‘Wova’ Apartments Basement Excavation Failure, Phillip ACT

Abstract

This paper presents a case study of a three-level (approximately 10 m deep) basement excavation failure at the Wova development in Phillip, ACT. The development comprises four residential towers over a common basement. During bulk excavation, a localised failure of the perimeter excavation occurred within jointed volcanic rock. Post-failure evidence indicates that stability was governed by discontinuity-controlled rock mass behaviour rather than intact rock strength. The geological conditions are examined with particular emphasis on the apparent inclination, persistence and interaction of discontinuities within the rock mass. Because the investigation boreholes were vertical and the core was unoriented, true strike and dip directions could not be established from the borehole data. The failure mechanism is therefore interpreted from the available borehole logs, construction records and post-failure observations rather than from a deterministic three-dimensional structural model. The paper considers the limitations of conventional vertical boreholes for identifying low-frequency persistent defects, the implications for shoring design, and the need to distinguish intact rock strength from discontinuity-controlled stability. The observed failure is interpreted as a localised wedge or block release bounded by persistent defects, followed by collapse of overlying soil and weathered rock. The case study also examines the observational method during construction, emphasising systematic face mapping, explicit hold points, rapid design feedback and pre-agreed stabilisation measures. The principal lesson is that deep excavations in jointed rock require structural-geological characterisation and kinematic assessment to be integrated with conventional strength-based ground models, with the design verified and adapted as excavation exposes the rock mass.