Numerical Simulation of the Velocity Records from the SRI Grout Spheres Experiments

Spherically symmetric finite difference calculations are presented here which successfully simulate the particle velocity measurements from small scale grout spheres experiments and show that particle velocity measurements together with numerical simulations may be used to obtain dynamic material properties. In these experiments, 3/8 gm charges of PETN explosive are detonated in 11 in. diameter spheres of grout in a water tank which simulates overburden. Numerical simulations are presented for experiments in two types of grout, 2C4 rock-matching grout and a high-porosity, low-density grout, LD2C4. Successful matches to the particle velocity pulses are obtained for each grout using two very different numerical constitutive models, a strain rate and shock damage dependent model (the RDD model) and the rate independent effective stress model. For 2C4 grout, the simulations involve primarily changes in the laboratory measured static failure surface to account for increases in the strength during shock loading and decreases in the strength on unload. For LD2C4 grout, the simulations involve primarily backing out a loading (air void crushup) curve from the particle velocity measurement. Small changes in this curve at pressures below 0.25 Kb are shown to cause large variations in the calculated peak particle velocities and in the pulse shape. A later laboratory measurement of this crush curve is shown to be in excellent agreement with the crush curve derived from the particle velocity measurements.