<p>In remote or hazardous environments where traditional testing methods are impractical, rapid, invasive impact penetration techniques can assess in situ soil mechanical properties. Cone impact penetration testing (CIPT) in calibration chambers develops empirical correlations and validates numerical models. Understanding the cone penetration process requires quantifying soil’s response during penetration. This understanding enables CIPT measurements to be linked to surrounding soil conditions, thus improving interpretation methods. However, the mechanisms governing impact penetration in highly weathered sand remain poorly understood, limiting advances in related technologies. To address this gap, this study presents a meso- and macroscale investigation of impact penetration in highly weathered sand from Yangbajing, Tibet, integrating laboratory experiments, high-speed imaging via digital image correlation (DIC), and discrete element method (DEM) simulations. Calibration chamber tests with a newly developed impact penetrometer yielded in situ cone tip resistance and deceleration. Furthermore, a semi-sectioned calibration chamber was developed to enable direct observation of granular motion during penetration for numerical model validation. In parallel, DEM simulations replicated and analyzed sand behavior under dynamic loading, providing critical insights into energy dissipation, particle rearrangement, and force chain evolution. Key findings include a unique “twin peaks” phenomenon in the deceleration and cone tip resistance time–history curves for highly weathered sand. The underlying mechanisms governing this double-peak response were elucidated. This study advances understanding of impact penetration mechanisms in highly weathered sand under both wet and dry conditions, providing theoretical support for CIPT interpretation methods in such soils.</p>