Natural marine clays exhibit distinct dynamic behavior compared to remolded counterparts due to their inherent structural properties. Dynamic and static triaxial tests were conducted on both marine clay types to evaluate stress-strain behavior, double amplitude strains, pore water pressure, and dynamic elastic modulus, as well as post-cyclic strength attenuation. The results indicate that due to the structural properties, the effective stress path of undisturbed samples is more ductile than that of remolded samples. Also, there is a clear inflection point in the strain development curve of undisturbed samples. The structure exerts a certain degree of restraint on the strain development of the undisturbed samples, and has a distinct impact on the variation of pore water pressure at varying dynamic stress levels. Both marine clay types exhibited gradual reductions in dynamic elastic modulus and marked undrained strength attenuation. Critically, the attenuation of dynamic elastic modulus in undisturbed samples aligned with post-cyclic strength loss, while remolded samples exhibited greater dynamic elastic modulus loss relative to strength degradation. These findings clarify the role of soil structure in cyclic response and strength degradation, offering insights for the long-term stability assessment of structures and disaster mitigation in marine clay engineering.

Soil compaction has been found to deform soil structures and alter water flows. Although previous studies have suggested that a load exceeding the critical stress, determined by static load application, can be applied for a short duration without causing substantial damage to the soil structure, the immediate consequences of short loading times on structural integrity and the subsequent influence on soil water flow remain relatively underexplored. The principal objective of this research was to explore the effects of loading intervals, ranging from 0.1 to 2.5 s, commonly used by vehicles and machinery in the agricultural sector, on the changes in water-stable aggregates and saturated hydraulic conductivity (K-sat) associated with soil compaction, thereby enhancing our understanding of how transient external forces could affect the soil properties. Four distinct soils with varying soil organic matter (SOM) contents (13, 43, 77, and 123 g/kg) were collected from a typical Mollisol area in Northeast China, each characterized by different initial gravimetric soil water contents of 11%, 15%, 19%, and 24%, respectively. Under an applied load of 4.0 kg/cm(2), the short loading time resulted in an increase in small macroaggregates (SMAs) and a decrease in microaggregates within the distribution of water-stable aggregates, whereas it did not affect aggregate stability. K-sat decreased significantly (p < 0.05) as the loading time increased from 0.1 to 2.5 s. The effects of loading time and SOM on water-stable aggregates with particle sizes exceeding 0.25 mm, mean weight diameter, geometric mean diameter, and K-sat were identified as statistically significant or highly significant (p < 0.05 or p < 0.01). Notably, the initial soil water content remained unchanged during the short compaction period. A significant negative correlation was identified between SMAs and K-sat for each soil, with the loading time and initial soil water content (correlation coefficients ranging from -0.834 to -0.622). The results, combined with the structural equation modeling analysis, indicated that both a short loading time and SOM could directly increase SMA and decrease K-sat, with both factors influencing K-sat through SMA during the soil compaction process. This suggests that the loading time and SOM during a short duration under the same external force, rather than initial soil water content, can determine the potential degradation of the soil.

The traditional view of Na+ as harmful and Ca2+ as beneficial doesn't always apply in multi-cationic soil solutions. Initially, adding Ca2+ promotes Na+ leaching, reducing salinity, but excess Ca2+ becomes counterproductive. As Na+ leaches, the soil's Ca2+-Na+-Mg2+ mix shifts to Ca2+-K2+-Mg2+, Ca2+'s function changes, even causing the opposite effect. To investigate the complex mechanism of Ca2+ to Na+-Mg2+ and K+-Mg2+, we conducted an indoor soil column experiment using saline water (4 dS m(-1)) with different cation compositions [Na+-Ca2+-Mg2+ (NCM), Na+-Mg2+ (NM), K+-Ca2+-Mg2+ (KCM), K+-Mg2+ (KM)] and deionized water as the control (CK). The results showed that NM exhibited the highest crack volume, while KM had the greatest macropore volume, with NM having approximately 15 % more crack volume than KM. Notably, only NM displayed a more pronounced inclination towards pore anisotropy value of 0 when compared to CK. NCM and KCM had higher pore anisotropy values than NM and KM. KM and KCM had more cracks angled ranging from 45-90 degrees than NM and NCM. KCM notably decreased transitional macropores 0.05) observed in widths < 2.5 mm between KCM and KM. NM displayed the shallowest macropore distribution and the highest variability in macropore length among all treatments. Only NCM showed significantly reduced variability in both macropore length and width compared to CK. In summary, Ca2+ exhibited distinct action patterns on K+-Mg2+ and Na+-Mg2+. For specific soil types and cationic compositions, Ca2+ may not fully exert its amendment effects. However, Ca2+'s effect is soil-specific, necessitating comprehensive studies across varied soil types.