侧限条件下钙质砂颗粒破碎与蠕变特征

Particle breakage and creep characteristics of calcareous sand with lateral confinement

通过侧限条件下的蠕变试验,基于近景摄影测量技术对试验过程的动态捕捉,探讨了钙质砂的颗粒破碎与蠕变特征。侧限条件下,钙质砂的蠕变随时间的增加而增加,蠕变变形与时间关系符合Burgers模型,蠕变变形可分为减速蠕变阶段和稳态蠕变阶段,即,蠕变速率随时间增加先减小,后稳定。钙质砂的蠕变特性受应力条件和粒径影响。轴向应力越大,蠕变速率和蠕变量越大;低应力下,蠕变量随粒径增大而减小;高应力下,受颗粒破碎的影响,钙质砂的蠕变以及蠕变速率均随粒径增大而增大。与硅质砂相比,钙质砂的蠕变在较低应力(≤0.1 MPa)时,由于钙质砂具有多棱角特性,颗粒间嵌固力较大,限制颗粒间位移产生,蠕变较小;随着应力增大,钙质砂开始产生颗粒破碎,增加了钙质砂试样变形,蠕变逐渐显著并超过硅质砂的蠕变。钙质砂的颗粒破碎特性随粒径和应力增大而增大,其中粒径>5 mm的试样在竖向应力0.7 MPa附近开始破碎;蠕变过程中的试样变形由完整颗粒和破碎后的颗粒沿裂隙和内外孔隙移动提供。

Based on the creep tests with lateral confinement and the close-range photogrammetry technology, the characteristics of particle breakage and creep of calcareous sand are continually captured and explored in this study. It is found that the creep deformation of calcareous sand increases with time which satisfies the Burgers model. The evolution of creep can be divided into two stages, the primary creep stage with the creep rate decreasing with time and followed by the steady creep stage with a relatively stable creep rate. The creep characteristics of calcareous sand are affected by stress conditions and particle breakage. The greater the axial creep stress, the greater the creep deformation and creep rate. Under low stress, the creep strain decreases with the particle size increasing due to the interlocking between the irregular particles;under relatively high stress, creep deformation and creep rate increase with the particle size increasing on account of the influence of particle crushing. Under the low stress(≤0.1 MPa), because of the interparticle locking in calcareous sand with irregular particle shape, the interparticle rearrangement is harder to occur, hence a smaller creep deformation is obtained for calcareous sand compared with siliceous sand. However, with the increase of stress, particles of calcareous sand begin to crush, and the creep deformation of calcareous sand increases and becomes more significant than that of siliceous sand. The particle crushing of calcareous sand increases with the rising of particle size and stress. The samples with particle sizes larger than 5 mm begin to break around 0.7 MPa of the vertical stress, and the creep deformation is provided by the rearrangement of intact particles and broken particles along cracks and pores.