【论文】非饱和土水分迁移感测的主动加热光纤光栅法试验研究

作者:刘喜凤1, 朱鸿鹄*1,2, 王家琛1,3,4, 李杰1, 王静1, 曹鼎峰2,5, 施斌1

1.南京大学地球科学与工程学院,江苏 南京 200023
2.广东省海洋土木工程重点实验室,广东 广州 510275
3.中国长江三峡集团雄安分公司,河北 雄安新区 071700
4.长江三峡集团雄安能源有限公司,河北 雄安新区 071700
5.中山大学土木工程学院,广东 广州 510275

摘要:非饱和土水分迁移是诱发多种地质灾害和环境岩土问题的重要因素,对其机理的认识因测试技术的不足尚不明确。为探究主动加热光纤光栅(AH-FBG)法监测非饱和土水分迁移的效果,分析单探针和双探针AH-FBG法的误差来源及分布特征,开展了一组室内土柱试验。在试验中同时采用AH-FBG法和传统的频域反射(FDR)法监测毛细水上升和水分蒸发的全过程,对比单探针法和双探针法的监测精度,分析不同方法的适用工况。结果表明:基于单探针AH-FBG的3种数据分析方法中,热导率法的监测精度最高,但是单探针法在监测毛细水上升过程中,当湿润锋刚没过探针感测位置时,受纵向传热的影响会使得测量的含水率值偏低;相比于单探针法,双探针法受纵向传热的影响更大,监测土体水分迁移有较大误差,误差大小与测点位置处的土体含水率值及土柱纵剖面的含水率分布情况有关;为减小纵向传热影响,从传感器结构和数据处理两方面提出了AH-FBG法的改进措施。

关键词:主动加热光纤(AHFO)法, 单探针法, 双探针法, 蒸发, 毛细水

基金项目:国家重点研发计划项目(2018YFC1505104);广东省海洋土木工程重点实验室开放基金项目(LMCE202006);软弱土与环境土工教育部重点实验室开放基金项目(2019P05)

收稿日期:2021–05–16

*通信作者(E-mail: zhh@nju.edu.cn)

Experimental study on actively heated fiber Bragg grating method for sensing seepage in unsaturated soils

LIU Xi-feng1, ZHU Hong-hu*1,2, WANG Jia-chen1,3,4, LI Jie1, WANG Jing1, CAO Ding-feng2,5, SHI Bin1

1. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
2. Guangdong Key Laboratory of Marine Civil Engineering, Guangzhou 510275, China
3. Xiong’an Branch, China Three Gorges Corporation, Xiong’an 071700, China
4. Yangtze Three Gorges Group Xiong’an Energy Company Limited, Xiong’an 071700, China
5. School of Civil Engineering, Sun Yat-sen University, Guangzhou 510275, China

Abstract:The seepage in unsaturated soils is a key factor that induces various geohazards and geoenvironmental problems, but the mechanism has not been clearly understood due to the limitations of measuring techniques. A series of soil column tests are carried out to study the performance of actively heated fiber Bragg grating (AH-FBG) in monitoring the seepage in unsaturated soils and analyze the error sources and distribution characteristics of the single-probe and dual-probe methods. Both the AH-FBG and the frequency domain reflectometry are used to monitor the whole process of rise of capillary water and water evaporation. The monitoring accuracy of the single-probe and dual-probe methods is compared, and the applicable conditions of different methods are analyzed. The results show that the thermal conductivity method has the highest accuracy among the three data analysis methods based on the single-probe AH-FBG method. However, when the wetting front just exceeds the sensing section of the probe in the process of the rise of capillary water, the measured moisture content will be low due to the influences of longitudinal heat transfer. Compared with the single-probe method, the dual-probe method is more affected by longitudinal heat transfer and has a larger error in monitoring the seepage. The error is related to the value of moisture content of soils at the position of the measuring point and the distribution of moisture content of soils in the vertical profile of the soil column. In order to reduce the influences of longitudinal heat transfer, the improvement measures of AH-FBG method are proposed from two aspects of sensor structure and data processing.

Key words: actively heated fiber optic method single-probe method dual-probe method evaporation capillary water

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