EFFECTS OF WEAK LAYERS ON PARTICLE-VELOCITY MEASUREMENTS

Results are presented from a testing program to study the effect weak layers embedded in a strong rock strata have on particle velocity when subjected to explosive loading. A similar computational study had bee n conducted earlier with WONDY - a finite difference Langrangian code developed at Sandia National Laboratory. The experiments were conducte d using models fabricated from Hydrocal containing a single dry sand l ayer or clay layer through which the stress wave traveled. Particle ve locity was measured in front of and past the weak layer to determine a ttenuation, pulse shape changes, and displacement loss. The results fr om the model testing indicated that particle velocity amplitude decrea sed significantly when the stress wave passed through the weak layer. The velocity pulse width on the other hand was found to remain relativ ely constant when passing through the weak layer. The computational re sults from WONDY predicted similar behavior and hence were in good agr eement with the tests. In the experiments, the velocity loss across a sand layer was found to be much larger than the loss across a clay lay er. The stress wave velocity in the sand layer was found to be signifi cantly smaller than in the Hydrocal while the experimentally determine d wave velocity in the clay was nearly equal to the wave velocity in t he Hydrocal.