Study On The Deformation Characteristics And Micromechanism Of Soft Clay Under Dynamic Loading

Soft clay ground settlement control is a key problem in construction because of the great demand of urban rail traffic construction in coastal areas and excessive settlement during operation period.Confirming the deformation characteristics and microcosmic mechanism of soft clay under dynamic loading is the precondition to achieve the aim of settlement control.As a result,a systematic research in basic theory is needed.The soft clay deformation characteristics of saturated undisturbed soft clay in Tianjin Binhai was studied,under different dynamic loading through GDS dynamic triaxial test.Based on the dynamic triaxial test,scanning electron microscopy(SEM)test and mercury intrusion porosimetry(MIP)test were conducted to analysis the microstructure characteristics under cyclic dynamic loading.The relevance between macroscopic and microcosmic was obtained to establish the cumulative plastic strain formula.The specific research results are as follows:The dynamic triaxial test shows that the accumulated plastic strain development mode can be divided into developmental mode and stable mode.Under the same vibration times,the larger the dynamic stress ratio,the larger the cumulative plastic strain,and the larger the initial residual strain,and the more obvious the residual strain decreased with the vibration times.The lower the vibration frequency,the larger the initial residual strain,and the faster the decreased with the vibration times.Besides,the development mode was more sensitive to the frequency.Under low frequency dynamic loading,the strain development changed from stable mode to developing mode.When the dynamic stress was relatively high,the clay showed the slight strain hardening.When the dynamic stress was relatively low,it was the strain softening.The vibration frequency had little effect on the final value of the change index of the dynamic elasticity modulus,while the initial attenuation of the dynamic elasticity modulus was obvious during the low frequency.The soft clay in the Tianjin Binhai presents a flocculation structure,and clay with a diameter of less than 20?m account for a large proportion.Under low vibration times,the clump particles were broken,resulting in the increasing roundness,decreasing fractal dimension,reducing size,random distribution,and the number of small pores and micropores increased,the total volume of intergranular pores increased,and the complexity of pore morphology increased.Under high vibration times,the particles were changed to the state of inlaid contact,the directionality was increased,and showed the flat shape,the decreasing roundness and the decreasing fractal dimension.The particles were reassembled again and the size increased.The pores were compressed,and the morphology complexity was reduced.The edges tended to be smooth,and the overall volume decreased with the configuration tending to be consistent.The average particle size increased with the increment of dynamic stress ratio and with the decrement of vibration frequency.Increasing the stress level reduced the porosity ratio,and the decrease rate of pore volume decreased with the increase of vibration frequency.However,the change of dynamic loading mode had little effect on the shape and directionality of particles and pores,and the change law was not obvious.According to the gray relative analysis,the cumulative plastic strain was influenced by the average pore size,average particle size and fractal dimension of pore morphology.Based on the exponential model of strain calculation,the microstructure parameters were introduced to establish the practical cumulative plastic strain calculation.