中文摘要：

强胀缩性是膨胀性岩土的本质特性之一，开展膨胀土三向胀缩试验研究对于全面描述膨胀土湿胀干缩变形规律，合理分析边坡滑坍机理十分重要。利用自主研制的膨胀土三向胀缩测试仪，以宁明灰白色击实膨胀土为研究对象，通过开展三向胀缩系列试验，获得了膨胀土三向胀缩的基本规律。试验表明：干密度和三向应力状态是影响三向膨胀性的重要因素。随干密度的增大，膨胀土三向膨胀的差异性减小，膨胀势增大；应力越大，该方向的膨胀性越小，同时，一个方向应力的增减还将影响到其他方向，而宁明膨胀土三向收缩性差异不大，且与三向应力状态无关。

英文摘要：

Strong swell-shrink characteristic is one of the essential properties of expansive rock and soil. It is important to carry out the 3 D swell-shrink test of expansive soil for full descriptions of the wet swell and dry shrinkage deformation regularity of expansive soil and rational analysis of the slope failure mechanism. Using an independently developed expansive soil 3D swell-shrink test instrument, taking the Ningming gray compacted expansive soil as the study object, we carried out a series of 3D swell-shrink tests and obtained the basic 3 D swell-shrink regularity of expansive soil. The test result shows that （ 1 ） the dry density and the 3 D state of stress are the important influencing factors of 3 D swelling; （2） with the increase of dry density, the otherness of expansive soil 3D swelling decreases and the swelling power increases; （3） the greater the stress, the less the expansibility in that direction, and the change of stress in one direction can affect the change of stress in other directions, but the differences of Ningming expansive soil＇s 3D swell-shrink are little and are independent of 3D stress state.