Advanced numerical modelling for closure work assistance

Abstract

An internal bund was constructed for surface water management during the progressive closure of a tailings storage facility in northern Australia. Shortly after construction, and coinciding with the wet season's onset, significant longitudinal cracking was observed during routine visual inspections. Initial investigations involved more detailed visual inspections and satellite survey imagery to construct a timeline of events. Following this, three survey prisms were installed. Deformation modelling was complete to ascertain the extent of the cracking and settlement to establish potential ongoing and future consequences. The deformation modelling was conducted using Optum G2 with the modified cam-clay constitutive model being implemented based on the critical state concept. Model properties were derived from existing laboratory testing and field trials.Preliminary modelling results were used to determine appropriate locations for the additional installation of six survey prisms at critical locations anticipated to experience significant movement. Furthermore, vertical settlement recorded via survey prisms was utilised for model calibration and identification of the leading deformation mechanisms. Following calibration, the model was used to predict future settlement and to model several water management scenarios, such as incorporating potential decant pond increases and varying pumping capacity limits. The numerical model was instrumental in informing a management strategy for the closure works.The case study described herein shows how the use of numerical modelling as a tool was successfully employed to allow for more informed decision-making. This was accomplished by assessing the performance of geotechnical structures; in this case, the structure being an internal bund. Confidence in the numerical model was gained by calibrating results early during the deformation process and later using partial results for forward predictions.