Rock cavity reinforcement structures that can accommodate underground cavity closures of a few percent, and thus plastic deformation of the surrounding rock, are shown to take substantial advantage of the rock strength in carrying both symmetric and side-on far-field loads. The increase in load capacity is typically about a factor of three as compared with cavities limited to elastic deformation. A parameter study shows that this advantage is maintained for a wide range of rock (or soil) properties, characterized by elastic modulus and Poisson''s ratio, unconfined strength, and friction angle. Smallscale laboratory experiments on simple metallined tunnels and lined tunnels with backpacking confirm these results. Repeat loading experiments on the backpacked tunnels show that even when both rock and backpacking are loaded well into their plastic range, there is little or no additional rock cavity or liner closure upon reloading until the maximum previous loading is exceeded.


Buried structures are in common use as protection against enemy attack, accidental explosions, and planned explosions used in high pressure research and technology. As in any structure, an important goal in the design of underground cavity reinforcement structures is to make them light and inexpensive while still rugged enough to reliably sustain the design load. Placing the structure underground reduces direct blast loads while also adding the earth material as a structural component to help carry the load. This introduces the complexities of designing with natural materials, and requires an engineering solution that combines conventional structural design analysis with the soil and rock mechanics used in designing tunnels and underground power stations in a benign environment. For minimum-cost cavity reinforcement structures, as the design blast loading is increased, the cavity is placed at increased depth. The added depth results in shock attenuation which reduces the pressure arriving at the cavity.

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