Multicycle experiments performed by slowly tilting granular packings in the range $\pm {\theta }_M$ are analyzed for ${\theta }_M=21$, 22, 23, and $23.5^{\circ }$. Based on optical measurements of the free surface activity, a method is developed to detect numerous bead rearrangements associated to almost regular peaks of activity: on average, 1800 events are detected during an experiment. Occurring ${11}^{\circ }$ after the beginning of the inclination, precursors represent 75% of these events and the interprecursor angle tends to decrease when the surface activity increases. The evolution of the cumulative activity with the half-cycle number can be approximated by a stretched exponential function with an exponent $\beta$. The characteristic time for the system to reach a steady state of activity linearly increases with ${\theta }_M$. The residual activity also increases but reaches a plateau. The energy injected into the system by successive gravity destabilizations decreases with ${\theta }_M$: when ${\theta }_M\le {22}^{\circ }$, $\beta \le 1$ suggests relaxation processes and compaction induced by the precursors themselves increases the stability of the packing. An in-depth force sensor measures the precursor-induced activity at the wall of the grain container: a linear dependency relates wall and surface activities. In-depth acoustic measurements are used to trigger surface high-speed optical signals: during a precursor, which duration is of about 0.18 s, the elastic wave velocity inside the packing drops to few ${\mathrm{m}.\mathrm{s}}^{-1}$ because of weak intergrain contacts that allow beads to rearrange.

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• Granular avalanches
• Acoustic techniques
• Optical techniques