Long-term Deformation Monitoring of CERN Concrete-lined Tunnels using Distributed Fibre-optic Sensing
V. Di Murro, L. Pelecanos, K. Soga, C. Kechavarzi, R.F. Morton, L. Scibile
ABSTRACT: The Centre for European Nuclear Research (CERN) uses large and complex scientific instruments to study the basic constituents of matter by operating a network of underground particle accelerators and appurtenant tunnels. Long-term safety and structural health of this critical infrastructure highlighted the need for a sensing plan that could provide remote monitoring and resistance to high radiation. A pilot Distributed Fibre-Optic Sensing (DFOS) system using Brillouin scattering was used to instrument 8 tunnel sections and obtain a first set of short-term readings. These preliminary readings show minor tunnel ovalisation and will be used as baseline for future long-term readings.
KEYWORDS: Fibre-optic sensing, Tunnels, Soil-structure interaction, Brillouin scattering, Long-term monitoring
Distributed Brillouin Sensing for Geotechnical Infrastructure: Capabilities and Challenges
N. Noether and S. von der Mark
ABSTRACT: Distributed Brillouin sensing has become a state-of-the-art tool for strain and temperature monitoring in concrete and geotechnical applications throughout the civil construction industry. While commercially available systems are steadily advancing in terms of spatial resolution and measurement length, end-users in field installations often put the focus on softer parameters like linearity or optical budget when evaluating the performance of the technology.
This paper addresses the implications of high spatial resolution to the accuracy of relative and absolute strain and temperature data from the perspective of the Brillouin optical frequency domain analysis (BOFDA) technology, and outlines the need for a clear definition and a standardization scheme to make the terms dynamic range and optical budget comparable between different instruments and technologies. Data from field applications in concrete pile monitoring is used to discuss the above aspects.
KEYWORDS: Distributed fiber-optic Brillouin sensing, BOFDA, Spatial resolution, Dynamic range
State-of-the Art of Geotechnical Monitoring with Geodetic Techniques
W. Lienhart
ABSTRACT: This paper presents state-of-the-art knowledge on upheaval buckling, providing an overview on commonly used upheaval buckling soil models, latest uplift resistance results from experimental and numerical studies, investigations into the factors affecting the uplift resistance of soils and recommendations for design. The paper addresses the uplift resistance for both onshore and offshore pipelines. For onshore pipelines, the backfill soil cover could be dry, fully saturated or partially saturated. Thus, insight into the effects of degree of soil saturation on the uplift resistance is provided. For offshore pipelines, predicting the uplift resistance of buried pipelines has been a challenge due to uncertainty and randomness in the nature of soil cover created by various pipe burial techniques. This paper provides guidelines, supported by published literature, on the uplift resistance of different types of backfills such as sands, clays and blocky clays. An insight into the cyclic ratcheting mechanism, which is the driving mechanism leading to UHB pipeline failures, is also provided. It is expected that the paper will be a valuable source of information for designers and consultants undertaking pipeline designs both onshore and offshore.
KEYWORDS: Upheaval Buckling, Uplift resistance, Pipelines, Cyclic Ratcheting
Performance Assessment and Failure Prediction of Corroded Cast Iron Pipes
P. Rajeev and D. Robert
ABSTRACT: The increasing failure rate in deteriorating pipe and unplanned failures will increase economical loss and social impact. One of the important tasks in the asset management framework is to estimate the pipe stress of a certain pipe section subjected to operational loads and corrosion. These factors may, however, be considered uncertain not only at a given point of time, but also have substantial time variance. The probability of structural failure of pipes can be estimated using Monte Carlo type simulation conjunction with pipe stress analysis models. This paper assess the pipe performance using different pipe stress prediction models and 3-D finite element analysis. Further, the effect of corrosion was modelled and incorporated with stress prediction models to assess the pipe performance over the lifetime. Finally, the probability of failure was computed and discussed in application with a case study of buried cast iron pipe subjected to external corrosion and loadings.
