Prediction of High-Speed Penetration in Layered Sand Using Cone Penetration Tests

Abstract

The depth of burial (DoB) of projectiles penetrating soils at high velocities is of interest in a number of scientific and engineering applications. In this study, a phenomenological penetration model is presented for predicting the DoB of projectiles in layered sandy soils using cone penetration tests (CPT) and observed response in homogeneous soils. The model is based on high-fidelity laboratory measurements of velocity–time records from penetration of conical nose rod projectiles in both homogeneous and two-layer sands. The data were obtained using a novel two-channel photon Doppler velocimeter. Homogeneous and two-layer sand samples were prepared by means of dry pluviation. CPT were performed on the same soils for model development. An electropneumatic launcher was used to launch projectiles at impact velocities of 150 and 200 m/s. The response of homogeneous soils was captured with high accuracy using a Poncelet-type phenomenological penetration model incorporating CPT and two drag coefficients separated at a transition stress. The high-velocity and low-velocity drag coefficients were found to be 0.95 and 0.85 for loose sand, and 2.25 and 1.11 for dense sand, respectively. A universal stratification number was introduced to identify the depth during penetration that the projectile senses the presence of a second layer. The stratification number was found to only depend on the thickness of the top layer for the experiments reported. For a constant top layer thickness, the stratification number was essentially independent of impact velocity and relative density of the two layers, despite the strong influence of both parameters on DoB. The observations were used to develop a model to predict the penetration response and DoB of projectiles in sandy soils with reasonable accuracy.