非饱和粉土的抗拉强度研究及其预测

Experimental study and modeling of tensile strength in unsaturated silty soil

坡体失稳破坏和路基填土开裂等工程地质问题均与土体的抗拉强度密切相关。利用巴西劈裂试验对不同初始含水率的非饱和土压实样和脱湿样进行抗拉强度试验研究,旨在探究广含水率范围内非饱和土压实样和脱湿样抗拉强度的演化规律。结果表明:随含水率的降低,压实样的抗拉强度先增大再减小,存在1个临界含水率,在临界含水率处其抗拉强度达到最大值。与此相反,脱湿样的抗拉强度会不断增大并趋于稳定。这是由于压实样的抗拉强度主要与弯曲液面处产生的毛细吸应力相关,而脱湿样的抗拉强度主要与毛细吸应力和胶结力等相关。其次,利用电镜扫描试验所测得压实样与脱湿样的微观孔隙结构图对此进行分析与讨论。最后,基于考虑毛细和吸附作用的非饱和土有效应力公式,建立非饱和土抗拉强度预测模型,并利用不同类型土的实测数据验证模型的有效性。

Engineering geological problems,such as slope instability and cracking of roadbed fills,are closely related to the tensile strength of soil.The Brazilian splitting test was used to study the tensile strength properties of unsaturated compacted specimens and dehydrated specimen in this study.The objective was to study the evolution of the tensile strength in unsaturated compacted and dehydrated specimens across a broad range of the water content.Results show that with decreasing the water content,the tensile strength of compacted specimens initially increases and then decreases,reaching its maximum value at a critical moisture content.Conversely,the tensile strength of dehydrated specimens continues to rise and eventually approaches a stable level.The difference between these two types of specimens can be attributed to the fact that the tensile strength of compacted specimens is mainly affected by capillary suction stress generated at the bending liquid surface,whereas the tensile strength of dehydrated specimens is primarily influenced by factors such as capillary suction stress and cohesive forces.Then,microstructure images of both types of specimens obtained through electron microscopy scanning experiments were carefully analyzed and discussed.Finally,an unsaturated soil tensile strength model was established based on an effective stress formula that considers both capillary and adsorption effects.The effectiveness of this model was verified using measured data.