KEYWORDS: Cast iron, corrosion, pipe, probability of failure, asset management, numerical analysis
Comparative Study of Distributed Sensors for Strain Monitoring of Pipelines
B. Glisic
ABSTRACT: Natural calamities such as landslides, sinkholes, and earthquakes, as well as man-induced events such as vandalism and terrorist acts, can cause significant deformation and damage to pipelines with potentially devastating humanitarian, social, economic, and ecologic consequences. Therefore, a real-time assessment of the condition of pipelines during and after such events is crucial. Distributed fibre optic technologies are ideal candidates for monitoring pipelines, due to their large spatial range, and relatively small spatial resolution. Nevertheless, practical manufacturing and implementation of distributed strain sensors, as well as their response to various actions is not yet fully understood. The aim of this paper is to compare performances of different distributed fibre optic strain sensors in terms of strain transfer quality, costs, and implementation approaches. Comparison is made qualitatively, based on experience, and quantitatively, through large-scale testing, by simultaneously exposing different sensors bonded on the pipeline wall and embedded in the soil in its proximity, to various levels of artificially induced permanent ground movement.
KEYWORDS: Distributed fibre optic strain sensors, Pipeline monitoring, Strain and deformation monitoring, Strain transfer, Large-scale testing
Instrumented Laterally Loaded Pile Test using Distributed Fibre Optic Sensor
H. Mohamad, B.P. Tee, M.F. Chong, K.A. Ang, A.S.A. Rashid and R.A. Abdullah
ABSTRACT: Instrumented horizontal pile load test is widely used to evaluate lateral soil resistances/parameters and to verify design assumptions. Recent technological advancement of optical fibre sensing has led new ways in measuring the lateral load-deflection profile. The distributed sensing, namely Brillouin Optical Time Domain Analysis (BOTDA) is a novel technique of measuring strains in a spatially continuous manner. By installing distributed fibre optic strain sensing cables, continuous strain profile and deflection curve throughout the pile can be obtained. The objective of this article is to present one of the earliest deployment of BOTDA optical fibre sensors in lateral pile load test in Malaysia under offshore environment and share invaluable lessons learned from the instrumentation process. Installation method, lateral load test setup and data interpretation are also discussed. The computed lateral pile load-deflection profile was in excellent agreement with the measured pile top deflection using displacement sensors. The location of cracks detected based on continuous strain profile was also in good agreement with result of Low Strain Integrity Testing.
KEYWORDS: BOTDA, Pile instrumentation, Lateral load, Marine structure
Distributed Fibre Optic Sensing for Monitoring Reinforced Concrete Piles
C. Kechavarzi, L. Pelecanos, N. de Battista and K. Soga
ABSTRACT: Distributed fibre optic sensing (DFOS) presents several advantages over traditional point sensors, for measuring strain and temperature in civil and geotechnical infrastructure. DFOS techniques use light transmitted through an optical fibre to enable measurements to be taken all along an embedded or surface-mounted fibre optic cable, which can be up to several kilometres long. This makes DFOS particularly useful for monitoring linear structures and to detect the potential existence of any anomalies which are usually unpredictable. Hence, DFOS has gained in popularity for monitoring reinforced concrete piles, especially during pile testing.
The spatially continuous strain data from DFOS provide detailed information about load transfer along the pile but can also be used to calculate vertical displacements and shaft friction through numerical integration and differentiation, which are useful for validating relevant performance-based numerical models. This paper introduces the methodology and illustrates these advantages through an example obtained from an instrumented pile load test in London. While it synthesises a number of lessons learned in the application of DFOS for pile testing, it also supports the case for routine long-term monitoring of working piles.
KEYWORDS: Distributed fibre optic sensing, Pile load test, Strain, Shaft friction, Monitoring
State-of-the Art Knowledge on Upheaval Buckling of Buried Pipelines
Indrasenan Thusyanthan and Dilan Robert
ABSTRACT: This paper presents state-of-the-art knowledge on upheaval buckling, providing an overview on commonly used upheaval buckling soil models, latest uplift resistance results from experimental and numerical studies, investigations into the factors affecting the uplift resistance of soils and recommendations for design. The paper addresses the uplift resistance for both onshore and offshore pipelines. For onshore pipelines, the backfill soil cover could be dry, fully saturated or partially saturated. Thus, insight into the effects of degree of soil saturation on the uplift resistance is provided. For offshore pipelines, predicting the uplift resistance of buried pipelines has been a challenge due to uncertainty and randomness in the nature of soil cover created by various pipe burial techniques. This paper provides guidelines, supported by published literature, on the uplift resistance of different types of backfills such as sands, clays and blocky clays. An insight into the cyclic ratcheting mechanism, which is the driving mechanism leading to UHB pipeline failures, is also provided. It is expected that the paper will be a valuable source of information for designers and consultants undertaking pipeline designs both onshore and offshore.
