A hardening load transfer function for rock bolts and its calibration using distributed fiber optic sensing

Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.

Deformation and failure characteristics of sandstone under uniaxial compression using distributed fiber optic strain sensing

This paper investigates the deformation and fracture propagation of sandstone specimen under uniaxial compression using the distributed fiber optic strain sensing(DFOSS)technology.It shows that the DFOSS-based circumferential strains are in agreement with the data monitored with the traditional strain gage.The DFOSS successfully scans the full-field view of axial and circumferential strains on the specimen surface.The spatiotemporal strain measurement based on DFOSS manifests crack closure and elastoplastic deformation,detects initialization of microcrack nucleation,and identifies strain localization within the specimen.The DFOSS well observes the effects of rock heterogeneity on rock deformation.The advantage of DFOSS-based strain acquisition includes the high spatiotemporal resolution of signals and the ability of full-surface strain scanning.The introduction to the DFOSS technology yields a better understanding of the rock damage process under uniaxial compression.

Evolution mechanism of optical fiber strain induced by multi-fracture growth during fracturing in horizontal wells

A forward model for optical fiber strain was established based on a planar 3D multi-fracture model. Then the forward method calculating distributed fiber strain induced by multi-fracture growth was proposed. Based on this method, fiber strain evolution during fracturing of the horizontal well was numerically simulated. Fiber strain evolution induced by fracture growth can be divided into three stages: strain increasing, shrinkage convergence, and straight-line convergence, whereas the evolution of fiber strain rate has four stages: strain rate increasing, shrinkage convergence, straight-line convergence, and strain rate reversal after pumping stops. Fiber strain does not flip after pumping stop, while the strain rate flips after pumping stop so that strain rate can reflect injection dynamics. The time when the fracture extends to the fiber and inter-well pressure channeling can be identified by the straight-line convergence band of distributed fiber strain or strain rate, and the non-uniform growth of multiple fractures can be evaluated by using the instants of fractures reaching the fiber monitoring well.When the horizontal section of the fiber monitoring well is within the height range of a hydraulic fracture, the instant of the fracture reaching the fiber can be identified;otherwise, the converging band is not apparent. In multi-stage fracturing, under the influence of stress shadow from previous fracturing stages, the tensile region of fiber strain may not appear, but the fiber strain rate can effectively show the fracture growth behavior in each stage. The evolution law of fiber strain rate in single-stage fracturing can be applied to multi-stage fracturing.

Utilizing a novel fiber optic technology to capture the axial responses of fully grouted rock bolts

Rock bolts are one of the primary support systems utilized in underground excavations within the civil and mining engineering industries. Rock bolts support the weakened rock mass adjacent to the opening of an excavation by fastening to the more stable, undisturbed formations further from the excavation. The overall response of such a support element has been determined under varying loading conditions in the laboratory and in situ experiments in the past four decades; however, due to the limitations with conventional monitoring methods of capturing strain, there still exists a gap in knowledge associated with an understanding of the geomechanical responses of rock bolts at the microscale. In this paper, we try to address this current gap in scientific knowledge by utilizing a newly developed distributed optical strain sensing(DOS) technology that provides an exceptional spatial resolution of 0.65 mm to capture the strain along the rock bolt. This DOS technology utilizes Rayleigh optical frequency domain reflectometry(ROFDR) which provides unprecedented insight into various mechanisms associated with axially loaded rebar specimens of different embedment lengths, grouting materials, borehole annulus conditions, and borehole diameters. The embedment length of the specimens was found to be the factor that significantly affected the loading of the rebar. The critical embedment length for the fully grouted rock bolts(FGRBs) was systematically determined to be430 mm. The results herein highlight the effects of the variation of these individual parameters on the geomechanical responses FGRBs.

Distributed Fiber Optic Monitoring and Stability Analysis of a Model Slope under Surcharge Loading

In the discipline of geotechnical engineering, fiber optic sensor based distributed monitoring has played an increasingly important role over the past few decades. Compared with conventional sensors, fiber optic sensors have a variety of exclusive advantages, such as smaller size,higher precision, and better corrosion resistance.These innovative monitoring technologies have been successfully applied for performance monitoring of geo-structures and early warning of potential geohazards around the world. In order to investigate their ability to monitor slope stability problems, a medium-sized model of soil nailed slope has been constructed in laboratory. The fully distributed Brillouin optical time-domain analysis(BOTDA)sensing technology was employed to measure the horizontal strain distributions inside the model slope.During model construction, a specially designed strain sensing fiber was buried in the soil mass.Afterward, the surcharge loading was applied on the slope crest in stages using hydraulic jacks and a reaction frame. During testing, an NBX-6050 BOTDA sensing interrogator was used to collect the fiber optic sensing data. The test results have been analyzed in detail, which shows that the fiber optic sensors can capture the progressive deformation and failure pattern of the model slope. The limit equilibrium analyses were also conducted to obtain the factors of safety of the slope under different surface loadings. It is found that the characteristic maximum strains can reflect the stability of the model slope and an empirical relationship was obtained. This study verified the effectiveness of the distributed BOTDA sensing technology in performance monitoring of slope.

