Analysis and Design Approach for Treatment of Weak Geological Features in Underground Caverns

Altaf Usmani
Buffer storage of crude oil in large underground unlined rock caverns is one of the economical alternatives to ensure energy security of import dependent countries. Principle of storage essentially employs ground water pressure for containing the product within an unlined rock cavern. Initial site investigation campaign carried out involving geological, geophysical, geo-technical and hydro-geological investigations, establishes competency of rock formations in conjunction with ground water
more » ... tions for construction of unlined rock caverns. In such projects, engineering geology forms an important aspect not only during the initial feasibility stage of the project, but also in subsequent execution phase, wherein unlined rock caverns are built by conventional drill and blast technique. Design of underground structures exhibit lot of uncertainties in their basic approach and require an active and dynamic design intervention during construction progress. In this context predictive geological model is developed based on initial investigation results, which is continuously updated as the excavation progresses through stages of heading and benches. As part of this modeling exercise, critical segments of the caverns are identified as geological hotspot which undergoes additional stability analysis before excavation in order to take necessary counteractive steps. This approach based on pro-active construction methodology, helps to ensure preparedness to address the rock mechanical aspects of the identified segments, thus results in a reduced risk exposure. The study outlines, the process of identification and approach adopted to treat geological hotspots encountered during excavation for large underground rock caverns.