基于不同初始静偏应力的结构性软黏土动力特性试验研究

Experimental Study on Dynamic Characteristics of Structural Soft Clay Based on Different Initial Static Deviatoric Stress

以天津滨海新区结构性海积软土为研究对象,采用GCTS动静扭剪试验仪,基于正弦波与方波两种波形,在固结排水条件下施加不同初始静偏应力,通过考虑循环振次、应力幅值、振动频率以及围压等因素对土体结构的影响,研究结构性软黏土的动力特性。试验结果表明:初始静偏应力小于土体初始屈服应力时,施加静偏应力增加了土体固结度,提高了其结构强度,应变软化现象减弱,累积塑性应变曲线中屈服点对应的应力值大。初始静偏应力大于土体初始屈服应力时,土体初始结构破坏,出现严重的应变软化现象,累积塑性应变曲线迅速由稳定型转变为临界型,且在同条件下,方波应变值始终大于正弦波。孔压变化与初始静偏应力有关,随着静偏应力增大其孔压滞后现象严重。土体屈服应变随初始静偏应力增大而增加,静偏应力及振次相同时,方波作用下的土体屈服应变值小于正弦波。两种波形下,土体屈服应变随振次增加均呈减小趋势,且最终均会趋于一点,正弦波趋于相同数值下的振次远大于方波。土体动强度随应变标准提高而呈现增大趋势,应变标准为屈服应变值时,动强度曲线表现为先陡后缓,其他应变标准下动强度曲线较为平缓。两种波形下的动强度随振次增加而减小,最终均会趋于一点,且正弦波值大于方波。

Taking the structural marine soft clay in Tianjin Binhai new area as the research object,using GCTS dynamic/static torsional shear apparatus,based on the wave forms of sine wave and square wave,different initial static deviatoric stresses are exerted under consolidation drainage condition. Considering the influence of vibration times, stress amplitude, vibration frequency and confining pressure on the soil structure,the dynamic characteristics of structural soft clay is studied. The test result indicates that（ 1）when the initial static deviatoric stress is less than the soil initial yield stress,under deviatoric stress,the consolidation degree of soil could be strengthened and the structural strength could be increased,while the strain softening is decreased,the stress value corresponding to the yield point in accumulative plastic deformation curve is large;（ 2） when the initial static deviatoric stress is larger than the soil initial yield stress,with the damaged soil initial structure,the strain softening phenomenon is severe,the accumulative plastic deformation curve transforms from stable type into critical type immediately,and the square wavestrain value is always larger than the sine wave strain value under the same condition;（ 3） the pore pressure change is associated with initial static deviatoric stress,the pore pressure lagging phenomenon is serious with the increase of static deviatoric stress;（ 4） soil yield strain increases with the increase of initial static deviatoric stress,the yield strain under square wave is less than the value under sine wave with same static deviatoric stress and vibration frequency;（ 5） under 2 kinds of waveforms,the soil yield strain decreases with the increase of vibration frequency,and eventually tends to a point,and the vibration frequency under the same value tend of sine wave is larger than that under the same value tend of square wave;（ 6） the dynamic strength increases with the increase of the strain standard,the dynamic strength curve is steep at first and then slow when the strain criterion is the yield strain value,and the dynamic curve is gentle under other strain criterion;（ 7） the dynamic strengths under 2 waveforms decrease with the increase of the vibrational frequency,and eventually tend to a point,and the sine wave value is larger than the square wave value.