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Piping Particle Movement using a Seepage Test Based on NMR Technology

ABSTRACT Xu, Z.; Wang, X., and Chai, J., 2020. Piping particle movement using a seepage test based on NMR technology. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 12–17. Coconut Creek (Florida), ISSN 0749-0208. As a kind of seepage failure mode occurred in hydraulic earth structures (dikes, levies, or dams), piping could cause dam-break in earth-rock dams. Additionally, although many investigators have applied many experiments to study the mechanism of piping, the initiation and development mechanism of piping is still poorly understood. In this study, a vertical piping test was conducted on stained noncohesive soil by an experimental device to measure a serial of parameters (the critical hydraulic gradient, porosity, upper particle size of lost particles, and accumulated sediment) in the development of piping phases. The particle migration pattern and change of porosity were then observed by the nuclear magnetic resonance (NMR) technology. The results show that the phases of piping are controlled by the content of movable particles and the particle size distribution curve. Three migration types of particles can be distinguished by NMR results and stained noncohesive soil during the piping phase. On basis of the empirical formula between hydraulic gradient and flow rate, if it shows a liner that means the soil is still well graded during the piping; if it divides into two separate lines that means the soil is unstable in the range covered by the second line. Additionally, the critical hydraulic gradient is located around the lines' connection points.