In the study, the creep characteristics and meso-mechanism of calcareous sand under different stresses are explored through triaxial creep tests. The influence of particle size on calcareous sand creep is also considered. Furthermore, the particularity of calcareous sand creep is revealed by comparing with the creep behavior of silica sand. The results show that during creep, the calcareous sand is more stable than silica sand due to the interlocking of irregular particles. When creep deviatoric stress is small, the creep of calcareous sand is manifested as nonlinear attenuation creep (primary creep), and the creep deformation is smooth without creep failure. With the increase of creep deviatoric stress, the creep deformation is concentrated, resulting in a strain concentration zone similar to the shear band, and the associated creep rate first decreases and then suddenly increases, finally, creep failure occurs. With increasing particle size of calcareous sand, the particle crushing increases, which induces a higher creep deformation, however, the overall creep failure is not generated. During the graded creep of calcareous sand, an obvious creep structural effect is observed, which is temporary and results in a significantly reduction of creep rate. Only after the previous creep structure effect is destroyed by the continuously creep process, the creep response can restore to its original behavior. The meso-behavior is represented by particle morphology, i.e., the fractal dimension and aspect ratio. It is found that both confining pressure and particle size can influence the evolution of particle morphology during creep. With the increase of confining pressure, the fractal dimension of calcareous sand decreases which means that particle grinding is always existent, while the aspect ratio of small-sized calcareous sand after creep decreases first and then stabilizes (slightly increases), suggesting that the overall particle breakage is the main cause of deformation. However, the aspect ratio of large-sized calcareous sand continually decreases, indicating that the main contribution for its deformation is angular cracking. The mesoscopic behavior of silica sand is basically unaffected by creep, and its creep deformation is mainly caused by particle rearrangement.

本研究通过三轴蠕变试验探讨了不同应力作用下钙质砂的蠕变特征和细观机制。还考虑了粒径对钙质砂蠕变的影响。此外，通过与硅砂蠕变行为的比较，揭示了钙质砂蠕变的特殊性。结果表明，在蠕变过程中，由于不规则颗粒的互锁，钙质砂比硅砂更稳定。当蠕变偏应力较小时，钙质砂的蠕变表现为非线性衰减蠕变（一次蠕变），蠕变变形平滑，无蠕变破坏。随着蠕变偏应力的增大，蠕变变形集中，产生类似剪切带的应变集中区，蠕变速率先减小后突然增大，最终发生蠕变破坏。随着钙质砂粒径的增大，颗粒破碎作用增强，引起更大的蠕变变形，但不会产生整体蠕变破坏。钙质砂的级配蠕变过程中，观察到明显的蠕变结构效应，该效应是暂时的，导致蠕变速率显着降低。只有在连续蠕变过程破坏了先前的蠕变结构效应后，蠕变响应才能恢复到其原始行为。细观行为由颗粒形态表示，即分形维数和纵横比。研究发现，围压和颗粒尺寸都会影响蠕变过程中颗粒形态的演变。随着围压的增加，钙质砂的分形维数减小，说明颗粒磨削始终存在，而蠕变后小粒径钙质砂的长宽比先减小后趋于稳定（略有增大），说明颗粒整体磨削断裂是变形的主要原因。然而，大粒径钙质砂的长宽比不断减小，表明角裂是其变形的主要贡献者。硅砂的细观行为基本不受蠕变影响，其蠕变变形主要是由颗粒重排引起的。