Abstract

This paper presents the development of a three-dimensional (3D) geotechnical model for an existing water dam in Queensland, Australia. The model incorporated data from historic construction records, recent investigation data as well as previously developed two-dimensional cross section interpretations and geological mapping records. The 3D model provided the project team and other stakeholders the ability to interrogate the ground model to an unprecedented level of detail.

The geotechnical model development was complimented by an in-depth rock mechanics assessment to investigate kinematically feasible sliding mechanisms beneath the dam spillway and abutments. This package of work included creation of a discrete fracture network model. The DFN modelling in this study was undertaken in two stages, with an initial model built to be representative of sub-horizontal fractures (with a dip of <15°), followed by a refined model, built to be representative of all fractures at the site.

The paper presents the input parameters, derivation of these parameters along with the model generation process are presented for both stages. The modelling was undertaken for both rock mass visualization and sliced on two cross-sections for input into 2D Finite Element analyses. This was particularly targeted at understanding intact rock forming bridges between laterally persistent defects within the volcanic host rock that were previously identified as a key risk to dam stability in the event of an overtopping event.

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