KEYWORDS: Upheaval Buckling, Uplift resistance, Pipelines, Cyclic Ratcheting
Cost Effective Free Span Rectification for Offshore Pipelines
Indrasenan Thusyanthan
ABSTRACT: Offshore pipelines often experience free spans due to uneven seabed, local scour or a storm event. When free span lengths are beyond acceptable limits, vortex induced vibrations (VIV) can cause pipelines to undergo fatigue damage and severely reduce the pipeline’s design life. Therefore, surface laid offshore pipelines are periodically surveyed to ensure that there are no free spans that are beyond the acceptable limit. When such free spans are identified, they are rectified immediately, often by grout bags. While grout bag use is a standard solution for free span rectification, it does not always provide a long-term remedy to free spans. Often lines rectified by grout bags needs further free span rectification the following year. The onset of more free spans and the need for rectification cycle often continues annually when grout bags are used. This paper presents a cost effective long-term free span rectification method known as “Pipeline Lowering.” This unique solution will ensure the free span rectification is a long-term fix compared to grout bags that may be affected by scour and wave loadings. This paper provides vital technical knowledge for pipeline engineers, contractors and operators who need to ensure free spans are rectified safely and efficiently.
KEYWORDS: Free span rectification, Pipelines, Seabed, Mass flow excavator
Distributed Optical Fiber Sensors for Strain and Deformation Monitoring of Pipelines and Penstocks
D. Inaudi
ABSTRACT: Pipeline and penstock management present challenges that are quite unique. Their long length, high value, high risk and often difficult access conditions require continuous monitoring and optimizing maintenance interventions. One of the main concerns for pipeline owners involves the development of excessive strain due to external action, potentially leading to cracking or buckling. The onset of those strain hot-spots can be detected and localized using distributed fiber-optic sensors. Additionally, pipeline strain distribution and soil movement can be identified using the same technology. The aim of this review paper is to present the main technologies used for distributed strain and deformation monitoring of pipelines or penstocks and illustrate their applications through several application examples.
KEYWORDS: Distributed Sensing, Optical Fiber Sensors, Pipeline monitoring, Penstock monitoring, Deformation monitoring
A Methodology for Identification of Pipe Failure Hotspots
Ravin N Deo, Chunshun Zhang, Jian Ji, Suranji Rathnayaka, Benjamin Shannon, Jayantha K Kodikara
ABSTRACT: This study provides a methodology that can be utilised for identifying pipe sections, which can be considered under high risk of failure. Application of the proposed methodology is demonstrated using a case study involving an in-service large (~1.7 km) critical water main in Sydney, Australia. Geospatial features from Google Earth ProTM and Google Street ViewTM were used to assess and quantify typical urban environmental attributes, which can be used for identifying pipe failure hotspot locations. Failure history was used to verify the basis of the methodology developed. It was demonstrated that a sound assessment of the pipe conditions is possible through inexpensive geospatial feature analysis. This development can greatly enhance and reduce costs associated with current pipe condition assessment processes.
KEYWORDS: Pipe failure, Corrosion, Hotspots, Condition assessment, Geospatial platform
ADYTrack: Development of a Railroad Trackbed Model and Parametric Study of Track Modulus
Asif Arshid, Ying Huang, and Denver Tolliver
ABSTRACT: Deformation prediction of railroad trackbed has always been a challenge for the railroad designers and engineers. There are many complex interactions take place simultaneously between superstructure and subgrade of railways trackbed, which simply make the deformation predictions harder. Numerical models offer an alternative to simulate the performance of the substructure of railroad with considerable accuracy. In this paper, a finite element based three-dimensional (3D) model has been developed in MATLAB. This model has the capability to study the effects of track modulus, subgrade modulus, interactions between track and soil, the track geometry, and the wheel loads. The rails and ties are modelled as two node beam (line) elements and the substructure (ballast, subgrade etc.) is modelled as eight node isoperimetric hexahedron brick elements. The rail-tie interaction is modelled using a liner elastic spring elements. The model was first calibrated against an identical model built ANSYS (APDL), a reliable commercial software. The results of the ADYTrack are further validated with other numerical models and full-scale field test results reported in the literature. Following successful validation, a detailed parametric study is conducted to study the response of track modulus for a typical All-Granular trackbed using practical range of values for the variables involved. Numerical analysis showed that subgrade resilient modulus substantially impacts the track modulus. Furthermore, the depth of the ballast, moment of inertia of rail beams and tie spacing reasonably affected the track modulus, in a decreasing order.
