含水率对湛江组结构性黏土触变强度恢复有显著影响,为探讨其影响规律及作用机制,以重塑湛江组结构性黏土为研究对象,开展为期150 d的触变试验,对不同初始含水率(30%、33%、36%、39%)和不同触变时间(0、1、10、30、60、100、150 d)的试样,分别进行无侧限抗压强度试验、直接剪切试验及扫描电镜试验(SEM)。结果表明:试样强度随触变时间的延长逐渐恢复,其中无侧限抗压强度和黏聚力的恢复过程均呈现快速明显(0~30 d)和缓慢平稳(30~150 d)两阶段。含水率越高,触变强度恢复速率越快。对比基于无侧限抗压强度和黏聚力的触变强度比率,由于剪切作用使土体颗粒沿特定方向排列,使黏聚力表现出更高的触变强度比率。触变过程中,孔隙参数(孔隙度、丰度)和颗粒参数(概率熵、分布分形维数)随触变时间增加而减小。土体颗粒通过自适应调整,定向性有序性增强,在范德华力作用下团聚程度提高,团聚体间和团聚体内孔隙减少。水分通过改变颗粒相对位置、扩宽迁移通道等方式增强了颗粒活动能力,加速了触变强度恢复速率。研究成果可为具有触变性的黏土地基稳定性评价提供参考依据。

[Objective] This study focuses on water content as the key controlling factor to clarify the time-dependent patterns of thixotropic strength recovery of Zhanjiang Formation structural clay under different initial water contents. The microscopic mechanism is interpreted through three pathways: pore structure evolution, particle reorganization, and water action. The findings are expected to provide experimental evidence and theoretical support for predicting strength recovery and evaluating the stability of thixotropic clay foundations. [Methods] Remolded Zhanjiang Formation structural clay specimens were prepared and subjected to a 150-day thixotropy test. Specimens at different thixotropic durations were investigated using macroscopic and microscopic tests. For macromechanical testing, unconfined compressive strength (UCS) tests were conducted on cylindrical specimens. Direct shear tests were conducted on ring-knife specimens to obtain UCS, cohesion (c), and internal friction angle (φ), which were used to evaluate thixotropic evolution. A thixotropic strength ratio was defined as A_t = m_t/m₀, and two indicators—A_t(q) (based on UCS) and A_t(τ) (based on cohesion)—were used to compare recovery characteristics among different strength parameters. For microstructure, fabric evolution was observed using an SEM. Pore parameters, including porosity (M) and abundance (C), were extracted to quantitatively analyze pore structure evolution. Particle parameters, namely probability entropy (H) and distribution fractal dimension (D), were used to quantitatively characterize particle orientation/orderliness and aggregation degree, respectively. [Results] (1) Stage-dependent recovery: Both UCS and cohesion (c) increased with thixotropic duration and showed two stages: a rapid and significant recovery phase during 0-30 d, followed by a slower, stable phase during 30-150 d. The increment during 100-150 d was small, indicating near-stabilization, after which the test was terminated. (2) Dual effect of water content: At the same thixotropic duration, UCS generally decreased with increasing water content, reflecting weakened particle contacts and bonding and thus reduced instantaneous strength. However, higher water content resulted in a faster strength recovery rate, especially at early stage, indicating that water promoted the kinetics of self-adaptive structural adjustment during thixotropic process. (3) Indicator-dependent differences: Cohesion exhibited a higher thixotropic strength ratio and faster recovery within 1 d, suggesting that shearing promoted directional particle alignment and optimized the friction-bonding interface, making c more sensitive to structural rebuilding than UCS. (4) Coordinated micro-parameter evolution: As thixotropic duration increased, M and c decreased continuously. Pores shifted from “large and numerous inter-aggregate pores” to “small and fewer intra-aggregate pores”, while the overall pore shapes remained mainly quasi-equant but became denser. Additionally, H and D decreased synchronously, indicating enhanced particle orientation/orderliness and increased aggregation. These changes were most significant within the first 30 d, consistent with the rapid macroscopic recovery stage. SEM observations revealed a transition from an “open flocculated-dispersed” fabric to a “closed flocculated-aggregated” fabric. Pores between and within aggregates decreased, while particle contacts and continuity of force-transfer paths improved, thereby supporting strength recovery. [Conclusion] The thixotropic strength recovery of Zhanjiang Formation structural clay exhibits distinct time-stage characteristics and strong sensitivity to water content. Recovery generally progresses through a rapid phase (0-30 d) and a stable phase (30-150 d). Higher water content reduces the strength level but significantly accelerates the strength recovery rate. Cohesion exhibits a higher thixotropic strength ratio than UCS because shear-induced particle orientation facilitates more effective structural reconstruction. Microscopically, synchronous decreases in M/C and H/D indicate pore reduction, particle ordering, and aggregation densification. Water enhances particle activity by altering relative particle positions and expanding migration pathways, thereby accelerating self-adaptive adjustment and strength recovery during thixotropic process. Innovations included: (1) parallel comparison of UCS and rapid direct shear parameters within a single thixotropic framework, revealing the cohesion recovery advantage caused by shear-induced particle orientation; (2) linking the macroscopic two-stage recovery pattern with the coordinated evolution of M, c, H, and D, forming an evidence chain of “structural rearrangement—aggregation densification—strength recovery”; and (3) demonstrating that higher water content, while reducing instantaneous strength, accelerates recovery by enhancing particle mobility/activity.