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Optimization of early seepage detection in embankments using a distributed temperature system based on fiber optic sensing : doctoral dissertation
ID Ghafoori, Yaser (Author), ID Kryžanowski, Andrej (Mentor) More about this mentor... This link opens in a new window, ID Říha, Jaromir (Co-mentor), ID Logar, Janko (Thesis defence commission member), ID Vižintin, Goran (Thesis defence commission member), ID Fry, Jean-Jacques (Thesis defence commission member)

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Abstract
Seepage is the most important indicator in the safety assessment of embankments which requires continuous monitoring to maintain structural integrity. Punctual monitoring techniques for seepage in embankments can only provide limited information on the process. As the thermal behavior of embankments is affected by seepage, a continuous temperature measurement system can be established in embankments to identify the possible seepage flow. With the advancement of fiber optic measurement technology, measurement equipment is available that allows distributed temperature sensing. Optical fiber Distributed Temperature Sensor (DTS) was developed to measure the ambient temperature along the entire length of the fiber optic cable at an arbitrary time interval. There are two techniques to perform this measurement: passive measurement technique and active measurement technique, which, unlike passive measurement, require an additional power supply. The passive measurement technique measures the natural temperature of the soil and is therefore suitable for long-term temperature monitoring in embankments. In this thesis two objectives were set: first, that it is possible to detect the onset of seepage in embankments with a DTS fiber optic cable measurement system based on the passive measurement technique, and second, that the correct distribution of the DTS fiber optic cable system increases the ability to detect the onset of seepage in embankments at an early stage. The experimental part of the task was carried out in two phases. In the first part, a small-scale experimental model was developed to simulate the seepage phenomenon in embankments. The soil material was replaced in the model by quartz sand with three different granulometric compositions. The hydraulic and thermal properties of the materials were obtained from laboratory tests or the relevant literature. In the second part, a largerscale experiment was carried out under laboratory conditions, using only one type of silica sand. By simulating the seepage process under laboratory conditions, it has been shown that the DTS optical cable measurement system can detect any small temperature changes in the sand layer as a result of the seepage phenomenon. The system can detect the start of the seepage process in the initial stages, as well as monitor the progress of the seepage process, even in cases where there are small temperature differences between the soil and the seepage water. The numerical analysis was conducted for both the seepage process and the heat transfer progression in soil. A clear relation between the variation in the degree of saturation and temperature measurements was observed visually in experiments and in the numerical simulation. The application of passive DTS for seepage detection in embankments was validated. The efficiency of DTS application in seepage monitoring strongly depends on the optical fiber installation approach, calibration technique, temperature data interpretation, and post-processing. To achieve the accuracy of the measurement capture, a special method of laying the fiber-optic cable with loops was used, based on the configuration of the sensory ring, which allows precise point-to-point measurement capture. Some guidelines for optimization of optical fiber DTS application were provided by a comprehensive review of different techniques to interpret temperature data in terms of seepage information. Additionally, different methods for the calibration of DTS data were reviewed. Various techniques both in calibration and interpretation were classified and their comparison was provided that can be used for a more efficient DTS employment in seepage detection. A method was also suggested for the interpretation of DTS data based on the comparison of numerical results with the obtained temperature measurements in embankments.

Language:English
Keywords:Built Environment, civil engineering, doctoral thesis, embankment, seepage, temperature, optical fiber DTS, soil
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FGG - Faculty of Civil and Geodetic Engineering
Place of publishing:Ljubljana
Publisher:[Y. Ghafoori]
Year:2023
Number of pages:XXII, 136 str.
PID:20.500.12556/RUL-144087-f99d130b-9712-e7e8-a091-3bd3af402e19 This link opens in a new window
UDC:532.5:676.017.6:679.746.5(043)
COBISS.SI-ID:140567043 This link opens in a new window
Publication date in RUL:31.01.2023
Views:870
Downloads:108
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Secondary language

