Study On Deformation Characteristics Of Lignin-lime Improved Silt Under Long-term Cyclic Loading

The Yellow River alluvial silt spreads over many parts of Shandong Province and mostly belongs to Group C railway embankment filling.According to the current railway subgrade design specifications,it must be improved before it can be used.In this paper,a series of cyclic triaxial tests were carried out on the lignin-lime improved Yellow River alluvial silt.The impacts of dynamic stress,additive proportion,confining pressure and compaction degree on permanent deformation,hysteresis loop and resilient modulus of the Yellow River alluvial silt were studied.The shakedown behavior of the test specimens was analyzed by using the shakedown concept and the energy dissipation theory.Finally,for the samples with different shakedown ranges,long-term cumulative strain prediction models that could reflect their strain development characteristics were established.The main conclusions of the study are as follows:(1)The main frequency of dynamic stress in the embankment and the bed structure can be taken as 1 times and 2 times respectively of the frequency of the basic disturbance wavelength of the train length;in the cyclic triaxial test,the dynamic stress in the subgrade structure can be simulated by full-pressure sine wave.(2)Compared with other types of soil,the treated Yellow River alluvial silt with 6%lignin + 3% lime under the same test conditions has the maximum shakedown limits and resilient modulus,the minimum hysteresis loop area and the best improvement effect.The plastic shakedown limit is greater than the dynamic stress generated by the train load in the general railway subgrade structure.(3)The hysteresis loop area and its shape of the test samples vary with shakedown ranges,additive proportions,confining pressures and degrees of compaction;the increase of confining pressure and compaction can reduce the permanent deformation and the unit volume dissipation energy,increase the shakedown limits and the resilient modulus,and reduce the attenuation of resilient modulus,which is beneficial to the stability of the subgrade structure.(4)Both the shakedown concept and the energy dissipation theory can classify the permanent deformation behavior of the lignin-lime treated Yellow River alluvial silt samples to three categories,plastic shakedown,plastic creep and incremental collapse,and the results of the two theories are in good agreement,these tow methods can be used in combination to classify deformation of specimens.(5)For the plastic shakedown and plastic creep specimens,the calculation models conforming to their deformation law were established to fit and predict the permanent deformation.