基于PPP-BOTDA的膨胀土裂隙发育特征的分析与表征方法研究  

PPP-BOTDA BASED EXPERIMENTS ON CHARACTERIZATION AND DESCRIPTION METHODS FOR CRACKING OF EXPANSIVE SOIL

作　　者：王宏宪 张丹[1] 李长圣 独莎莎 

机构地区：[1]南京大学地球科学与工程学院,南京210093

出　　处：《工程地质学报》2014年第2期210-217,共8页Journal of Engineering Geology

基　　金：国家自然科学基金项目(41272315);地质灾害防治与地质环境保护国家重点实验室开放基金资助项目(SKLGP2011K011);国家重点基础研究发展计划(973计划)课题(2011CB710605)资助

摘　　要：为了解非饱和膨胀土在干湿循环过程中土体应变的状态、变化以及土体裂隙的发育规律,在室内设计了一个长150cm、宽10cm、高60cm的模型箱,将传感光纤分4组按不同深度埋入土中,每组传感光纤包括4种类型,采用高空间分辨率的分布式光纤应变测量技术PPP-BOTDA,对干湿循环过程中土体的应变状态进行了监测。试验发现:埋深较浅的光纤受到裂隙发育的影响,在空间上,光纤应变状态呈现不均匀的拉压分布;在时间上,随着土体含水率的降低,裂隙区域的光纤应变呈现出先压缩后拉伸的变化规律,而且光纤应变变化同总裂隙张开度具有一定的相关性;随着光纤埋藏深度的加深,由于受土体裂隙的影响减小,光纤应变分布较为均匀;吸湿过程中,土体裂隙逐渐闭合,裂隙区域光纤应变由拉伸状态转变为压缩状态,而裂隙两侧区域光纤应变逐渐转变为拉伸状态。结果表明,通过PPP-BOTDA技术可以反映膨胀土干湿过程中土体的应变状态,并对土体裂隙进行准确的定位,从而为土体变形监测及灾害评价提供了新的技术手段。This paper is to find out the strain state,variation and development of cracking in unsaturated expansive soil during dry-wet cycle.A model box with 150cm long,10cm wide and 60cm high is designed.A high spatial resolution distributed optical fiber strain measuring technique（PPP -BOTDA）is used to monitor the strain status of the sensing fibers embedded in unsaturated soil at 4 different depths during the dry-wet cycle.At the same depth, the sensing fibers include 4 different kinds and are laid along the longitudinal direction of the model.The experiments show that strain of the sensing fiber is under the influence of soil cracking.Spatially,the strain status is not uniform and characterizing with alternate distribution of tension and compression.Temporally, with the decreasing of soil water content,the stain state of the sensing fibers across cracking zone changes from compression to tension and the stain value has correlation with the total crack opening.With the increasing of the embedded＆amp;nbsp;depth,strain distributions of the sensing fibers are more uniform as the influence of the surface cracks to the deep fibers is relatively small.During the wetting process,the strain state of the sensing fibers across the cracks changes from tension to compression with the closing of cracks,whereas the fiber strain near the cracks goes tensile.The results indicate that PPP-BOTDA based distributed optical fiber sensing technology can monitor the strain state of expansive soil during dry-wet cycle and locate the cracks of the soil accurately.The PPP-BOTDA can be a new technical means for soil deformation monitoring and disaster assessment.

关 键 词：裂隙 膨胀土 分布式传感 光纤 应变 

分 类 号：P642.139[天文地球—工程地质学]