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Physical model testing of slope stability based on distributed fiber-optic strain sensing technology

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Abstract

Fiber optic sensing is a newly-developed distributed monitoring technology; it has great potential in slope engineering. A new method to evaluate the stability condition of slope based on strain distribution of slope mass measured by sensing fiber in real-time is proposed. A slope model test is conducted in laboratory and the Brillouin optical time-domain analysis (BOTDA) technology has been used to measure the horizontal strains at different depths of the slope model subjected to loading on the slope crest. The test results show that the tight-buffering optical fiber packaged by heat-shrinkage tubes can be used for monitoring strain distribution within the slope. In order to take temperature compensation into consideration and achieve the purpose of accurate positioning, the installation of loose fiber sections at key locations along the sensing fiber is recommended. The potential slip surface can be estimated based on the distributed strain monitoring results. The deformation behavior and stability condition of the slope model during testing was analyzed in detail. It is found that there is an empirical relationship between the averaged maximum horizontal strains and the factor of safety of slope, so as to provide a new approach to evaluate slope stability and perform early warning of landslides.
32 4 岩石力学与工程学报 Vo l. 3 2 N o .4
2013 4 Chinese Journal of Rock Mechanics and Engineering April2013
收稿日期:20120925修回日期:20121226
基金项目:国家重点基础研究发展计划(973)项目(2011CB710605)国家自然科学基金资助项目(41102174);教育部高等学校博士学科专项科研基金项
(20120091120012)
作者简介:朱鸿鹄(1979),男,博士,2002 年毕业于浙江大学土木工程专业,现任副教授,主要从事地质工程、岩土工程方面的教学与研究
工作。E-mailzhh@nju.edu.cn
基于分布式光纤应变感测的边坡模型试验研究
朱鸿鹄 1 11 1 1 12 3
(1. 南京大学 地球科学与工程学院,江苏 南京 2100932. 山东大学 控制科学与工程学院,山东 济南 250061
3. 同济大学 地下建筑与工程系,上海 200092)
摘要光纤传感是近年来发展起来的一种分布式监测技术,这种方法在边坡工程监测领域有着巨大的潜力和应用
价值。提出一种通过监测坡体应变分布来实现边坡稳定性评估的新方法,通过一组边坡模型试验,采用布里渊光
时域分析(BOTDA)技术,对坡顶加载过程中边坡模型不同深度处的水平向应变进行连续监测。试验结果表明:
过热缩管封装的直埋式紧套光纤适用于边坡应变分布的监测;铺设传感光纤时,在关键位置预留自由段可达到温
度补偿和精确定位的双重效果;边坡滑裂面的位置可以通过对分布式应变监测数据的分析大致推算出来。通过分
析试验中受荷边坡变形和稳定性状态的演化过程,证明最大水平向平均应变值和边坡安全系数具有一定的经验关
系。该研究成果为边坡稳定性评估和滑坡预警提供一种新的思路和方法。
关键词边坡工程;边坡稳定性;光纤传感器;应变分布;布里渊光时域分析(BOTDA);分布式监测
中图分类号P 642 文献标识码:A 文章编号:10006915(2013)04082108
PHYSICAL MODEL TESTING OF SLOPE STABILITY BASED ON
DISTRIBUTED FIBER-OPTIC STRAIN SENSING TECHNOLOGY
ZHU Honghu1SHI Bin1YAN Junfan1CHEN Cheng1LI Yu1WANG Jing12ZHANG Jie3
(1. School of Earth Sciences and EngineeringNanjing UniversityNanjingJiangsu 210093China2. School of Control Science
and EngineeringShandong UniversityJinanShandong 250061China3. Department of Geotechnical EngineeringTongji
University
Shanghai 200092China)
AbstractFiber optic sensing is a newly-developed distributed monitoring technologyit has great potential in
slope engineering. A new method to evaluate the stability condition of slope based on strain distribution of slope
mass measured by sensing fiber in real-time is proposed. A slope model test is conducted in laboratory and the
Brillouin optical time-domain analysis(BOTDA) technology has been used to measure the horizontal strains at
different depths of the slope model subjected to loading on the slope crest. The test results show that the
tight-buffering optical fiber packaged by heat-shrinkage tubes can be used for monitoring strain distribution within
the slope. In order to take temperature compensation into consideration and achieve the purpose of accurate
positioningthe installation of loose fiber sections at key locations along the sensing fiber is recommended. The
potential slip surface can be estimated based on the distributed strain monitoring results. The deformation behavior
and stability condition of the slope model during testing was analyzed in detail. It is found that there is an
empirical relationship between the averaged maximum horizontal strains and the factor of safety of slopeso as to
provide a new approach to evaluate slope stability and perform early warning of landslides.
