基于PIV技术的非饱和膨胀土径向劈裂试验研究

Experimental study on diametric splitting of unsaturated expansive soil based on PIV technology

非饱和膨胀土的径向劈裂强度与裂隙扩展之间存在密切联系,分析不同含水率下非饱和膨胀土的裂隙演化机制,对南水北调中线工程膨胀土渠段的工程灾害防治具有重要的理论意义和工程实用价值。联合运用WP4C仪、压力板和PIV(Particle image velocimetry,PIV)劈裂试验系统,对南水北调中线工程邓州段某高填方渠堤非饱和膨胀土进行了一系列的持水特性试验和劈裂试验,结合持水特征曲线,揭示了不同含水率膨胀土的劈裂强度、裂隙演化过程、位移矢量场的变化规律及其内在机理。试验表明:(1)膨胀土的含水率和饱和度均随吸力的增大而减小。在低吸力范围内膨胀土试样含水率和饱和度随吸力的增加而减小趋势缓慢;在高吸力范围内,含水率和饱和度与吸力基本呈线性关系,随吸力的增加,试样的含水率和饱和度显著减小。(2)含水率对膨胀土的劈裂强度具有显著影响。随含水率的增加,试样的劈裂峰值荷载呈先增加后减小的变化规律,劈裂峰值荷载在含水率为3%~12%范围内持续增加,而在12%~24%范围内持续减小;上述试验现象与不同含水率膨胀土试样具有不同的颗粒间液桥作用有密切的内在联系。(3)不同含水率下膨胀土劈裂试验荷载-位移曲线均可分为荷载接触阶段、荷载线性增加阶段、张拉破坏阶段和残余阶段。膨胀土劈裂试验不同阶段的裂隙、位移矢量场的变化规律与荷载-位移曲线变化之间存在着一一对应关系。

There is a close connection between radial splitting strength and cracks expansion of unsaturated expansive soil,and analyzing the cracks evolution mechanism of unsaturated expansive soil under different water contents has important theoretical significance and engineering practical value for engineering disaster prevention and control of expansive soil canal section of the Central Line Project of South-to-North Water Diversion.Jointly utilizing WP4C instrument,pressure plate and PIV(Particle image velocimetry,PIV)splitting test system,a series of water retention characteristic tests and splitting tests were carried out on a high-fill canal embankment unsaturated expansive soil in Dengzhou section of the Central Line Project of South-to-North Water Diversion,which,combined with the water retention characteristic curves,revealed the splitting strength and the cracks evolution process of expansive soil with different water contents,displacement vector field and its intrinsic mechanism.The experimental study shows that:(1)the water content and saturation of expansive soil decrease with the increase of suction force.In the range of low suction force,the water content and saturation of expansive soil samples decrease slowly with the increase of suction force;in the range of high suction force,the water content and saturation are basically linear with suction force,and with the increase of suction force,the water content and saturation of the samples decrease significantly.(2)The water content has a significant effect on the splitting strength of expansive soil.With the increase of water content,the splitting peak load of the sample shows the change rule of increasing first and then decreasing,the splitting peak load in the range of 3%~12%water content continues to increase,and in the range of 12%~24%continues to decrease;the above test phenomenon is closely related to the different water contents of expansive soil samples with different intergranular liquid bridge action.(3)The load-displacement curves of the splitting test of expansive soil with different water contents can be divided into load contact stage,load linear increase stage,tension damage stage and residual stage.There exists a one-to-one correspondence between the change rule of cracks and displacement vector field and the change of load-displacement curves in different stages of expansive soil splitting test.