揭示干湿循环作用下膨胀土力学特性的演化规律对防治膨胀土灾害有重要指导意义。提出了一种基于超微型贯入试验的土体内部力学特性研究方法，在干湿循环条件下对重塑膨胀土开展了一系列贯入试验，获得3次干燥过程中试样贯入阻力随深度和含水率的变化曲线。结果表明：（1）通过超微型贯入试验能够简单、快速和有效地掌握膨胀土在干湿循环过程中力学特性的时空演化特征；（2）试样的贯入阻力在干燥过程中总体呈增加趋势，相对于深部土体，表层土体的贯入阻力对干燥作用更加敏感；（3）干湿循环作用对膨胀土的力学特性有重要影响，随干湿循环次数的增加，膨胀土的贯入阻力总体上呈减小趋势，贯入曲线由单峰结构逐渐向多峰结构过渡，贯入阻力的空间差异性更加突出，且该现象在低含水率区间更加明显。基于土力学、土结构的基本理论以及试验中观测到的一些现象，对干燥过程和干湿循环作用下膨胀土的贯入力学特性进行了分析和探讨。干燥过程中土颗粒收缩靠拢、密实度和颗粒接触点增加及土吸力增加是导致膨胀土贯入阻力增加的重要原因，而干湿循环作用导致的土结构松散化、裂隙化则是引起膨胀土整体力学性质弱化的重要原因。

Revealing the evolution law of soil mechanical characteristics under wetting-drying cycles is highly significant for preventing the disaster of expansive soil. In this study, a method of super-mini-penetration (SMP) test for describing soil internal mechanical characteristics is proposed. A series of penetration tests is conducted on the remolded expansive soil specimens under cyclic wetting-drying conditions. The evolution law of penetration resistance with penetration depth and moisture content during three sequences of drying process are obtained. The results show that the proposed SMP test is a simple, quick and effective method to describe the spatiotemporal evolution characteristics of mechanical properties of expansive soil as subjected to drying-wetting cycles. The penetration resistance of the specimen generally increases with increasing drying time. Especially, the penetration resistance of the surface soil relative to the deep soil is more sensitive to drying. The effect of wetting-drying cycles on the spatiotemporal evolution characteristics of the mechanical properties of expansive soil is significant. With an increase in cycles, the penetration resistance of expansive soil decreases. The penetration curves gradually convert from typical mono-peak structure to multi-peak structure; and the spatial difference of penetration resistance becomes more evident, which is more obvious in the relatively low moisture content range. In addition, the relevant mechanisms of the penetration mechanical behaviour of expansive soil under drying and wetting-drying cycles are analyzed by drawing knowledge from soil mechanics and soil structure. During drying, the increase of the penetration resistance of expansive soil is mainly due to the decrease of porosity, the increase of soil density, inter-particle contacts and soil suction induced by shrinkage. The loose structure and cracks resulted by wetting-drying cycles are the main reasons responsible for the weakening of the overall mechanical properties of expansive soil.