HE Simulation of Ground Shock-Induced MX Trench Collapse.

In order to address the problem of energy coupling to an MX trench due to collapse initiated by strong direct-induced ground shock, an HE simulation experiment was defined. The nuclear environment to be simulated was extracted from a detailed calculation of 1 megaton surface burst performed by Systems, Science, and Software, Inc. The range from ground zero for the nuclear surface burst was chosen to be 12.5 m. This results in a peak pressure of 90 Kbar at the trench. The simulation experiment consisted of a rectangular slab of high-explosive positioned on the ground surface over a buried trench. The primary instrumentation was high-speed photography to record details of the collapse and time-of-arrival and pressure gauges down-pipe from the region of rapid collapse to define the shock launched along the trench. Pressure in the soil and at the bottom of the trench was also measured. The emphasis of the simulation experiment was on energy coupling rather than pipe flow. A two-dimensional prediction calculation was performed to try to guide guage settings and timings. Two pre-shot tests were performed which validated the concept: the main experiment gave good data return. A cross-correlation of the various diagnostics which yielded believable results seemed to confirm the implications of the calculations that strong ground-shock induced trench collapse is not an efficient method for coupling energy down the trench. It is concluded that the off-line burst does not pose a critically stressing environment from a systems design viewpoint. (Author)