Response of earth-covered slabs in clay and sand backfills

TLDR: In this article, five tests were conducted, three static and two dynamic, on identical 2-foot-wide, one-way reinforced concrete slabs, each slab was 2 feet long and had a span-to-effective-depth ratio of 10.

Abstract: : Five tests were conducted, three static and two dynamic, on identical 2-foot-wide, one-way reinforced concrete slabs. Each slab was 2 feet long and had a span-to-effective-depth ratio of 10. Static test were conducted using water over a waterproof membrane to apply a uniform surface pressure with the test slabs surface flush, 1 foot deep in clay soil backfill, and 1 foot deep in a sand backfill. The clay and sand backfill conditions were repeated in the two dynamic tests. The reaction structure supporting the slabs was rigid enough to prevent any slab support rotation at the clamped edges. The rigid reaction structure also eliminated any inplane thrust generated by lateral earth pressures. Therefore, compressive membrane thrust was not a variable between the tests. The surface-flush static test slab failed at about 174 psi, failure in the static clay backfill test occurred at about 835-psi overpressure. The approximately fivefold increase in static capacity in the sand backfill was due to soil arching in the high-shear-strength sand backfill. Peak dynamic pressure in the dynamic sand backfill test was approximately 3,300 psi and in the dynamic clay backfill about 860 psi. These test results indicate that soil arching, both static and dynamic, is much more important than current calculations indicate at this very shallow burial depth. The dynamic tests approximately simulated 0.027- and 0.010-KT nuclear weapons at about 3,300- and 860-psi peak overpressures, respectively. Assuming a 16-foot prototype span, these weapons scale up to approximately 14 and 5 KT, respectively.