# Dynamic Characteristics of Post-Cyclic Saturated Loess
## 2 Methodology
### Test Methods  
The test methods of the dynamic triaxial tests (including pre-shock tests) follow the Chinese Code GB50123-2019 and the ASTM Code ASTM D3999-2003 [42; 46]. The process of pre-shock is simulated using the WF-HCA. Firstly, latex film is wrapped around the sample with a film-bearing cylinder. Then, a permeable stone and a filter are put successively on the sample platform of the WF-HCA. The specimen coated with latex film is carefully placed on the filter paper, and another filter and permeable stone are put on top of the specimen. Make sure the second permeable stone just touches the top seat by adjusting the height of the sample platform. The two ends of the latex film are respectively set on the sample platform and the top seat and tied tightly with rubber rings to prevent water leakage. The chamber is filled with water and the surrounding pressure is simulated by the air-water conversion system. All sensors need to be zeroed out. Before pre-shock tests, the specimen should be pre-consolidated to simulate the original stress state. The axial pressure is determined based on the natural density and sampling depth of the samples. A noninotropic consolidation mode was adopted for the specimens, and the coefficient of cell pressure was 0.59 [1]. The standard for sample consolidation stability is determined when the axial strain within 1 h is no more than 0.01%. After the sample is stabilized, a sinusoidal load with a frequency of 1 Hz is conducted on the sample in axial for cyclic shearing. The amplitude of the load is calculated based on Equations (1) and (2) [25; 30; 47] where \(\sigma_{d}\) is the dynamic stress; \(\tau_{d}\) is the dynamic shear stress; \(a_{max}/g\) is the seismic coefficient, indicating the ratio between the peak ground acceleration (PGA) and the gravitational acceleration. Figure 5: Test instruments: (**a**) the WF-12440 dynamic triaxial torsional shear test system, and (**b**) the KYKY-2800B scanning electron microscope. is the reduction coefficient of depth, which can be calculated according to Equation (3); \(\gamma\) is the unit weight of the soil; \(d\)s is the depth of the soil sample. \[\sigma_{d}=2\tau_{d} \tag{1}\]  
\[\tau_{d}=0.65\frac{a_{max}}{g}.k_{d}.\gamma\cdot d_{s} \tag{2}\]  
\[k_{d}=1-0.00765d_{s} \tag{3}\]  
To make sure the damage of the pre-shock action on the soil was more obvious and to increase the comparability of the test results, the seismic coefficient \(a_{\max}/g=0.4\) was taken in this study by considering the historical strong earthquakes and the seismic ground motion parameter zonation results in the study area [48; 49]; it is indicated that there exists strong earthquake action with a simulated earthquake intensity of IX degree. Therefore, the maximum cyclic number for the pre-shock test is 30 [50]. The pre-shock specimens are removed from the platform carefully. Plastic bags are placed on the specimens with the wrapped latex film, and then the bags are tied tightly and placed in a dry dish for 24 h before the dynamic triaxial tests. After that, the specimens are placed again in the chamber of the WF-HCA in the same way as the pre-shock tests. Then, the specimens are saturated on the WF-HCA using a backpressure saturation method. A small cell pressure (approximately 20 kPa) is loaded on the specimen, and then the degassed water is drained into the specimen from bottom to top to fully discharge the air inside it. After the air in the specimen is fully discharged, a series of confining pressure and back pressure is alternately uploaded to the specimen step by step, and the degassed water is drained after each level of the back pressure. Furthermore, the B value is measured after the next cell pressure upload to determine the saturation degree of the specimens. The specimens are determined to have fully saturated when the B value reaches 0.95. An isotropic consolidation method is used to consolidate the specimens, and the axial pressure is calculated based on the saturation density and sampling depth of the specimens [3].