Rate Dependence of Penetration in Sandy Soils

In our previous APS paper on sand penetration, we reported on penetration of rods at relatively high velocity. Data were consistent with a Poncelet-type equation, and they provided good calibration for the Poncelet drag that mainly influences high velocity effects, but poor resolution of the velocity-independent term that is due to strength and friction. Now we have complemented those studies with both low impact velocity and ``static'' penetrometer data, which provide excellent resolution for the low speed penetration resistance. We find that the penetration resistance for inertial and driven rod penetration depends on depth-squared until full embedment. This is apparently due to side friction which dominates end bearing strength. However, simple depth-dependent friction force model cannot explain these results with reasonable values of friction coefficient.