Session 4B
ABSTRACT
Recent catastrophic tailings dam failures have driven the identification and need for dam stabilisation solutions worldwide in an effort to improve factors of safety under a post-seismic loading condition, where contractive materials are present within the structural foundation zone. Although not common place, specific circumstances (i.e. limited footprint, lack of buttress material, etc.) may drive the use of ground improvement (GI) as part of a wider dam stabilisation solution.
GI techniques for dam stabilisation typically aim to create a structural block to cut-off problematic foundation layers (i.e. soft/liquefiable materials). This, in combination with a berm/buttress can provide a satisfactory stabilisation solution. Stone columns (SCs) are a GI technique that has been used successfully in a number of dam stabilisation projects.
To confirm that SC construction achieves the design intent, robust construction quality control (QC) is necessary. Some common considerations for SC QC include assessment of stone column construction depth, termination amperage, stone column diameter, pre-drill depth (if required) and the actual installed soil replacement ratio. As well, it is common to conduct cone penetration tests (CPTs) following SC construction to confirm the achieved undrained shear strength of the densified soil between the columns.
This paper discusses the key considerations for SC QC for dam stabilisation and presents how these QC considerations can be implemented using data from a recent tailings dam stabilisation project, including identification of some challenges encountered during construction. The implementation of a detailed SC QC program during construction allowed early identification of remediation works/areas. The paper discusses how potential non-conformances were assessed and addressed without causing significant project delays and/or potentially unrealistic remediation works with a design intent verification example.
AUTHORS
- Jonathon Eldridge, SRK Consulting
- Ricardo J. Dellamea, SRK Consulting
- Joe Rola, SRK Consulting
