中国南海钙质砂蠕变-应力-时间四参数数学模型

Creep-stress-time four parameters mathematical model of calcareous sand in South China Sea

钙质砂是一种海洋生物沉积形成的具有特殊结构和力学性质的岩土材料,是我国南海岛礁吹填工程的物源材料。为进一步了解其蠕变特性,采用三轴流变仪对取自中国南海某岛礁的钙质砂进行不同围压条件下的长期蠕变试验研究。试验结果表明,在小于其破坏强度的恒定应力作用下,饱和钙质砂发生衰减蠕变,随时间增加,变形不断增加,但变形速率不断减小,直至变形稳定,所受应力越大则达到变形稳定所需时间越长,且蠕变变形量与所受偏应力正相关、与有效围压反相关。应力-应变与应变-时间均为非线性关系。试验研究发现,可采用幂函数对钙质砂蠕变应变-时间进行数学描述,基于试验结果,提出了一种蠕变应变与时间、偏应力和有效围压相关的四参数新的蠕变模型,可以对钙质砂的蠕变过程进行较好的数学描述;与经典的Mesri蠕变模型相比,所提出的数学蠕变模型不需要开展常规三轴压缩试验确定破坏时的峰值偏应力,减少了试验工作,具有一定的优势。

Calcareous sand, a type of geo-material with special structure and mechanical properties formed due to the marine biological deposition process, is the material used in the dredger filling engineering of South China Sea. To further understand its creep properties, a series of long-term creep tests under different confining pressures were carried out using triaxial rheological apparatus on calcareous sand sampled from a coral reef island located at South China Sea. Experimental results show that the damping creep of saturated calcareous sand occurs under constant pressure load that is less than the failure strength. The deformation increases with time, while the deformation rate decreases until the deformation becomes stable. The larger the applied stress is, the longer the deformation becomes stable. The creep deformation is positively correlated with the deviatoric stress, while it is inversely correlated with the effective confining pressure. The relationships of strain-stress and strain-time are nonlinear. It is found that the strain-time relationship of calcareous sand can be described by power function. A new creep model of calcareous sand, considering the relationships of four parameters(i.e. creep strain, time, deviatoric stress and effective confining pressure), is proposed in this paper.Compared with the traditional empirical Mesri creep model, it is unnecessary to perform the conventional triaxial test to determine the peak failure strength in the proposed new model. Less experimental work is required and thus it is much easier to be used.