砂土压缩变形传感光缆耦合试验分析与预测模型研究

灾害监测、预测是地质与岩土工程领域一项极为重要的任务。分布式光纤传感技术凭借其连续、实时、抗干扰、稳定性好等优点在长距离、长周期、高隐蔽性、强突发性的灾害监测中发挥了显著的作用。然而,针对不同工程问题,评价与解决传感光缆与被测岩土体协调变形问题,是精细化分析岩土体变形分布与研究演化规律的关键所在。利用自主研制的三维主动变形可控围压光缆-砂土耦合试验装置,探究了0~4.0MPa围压条件下金属基索传感光缆与粗砂介质压缩变形的协调性问题。试验结果表明:低围压条件下金属基索传感光缆与砂土压缩变形协调性较差,变形表现为非线性变化特征;随着围压增大,传感光缆与砂土耦合效果提高,变形呈现线性变化特征,当围压达到1.6MPa后,两者协调变形一致性明显提高,其形变由非线性向线性转变。基于上述变形特性,提出了一种围压曲面投影数值模型,采用非扭结边界条件的样条插值算法对非试验数据实际位移进行预测,结果表明该模型具有较好的可靠性。试验研究认为金属基索光缆用于高围压条件下砂土变形测试具有更高的准确性,研究内容可以为分布式光纤传感测试技术用于深部地层变形监测提供科学的参考依据。

基于双斜坡法的光纤应变快速测量方法

为了提高基于布里渊散射的光纤应变测量的实时性,将仅根据两个工作点布里渊增益计算布里渊频移的双斜坡法用于光纤应变测量。介绍双斜坡法的基本原理,基于仿真布里渊谱研究左右两侧工作点选择对布里渊频移计算准确性的影响规律,确定最佳的工作点。基于确定的最佳工作点和不同信噪比的布里渊谱,研究信噪比(signal-to-noise ratio, SNR)对双斜坡法和最小二乘拟合法准确性的影响规律。结果表明:双斜坡法的两个工作点围绕光纤沿线布里渊频移的均值对称时误差最小;随两个工作点频率之差的增加布里渊频移误差先减小后增大。相似准确性下双斜坡法的布里渊谱测量时间仅为最小二乘拟合法的约1/30,布里渊频移的计算时间仅约为后者的1/480。

浅谈配网自动化光纤通信系统施工技术

为了保证配网自动化光纤通信系统的稳定运行和信号的可靠传输,论文简要介绍了配网自动化光纤通信系统,对配网自动化光纤通信技术在施工过程中的施工要求、关键要点和注意事项进行了探究。

钢-连续纤维复合筋珊瑚混凝土梁式拉拔粘结应力分布研究

为探究钢-连续纤维复合筋(SFCB)在珊瑚混凝土中的粘结应力分布,使用梁式拉拔试验方法,对碳纤维增强复合材料(CFRP)筋和不同直径SFCB珊瑚混凝土进行拉拔,并采用光纤Bragg光栅(FBG)传感技术对筋材应力分布变化动态监测。研究结果表明:SFCB直径和钢芯直径均会影响荷载-滑移曲线形状;箍筋对筋材初始粘结刚度和SFCB纤维层加载端应变有明显提升;箍筋一定程度可以增强螺纹钢芯的粘结,对光圆钢芯粘结影响不大;SFCB屈服后的粘结应力分布与屈服前有明显差异,钢芯屈服后应力传递现象更明显;由于钢芯具有较高的弹性模量,在相同荷载下SFCB纤维层粘结段各处粘结应力均要大于CFRP筋。

基于光纤传感技术的工程监测应用研究

光纤传感技术作为当前热门技术之一,在工程监测领域有着许多重要应用。通过探讨光纤传感技术在工程形变监测中的应用案例,展示了其在工程监测领域的重要性。光纤传感技术利用光纤作为传感元件,可以实现对形变的连续、实时监测,并提供高精度的监测数据。通过布设应变光缆和温度补偿光缆,在合璧津高速公路K134段高架桥上进行了监测实验。结果表明,光纤传感技术能够准确评估结构的变形情况,并通过温度补偿算法消除了温度变化对数据的影响。通过几何方法计算沉降位移,可以实现对沉降位移的估算。

