复杂应力路径下钙质砂颗粒破碎及抗剪强度特性

Particles breakage and shear strength characteristic of calcareous sand under complex stress path

对中国南海钙质砂开展了一系列复杂应力路径下的排水三轴剪切试验,系统研究了应力路径对钙质砂颗粒破碎和抗剪强度的影响机制。研究表明:钙质砂的各项力学特性均随着剪切加载方向的偏转呈现规律性变化,当应力路径处于加荷区,随着应力路径顺时针偏转,钙质砂的软化程度和抗剪强度逐渐增大、剪胀性降低、颗粒破碎程度增大、峰值内摩擦角减小。而应力路径处于卸荷区时,钙质砂破坏具有突然性,颗粒破碎程度也较大。存在“0初始应力影响”应力路径分界线,使得初始平均有效应力对其两侧应力路径区域内体变的影响完全相反。基于分形理论建立了不同初始平均有效应力、固结方式和剪切路径下预测相对颗粒破碎指标B_(r)值的经验公式,并揭示了应力路径和颗粒破碎耦合作用对钙质砂剪切行为的复杂影响机制。根据试验结果,应用广义加性模型(generalized additive model,简称GAM)推导了考虑颗粒破碎和应力路径影响的强度包线,可作为预测钙质砂在不同应力路径下峰值强度的依据。

A series of drainage triaxial shear tests under different stress paths is carried out on calcareous sand in the South China Sea.The particle breakage and shear strength characteristics of calcareous sand under complex paths are systematically studied.The research shows that the mechanical properties of calcareous sand change regularly with the deflection of the shear loading direction.When the stress path is in the loading zone,with the clockwise deflection of shear path,the softening degree and shear strength increase;the dilatability,the peak internal friction angles decrease,and particle breakage increases.When the stress path is in the unloading zone,the calcareous sand breaks suddenly,and the particle breakage is relatively large.There is a"0 initial average effective stress"stress path boundary,and the effect of initial average effective stress on the volume change on both sides is completely opposite.Based on fractal theory,an empirical formula for predicting B_(r)value under different consolidations,shear paths and initial average effective stress is established,and the complex influence mechanism of stress path and particle fracture coupling on the shear behavior of calcareous sand is revealed.According to the test results,the generalized additive models(GAMs)are used to derive the strength envelope considering the effects of particle breakage and stress paths,which can be used as the basis for predicting the peak strength of calcareous sand under different stress paths.