KEYWORDS: Railroad, Numerical Models, Finite Element Analysis, Subgrade Soil, Track Modulus
Leakage-induced Pipeline Stressing and its Potential Detection by Distributed Fiber Optic Sensing
A. Klar, A., Linker, R. and Herrmann, S.
ABSTRACT: The paper aims to develop an approximated analytical solution to model the bending moment profile in a sewage pipe, buried within an unsaturated soil, which occurs as a result of a leak. The solution involves evaluation of the greenfield displacements due to a buried point source, and its use as an input to a soil-pipeline interaction problem. The solution is extended for a general wetted sphere (having different degree of saturation with the radial distance). The final model is tested against finite element simulations of the coupled problem without the simplified assumptions and approximations, and is found to be satisfactory. The work may be considered a first step towards realization of a distributed fiber optic sensing system that, together with an appropriate spatial signal analysis, could identify leaks at their early stage. The current analysis indicates that the developed strain signal (and its profile) could be detectable for leaks having liquid loss as little as 300 to 500 liters.
KEYWORDS: Pipelines, Leaks, Soil-pipe interaction, Elastic solution, Sewage
Smart Geosynthetics based on Distributed Fiber-optic Sensors in Geotechnical Engineering
A. Wosniok and K. Krebber
ABSTRACT: Smart geosynthetics with embedded optical fibers as distributed sensors provide solutions both for applications in geotechnical engineering and for cost-effective monitoring of critical infrastructures. The incorporation of glass or polymer optical fibers (GOFs or POFs) in geotextiles and geogrids allows early detection of mechanical deformations, temperature and humidity. This paper presents selected examples of smart geosynthetics based on Brillouin and Rayleigh scattering effects in incorporated fiber optic sensors for monitoring of large geotechnical structures like dikes, dams, railways, embankments or slopes. The focus of the presented work is on real field tests of measurement capability with respect to the chosen measurement principle and used fiber type.
KEYWORDS: Smart geosynthetics, Fiber optic sensor, Distributed sensing, Glass optical fiber (GOF), Polymer optical fiber (POF)
Loss of Flexibility in Geosynthetics Subjected to Chemical Exposure: Experiments, Constitutive Models and Computations and Estimates for Contaminant Leakage
A. P.S. Selvadurai
ABSTRACT: The paper presents results of recent research related to the development of advanced mathematical models for describing the behaviour of strain rate sensitive materials such as geosynthetics that are used extensively as barriers to the migration of contaminants and other hazardous materials. The important finding of the research is that the leaching of the plasticizer from the geosynthetic can lead to a loss of hyperelasticity of the material, which is a key functional requirement for a geosynthetic. It is also shown that constitutive models can be developed to describe the mechanical behaviour of the geosynthetic in its virgin state and upon direct exposure to pure ethanol for thirteen months. A computational approach is used to evaluate the results of separate laboratory experiments involving transverse indentation of geosynthetic membranes that are fixed along a circular boundary and tested in either its untreated state or after prolonged exposure to ethanol.
KEYWORDS: Geosynthetics, Loss of plasticizer, Constitutive modelling, Membrane indentation tests, Computational modelling
Monitoring of Buried Pipeline using Distributed Fibre Optic Technologies: Combined Acoustic-Temperature-Strain sensing
C. Prohasky, R. Vivekanantham, P.Rajeev, H. Bao, and S. Roy
ABSTRACT: This paper presents the development of distributed optical fiber sensing system, which combined acoustic-temperature-strain sensing to enhance the condition monitoring of buried pipeline. The developed optical fiber system was tested using the 140 m long pipe-soil test facility built in the Hawk testing yard. Cement lined steel pipes with the diameter of 100 mm and 500 mm were buried at the depth of 800 mm and optical fiber cables were attached at four different locations around the pipe section. The pipe section was also instrumented with contact microphones to detect the acoustic signal. Various size of leaks were made along the pipe section and monitored using the acoustic signal and temperature sensing. Both acoustic and temperature sensing detected the leak reliably with required accuracy up to distance of 40 km. Using the combination of acoustic and temperature helped confirm the leak and reduce the false positives.
KEYWORDS: Brillouin scattering, Rayleigh scattering, Raman scattering, Distributed sensor, COTDR, Buried pipe
Benefits of Standards for Fiber-optic Sensors in Soil-structure Interaction
W. R. Habel and J. K. Jeyapalan
ABSTRACT: Measurement and data recording systems are important parts of a holistic Soil-Structure Interaction Health Monitoring (SSIHM) system. New sensor technologies such as fiber-optic sensors (FOS) are regarded at times as experimental despite the strong track record; standards or at least guidelines not being widely available internationally has always been an impediment. This lack in standardization makes the acceptance of FOS technologies in SSIHM systems more difficult. Some success has been made in publishing first standards to fill this gap over the past decade. Much more effort is needed in this area and this paper gives an overview of what has been accomplished, what is in progress, and what obstacles were along the way. A case is made for a truly independent standard writing platform that can govern itself for the fiber-optic sensing industry composed of its sellers, buyers and subject matter experts.
