镍铁渣-黏土-水泥改性土力学特性试验及修正的邓肯-张模型

Mechanical Properties and Modified Duncan-Chang Model of Ferronickel Slag-Clay-Cement Modified Soil

为研究镍铁渣-黏土-水泥(FNSCC)改性土的力学特性,开展不同镍铁渣掺入比、含水率及养护时间下,FNSCC改性土不固结不排水三轴压缩试验,获得了不同工况下FNSCC改性土试样的应力-应变关系曲线及割线弹性模量,分析了其力学特性影响机理及破坏模式;基于试验结果,建立了适用于FNSCC改性土的修正邓肯-张本构模型。结果表明:FNSCC改性土的应力-应变曲线具有明显的应变软化特征;其峰值强度随含水率的增加先增大后减小,含水率约为15%的试样,鼓胀破坏特别明显;镍铁渣掺入比减小,FNSCC改性土峰值强度增大,随镍铁渣掺入比的增大,试样的破坏模式由鼓胀破坏向剪切破坏转变;随着养护时间增长,改性土试样破坏模式由鼓胀变形等塑性破坏向局部张裂等脆性破坏转变。FNSCC改性土的割线弹性模量随轴向应变增加而减小,轴向应变小于2%时,镍铁渣掺入比、含水率及养护时间对割线弹性模量的影响较大;当轴向应变大于2%,各因素对割线弹性模量的影响很小。修正的邓肯-张模型能较好地反映FNSCC改性土的应变软化现象;该模型中,参数m、n及Ɩ与围压近似呈线性关系,模型参数m受FNSCC改性土配比的影响最大,养护时间次之,含水率最小;由修正邓肯-张模型计算得到的曲线与实测曲线吻合较好,验证了该模型拟合参数的合理性。

To study the mechanical properties of ferronickel slag-clay-cement(FNSCC)modified soil,the undrained triaxial compression tests of FNSCC modified soil under different ferronickel slag mixing ratios,moisture content and curing times were carried out.The stress-strain curve and secant elastic modulus of FNSCC modified soil samples under different working conditions were obtained,and the influence mechanism and failure mode of mechanical properties were analyzed.Based on the experimental results,the modified Duncan-Chang constitutive model suitable for FNSCC modified soil was established.The results show that the stress-strain curve of FNSCC modified soil has obvious strain softening characteristics.The peak strength first increases and then decreases with the increase of water content.The swelling failure of the sample with a water content of approximately 15%is particularly obvious.The peak strength of FNSCC modified soil increases with the decrease of the ferronickel slag incorporation ratio.With the increase of the ferronickel slag incorporation ratio,the failure mode of specimens changed from bulging failure to shear failure.With the increase of curing time,the failure mode changes from a plastic failure such as bulging deformation to a brittle failure such as local tension crack.The secant elastic modulus of FNSCC modified soil decreases with the increase of axial strain.When the axial strain is less than 2%,the addition ratio of ferronickel slag,water content,and curing time have a great influence on the secant elastic modulus.When the axial strain is greater than 2%,each factor has little effect on the secant elastic modulus.The modified Duncan-Chang model can better reflect the strain softening phenomenon of FNSCC modified soil.The model parameters m,n and l are approximately linear with confining pressure.The model parameter m is most affected by the ratio of FNSCC modified soil,followed by the curing time,and the moisture content is the smallest.The curve calculated by the modified Duncan-Chang model is in good agreement with the measured curve,which verifies the rationality of the fitting parameters.