An analysis of model tests on rock cavern damage induced by underground explosion
The rock cover thickness required for construction of underground ammunition facilities can be designed based on currently existing design manuals, mainly US DoD 6055.STD1, NATO AASTP-1 Part III 2, and UK JSP 482.3 It is found that rock cover requirement is scattered from 0.8 Q1/3 to 1.2 Q1/3 (Q: Charge Weight in kg) according to different manuals, where the effects of loading density and rock mass strength have not been incorporated. The damage pattern and intensity of rock cover are not addressed in the design manuals. Due to the fact that full scale underground explosion tests are extremely expensive, it is almost impossible to evaluate rock cover damage based on full scale tests. The traditional analysis simplifies rock cover failure using a quasi-static approach, which ignored dynamic failure feature of the rock mass.4−7 The design manuals for rock cover are empirical and lack significantly theoretical basis. A rock cover damage model based on dynamic analysis is of special interests for underground ammunition storage design. The objective of the proposed blast test project is to investigate rock cover damage induced by underground explosion to support the development of rock cover design criteria for underground ammunition storage. The effects of rock mass strength, loading density, and cover depth on the dynamic failure of the rock cover will be studied through model tests of underground explosions, and to find the critical overburden of rock chambers under the conditions of scheduled underground cave room and ammunition quantity through explosion tests on rock chambers. The model tests include: (a) Two different rock types, i.e. soft rock and hard rock; (b) Rock chamber with different depths; (c) Detonation with different loading densities. It is expected that the test results can provide some insight understanding on rock cover damage induced by underground explosion.