液限对南阳原状膨胀土抗剪强度影响的研究

Study on effect of liquid limit on shear strength of undisturbed expansive soil in Nanyang

为探讨膨胀土液限与黏粒含量的关系,以及液限对膨胀土峰值强度摩擦角和残余强度摩擦角的影响,利用电动应变控制式剪切仪和ShearTracⅡ反复直剪仪对26种原状膨胀土进行快剪试验(快剪、饱和快剪、饱和固结快剪)和反复剪试验。结果表明:膨胀土液限与黏粒含量呈良好的线性正相关关系;不同状态下试样的峰值强度大小顺序为饱和固结快剪强度>快剪强度>饱和快剪强度;随着液限增加,峰值强度的摩擦角逐渐减小,且液限对饱和快剪摩擦角的削弱作用强于对其他两者的削弱作用,当液限超过57%后,饱和快剪摩擦角略微增大,但不明显,三者摩擦角大小排序与峰值强度排序相同;低法向应力下,饱和样残余强度应力位移曲线的应变软化特性相较天然样有所减弱,峰态也逐渐减弱或消失;随着液限增加,试样残余强度摩擦角呈多项式逐渐减小趋势。

In order to study the relationship between liquid limit and clay content of expansive soil and the effect of liquid limit on the friction angle of peak strength and residual strength friction angle of expansive soil,quick shear(including quick shear,saturated quick shear,saturated and consolidated quick shear)and repeated reversal direct shear tests were conducted on 26 kinds of undisturbed soil by using electric strain controlled direct shear apparatus and ShearTrac II repeated direct shear apparatus.The results showed that:there was a good linear positive correlation between the liquid limit and clay content in expansive soil;the order of peak strength in different states of samples was that saturated and consolidated quick shear strength>quick shear strength>saturated quick shear strength.The friction angle of peak strength decreased with increase of liquid limit,and the weaking effect of liquid limit on friction angle of the saturated quick shear was much stronger than that on the other two.When the liquid limit increased to 57%,the friction angle of saturated quick shear increased slightly,but not obviously,the order of these friction angles was same as that of peak strength.Under low normal stress,the residual strength stress and displacement curve’s strain softening characteristic of saturated samples was weaker than natural samples’,and the state of peak also would weaken or disappear.With the increase of liquid limit,the friction angle of residual strength decreased gradually in a polynomial manner.