This paper discusses the experience of the authors with two large failures that occurred in the roof strata of a storage facility for LPG which was being constructed deep below the ground surface in Hawkesbury Sandstone in the Sydney Basin, NSW, Australia.
Examination of the failure areas showed that each had been subject to severe distortion of the roof strata resulting in failure of the support systems. It was apparent that the strata had been subject to high lateral stresses and that the impact of these stresses on the roof of the excavation, coupled with the unique requirements for gas tightness, had contributed to the failures.
This paper describes the two roof failures and the particular geotechnical conditions associated with each.