Introduction

SRK Consulting UK (SRK) has been engaged by Rio Tinto (the Client) to undertake the site-specific seismic hazard assessment of the Simandou Mine area. Simandou iron ore mine is located in the mountain range of southern Guinea’s Nzérékoré Region. The project is composed of several earthwork structures: railroad foundations, embankments for conveyors, cut slopes in natural soils and large waste rock dumps.

This study provides an estimate of the seismic hazard of the project area for a representative site condition and presents seismic design criteria and guidance for the listed earthworks in terms of ground acceleration, spectral accelerations and horizontal seismic coefficients for use in stability analysis.

Objectives and scope

The main objectives of the study are as follows:

  • Outline the tectonic framework of the study area and identify all seismically active fault systems within 500 km of the site. Review the strong motion catalogues and identify the maximum considered earthquakes of potentially seismogenic faults.

  • Identify and characterise seismic sources capable of producing significant ground motion at the site and define the source geometry and probability distribution of potential rupture locations within the source.

  • Select ground-motion prediction equations (GMPE) appropriate for the region under study and calibrate the specific parameters of each model to the particular conditions of each source model (PSHA) and each seismic scenario (DSHA).

  • Characterise the earthquake scenarios in terms of location, strike, geometry, slip, rupture area, and earthquake occurrence rates for all magnitudes of significance to the site hazard and identify the controlling earthquake scenario. Provide an estimate of the maximum credible earthquakes (MCEs) expected from all scenarios in terms of PGA and Sa(T)

  • Perform a full probabilistic seismic hazard assessment for the Simandou Site and provide an estimate of the annual probability of exceeding (AEP) a specific level of seismic intensity due to the potential occurrence of earthquakes from all sources.

  • Select the maximum design earthquakes (MDEs) expected at the site for different service levels and target AEPs in rock site conditions.

  • Characterise the foundation soil in terms of the shear wave velocities of the upper 30 m (Vs30) and provide an estimate of the expected amplification over different spectral ordinates in hard soil, for different target site conditions.

  • Define the target level of permanent displacements (performance objectives) during different operational and closure stages (level of service) and provide a set of seismic (pseudo-static) coefficients for performance-based design of waste rock dumps, slopes and embankments.