To investigate the expansion deformation of predisintegrated shale as subgrade soil and develop a calculation model to describe its expansion characteristic, the nonloaded and loaded expansion tests as well as expansion force tests were conducted on the typical predisintegrated shale under varying conditions. The results show that the expansion rate of compacted predisintegrated shale is greatly affected by initial water content, dry density, and overburden load, and that its expansion characteristics can be divided into three stages. After compaction, the expansion force of predisintegrated shale has a strong correlation with the initial dry density and initial water content, and 1.45 gcm(-3) can be used as threshold density for the rate of expansion force growth. Moreover, a comprehensive calculation model for the expansion rate and expansion force considering the coupling effects of various factors was proposed. This study proposes an alternative subgrade material using shale, which can efficiently save land resources and reduce engineering costs.

Expansive soil due to wet expansion and dry contraction of engineering properties, resulting in the stability of the riffle slope, has been one of the key issues in the expansion of soil area earthworks; this paper, through the three representative riffle slope site field visits and indoor tests, respectively, from the dry bulk weight, unconfined compressive strength, three-way expansion force and expansion with the change rule of the depth of the law to be explored. The three-way expansion force test shows that the extension and proximity direction of the horizontal expansion force are the same. The vertical direction is greater than the horizontal direction, and its ratio is about 0.5. Further analysis of the relationship between the characteristics of the parameters with the depth can be seen: the surface soil indicators are more varied, between 0.5 and 1.0 m, the soil layer dry density is small, the expansion of the soil wet expansion and drying shrinkage is significant, and the unconfined compressive strength is close to or has reached the lowest value; expansion force and expansion volume test indicators along the depth of the graben slope, the expansion force and expansion volume test indicators are more varied. Expansion force and expansion amount test indexes change along the depth of the riffle slope but remain unchanged after 2.0 m. Therefore, the damage of the expansion soil riffle slope mainly occurs in the soil layer near the depth of 1.0 m, which is manifested explicitly as a failure to adapt to the change of stress in the soil and the inability to adjust to the atmospheric natural camping force.