Fig. 2
Fiber position–strain distribution plots. (a) Fiber length (m) is shown on the horizontal axis and strain (µε) on the vertical axis. Colored horizontal arrows with numbers on the top indicate the positions of the six vertical fiber segments. At 14:29:30, six distinct negative strain pulses appear, each corresponding to one of the six vertical fiber sections, with measurable pulse widths. By 15:17, the widths increase, though not uniformly across all fiber positions. Downward bending of the strain curve is observed at bottom support points A, C, and E due to the added weight of percolated water, while no significant strain changes occur at the top support points B and D. At 16:17:47, the water–sand system reaches dynamic equilibrium between gravitational forces from water and sand (acting on support points A, C, and E) and buoyant forces (blue arrows) acting on all six fiber sections. (b) Time series of fiber position–strain distribution plots for fiber segments #1 and #2, with fiber length (m) on the horizontal axis and strain amplitude (µε) on the vertical axis. From 14:29:30 to 16:04:23, pulse widths gradually widen (highlighted by red arrows and blue dashed lines), reflecting increasing depths influenced by water percolation. The reverse-symmetric widening between segments #1 and #2 results from their opposite fiber orientations.
