Explosive cratering on earth embankments and dams using a geotechnical centrifuge

Geotechnical centrifuge simulations are proving to be a useful tool in modeling induced explosions. The centrifuge applies a centripetal acceleration or "g" force which produces higher gravity on a selected experiment. The term "g" force constitutes the gravitational acceleration of the earth. Therefore, increasing "g" using a centrifuge can allow a small amount of explosive to produce the same effects that a higher amount of explosive would incur at 1 g. This allows the study of large detonations on a prototype scale by using small amounts of explosives on a scaled model structure. This research entailed experiments run at 80 g using a geotechnical centrifuge. Surface charges were detonated on saturated and partially saturated earth embankments and dams during flood conditions, and their resulting craters were measured and analyzed. The saturated tests utilized two different water levels; 0.5 m below the breach level (top surface of the dam) and flush to breach level. The partially saturated tests had a geomembrane/kaolin clay core and were run with a water level flush to the breach surface. Each model embankment consisted of a mixture of 85% Nevada sand and 15% kaolin clay. The explosives used in the testing were exploding bridgewires (EBW). Three different size charges were used for each type of test. The apparent scaled crater dimensions produced from the EBWs were plotted versus a scaled TNT equivalency. This information allows the prediction of the amount of explosive required to cause catastrophic failure in this type of dam during flood conditions. The results of this research is a valuable step in understanding the phenomenon of explosive cratering on saturated and partially saturated soils. The data acquired should help to provide the means to ensure the safety of earth dams and embankments.