Crack propagation tests are conducted on expansive soil under various temperature (15 °C, 20 °C, 25 °C, and 30 °C) and relative humidity (31%, 43%, 52%, and 67%) conditions. An innovative method for determining the volumetric crack rate is proposed, and the following conclusions are drawn. (1) The rate of water evaporation in soil samples plays a decisive role in the expansion of apparent cracks in expansive soil. (2) The higher the environmental temperature is, the higher the cracking water content and the lower the stable water content. When the environmental humidity is high, the lower the cracking moisture content is, the higher the stable moisture content. (3) There is a unified law for the expansion of apparent cracks in expansive soil under different environmental factors. The variations in the plane crack rate over time under different conditions are found to conform to the logistic law. (4) The volumetric fracture rate is a key indicator that comprehensively reflects the degree of fracture development. With increasing environmental temperature, the fracture volume increases from 9 to 11%. With increasing environmental humidity, the fracture volume decreases from 10 to 7.5%. (5) When the evaporation of water and the exchange of air reach equilibrium, the moisture stress in the soil is balanced, and the cracks expand to a stable state.

在不同温度（15°C、20°C、25°C 和 30°C）和相对湿度（31%、43%、52% 和 67%）条件下对膨胀土进行裂纹扩展试验。提出了一种确定体积裂纹率的创新方法，并得出以下结论。 (1)土样水分蒸发速率对膨胀土明显裂缝的扩展起决定性作用。 (2)环境温度越高，裂解水含量越高，稳定水含量越低。当环境湿度较高时，裂解含水率越低，稳定含水率越高。 (3)不同环境因素下膨胀土表观裂缝的扩展存在统一的规律。发现不同条件下平面裂纹率随时间的变化符合逻辑斯蒂定律。 (4)体积裂缝率是综合反映裂缝发育程度的关键指标。随着环境温度的升高，裂缝体积从9%增加到11%。随着环境湿度的增加，裂缝体积从10%减少到7.5%。 (5)当水分蒸发和空气交换达到平衡时，土体中的水分应力平衡，裂缝扩展至稳定状态。