Key wordsslope engineeringslope stabilityfiber optic sensorstrain distributionBrillouin optical time-domain
analysis(BOTDA)distributed monitoring
822 岩石力学与工程学报 2013
1
边坡现场监测是边坡工程防灾减灾的一个重要
途径,现场的实测数据可以为边坡稳定性评估提供
可靠的数据支撑。传统的分析方法主要借助常规仪
器如测斜仪、引伸计等,根据边坡位移的模式和速
率等指标,实现对边坡稳定状态的判断[1]。近年来
随着光纤传感技术的快速发展,这种以光为载体、
光纤为媒介,将传感和传输合为一体的新型监测技
术越来越受到土木、水利、交通等工程领域的青
睐。光纤传感器的优点主要包括:抗电磁干扰、精
度高、耐久性好、体积小巧等。尤其重要的是,借
助波分复用(WDM)和时分复用(TDM)等技术,光纤
传感器可以采用并联、串联或混合连接等方式,建
立准分布式或全分布式的测量网络[2]。正是由于这
种独特优点,使得光纤传感技术逐渐成为实现点式
监测向分布式监测过渡的主要手段。
近年来,在分布式光纤监测方面,边坡工程领
域出现了一批有代表性的研究成果。例如,Y. T. Ho
[3-5]研发了基于光纤布拉格光栅(FBG)传感器的边
坡监测设备,包括测斜仪、倾斜计等,并成功应用
于实际边坡的长期监测。丁 勇等[6] 设计了一种布设
于边坡表面的光纤传感网络,通过布里渊光时域反
(BOTDR)技术可获得有关坡表稳定状态的监测
信息。隋海波等[7]全面总结了 BOTDR 技术在边坡
工程中的应用方法,并用实例证明了该技术在边坡
变形监测以及变形区域空间定位等方面的有效性。
李焕强等[8-9]和王宝军等[10]则分别将 BOTDRFBG
等传感技术应用于室内边坡模型试验的监测,得到
了传统测试技术无法获取的、与边坡稳定相关的监
测信息。但是作为一种全新的技术,分布式监测仍
存在一些尚待解决的问题,例如全分布式监测数据
的空间定位、应变读数的自动温度补偿、传感光纤
在岩土体中的布设工艺等。
本文基于布里渊光时域分析(BOTDA)传感技
术,提出了边坡稳定性的分布式应变监测方法,并
研究了这一方法的特点和实际效果。在有限元分析
的基础上,将应变传感光纤经封装后水平埋入边坡
模型土体中,并在坡顶逐级加载。通过对边坡应变
分布式监测结果的分析,实现了潜在滑裂面位置的
推测,并建立了光纤最大应变值和边坡安全系数之
间的数学关系,为这一传感技术应用于边坡稳定性
的评估和灾害预警提供了理论和技术基础。
2 布里渊光时域分析技术
布里渊光时域分析(Brillouin optical time-domain
analysis,简称 BOTDA)技术的测量原理见图 1
该技术基于受激布里渊散射(stimulated Brillouin
scattering,简SBS)原理,利用了光纤中的布里渊
散射光频率变化量(频移量)与光纤轴向应变或环境
温度之间的线性关系来实现传感,该关系[11]可以表
示为
B
BB00 0
()
()( ) ( )
vT
vTv T
 

,,
B
0
()
()
vT
TT
T
(1)
式中: B()vT
B0 0
()vT
分别为测试前、后光
纤中布里渊散射光的频移量;
0
分别为测试
前、后的轴向应变值(一定空间分辨率下的平均应
)T0
T分别为测试前、后的温度值。比例系数
B
{( )}/vT
,和
B
{( )}/vTT
, 的值分别约为
0.05 MHz/1.2 MHz/℃。
1 BOTDA 传感原理图
Fig.1 Schematic diagram of BOTDA sensing principle
BOTDA BOTDR 两种技术的区别主要在于:
BOTDA 技术利用了 SBS 原理,根据脉冲光和连续
光之间的相互作用,使得布里渊频谱受激放大,因
此可以获得比 BOTDR 技术更高的空间分辨率和精
度。目前基于 BOTDA 技术的商业化解调仪可以实
5 cm 的空间分辨率和 7 的应变测试精度,完全
可以满足边坡工程的应变监测要求[2]
与传统技术相比,布里渊光时域分析技术的优
势在于:它是一种完全分布式的应变、温度监测技
距离
距离
应变或温度
光强
频率
光纤受拉或
温度升高
o
o
32 4 朱鸿鹄等:基于分布式光纤应变感测的边坡模型试验研究823
术,光纤本身集传感、传输于一体,易于实现网状
监测。该技术的布设工艺相对简单,只需将传感光
纤按照一定的规律敷设在边坡表面或埋入支护体系
中。由于传感光纤为普通单模光纤(或光缆),监测
成本可以得到较好的控制。在现场监测时,可按照
一定空间分辨率对光路进行逐段扫描,以获取监测
