Abstract: Creep deformation of rockfill materials is a key factor affecting the long-term safety of high earth-rock dams, and may lead to face slab voids, cracking and failure of the seepage control system. Existing creep models are mostly established on the basis of single-stage loading creep tests, thus hardly reflecting the loading–creep coupling effect, and there is a lack of systematic investigation into the influence of stress unloading on subsequent creep behavior. To this end, multistage loading creep tests of rockfill materials considering unloading were carried out. The results show that the post-unloading creep behavior can be divided into a positive creep zone, a no-creep zone and a reverse creep zone according to the unloading magnitude: in the positive creep zone, the creep deformation gradually decreases with increasing unloading magnitude until approaching zero; in the no-creep zone there is almost no creep development; after large unloading, slight reverse creep may occur. Under the post-creep-unloading condition, almost no creep occurs over most of the unloading range. Based on the accumulation rule of hardening creep strain, the influence of stress history such as loading and unloading on subsequent creep behavior can be uniformly characterized, and its applicability is verified by complex loading–unloading stress path tests. This study provides experimental basis and theoretical support for improving the creep theory of rockfill materials and predicting the long-term deformation of high dams, and has important reference value for engineering practice.

Key words: rockfill materials, loading-creep coupling effect, accumulation law, unloading