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主应力轴方向旋转变化是地基在波浪、车辆等荷载作用下经受的一种复杂而典型动力路径特征,为研究粉土在不同主应力轴方向变换条件下的强度特性差异,以初始密实度为70%的长江入海口饱和粉土空心试样为对象开展主应力轴旋转、拉压交变动三轴和双幅扭剪三轴试验。试验发现,等压固结条件下3种路径均使试样出现小应变崩塌液化破坏,且崩塌应力状态,可在p’-q空间中用近似平行的一组准不稳定相态线归一。而在液化和崩塌振次上,以同剪应力峰值的动扭剪下最高,动三轴次之,主应力轴旋转最低。在此基础上,提出采用崩塌损耗能对不同路径下土体动强度进行评价,结果表明,崩塌损耗能与剪应力幅值无显著关系,而在上述3种动力路径中,试样崩塌损耗能依次降低,这与3种路径下得到崩塌时刻递增的有效围压特征相匹配。崩塌能强度标准的采用,克服了复杂动力路径下由于剪应力恒定或循环变化造成应力水平无法统一而干扰强度评价的不足。
The rotation of the principal stress axis is a complex and typical dynamic path characteristic of the foundation subjected to loads of waves and vehicles. In order to study the difference in strength characteristics of silt under different principal stress axis transformation conditions, the initial compactness is 70% of the Yangtze Estuary saturated silt hollow sample as the object to carry out the principal stress axis rotation, tension and pressure to change the three-axis and two-frequency triaxial shear triaxial test. It is found that all the three paths under the condition of isobaric consolidation make the specimen liquefied by small strain collapse and the collapse stress state can be normalized by a set of quasi-unstable quasi-unstable phase lines in p’-q space . In the liquefaction and collapse vibrations, the highest shear force is the highest with the dynamic shear of the same shear stress, the second is the dynamic triaxiality, the lowest is the principal stress axis rotation. Based on this, it is proposed that the collapse loss can be used to evaluate the dynamic strength of soils under different paths. The results show that there is no significant relationship between the collapse loss and the amplitude of shear stress. In the three dynamic paths, the collapse loss energy Which in turn decreases, which matches with the effective confining pressure characteristics with increasing collapse time under the three kinds of paths. The adoption of the criterion of strength of collapse energy overcomes the shortcoming of the assessment of the disturbance intensity under the condition that the stress level can not be unified due to the constant shear stress or the cyclic change in the complex dynamic path.