荆门非饱和膨胀土的变形与强度特性试验研究

Experimental study of deformation and strength characteristics of Jingmen unsaturated expansive soil

通过压力板试验,对比分析了荆门原状膨胀土与石灰改良土持水特征的差异性;应用非饱和土三轴仪,开展了原状膨胀土、石灰改良膨胀土与重塑膨胀土的变形及强度特性试验。结果表明:①石灰改良膨胀土与原状膨胀土相比,其进气值有显著降低,残余含水率显著升高,土-水特征曲线两个特征点的斜率较为平缓,说明其水稳定性较好,土体性状更为稳定;②原状膨胀土和石灰改良膨胀土在非饱和与饱和状态的应力-应变关系曲线均呈应变软化型,随净围压的增大,应变软化的程度趋缓;随含水率的减小,峰值应力增大,应力峰值点有所提前,应变软化现象更加显著。饱和重塑膨胀土的应力-应变关系呈应变强化型,非饱和重塑膨胀土则呈现为应变软化型,但其应变软化的程度较前两类土大为趋缓;③经石灰改性后,膨胀土强度参数值有大幅度提高,即使在湿化饱和后,石灰改良膨胀土仍保持了相对稳定的力学性质和较高的抗剪强度参数值。相比之下,无论是重塑膨胀土,还是原状膨胀土,对湿化作用均十分敏感,其强度参数值或波动较大,或整体水平较低。

The comparative analysis on the diversity of water retention characteristics between Jingmen intact and lime-treated expansive soils is investigated by the pressure plate tests.The deformation and strength characteristics of unsaturated and saturated intact,lime-treated and compacted expansive soils are studied by unsaturated triaxial tests.The results show that the air-entry value decreases markedly,the residual water content increases notably and the slope between the two characteristic points is more gradual,which demonstrates that the water stability is improved after the lime-treated.Secondly,the types of stress-strain relation curves of intact and lime-treated expansive soils are all strain softening under the unsaturated and saturated conditions,the grade of strain softening is more gradual with increasing net confining pressure,and the peak stress increases with decreasing water content.The types of saturated and unsaturated compacted expansive soils are strain hardening and strain softening respectively,but the grade of strain softening of unsaturated compacted expansive soils is more gradual than the other soils.And far more important,the values of shear strength parameters are improved significantly after the lime-treated,lime-treated expansive soil can maintain the higher values of strength parameters and fairly stable mechanical properties even under the saturated condition.By contrast,the strength of intact and compacted expansive soils is very sensitive to wetting effect.