Commissioning Of Compressive And Torsional Vibration Test Instrument And Dynamic Characteristics Of Loess Under Complicated Stress Conditions

The dynamic characteristics of soils, including the dynamic strength and deformation characteristics, are the basis of soil dynamics. Torsional Vibration shear triaxial apparatus is an advanced state of geotechnical equipment that is able to simulate complex initial stress conditions and complex cyclic shear stress. Therefore, it has the great theoretical and practical significance to correctly reveal the dynamic characteristics of soils by the adoption of advanced equipment.Based on predecessors research on the dynamics of loess and testing technology, on the one hand I was debugging the electro-hydraulic servo pressure-torsional vibration triaxial apparatus continuously that was developed by the Xi'an University of Technology,on the other hand the torsional vibration triaxial apparatus was applied to test the dynamics characteristics of loess under complicated stress conditions, including the loess dynamic strength, dynamic damage deformation properties, constitutive relations, and deepen the understanding of dynamic characteristics of loess.In the aspect of test equipment, through the researching actuality analysis of torsional vibration triaxial apparatuses at home and abroad the characteristics were expressed through comparing with different servo compressive-torsional drivers. The design principle of new electro-hydraulic servo compressive-torsional vibration test instrument was also discussed by the apparatus host structure, driver structure, compression and torsion coupling and independently loading in different direction. The new electro-hydraulic servo compressive-torsional vibration instrument has the advantage of decreasing the interaction effect between compression and torsion drivers. In the trial process of commissioning, the system friction effecting measurement precision was decreased through improving the measuring device connecting the load transducer, and the structure of defects in mainframe was improved through perfecting the work principle and producing the corresponding accessories. And the matching control procedure in the test-phase was developed by self. In the aspect of test study, the dynamic characteristics of Q₃ loess under complicated stress state was tested through the cyclic torsional shear test instrument.(I has studied the dynamic characteristics of Q₃ loess under complicated stress state through the cyclic torsional shear test instrument.) Based on the basic dynamics properties of loess and testing results, the dynamic strength change characteristic onÏ€plane in 3D space and the relationship between residual deformation and dynamic damage were investigated respectively. Test results show as follows. The stress-strain backbone curve of loess under the cyclic torsion shear test conditions is in softening, which reflect structure change impacting on the dynamic deformation. Because of the dynamic strength of loess related with the initial consolidation stress and the structure conditions, the dynamic strength curves and cumulative energy of loess are closely related to stress paths in different static and dynamic stress conditions; the vibration damage is also related to cyclic torsional shear stress path. Based on the strength analysis in 3D stress space of consolidation stress pulsing cyclic shear stress, the dynamic strength curves on the different q-p plane are linear and the intercept of line is near zero; the dynamic strength point located the place that between Mises curve and SMP curve. According to the analysis of loess damage changing cumulatively with cyclic loading, the loess's dynamic modulus, damping ratio and residual deformation modulus were investigated through introducing a damage ratio determined by cumulative consuming energy and total of consuming energy at failure.