# Dynamic Characteristics of Post-Cyclic Saturated Loess
## 5 Conclusions  
This study proposes the effect of pre-cyclic and reconsolidation on the nonlinear dynamic characteristics of the saturated loess and illustrates the possible mechanism for the variation of the nonlinear dynamic characteristics during the strong earthquake and post-earthquake reconsolidation via microstructure analysis of the loess in different scenarios. Through simulating the physical processes of saturated loess under the strong earthquake and reconsolidation in the laboratory and conducting a series of dynamic triaxial tests, the impaction of pre-shock and reconsolidation action on the nonlinear dynamic parameters of the saturated loess was investigated. The following conclusions are drawn:  
1. Strong earthquakes may lead to a significant attenuation of the kinetic stiffness of the saturated loess. The variation of the \(G_{d}/G_{dmax}-\gamma_{d}\) curves before and after pre-seismic is more obvious in the large shear strain stage. With an increase in the OCR, the \(E_{d}\) of the saturated loess after pre-shock increased continuously. When the OCR reached two, the trend of \(G_{d}/G_{dmax}-\gamma_{d}\) curves of the pre-shock saturated loess was similar to that of the original saturated loess.
2. The \(D\) of the saturated loess tended to grow more obviously with the increase in \(\varepsilon_{d}\) after the action of a strong earthquake. The stability under the dynamic load tended to weaken. The influence of pre-shock on the \(D-\gamma_{d}\) curves was mainly manifested in the large shear strain stage. The action of reconsolidation can lead to a significant decrease of \(D\) at the same strain level, and the growth of the curve tends to flatten with an increase in the OCR. This effect is expressed in the whole shear strain range.
3. Compared with the original saturated loess, the \(G_{d}\) of the post-earthquake loess was significantly reduced and the \(D\) was obviously increased. The loess was more likely to be damaged when strong aftershocks occurred. Furthermore, the impaction of the reconsolidation on the nonlinear dynamic parameters of the post-earthquake loess is remarkable. The kinetic stiffness of the saturated loess is significantly enhanced after experiencing the over-consolidation, and its damage will be obviously weakened under strong aftershocks.
4. Strong earthquake caused the weakening of the connection between particles of the soil. In addition, the trellis pores were consecutive and the structure was rearranged. The changes in structure led to the enhancement of dynamic nonlinear of the saturated loess. However, the compaction effect of reconsolidation increased the interparticle friction and healed some microfractures, which led to the increased stiffness of the saturated loess.  
Conceptualization, Q.W. and W.M.; methodology, Q.W.; tests, Y.W. and W.M.; analysis, Q.W. and D.T.; investigation, Q.W. and D.T.; data processing, Q.W. and Y.W.; writing--original draft preparation, Q.W.; writing--revised draft preparation, Q.W. and W.M.; project administration, Q.W.; funding acquisition, Q.W. All authors have read and agreed to the published version of the manuscript.  
This research was conducted with the support of the Scientific Research Fund of Institute of Engineering Mechanics, China Earthquake Administration (Grant Nos. 2020D17, 2020 EEEVL0409), the Open Fund of State Key Laboratory of Frozen Soil Engineering (Grant No. SKLFSE202005), the National Natural Science Foundation of China (Grant No. 51778590), and the Fund of Creative and Innovative Talents of Gansu Province (Grant No. 2022 LQGR46).  
Not applicable.