West Gully Upper – innovative rockfall and debris flow protection systems

Authors: Anderson, HP; Teen, A; Salzmann, H Download Paper

DOI https://doi.org/10.36487/ACG_rep/1308_88_Anderson

Cite As:
Anderson, HP, Teen, A & Salzmann, H 2013, 'West Gully Upper – innovative rockfall and debris flow protection systems', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 1245-1259, https://doi.org/10.36487/ACG_rep/1308_88_Anderson



Abstract:
Within PT Freeport Indonesia’s (PTFI) mining operation in Papua, Indonesia the Mill Area complex is subject to rockfall and debris flow events which initiate from a source area approximately 1,000 m up in a steep gully known as the ‘West Gully’. Active barrier protection systems, RXI-500 (5,000 kJ) barrier, were installed to reduce likelihood of these geohazards impacting the Mill Area. However, during August 2011 an estimated 45,000 m³ failure event occurred from the West Gully Upper source area due to differential erosion and the sites tectonic setting. The mass and velocity of this failure easily exceeded the capacity of the two RX-500 barriers located in the lower section of the gully. The failure event caused significant damage and economic interruption to the Mill Area complex and blocked the critical transport corridor (Ridwan Napitupulu Road). Following a site visit Geovert provided an options report and formally recommended increasing the overall capacity of the rockfall/debris flow protection system for the West Gully by significantly increasing individual barrier capacity from 5,000 to 8,000 kJ. PTFI as a true industry innovator committed to the GBE8000A system prior to public knowledge of its existence and prior to the system achieving certification at the Swiss Governmental testing facility in Walenstadt. Certification was later achieved at Walenstadt in October 2011. Free Fall Geotechnical Engineering ZT GmbH modelled rockfall and debris flow anticipated trajectories and impact forces for the West Gully protection system. This modelling supported recommendations to increase the protection system capacity utilising GBE-8000A barrier technology. Rockfall 7.1 beta, by Dr. Spang Ltd, modelling confirmed 3 locations for GBE-8000A barriers to suitability retain rockfall and debris flow events in the West Gully. The proposal included provision for installation of temporary protection works to protect against geohazards while constructing barrier’s in the West Gully and contingency planning to allow for safe repair works of barrier systems if a major failure event occurs. Climatic, environmental and physical conditions were critical in pre-construction planning and during construction execution to compensate for; frequent heavy bursts of precipitation (estimated at 11 m/yr at the Mill Area complex), consideration of the project site situated at approximately 3,600 masl and no road access to the site resulting in complete reliance on tailored Helicopter transportation of all personnel, equipment and materials to site.

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