KEYWORDS: Fiber-optic sensor, distributed sensor, standard, temperature, strain, monitoring
Rational Methods of Steel Pipe Design Accounting for Poor Native Soils and Soil Migration
J. K. Jeyapalan, G. Leonhardt, P. Rajeev, and A. M. Britto
ABSTRACT: In poor native soils there is always a concern whether sufficient embedment support around the haunch and spring line level exists to prevent over-deflection of steel pipe. Engineers become confused given the two extreme positions on trench width – steel pipe suppliers advocating two pipe diameters while a government agency like U.S. Bureau of Reclamation (USBR) recommending the use of five pipe diameters. Methods from the German ATV A127 or Leonhardt, rely on a ratio of the side fill En’ to the embedment Eb’ and the ratio of the trench width to the outer diameter of the pipe to select site specific trench width. When pipe suppliers quote Marston’s work on rigid concrete pipe from 1913, to make their case that a relatively narrow trench is better in poor native soils even for flexible steel pipe, they introduce the risk of inducing the buyers to ask – has the pipeline industry not seen new developments over the past 100 plus years? This paper reviews the fallacies surrounding various methods on how to cope with poor trench wall conditions and provides a rational method. This paper also covers the phenomenon of soil migration, its significance in buried pipeline design and performance and the adverse consequences if not considered.
KEYWORDS: Steel pipe, Embedment, Native soil, Combined E’, Soil migration
Technical Challenges and Solutions for Super-Long Mountainous Tunnels at Great Depth
Yan Jinxiu
ABSTRACT: There are various technical challenges faced by the construction of super-long mountainous tunnels at great depth, and also a series of new requirements for tunnelling arising from such aspects as geological investigation, construction duration, special geological conditions (high ground stress, high geothermal temperature and high-pressure groundwater), disaster prevention & evacuation and social development. Based on an analysis of the above-mentioned technical challenges, this paper presents technical views on solutions to those challenges and specifies the objectives of related technical development in the future. To improve the validity and accuracy of the geophysical prospecting, it is necessary to not only increase the accuracy of ground geophysical exploration at great depth, but also carry out research on the application of such techniques to tunnel investigation as airborne geophysical prospecting and HDD combined with borehole geophysical exploration. To maximize the benefits of tunnel projects, it is of importance that more attention should be paid to those issues relating to the tunnel design concept, such as the multiple functions of tunnel projects, energy saving and emission reduction, and environmental protection. As for tunnel support theories, in addition to optimizing the current theories, some unconventionally new lining theories need to be put forth to make the tunnel structure more durable and economical. It is also suggested that, in terms of construction, sustained efforts should be put into the development of innovative tunnelling techniques for a better, faster and more economical tunnelling, as well as the realization of intelligent mechanized tunnelling. When it comes to operation, it is obvious that there will be a trend towards intelligent maintenance in the future.
KEYWORDS: Tunnels at great depth; Super-long tunnels; Mountainous tunnels; Technical challenges; Solutions; Development trend
Risk Analysis and Countermeasure Study of Shield Tunnelling in Karst Stratum of China
Zhong Changping, Zhu Weibin, Huang Weiran, Zhu Siran and Xu Minghui
ABSTRACT: In China, many cities have the experience of shield construction practice in Karst stratum, such as Guangzhou, Nanning, Changsha, Wuxi and Dalian. In the Karst area, there are many construction risks such as groundwater inflow, sand inflow, surface subsidence, cutter head damage and expulsion-retarded of slurry shield. Based on the analysis of the development mechanism of the Karst and the practice of the shield tunneling in the Karst stratum of Guangzhou and Nanning Metro, this paper analyses the main risks in the process of shield tunneling, and according to concrete construction risks, it proposes concrete controlling measures from the aspects of planning of the line shallow buried, the pretreatment of the Karst cave and shield selection and construction control, which provides significant guidelines for the shield tunneling under the similar Karst stratum condition.
KEYWORDS: Karst stratum, Shield tunneling, Risk analysis, Countermeasure study
