Analysis and Design Approach for Large Storage Caverns

This paper presents a case study of an underground crude oil storage project. This storage site is researched with detailed field and laboratory investigations. The layout, cross section, and elevation of the caverns are analyzed and designed based on geological and geotechnical information obtained during these investigations. In this study, two-dimensional (2D) elastoplastic analysis is performed using the finite-element code Phase 2D to study the rock mass behavior caused by staged excavation of the cavern ($20 \text{m wide}\times 30 \text{m high}$). The excavation of the cavern is simulated with different stages, i.e., excavation of a pilot tunnel and subsequent side slashing followed by excavation for a pilot bench and subsequent side slashing with a total of three benches. Displacement values obtained analytically are compared with the observed displacement as the excavation progresses. Because the 2D FEM code is based on the plain strain concept, it could not take into account the effect of excavation in other directions that is very obvious at the intersection with tunnels and shafts. Therefore, these intersections were analyzed using a linear three-dimensional (3D) boundary element code, Examine3D. The stability analysis of rock wedges formed from various joint patterns is also studied using the UNWEDGE software based on block theory for each section of the cavern.