基于BOTDA的砂土地基预应力管桩抗拔静载试验研究

针对砂土地基抗拔桩受力性能与荷载传递机理研究不足问题,将布里渊光时域分析(BOTDA)光纤传感技术应用于长江下游地区厚层砂土地基预应力管桩原位抗拔静载试验研究,采用特殊设计的桩身刻槽钻孔、光纤粘贴保护、接桩过程连续植纤等技术工艺,实现了预应力管桩在拉拔过程中桩身受力变形状态的分布式测量与数据精确定位。研究结果表明:在上拔荷载作用下,试验桩桩身轴力沿桩身方向逐渐减小;桩侧摩阻力在下桩发挥效果较好,上桩侧摩阻力较小,全桩长侧摩阻力最大值在桩底;抗拔桩随上拔荷载的增加,轴力逐渐向下传递,向下传递的轴力主要由预制管桩侧摩阻力承担;分布式光纤应变传感技术能较好地监测预应力管桩桩身贯入施工因素对抗拔承载特性的影响。研究结果可在其他类型抗拔桩受力特性监测项目中推广应用。

边坡全维度监测技术与模型试验研究

中国是世界上地质灾害最严重的国家之一,其中滑坡常年位于各类地质灾害首位,因此对滑坡灾害进行深层次的研究至关重要。边坡工程常常会受到人类工程活动与自然地质作用叠加效应的影响,从而增加了对边坡变形失稳机理的科学认知难度。为精准掌握边坡状态信息与变形失稳过程,可通过建立全维度的监测体系以实现边坡状态信息的动态解译与表征,据此获得更加精准、可靠、直观的边坡稳定性评价依据。文章围绕边坡破坏模式及典型边坡监测技术,在厘清边坡变形演化过程的基础上,对边坡“天—空—地—体”一体化监测技术体系进行了全面分析;概述性总结了基于DFOS的边坡监测技术,重点阐述了基于DFOS的边坡多源多场监测研究思路与实施路径;系统性梳理了基于典型监测技术与DFOS技术的边坡物理模型试验研究过程与结果,以期为开展边坡加固方案设计与防灾减灾控灾提供重要的参考依据。

高铁地震波场的高精度密集观测及应用前景:基于通讯光缆的观测和处理结果

利用高清分布式光纤声波传感(HD-DAS)系统,进行高铁地震波场的高精度分布式采集。传感单元采用结构简单、成本低廉的通信光缆即可实现很好的监测效果,可以方便地根据实际环境进行布设,大大提高了野外观测的效率。采用多光缆并行布放,信号叠加后可有效地抑制噪声,提高高铁地震信号的信噪比。对HD-DAS系统采集到的高铁地震信号进行数据分析,发现高铁地震信号呈现分立谱特性。通过分析地震波信号的衰减规律,并通过频率-波数谱得到地震波在近地表的传输速度,表明光纤采集的高铁地震波信号可用于探测地下结构,并进一步实现对介质状态变化的监测,从而保障高铁的运行安全。

DT-CWT-LMS自适应降噪模型构建及其在隧道监测工程中的应用

针对隧道工程监测现场应用布里渊光时域反射仪(BOTDR)系统存在的问题,提出基于双树复小波变换(DT-CWT)和改进的LMS算法的组合降噪模型,用于对BOTDR分布式光纤监测信号进行降噪处理。首先,基于双树复小波变换算法分解原始信号;然后,使用样本熵作为目标函数自动选择最优小波分解层数的模型,并基于优化双曲余弦函数改进LMS算法的收敛速度和收敛性;最后,为验证所提出算法的有效性,进行BOTDR温度信号降噪试验。试验结果表明:1)DT-CWT-LMS算法的降噪效果明显优于传统的小波阈值降噪方法,在6个温度梯度上的平均SNR值比WDD、EMT、EMD分别高出43.98%、17.5%、8.4%,平均RMSE值分别降低33.18%、17.14%、9.23%,平均SE值分别降低29.04%、21.17%、20.67%。为验证所提算法在工程现场的有效性,依托北京地铁隧道监测项目,使用DT-CWT-LMS算法对光纤监测信号进行降噪研究,降噪后信号的样本熵平均降低幅为64.03%;2)和常规WDD、EMT、EMD 3种方法相比,DT-CWT-LMS算法在3条光纤上的表现均优于其他3种算法,在1号、2号、3号光纤上的SNR指标比其他3种算法的平均值分别高出22%、38%、27%,说明该算法可作为隧道工程光纤监测信号的一种有效降噪方法。