对象整体整体的温度、变形、受力等状况。在工程
应用层面,该技术也存在一些固有的缺陷。例如,
由于该技术需进行双端测量,因此现场布线时必须
防止光纤意外断裂,或者采取预设后备光纤的措施。
另外在数据采集方面,由于每次测试需要占用一定
的频谱扫描时间(通常为几分钟到十几分钟),因此
目前无法实现高频的数据采集。
基于以上布里渊光时域分析技术的传感特点,
它适用于大型边坡()的变形监测,可实现关键区
域位置不确定的大范围边坡稳定性监测、滑坡蠕变
过程监控、边坡潜在滑裂面定位等功能。
3 荷载作用下的边坡应变分布规律
将分布式光纤监测技术应用于边坡应变的获
取,首先必须对边坡的应变分布有一定的认识。为
了分析均质土坡在坡顶局部荷载作用下的应变分布
规律,使用加拿大 GEO-STUDIO 软件建立了如图 2
所示的二维有限元模型。该边坡模型的左右边界固
定了 x向位移,下边界固定了 xy向位移,坡顶的
均布荷载宽度取 0.6 m,边坡土体采用莫尔–库仑
模型模拟。表 1为有限元分析中所采用的参数。
2 受坡顶荷载的边坡有限元模型
Fig.2 Finite element model of a locally loaded slope
1 有限元分析参数
Table 1 Parameters used in finite element analysis
抗剪强度指标
容重/
(kNm3)
变形模量/
MPa 泊松比 黏聚力/kPa 内摩擦角/(°)
20 100 0.33 12.5 25.0
在有限元模拟的同时,采用瑞典条分法和简化
Bishop 法计算了该边坡在不同荷载下的安全系数
(见表 2)。图 3中显示了由简化 Bishop 法和有限元
法算得的边坡滑裂面位置。经计算发现,有限元法
和极限平衡法得到的滑裂面位置基本吻合;在坡顶
荷载位置不变的情况下,边坡滑裂面的位置基本不
受荷载大小的影响。
2 由极限平衡法得到的边坡安全系数
Table 2 Factors of safety of slope calculated by limit
equilibrium methods
安全系数
荷载/kPa 瑞典条分法 简化 Bishop
0 5.225 5.281
20 2.358 2.495
40 1.631 1.767
60 1.303 1.434
80 1.113 1.242
100 0.989 1.116
120 0.897 1.025
3 应变观测线以及极限平衡法、有限元法得到的边坡滑
裂面位置(p = 100 kPa)
Fig.3 Locations of the strain measuring lines and slope slip
surfaces obtained by limit equilibrium method and
finite element method(p = 100 kPa)
通过对坡顶的模拟加载,得到了各级荷载情况
下边坡各指定位置(3中选取了4个水平向监测断
面、3个竖向监测断面)的水平向、竖向应变分布。
45分别为不同荷载下边坡的水平向和竖向应
变分布曲线,图中拉应变为正,压应变为负,各竖
向箭头分别对应于所选取的监测断面与潜在滑裂面
的交点位置。
(a) 20 kPa
o
824 岩石力学与工程学报 2013
(b) 60 kPa
(c) 100 kPa
4 不同荷载下边坡的水平向应变分布曲线
Fig.4 Distributions of horizontal strain in slope mass under
different loading magnitudes
(a) 20 kPa
(b) 60 kPa
(c) 100 kPa
5 不同荷载下边坡的竖向应变分布曲线
Fig.5 Distributions of vertical strain in slope mass under
different loading magnitudes
根据以上的模拟结果可知,当坡顶荷载较小时,
边坡大部分区域的水平向应变为拉应变,但坡脚处
水平向应变为压应变,表明该位置处于压剪状态;
坡体的竖向应变则均表现为压应变,真实反映了边
坡在竖向荷载作用下的受力状态。随着坡顶荷载的
增大,坡体各部位的拉、压应变值都迅速增大,靠
近滑裂面附近的坡体无论是水平向还是竖向应变都
呈现分布不均的现象。当边坡安全系数接近于 1
时,各监测断面的水平向、竖向应变最大值都突破
1 000 000 με,说明坡体多处区域发生了剧烈的
切形变。
为了研究各级荷载作用下边坡整体应变和对应
的安全系数之间的关联性,取各级荷载下各个水平
向应变监测断面的应变最大值,再对其进行平均化
处理,以代表边坡整体的应变状态,即
h
1
hmax
max( )
