宽广吸力范围非饱和土剪切强度试验研究及其预测

Experimental study on shear strength of unsaturated soil over a wide suction range and its prediction

以弱膨胀土为试验材料,开展了宽广吸力范围内非饱和土的持水和强度特性试验研究,并提出适用于宽广吸力范围的非饱和土强度模型。结果表明,在广吸力范围内,应力−应变曲线随吸力增加而增高,在低吸力范围呈现应变硬化,在高吸力范围呈现应变软化。低吸力范围,试样呈现剪缩变形;高吸力范围,试样在轴向应变2%处开始呈现剪胀趋势。此外,提出一种区分吸附水和毛细水的土−水特征曲线模型,并假设吸力引起的强度增强部分主要由毛细水决定。将有效应力系数用毛细水饱和度替代,并代入Bishop非饱和土强度公式,利用不同类型土剪切强度的实测数据和文献中剪切强度模型对比,表明该强度模型可以很好地描述宽广吸力范围内的非饱和土强度。

In this paper,the experimental studies on the water retention and strength properties of unsaturated weakly expansive soil in a wide suction range were carried out,and a strength model of unsaturated soil over a wide suction range was proposed.The results show that in the wide suction range,the stress-strain curve increases with the increase of suction.The strain hardening occurs in the low suction range,while the strain softening appears in the high suction range.In the low suction range,the sample presents shear deformation,while in the high suction range,the sample begins to show a shear dilation trend at the axial strain of 2%.In addition,a soil-water retention curve model was proposed to distinguish adsorbed water from capillary water,assuming that the strength increment caused by suction is mainly determined by capillary water.The degree of saturation of capillary water was used to replace the effective stress coefficient and then it was substituted into the Bishop’s unsaturated soil strength formula.The proposed model was verified by test data of various soil types and compared with the models in the literature.The results show that the proposed model can well describe the strength of unsaturated soil in a wide suction range.