient of intermediate principal stress andrnorientation of principal stress on strength and deformation behavior arernexamined on the basis of monotonic shear tests. The variation patternsrnused in cyclic shear tests are able to reproduce the stress conditions inrnseabed under wave loading. Therefore the deformation behavior ofrnloose sand under complex consolidation condition subjected to cyclicrnloading is discussed. Based on the experimental data the followingrnconclusions can be given. (1) Under the application of monotonic shearrnstress, orientation of principal stress obviously influence the effectivernstress path and stress-strain relation of sand. When orientation of majorrnprincipal stress approaches the vertical, loose sand behaves hardeningrnwith dilatancy. When the orientation angle between major principalrnstress and the vertical become larger, loose sand displays noticeablernstrain softening with shear contraction and then strain hardening withrndilatancy etc. To compare with the effect of orientation of principalrnstress, influence of intermediate principal stress on shearingrndeformation behavior seems not obvious, but its effect on frictionrnangles mobilized both at phase-transformation state and at steady staterncannot be overlooked. Coefficient of intermediate principal stress hasrneffects of amplification and regionalization on the friction angle. Thernfriction angle under triaxial tension condition is considerably largerrnthan that under triaxial compression condition. (2) Under the conditionrnof cyclic loading, the influence of orientation of principal stress ofrninitial consolidation is remarkable. When pre-shear stress is imposed onrnthe application plane of dynamic stress, shearing deformation of loosernsand results mainly from the accumulated deformation. When no initialrnshear stress is applied on the application plane of dynamic stress, mostrnof shearing deformation is of cyclic nature, and the generalized shearrnstrain arises essentially from the axial strain caused by deviatoric stressrninduced by the difference of normal stresses in different directions.rnBased on comparison between the test results of monotonic and cyclicrnshear obtained from torsional shear tests, it is manifested that for thernsame initial stress state, the effective deviatoric stress ratio at steadyrnstate and the effective deviatoric stress ratio at phase-transformationrnstate are equal to each other respectively for both monotonic shear andrncyclic shear. Therefore, the effective deviatoric stress ratio at steadyrnstate and the effective deviatoric stress ratio at phase-transformationrnstate can be used as two characteristic parameters which are able tornrepresent the comprehensive influence of complex stress conditionrnincluding orientation of initial principal stress and coefficient ofrnintermediate principal stress for monotonic and cyclic shear conditions.