n
i
i
n
(2)
式中: hi
(i = 12,……,n)为第 i个监测断面测
得的水平向应变值, hmax
为边坡的水平向特征应
变值。
hmax
和边坡安全系数的关系曲线作于对数
坐标图内(见图 6)。图 6显示,随着边坡水平向特征
应变值的增大,安全系数逐渐减小,两者之间有着
较好的相关性。该关系可以用下式表示:
hmax
()
b
Ka
(3)
式中:K为根据极限平衡法算得的安全系数;ab
均为拟合常数。
6 安全系数和水平向特征应变的关系曲线
Fig.6 Relationships between factor of safety and horizontal
characteristic strain
以上的有限元分析说明:第一,坡体的应变是
综合反映边坡稳定状态的一个客观指标;第二,根据
应变分布情况虽然无法精确获得边坡滑裂面的位
置,但能够肯定的是,在滑裂面附近区域有应变分布
32 4 朱鸿鹄等:基于分布式光纤应变感测的边坡模型试验研究825
不均的现象。需要指出的是,以上的有限元分析假定
边坡土体为均质的理想弹塑性体,对于坡体的不均
匀性和土的非线性本构关系不能准确反映,因而式(3)
只是定性分析的结果,与实际情况可能有着较大的
差别,拟合常数 ab的取值需要通过试验来确定。
当采用 BOTDA 传感技术进行边坡的应变监测
时,传感光纤一般选用普通单模单芯光纤,而这类
光纤裸纤的外径仅 500 µm,经过紧套封装后外径一
般也只有 900 µm。同时,虽然纤芯的主要成分为
SiO2,弹性模量达 72 GPa,但其涂覆层和高分子材
料护套模量非常低[12]使得传感光纤的平均弹性模
量仅几百到几千个兆帕,和土体模量较为接近。所
以,当光纤埋入边坡土体后,只要保证光纤和土体
没有相对滑移,即可认为传感光纤所测得的轴向应
变值就是边坡土体在光纤埋设方位的应变值。由于
传感光纤用于压应变测量前需要特殊的预拉措施,
同时坡体竖直方向的应变主要为压应变,所以不建
议将传感光纤沿竖向布置在坡体内。相反的,在荷
载作用下边坡的水平向应变基本为拉应变,将传感
光纤水平埋设在坡体内测量坡体拉应变,更具有便
利性和可操作性。
4 边坡模型试验
4.1 试验概况
为了验证边坡分布式光纤监测的有效性,在由
南京大学研制的新型边坡多场作用模型箱中进行了
一组边坡模型试验。该模型箱长 3.0 m,宽 1.5 m
1.5 m,一个侧面为加肋的钢化玻璃,其余 3
侧面和底面为加肋的 10 mm 厚钢板,见图 7。边坡
的加载系统包括工字反力梁、千斤顶和传压板,模
型箱左、右两侧各设置了一个水箱,用于边坡内水
位线的控制。
7 边坡模型试验箱
Fig.7 Photograph of the slope model test chamber
边坡模型采用河砂和高岭土按一定比例混合后
填筑而成,其模型尺寸见图 8。该3.0 m,宽
1.5 m,净高 0.9 m,坡角为 42°。边坡采用土钉加
固,土钉用直径 10 mm、长 1.2 m 的铝棒进行模拟。
土钉呈十字形布置,竖向和水平向间距均为 25 cm
所有土钉与水平面夹角均为 15°。试验前,通过水箱
控制边坡内水位在 1.2 m 高程处,坡脚处水位和地
面齐平。然后,采用千斤顶在坡顶进行局部加载,
加载宽度取 0.4 m。坡顶荷载为分级施加,试验过
程中从 12.5 kPa 逐级加至 34.0 kPa
8 边坡模型尺寸图(单位:mm)
Fig.8 Dimensions of the slope model(unitmm)
4.2 光纤监测布置
应变传感光纤的铺设工艺是模型试验中的一个
关键问题。本次试验中采用了直径为 900 µm 的紧
包单模单芯光纤监测,光纤布置见图 9。边坡共布
3层光纤,从下而上分别编号为第 H1H2H3
层。每层光纤呈 S型布设,即光纤沿 z轴存在 3
水平向(x轴方向)应变的传感段,从前到后分别编号
为第 123段。
9 BOTDA 传感光纤布置图(单位:mm)
Fig.9 Layout of the BOTDA sensing fiber(unitmm)
千斤顶和反力梁
水箱
边坡模型
o
826 岩石力学与工程学报 2013
为了达到精确定位和温度补偿的双重作用,需
要在传感光纤的各个特征位置各隔离出 1 m 左右长
度的光纤。本次试验采用将该段光纤盘绕在特制的
开孔塑料盒内的方法。在试验中,这些光纤段的布
里渊频移量只受温度的影响,而不受荷载的影响。
另一方面,为了保证应变传感光纤和土体之间的耦
合性,采用直径 3 mm 的热缩管对光纤进行了定点
封装,热缩管布设间距取 30 cm。这一方法可以有
效地增加光纤和土体之间的摩阻力,使得光纤在土
体中相当于定点埋设,从而保证两者的变形协调性
