Considering the large volume and different types of material stored in salt caverns, it is important to ensure that the salt cavern be designed, constructed and operated safely. Since salt caverns are constructed in a geological formation, the structural safety problem of a salt cavern is essentially a geotechnical problem. In this paper, we describe the application of the Geotechnical Safety Program (GSP) to a gas storage cavern in salt, focusing on the first two components - performance criteria and design assessment. To develop the performance criteria, we considered performance aspects in different categories. For each performance aspect, we developed the performance criteria by determining the consequences of failure, selecting a tolerable level of risk, establishing criteria of performance, and ensuring that the criteria meet appropriate legal requirements and accepted standards of practice. The design assessment was conducted by checking the design conditions, identifying the critical mechanisms of performance, identifying typical and critical sections, reviewing the field and laboratory data, identifying major uncertainties and critical aspects of performance, and recommending actions to improve safety. Based on the design assessment, we identified several performance aspects which do not meet the performance criteria and recommended changes and/or measures so that the performance criteria can be met.
Caverns in salt are used worldwide for the storage of different products, including crude oil, liquefied petroleum gas (LPG), chemical waste, natural gas, and hydrogen [1-3]. There have been serious incidents associated with cavern failures or operational problems. These incidents can happen in the cavern development period or in the operation period. For example, on December 24, 1949, a sinkhole formed where salt solutioning operations were in progress at the Blue Ridge salt dome, Texas [4]. It is believed that the caprock above the solutioned cavity collapsed, resulting in the formation of the surface sinkhole. On September 17, 1980, a drop in pressure was recorded in one of the cavities containing LPG at Mont Belvieu, Texas [5]. On October 3, gas (70% ethane, 30% propane) that had accumulated in the foundation of a house in the area exploded as a result of a spark from an electrical appliance. The cavity in which the pressure had dropped was then filled with brine; in the days that followed, gas appeared haphazardly around the area, and approximately 50 families had to be evacuated. Holes were drilled into the water tables above the salt to find and vent the gas. Therefore, it is important to ensure that the salt cavern be designed, constructed and operated safely. Since salt caverns are constructed in a geological formation, the structural safety problem of a salt cavern is essentially a geotechnical problem. Lambe et al. [6] developed a comprehensive Geotechnical Safety Program (GSP) for important, complex geotechnical facilities. The GSP has nine components: performance criteria, design assessment, field measurement system, construction assessment, surveillance/performance monitoring, performance evaluation, safety assessment, remedial measures, and contingency plan. The GSP has been successfully applied to different geotechnical problems, including dams and landfills.