光加热光纤光栅阵列液位测量方法研究

安全可靠的液位测量是现代工业领域的重要技术需求之一,提出一种基于光加热光纤光栅阵列的液位测量方法,即利用泵浦光加热掺钴光纤,控制温度场,利用光栅阵列测量温度场分布,由于气液导热性能的差别,气液界面处温度突变,从而确定液位。实验中,将掺钴光纤与密集光栅阵列紧密固定在一起,将1.5 W的泵浦光输入衰减系数分别为0.71 dB/cm和0.28 dB/cm的掺钴光纤中,沿着光传播的方向,温度变化均呈指数函数衰减。液位测量的精度与范围由主要取决于泵浦光功率、掺钴光纤吸收系数,经对比最终选定0.28 dB/cm的掺钴光纤作为液位实验的加热光纤。实验测量了不同液位下的温度场分布,证明了利用测量温度分布来测量液位的可行性,液位变化范围0~88 mm以内的误差为2 mm。所提出的传感系统结构简单,成本低廉,在液位测量方面具有潜在的应用价值。

基于分布式光纤传感技术的北京宋庄地面沉降和地裂缝综合监测

针对地面沉降及地裂缝,传统点式监测技术手段难以实现地质体变形的连续监测,且无法通过地面沉降、地裂缝的综合监测定量分析两者之间的关系。基于钻孔全断面分布式光纤监测技术实现了地面沉降和地裂缝同步监测,根据监测结果对北京宋庄地区地下水-地面沉降-地裂缝之间的关系进行了分析。监测结果表明,宋庄地面沉降主要受到地下水开采影响,含水砂层抽水发生压缩变形,地裂缝两侧均存在明显的地面沉降,且差异沉降显著;差异沉降量和地裂缝变形量均持续增大,但增大速率放缓。地面沉降、地裂缝同步监测结果表明,该地区地裂缝发育主要受地层差异沉降影响。

基于分布式光纤传感技术的风电叶片变形监测研究

为研究风电叶片在服役过程中的变形特性,采用分布式光纤传感技术,对叶片在静力试验中的应变场进行监测。试验结果表明,分布式光纤光栅(FBG)传感器能够有效测量风电叶片在静力试验中的各关键部位的应变信息,能承受大载荷下的高应变,测量结果与电阻应变片测量值基本吻合,验证光纤传感技术在风电叶片监测上的可靠性和有效性,为以后风电叶片的挂机在线监测提供可行方案。

埋入式应变感测光缆-冻土界面渐进破坏机制研究

冻胀融沉作用引起的地基土体变形是冻土地区工程建设的典型地质灾害,光纤传感技术为冻土变形的精细化、分布式实时监测提供了重要的技术手段。为探究分布式光纤应变传感在监测冻土变形方面的可行性,利用自主研制的光缆-冻土界面力学特性试验仪,探究了不同干密度和初始含水率的冻土试样中缆-土界面的破坏机制。试验结果表明,光纤应变监测结果准确地反映出缆-土界面呈现渐进性破坏特征,应变软化模型能够较好地描述界面的力学特性。在冻结过程中,土体内液态水相变成冰,引起了冻结锋面移动和水分迁移,使得界面的力学特性存在显著的差异性。不同深度处缆-土界面剪应力的演化过程反映了在光缆拉拔过程中与冻土的变形协调状态,表明光缆测量范围、界面耦合性与土体干密度、初始含水率密切相关。该研究为光纤传感技术在寒区冻土地基变形监测中的应用提供了参考。

水力压裂多裂缝扩展诱发光纤应变演化试验研究

为解决光纤监测水力压裂过程中裂缝扩展形态认识不清的难题,提出了一种基于光纤应变监测的水力压裂物理模拟试验方法。将基于光频域反射(OFDR)技术的分布式光纤解调器与大型真三轴压裂物理模拟试验相结合,开展了人造试样及页岩试样水力压裂光纤实时监测物理模拟试验。试验结果表明,基于OFDR的分布式光纤传感技术可以高空间分辨率、高精度监测应变的演化,光纤的应变数据可以清晰地反映裂缝的产生、扩展和闭合。根据试验结果提出了一种基于光纤应变感测的水力压裂裂缝形态判别准则,该准则可以根据光纤应变演化信息判断部分裂缝类别。研究结论可高效地指导分布式光纤数据解释工作,可为光纤压裂监测的现场规模应用提供参考。

基于分布式光纤的地铁隧道安全风险监测技术及其应用

全站机器人监测系统是地铁隧道安全风险监测的重要技术手段之一,但监测点相对有限。本文基于分布式光纤测量数据,提出了一种基于分布式光纤的地铁隧道安全风险监测技术。首先,将分布式光纤监测系统获取的应变数据映射为更加直观的变形位移数据;然后,通过确定3个输入参数、2个隐含层、1个输出参数,构建基于BP神经网络的应变-位移转换模型,验证结果表明,预测值和真实值的误差在0.2 mm以内,说明所建模型能较好地拟合数据的变化规律;最后,将其应用于青岛地铁1号线某区间,确定401.66~699.45με作为各测点预警值的安全区间,202.49~899.98με作为控制值的安全区间,计算结果与现场实测结果相吻合,误差满足工程需要。