由于热缩管的长度仅为 2 cm,远小于传感段长度,
故热缩管的存在几乎不影响应变数据的准确性。在
试验监测时,BOTDA 解调仪的空间分辨率设定为
10 cm,以获得最佳的监测精度。
根据简化 Bishop 法得到了边坡在坡顶局部荷
载作用下的滑裂面位置(见图 10)。图 10 中虚线为地
下水位线,黑色横线即模型试验中 H1H2 H3
光纤埋设的位置,可以据此确定传感光纤和潜在滑
裂面相交的点位。在稳定性分析时,取土钉和土体
之间的黏结强度为 10 kPa,其他相关的计算参数见
3
竖向均布荷载
H1
H2
H3
10 极限平衡分析得到的边坡滑裂面
Fig.10 Calculated slip surface of the slope from limit
equilibrium analysis
3 边坡稳定性分析参数
Table 3 Parameters used in slope stability analysis
抗剪强度指标
土类 容重/
(kNm3) 黏聚力/kPa 内摩擦角/(°)
非饱和砂土 20 12.3 25.4
饱和砂土 20 6.5 15.7
5 监测结果及分析
5.1 分布式应变监测结果
经过温度补偿处理,得到了 BOTDA 传感光纤
测得的剔除了温度效应的边坡应变值,监测结果见
1112图中虚线为每层土体中平行的 3段传感
光纤经过平均后的应变值,主、被动区分界线对应
于由条分法算得的滑裂面所通过的位置。光纤监测
结果显示,各层土体的 3个应变监测段得到的应变
值有一定的差异,但其分布形态较为接近,因此其
平均值可以较为真实地反映边坡变形的性态。在较
小的外荷载作用下,边坡的水平向应变保持在一个很
小的量级里,主要表现为拉应变;边坡下层(H1 )
靠右侧的位置为明显的压应变区,表明此处受到上部
不稳定土体的挤压。随着坡顶荷载的增大层土
应变也相应增大,与荷载增量有着较好的相关性。
在各级荷载下,边坡两侧应变较小,接近中部的区域
(滑裂面附近)应变逐渐累积,表明边坡中的潜在滑裂
面正在逐渐生成。在接近坡顶荷载作用处(H3 )
应变局部集中的现象。当加荷到接近破坏时,坡体
应变的不均匀性表现得非常明显,这种应变分布
均从侧面反映了控制边坡滑裂面形成的剪应变逐渐
发生累积。此时,边坡下层的被动区应变很大,主动
区相对较小;边坡上层则相反,主动区应变远大于被
动区;边坡中层应变最大点即滑裂面经过的位置。
(a) H1
(b) H2
(c) H3
11 12.5 kPa 荷载下的边坡应变监测结果
Fig.11 Strain monitoring results of the slope mass under
local loading of 12.5 kPa
竖向均布荷载
H3
H2
H1
32 4 朱鸿鹄等:基于分布式光纤应变感测的边坡模型试验研究827
(a) H1
(b) H2
(c) H3
12 34 kPa 荷载下的边坡应变监测结果
Fig.12 Strain monitoring results of slope mass under
local loading of 34 kPa
5.2 边坡稳定性评估
从以上的分析看,在边坡模型试验中,通过合
理布设分布式应变传感光纤,可得到反映边坡整体
稳定性的特定监测信息,有助于边坡稳定性的科学
评估及边坡滑裂面位置的推测。
13 给出了坡顶荷载–安全系数–水平向特
征应变的关系曲线。该图显示,随着荷载的增大,
13 坡顶荷载–安全系数–水平向特征应变的关系曲线
Fig.13 Relationship curve of surcharge loading-factor of
safety-horizontal characteristic strain
安全系数逐渐减小,应变则相应增大,表明三者之
间有较好的相关性。采用式(3)拟合得到 ab值分
别为 2.66 0.109R2 = 0.994,说明根据该经验
关系来推算边坡的安全系数是可行的一种稳定性评
判方法。
6
(1) 通过数值模拟,验证了边坡的水平向应变
的变化可以在一定程度上反映边坡的稳定状态,因
而可以估算安全系数,并有助于滑裂面大致位置的
推测。
(2) 解决了边坡模型试验中的传感光纤布设工
艺。通过在传感光纤上预留自由段,以实现温度补
偿和精确定位的双重作用。通过对 900 µm 直径的
紧包光纤的热缩管封装,保证了光纤和土体之间的
变形协调性。
(3) 通过对应变监测结果的分析,得到了边坡
内的应变分布规律,得到了最大水平向应变和安全
系数之间的经验关系,说明该方法用于边坡稳定性
评估的可行性。
本研究初步揭示了分布式光纤应变监测技术在
边坡稳定性分析方面具有的巨大潜力。但需要指出
的是,以上的研究结果均基于室内模型试验的情况,
