Subsidence backfilling operation of Padcal: a unique case in block caving

Authors: Monis, JA

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DOI https://doi.org/10.36487/ACG_repo/2645_59

Cite As:
Monis, JA 2026, 'Subsidence backfilling operation of Padcal: a unique case in block caving ', in A van As, D Cumming-Potvin & J Wesseloo (eds), Caving 2026: Proceedings of the Sixth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1-15, https://doi.org/10.36487/ACG_repo/2645_59

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Abstract:
The Padcal Mine in Benguet, Philippines is one of the world’s longest continuously operating block caves, having transitioned from open pit to underground caving in 1963, and operates under high rainfall, steep topography and thick unconsolidated overburden. Progressive cave growth under these conditions produced large subsidence craters, creating direct hydraulic and material connectivity between surface water, loose overburden and active drawpoints. This led to recurring mud rush events, drawpoint instability and loss of cave confinement. Unlike conventional block cave operations that allow subsidence craters to evolve freely, Padcal has implemented a long-term strategy of systematic subsidence backfilling using waste rock to offset surface subsidence and control water infiltration. This paper documents how subsidence backfilling has been integrated with draw control and mud rush risk management in a mature, deepening cave. Subsidence backfilling strategy, rainfall response and drawpoint behaviour are analysed to demonstrate how Padcal caving operations suppresses fines migration and stabilises cave flow to avoid catastrophic mud rush events. The Padcal experience provides a rare, field-scale demonstration of engineered subsidence control in block caving and offers directly transferable guidance for caves operating in high rainfall or infrastructure-constrained environments.

Keywords: block caving, subsidence management, crater backfilling, mud rush, draw control

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