Abstract: To study the influence of suction and degree of compaction on the deformation of unsaturated filling soils, one-dimensional confined compression test of unsaturated soil was carried out to control suction condition and degree of compaction. Results show that the gentle stage of the compressive curve extends with the increase of compaction and suction, indicating the synchronously improved yield strength of soil samples. The saturated soil sample has the largest difference of the specific volume v during the test, and the dehydration soil sample changes the smallest. The greater the suction is, the smaller the difference of specific volume v is. Compressibility of compacted soil decreases after dehydrating or suction growth. The suction compressibility coefficient and its empirical model are defined and established to characterize the influence of suction and compaction on compressive characteristics and measure the influence degree. It is found that the model exhibits exponential decay with increasing the vertical stress. The relationship between the parameters of the model and relevant parameters of compacted soil are analyzed and discussed. The average value of the parameters corresponding to the different suctions of the same compacted soil sample decreases linearly with the increase of compaction level. The parameters generally increase with the increase of suction. However, with the increase of compaction degree, the contribution of suction to the compressive strength decreases and the experimental value point is close to the linear approaching line. The compressibility of soil samples is adjusted dynamically with the change of compaction and suction. Based on the basic principle of the layered summation method, a modified calculation model for the compressive deformation of the high fill unsaturated filling soils (MS) is established. The application of this model should be established on the study of the relationship between soil and water of unsaturated compacted filling soils on the loading state.

Key words: unsaturated loess, compaction degree, suction, load, compressive deformation, compressibility coefficient