We investigate the restoration of topological protection at armchair interfaces in quantum valley Hall systems by introducing an adiabatic geometry. In conventional armchair boundaries, strong intervalley mixing between K and ${\mathrm{K}}^{\prime }$ valleys opens a gap in the interface modes and degrades topological protection. Here, we show that a smoothly varying mass domain wall suppresses intervalley mixing and closes the inner band gap of the interface modes, leading to the recovery of topological protection over a wide frequency range within the bulk band gap. Numerical transport simulations demonstrate enhanced transmission efficiency and strong robustness against structural defects. We further implement the adiabatic topological geometry as microelectromechanical system-based phononic waveguides, and experimentally verify robust wave propagation through sharply bent (${90}^{\circ }, {120}^{\circ }$, and ${150}^{\circ }$) interfaces. Suppressing valley mixing via adiabaticity provides a versatile design framework for topological waveguides and enables robust topological characteristics across a wide range of wave phenomena.

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• Acoustic phonons
• Topological edge modes
• Topological mechanics
• Topological phases of matter
• Valley degrees of freedom
• Honeycomb lattice
• Micromechanical devices