混合均匀度对粗粒土强度特性影响的试验研究

Study on strength characteristics of coarse-grained soil considering influence of mixing uniformity

现有研究普遍将粗粒土视为均匀的二元混合料,忽略了粗细颗粒混合均匀程度对其强度特性的影响。为此,首先,提出了一种描述粗粒土混合均匀程度的定量指标Me;其次,通过静三轴试验探讨了应力-应变曲线、弹性模量、破坏强度及抗剪强度指标与混合均匀度Me的内在关系;最后,基于静三轴试验结果,建立了一种综合考虑围压和Me影响的修正邓肯-张模型,并对其适用性及合理性进行鲁棒性验证。研究结果表明:应力-应变曲线随着围压增大而逐渐由应变软化型向应变硬化型曲线过渡;随着Me减小,应力-应变曲线由应变硬化型逐渐发展为应变软化型曲线;当围压与Me增大时,弹性模量与破坏强度均随之增大,且弹性模量在Me从0.25降低至0的过程中衰减幅度可达总衰减幅度的41.3%,破坏强度在Me从1降低至0的过程中衰减幅度可达总衰减幅度的40%以上;随着Me逐渐下降,试样的整体骨架-密实结构在不同区域分别向局部骨架-空隙结构、局部悬浮-密实结构转变,进而致使黏聚力、内摩擦角均随Me下降而逐渐衰减。

In the existing research,coarse-grained soil is generally regarded as a homogeneous binary mixture,and the influence of of mixing uniformity between coarse and fine particles on its strength characteristics are ignored.Firstly,a quantitative index(Me)was proposed to describe mixing uniformity in coarse-grained soil.Secondly,through static triaxial tests,the inherent relationship between stress-strain curve,elastic modulus,failure strength and shear strength indicators and the Me were explored.Finally,based on the results of static triaxial tests,a modified Duncan-Chang model considering both confining pressure and Me effects was established,and its applicability and rationality were robustly verified.The results show that the stress-strain curve gradually transforms from strain-softening type to strain-hardening type with the increase of confining pressure.As Me decreases,it gradually develops into strain-softening type from strain-hardening type curve.When both confining pressure and Me increase,both elastic modulus and failure strength increase accordingly.The elastic modulus attenuates by 41.3%when Me decreases from 0.25 to 0,and the failure strength attenuates by more than 40%when Me decreases from 1 to 0.As Me gradually decreases,the overall skeleton-dense structure of the sample changes to the local skeleton-void structure and the local suspension-dense structure in different regions,which leads to gradual attenuation of cohesion and internal friction angle with decreasing Me.