Horizontal Penetration in Granular Media: Effect of Intruder Shape, Depth, Orientation, and Material Density on Penetration Forces

Understanding the mechanics of horizontal penetration is fundamental for the development of new burrowing techniques for subsurface characterization/monitoring, infrastructure construction, and the exploration of extreme environments. This contribution uses 3D discrete element simulations and 1-g physical model tests to study the effects of tip shape, intruder depth, soil density, and tip orientation on the drag, lift, and lateral forces that develop during horizontal penetration. The intruder tips tested include the standard CPT tip and three tip morphologies optimized in a prior research study to reduce drag and/or lift forces. The data generated reveal that using the optimized tips can reduce drag forces by up to 45% (compared to a standard cone penetration conical tip). The lift forces are depth-dependent, suggesting that a single intruder geometry cannot yield minimum lift for all depths. The penetration forces increase nonlinearly with penetration depth, indicating a transition between shallow and deep failure mechanisms. The penetration forces increase with soil density due to the increase in the peak friction angle of the material. Tip rotation effectively changes the lateral/vertical forces during penetration. Still, continuous measurement and adaptation are needed to account for instrument compliance, soil variability, and path deviations.