Seismic study of soda straws exposed to nearby blasting vibrations

Abstract

This study aims to protect an exceptional population of soda straw stalactites from vibrations generated by nearby rock blasting activities. The Choranche Cave, located in the Vercors region of France, hosts thousands of remarkably slender soda straws, reaching several meters in length while measuring approximately 0.5 cm in diameter. These speleothems are particularly susceptible to vibrations because of their structural fragility and potential for dynamic amplification. Our analyses revealed that their fundamental natural frequencies fall within the frequency range of nearby blasting-induced vibrations, typically spanning tens to hundreds of hertz. To assess the effects of blasting, we combined in situ vibration measurements, laboratory-based material characterization, and dynamic two-dimensional finite element simulations to estimate the loads experienced by the soda straw population. The results indicate that resonance can amplify the induced loads by a factor of five. Consequently, shorter soda straws (0.1--1 m) were found to be more vulnerable to blasting-induced vibrations than longer speleothems (>1 m), despite the greater weight and inertial forces associated with the latter. Based on simulations of several blasting tests, we established an allowable peak particle velocity (PPV) threshold of 2.4 mm/s within the cave. Subsequent blasting operations were conducted in compliance with this limit, successfully protecting the soda straw population from damage. We also investigated the dynamic response of soda straws to regional earthquakes. In contrast to blasting-induced vibrations, the lower-frequency content of earthquake ground motions preferentially excites resonance in longer speleothe