在现场边坡的监测工作中应考虑更多的制约因素。
例如,如何将传感光纤水平铺设在坡体中,光纤和
边坡岩土体之间如何保证不发生相对错动等等。以
上这些问题还有待于通过进一步的试验分析加以解
决。另外,关于土钉等支护体的设置、地下水位的
变动及渗流的存在对于边坡应变状态变化的作用规
律,也还需要更深入的探索。
致谢 感谢本科生孙利萍、李 博以及苏州南智传
感科技有限公司的多位技术人员在边坡模型试验开
展过程中提供的协助!
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Monitoring ground movement manually by lowering an inclinometer probe (IP) in a grouted-in-place casing has been in practice for decades. It is possible to install multiple IP units at various depths in an inclinometer casing to allow automated data logging. The high cost and other problems associated with transmitting signals electrically make an automated IP rather impractical for long term and/or massive deployment. In addition to its small size, available technologies allow optical signals to be transmitted over many kilometres and not be affected by electromagnetic interference. The optical fibre Bragg grating (FBG) is one of the many available fibre optic sensor technologies. The authors used FBG as a sensing medium and developed a ground movement monitoring device referred to as the FBG segmented deflectometer (FBG-SD). The FBG-SD, designed to be inserted into the conventional inclinometer casing, measures the relative deflection between the segments. The amount of lateral movement is computed on the basis of the distribution of the segmented deflections. To verify the effectiveness of the new system, the authors performed indoor as well as field experiments where results from FBG-SDs were compared with conventional IP readings. This paper introduces the design principles of the FBG-SD and describes the performance of the system in their indoor and field applications.
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Monitoring of lateral displacements of a slope using a series of special fibre Bragg grating-based in-place inclinometers
  • Pei H Fyin J Hzhu H H
PEI H FYIN J HZHU H Het al. Monitoring of lateral displacements of a slope using a series of special fibre Bragg grating-based in-place inclinometers[J].