###### Abstract  
Understanding the mechanical behavior of frozen clay subgrade soils was essential for ensuring the safe and stable operation of transportation lines. However, the influence of remolding water content \(w\) on this behavior remained unclear. To address this gap, this study examined the effect of \(w\) through monotonic triaxial testing. Three typical remolding water contents (\(w=19\%\), \(27.5\%\) and \(35\%\)) and three confining pressures (\(\sigma_{3}=200\) kPa, \(700\) kPa and \(1200\) kPa) were considered. Results showed that the mechanical behavior of frozen clay soils displayed a clear dependence on \(w\), which was controlled by microstructural evolution. As \(w\) increased, the shear strength \(q_{\text{max}}\), resilient modulus \(E_{0}\) and cohesion \(c\) increased, which resulted from the progressive development of ice bonding within the shear plane. A threshold \(w\) value was found at \(w_{\text{opt}}=27.5\%\), marking a structural transition and separating the variations of \(q_{\text{max}}\), \(E_{0}\) and \(c\) into two regimes. When \(w\leq 27.5\%\), the soil fabric was controlled by clay aggregates. As \(w\) increased, the growth in ice cementation was confined within these aggregates, leading to limited increase in \(q_{\text{max}}\), \(E_{0}\) and \(c\). However, as \(w\) exceeded \(27.5\%\), the soil fabric transitioned into a homogeneous matrix of dispersed clay particles. In this case, increasing \(w\) greatly promoted the development of an interconnected ice cementation network, thus significantly facilitating the increase in \(q_{\text{max}}\), \(E_{0}\) and \(c\). The friction angle \(\varphi\) decreased with \(w\) increasing, primarily due to the lubrication effect caused by the growing ice. In addition, the enhanced lubrication effect in the clay particle-dominated fabric (\(w>27.5\%\)) resulted in a larger reduction rate of \(\varphi\). Regarding Poisson's ratio \(v\) and dilation angle \(\psi\), the \(w\) increase led to growth in both parameters. This phenomenon could be explained by the increased involvement of solid ice into the soil structure. clay soils; frozen soils; remolding water content; soil microstructure; mechanical behavior 202020251579 railway/highway construction in seasonal frozen soil area. As an essential part of the railway/highway structure, the subgrade played an important role in load bearing, and its mechanical behavior was crucial for ensuring the safe and stable operation of transportation lines. Till now, the relevant aspects have drawn many attentions and were widely investigated [1; 2; 3], and these studies were the basis for numerical modeling [4]. During the subgrade construction, the clay soils were usually used as fillings materials. According to the JTG D30-2015 [5], the compaction of clay soils should be carried out at optimum water content \(w_{\text{opt}}\). However, owing to complex in situ construction conditions, the actual remolding water content \(w\) during compaction could not be strictly controlled and differed across different sites, which caused variations in soil fabric [6; 7; 8]. Such variations in soil structure have been shown to significantly influence the mechanical behavior of thawed soils. Moreover, after being frozen, the mechanical behavior of frozen clay soils might exhibit variability. From a practical point of view, this aspect should be studied. Till now, many investigations have been carried out on frozen fine-grained soils. [PERSON] et al. [9] investigated the strength of the frozen clay soils at the water content corresponding to the in situ one, and found that under high confining pressure, the stress-strain behavior exhibited characteristic of strain hardening. In the study of [PERSON] et al. [10] with silty clay at one given water content, it was found that the increase in confining pressure enhanced the plastic deformation capacity of frozen soils. [PERSON] et al. [11] and [PERSON] et al.