Abstract: In this article, the mechanical behavior of soft rock filling material for dam construction before and after degradation is investigated through laboratory tests at different consolidation pressures and compaction degrees. The degradation in strength and deformation characteristics of the rockfill material is analyzed. The relationship between degree of compaction and normalized strength, and the relationship between degree of compaction and normalized deformation modulus are built respectively. The controlling degree of compaction is also given for construction. Furthermore, according to results from underwater test of repose angle, the nonlinear strength, in particular, the strength at low stress state is studied. Research findings conclude that the degradation leads to the decline of volume strain,and poses larger impact on deformation modulus than strength;a 96% degree of compaction is reasonable for
soft rock filling material as it ensures a normalized strength larger than 0.9 and normalized deformation modulus larger than 0.8, and guarantees the compaction efficiency as well. Moreover, the strength parameters of soft rock filling material can be acquired from underwater repose angle test on compacted samples; and the nonlinear strength can be obtained through triaxial test. The research findings can be utilized to evaluating the stress-strain rules of rockfill dam built in soft rock and to providing guidance for dam construction.

Key words: soft rock, rockfill material, degradation characteristics, degree of compaction, nonlinear strength