Language:Slovenian
Title:Optimizacija postopka zgodnjega zaznavanja pojava precejanja vode v nasipih na podlagi spremljanja temperaturnega polja z optičnimi kabli : doktorska disertacija
Abstract:
Precejanje je najpomembnejši kazalec pri izdelavi ocene varnosti nasutih pregrad in nasipov in zahteva izvajanje stalnega nadzorstva s ciljem ohranjanja kondicijskega stanja objektov. S konvencionalnimi tehnikami s točkovnim spremljanjem precejanja v nasipih in nasutih pregradah lahko pridobimo le omejene informacije o poteku procesa. Ker pojav precejanja vpliva na toplotno obnašanje nasipov, lahko morebitni pojav precejanja ugotavljamo z vzpostavitvijo stalnih meritev temperature v nasutih pregradah in nasipih. Z napredkom merilne tehnike z uporabo optičnih vlaken je na voljo merska oprema, ki omogoča porazdeljeno zaznavanje temperature - porazdeljeni temperaturni senzor (DTS), ki meri temperaturo okolice vzdolž celotne dolžine optičnega kabla v poljubnem časovnem intervalu. Pri tej merilni tehniki razlikujemo dva načina izvedbe meritev: s pasivno merilno tehniko in aktivno merilno tehniko, ki za razliko od pasivne merilne tehnike zahteva dodatno energetsko napajanje. S pasivno merilno tehniko izvajamo meritve temperature zemljine, zato je ta metoda primerna za dolgoročno spremljanje temperature v nasutih pregradah in zemeljskih nasipih. V disertaciji smo postavili dva cilja: prvič, da je možno pojav precejanja v pregradah zaznati z merskim sistemom DTS z optičnimi kabli, ki temelji na pasivni merilni tehniki in drugič, da pravilna porazdelitev sistema DTS z optičnimi kabli poveča sposobnost zgodnje zaznave pričetka precejanja v nasutih pregradah in nasipih. Eksperimentalni del naloge smo izvedli v dveh fazah. V prvem delu smo pripravili manjši poskusni model za simulacijo pojava precejanja v nasipih. Zemeljski material smo v modelu nadomestili s kremenčevim peskom s tremi različnimi granulometričnimi sestavami. Hidravlične in toplotne lastnosti materialov so bile pridobljene iz laboratorijskih preskusov ali iz ustrezne literature. Osnovni namen tega preliminarnega poskusa je bilo opredeliti osnovne parametre za izdelavo poskusnega modela v večjem merilu (izbira in način vgradnje materiala, namestitev merskega kabla, simulacija precejanja v sloju kremenčevega peska,...). V drugem delu smo izvedli poskus v večjem merilu v laboratorijskih razmerah, pri čemer smo uporabili samo en tip kremenčevega peska, ki se je v predhodnih preiskavah izkazal kot najustreznejši. S simulacijo procesa precejanja v laboratorijskih razmerah smo dokazali, da je z merskim sistemom DTS z optičnimi kabli mogoče zaznati kakršne koli majhne spremembe temperature v peščenem sloju, ki so posledica pojava precejanja. Sistem omogoča zaznavo pričetka poteka precejanja v začetnih fazah, kot je spremljanje napredujočega procesa precejanja, tudi v primerih, ko gre za majhne temperaturne razlike med zemljino in precejno vodo. V nadaljnjem koraku smo izvedli numerično analizo, tako za potek procesa precejanja, kot tudi za potek prenosa toplote v tleh. Dokazali smo jasno povezavo med variiranjem stopnje zasičenosti in izmerjene temperature tako z vizuelnim zapažanjem pri izvajanjulaboratorijskih preskusov, kot pri numeričnih simulacijah. Potrdili smo ustreznost uporabe pasivnega sistema DTS za zaznavanje precejanja v nasipih. Ugotovili smo, da je učinkovitost uporabe DTS pri spremljanju pojava precejanja močno odvisna od načina namestitve optičnih vlaken, tehnike umerjanja, interpretacije temperaturnih podatkov in naknadne obdelave rezultatov meritev. Za dosego natančnosti zajema meritev smo uporabili poseben način položitve optičnega kabla z zankami, ki temelji na konfiguraciji zaznavnega obroča in omogoča natančen točkovni zajem meritev. Na podlagi celovitega pregleda različnih tehnik za interpretacijo podatkov o temperaturi v zvezi s pojavom precejanja smo podali smernice za optimizacijo uporabe merskega sistema DTS z optičnimi kabli. Poleg tega smo pregledali različne metode za umerjanje rezultatov meritev s sistemom DTS z optičnimi kabli. Razvrstili smo različne tehnike, tako pri umerjanju kot pri interpretaciji meritev in jih primerjali glede njihove uporabnosti za učinkovitejšo uporabo sistema DTS z optičnimi kabli pri ugotavljanju poteka precejanja. Predlagana je bila tudi metoda za interpretacijo podatkov DTS, ki temelji na primerjavi numeričnih rezultatov z dobljenimi meritvami temperature v nasipih.

Keywords:Grajeno okolje, gradbeništvo, disertacije, nasipi, precejna voda, temperatura, optični kabel, zemljina

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