荆门膨胀土土–水特征曲线特征参数分析与非饱和抗剪强度预测

ANALYSIS OF CHARACTERISTIC PARAMETERS OF SOIL-WATER CHARACTERISTIC CURVE(SWCC) AND UNSATURATED SHEAR STRENGTH PREDICTION OF JINGMEN EXPANSIVE SOIL

为探讨荆门原状、压实、石灰改良膨胀土的非饱和抗剪强度与土–水特征曲线(SWCC)的相关关系,利用Fredlund-Xing模型对3种膨胀土的SWCC试验数据进行非线性拟合,获得相应模型参数;利用Fredlund公式(1996年)对3种膨胀土控制吸力下的固结排水剪三轴压缩试验抗剪强度成果进行相关分析。分析结果表明:(1)使用Fredlund-Xing模型拟合3种膨胀土SWCC试验数据的效果均较好。(2)荆门原状、压实、石灰改良膨胀土的进气值分别为210,68和18kPa;石灰改良膨胀土的持水能力(水稳定性)最强,压实膨胀土次之,原状膨胀土最弱;3种膨胀土的残余吸力可均取为3000kPa。(3)3种膨胀土的有效内摩擦角(′)和与基质吸力相应的内摩擦角(b)均非常数;′与基质吸力相关,b与基质吸力和应力状态均相关,这意味着Mohr-Coulomb破坏包面是双向弯曲的。(4)使用Fredlund公式,能够在较大的吸力范围内较好地预测荆门膨胀土的非饱和抗剪强度,原状、压实、石灰改良膨胀土的土性参数κ分别为2.4,2.7及3.4。(5)预测值与实测值间存在差别的主要原因是Fredlund公式本身未考虑到b与应力状态相关,若要考虑该因素,可将应力状态对SWCC的影响引入到Fredlund公式中。

In order to discuss the relationship between the unsaturated shear strength and the soil-water characteristic curve（SWCC） of Jingmen intact,compacted and lime-treated expansive soils,nonlinear curve fittings are carried out to fit the experimental data of SWCC based on Fredlund-Xing model,and the correlation analysis is presented for the shear strength results of the suction-controlled consolidated-drained triaxial compression tests based on the Fredlund equation（1996） for predicting shear strength with respect to SWCC. The results show that the experimental data of SWCC for the three types of expansive soils can be well fitted by the Fredlund-Xing model. The air entry value of Jingmen intact,compacted and lime-treated expansive soils is 210,68 and 18 kPa respectively. For the water stability,the lime-treated expansive soil is the best,followed by thecompacted one,and the intact one is the worst;each of the residual suction of the three types of expansive soils can be taken as 3 000 kPa. For the three types of expansive soils,neither the effective angle of shearing resistance（＇） nor the angle of shearing resistance with respect to matric suction（b） is constant,where ＇ is influenced by the matric suction,and b is influenced by matric suction and stress state,which means the Mohr-Coulomb failure surface is bidirectional bending. The unsaturated shear strength of the three types of expansive soils can be well predicted by the Fredlund equation over a wide matric suction;and the soil parameter κ of Jingmen intact,compacted and lime-treated expansive soils is 2.4,2.7,3.4,respectively. The main causation of the difference between the predicted shear strength;and the test results show that the Fredlund equation does not consider that b is influenced by stress state.