3D researches on conduits and karsts networks
Résumé
Underground karst is an object that can be studied using 3D approaches, and new technological breakthroughs now allow revisiting subterranean karst. Lasergrammetry in particular allows fast dense point clouds acquisition. Their protocol allows to shape analyses without any contact and to reduce the time spent within the cave. When studying underground topographic matters, pipe sections are usually considered as spindly skeletons. Stations are sampled one after another, in polar geometry (distance, direction, angle). Gallery sections allow to recognize large changes in conduit dimensions. Lasergrammetry, based on Lidars uses, help to acquire very numerous point measurements during minimal time. The point cloudis then meshed to obtain a TIN model. This oneis significantly helpful to inform about neighbouring information and topology. This is of prior importance to the rest of the analyses, in particular to identify morphology breaks or segmentation operations. The model conformity must be checked. Once these treatments are achieved, it is possible to analyse the numerical clone.These analyzes wereapplied to different objects: drains, walls, speleothems... It was shown that the use of 3D analysis on a numerical clone may be fruitful. It allows breakthroughs compared to classical approaches. First of all, it allows investigation of all the objects. Indeed, height, darkness, limited residence time, conservation constraints and limited moves within high patrimonial value objects are limiting factors to an in situ analysis. This completeness when investigating underground karst allows to notably statistically validate results that, used to be limited and reduced to preselected objects. The aim here was to explore the potential of 3D modelling of underground environments, keeping in mind the ever geomorphologic issues that drive our research.