Drying-induced soil shrinkage and desiccation cracking monitoring with distributed optical fiber sensing technique
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ORIGINAL PAPER
Drying-induced soil shrinkage and desiccation cracking monitoring with distributed optical fiber sensing technique Qing Cheng 1 & Chao-Sheng Tang 1 & Cheng Zhu 2 & Ke Li 1 & Bin Shi 1 Received: 24 July 2019 / Accepted: 10 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Monitoring of drying-induced volume shrinkage and desiccation cracking in clayey soils is of great importance in geological and geotechnical engineering. Compared with conventional strain monitoring methods providing discrete measurements, the Brilliouin optical time domain reflectometer (BOTDR) technique enables continuous measurement of the distributed strain generated along optical fibers. In this study, a physical model test is conducted to investigate the feasibility of monitoring drying-induced soil shrinkage and desiccation cracking using BOTDR. Three optical fibers with different surface protections (thermoplastic polyester elastomer (TPEE) jacket, nylon jacket, and acrylate coating) are tested and compared. Experimental results validate that BOTDR is applicable for the direct strain monitoring of desiccation cracking soils. Monitored strain values are strongly influenced by water content, soil cracking, and fiber types. The strain measured by the optical fiber reaches only several micro strains when the soil is over-saturated, gradually increases with the decreasing water content and the increasing soilfiber interfacial shear stresses, and drops rapidly after the occurrence of decoupling between fiber and soil resulting from the mature development of desiccation cracks. The optical fiber with acrylate coating is not suitable because of its fragility and the poor interfacial coupling with the soil. Optical fibers covered with TPEE jacket or nylon jacket are both applicable for soil strain monitoring, with the former one more sensitive to water content variations. The study is the first attempt to apply the BOTDR technique for the direct and continuous monitoring of drying-induced soil shrinkage and desiccation cracking process. It is expected bring new insights into the fundamental understanding of volumetric shrinkage and desiccation cracking in clayey soils. Keywords Volumetric shrinkage . Brilliouin optical time domain reflectometer (BOTDR) . Optical fiber sensing . Desiccation crack . Strain monitoring
Introduction * Chao-Sheng Tang [email protected] Qing Cheng [email protected] Cheng Zhu [email protected] Ke Li [email protected] Bin Shi [email protected] 1
School of Earth Sciences and Engineering, Nanjing University, 163 Xianlin Avenue, Nanjing, China
2
Department of Civil and Environmental Engineering, Rowan University, 201 Mullica Hill Road, Glassboro, NJ 08028, USA
In recent years, drought events increase in frequency, severity, and duration due to global climate change (IPCC 2015). Consequently, soils experience significant water evaporation as well as volume shrinkage, resulting in ground subsidence and severe damage to buildings and infrastructures (Corti et al. 2009; Cui
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