Study On Dynamic Deformation Characteristics Of Remolding Red Clay Under Bidirectional Dynamic Loads

Red clay is a soil that is widely distributed in tropical and subtropical areas witn special engineering geology,in China,red clay is mainly distributed in the central and western parts,so it has positive significance for anti-seismic design in red clay areas to study dynamic characteristics of red clay.In the past,the research on the dynamic characteristics of soil is usually carried out by using dynamic triaxial apparatus under the unidirectional dynamic load,and using the stress on the surface of the 45° to simulation the horizontal shear load that produced by the seismic load for the soil when the shallow earthquake or weak earthquake happens,but when the deep source earthquake or strong earthquake happens,it is unreasonable that only consider reducing seismic load to horizontal shear load but ignore the tension and compression dynamic load caused by the seismic longitudinal wave on the soil.At present,the research on dynamic characteristics of red clay under bidirectional dynamic loads is not launched,but the traditional research that using unidirectional dynamic load to simulation seismic load has limitations.According to the research status above,in this paper,the dynamic deformation characteristics of red clay under bidirectional dynamic loads are explored by using SDT-20 dynamic triaxixal apparatus,and how the moisture content,consolidation stress,consolidation retio,radial vibration amplitude and phase difference affect the ?d-?d curves,dynamic shear modulus,dynamic shear strain,hysteretic curve and damping ratio is analyzed.The conclusions obtained from the experimental research are showed below:(1)When the consolidation stress is not at the same time,the ?d-?d curves shows diffrernt characteristics with the change of initial bidrectional dynamic load coupling,when consoladition stress is 100 kPa,the bigger of the radial vibration amplitude,namely the stronger of the initial bidrectional dynamic load coupling,the ?d-?d curves is steeper and higher in the early applying dynamic loading;when consoladition stress is 200 kPa and 300 kPa,with the stronger of the initial bidrectional dynamic load coupling,the ?d-?d curves is first steeper and higher and then slower and lower.(2)Under the bidirectional dynamic loads,the Gd~?d curves of red clay distributes in a small scale,but the Gd~N curves separate clear,dynamic shear modulus at the same cycle gets smaller with the rise of radial vibration amplitude;the increasing of consolidation ratio makes dynamic shear modulus at the same shear strain lager;the initial dynamic shear modulus of red clay first decrease and then increase with the increasing of the phase difference,and reaches to the lowest level at the phase difference of 180°.(3)The increase of radial vibration amplitude accelerates the the development of dynamic shear strain,while with the rise of initial shear stress and consolidation stress,dynamic shear strain at the same cycle becames smaller.The development speed of dynamic shear modulus first increase and then decrease with the increasing of phase difference,and reaches to the highest level at the phase difference of 180°.(4)Under the bidirectional dynamic loads,the hysteresis curve is crescent instead of oval,this is because the test date of dynamic triaxixal apparatus includes plastic deformation;under equipressure consolidation,moisture content and consolidation stress affect the failure mode of red clay,when the moisture content is low or consolidation stress is small,the tensile deformation develop faster,the specimen is tensile failure,while the moisture content is high or consolidation stress is big,the compression deformation develop faster,the specimen is conpression failure;the failure mose don't change but the hysteretic curve is left bias with the increase of radial vibration amplitude in a certain range,compression deformation are suppressed,this shows that the applying of radial vibration amplitude is conducive to the develop of tensile deformation.(5)The moisture content affects the damping ratio of the red clay,when moisture content is less than 20%,damping ratio increase with the increase of moisture content,while moisture content is more than 20%,the influence of moisture content on damping ratio can be neglected;the law that damping ratio change with the changing of radial vibration amplitude is not obvious;when dynamic shear strain is less than 1%,there aren't laws in the change of damping ratio,while dynamic shear strain is more than 1%,damping ratio is stable,this paper propuses than the damping ratio calculated in the stable equilibrium phase shoubled be used as reference.