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Análise da estabilidade geomecânica da escavação subterrânea no jazigo de S. João (minas de Aljustrel)
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A presente dissertação centra-se na análise de estabilidade das escavações subterrâneas no jazigo
de S. João, pertencente às Minas de Aljustrel. A caracterização e avaliação geotécnicas e geomecânicas
mineiras do maciço incluíram o tratamento de dados geológico-geotécnicos provenientes de 94
sondagens direcionadas à massa mineral. Nestes dados, aplicaram-se os sistemas de classificação
Q-System e a correlação com o GSI. Devido à fraca qualidade do maciço e à dificuldade em obter
amostras que atendam aos requisitos mínimos para ensaios laboratoriais, os parâmetros de resistência
foram estimados com recurso a correlações e a ensaios expeditos. Estes parâmetros foram
posteriormente utilizados na modelação numérica. Com as propriedades geomecânicas definidas e
os zonamentos geotécnicos balizados, avançou-se para a modelação numérica 2D no software RS2. O
estudo da geometria das galerias demonstrou que uma secção de coroa abobadada otimiza a transferência
de tensões e reduz os deslocamentos do maciço. Com base nesses resultados, dimensionou-se
o sustimento para as diferentes zonas geotécnicas já definidas no jazigo. Previu-se a necessidade de
uma contenção mais pesada nas zonas intersectadas por falhas. Foram testados dois métodos de
exploração, o já utilizado Bench-and-fill e o Cut-and-fill, para mitigar ao máximo o estado de tensão
do maciço. Por fim, simulou-se a sequência de lavra de um pilar de soleira. A análise confirmou que a
estabilidade global de todo o bloco de exploração depende criticamente da extração inicial das bancadas
primárias e da rigidez do material de enchimento pastefill, garantindo, assim, o confinamento
e a estabilidade necessários para a posterior lavra das bancadas secundárias.
This dissertation focuses on the stability analysis of underground excavations in the S. João orebody of the Aljustrel Mines. The geotechnical and geomechanical characterization and assessment of the rock mass included processing geological–geotechnical data from 94 boreholes targeting the ore mass. These data were analyzed using the Q-System classification and correlated with the GSI. Due to the poor quality of the rock mass and the difficulty in obtaining samples that meet the minimum requirements for laboratory testing, strength parameters were estimated using empirical correlations and rapid field tests. These parameters were subsequently used in numerical modelling. With the geomechanical properties defined and the geotechnical zoning established, 2D numerical modeling was performed using the RS2 software. The study of drift geometry showed that an arched crown section optimizes stress redistribution and reduces rock mass displacements. Based on these results, the support systems were designed for the different geotechnical zones defined within the orebody. A heavier support was deemed necessary in zones intersected by faults. Two mining methods were tested — Bench-and-fill (currently used) and Cut-and-fill — to minimize the stress state within the rock mass. Finally, the extraction sequence of a sill pillar was simulated. The analysis confirmed that the global stability of the entire mining block critically depends on the initial extraction of the primary benches and the stiffness of the pastefill material, thereby ensuring the confinement and stability required for the subsequent extraction of the secondary benches.
This dissertation focuses on the stability analysis of underground excavations in the S. João orebody of the Aljustrel Mines. The geotechnical and geomechanical characterization and assessment of the rock mass included processing geological–geotechnical data from 94 boreholes targeting the ore mass. These data were analyzed using the Q-System classification and correlated with the GSI. Due to the poor quality of the rock mass and the difficulty in obtaining samples that meet the minimum requirements for laboratory testing, strength parameters were estimated using empirical correlations and rapid field tests. These parameters were subsequently used in numerical modelling. With the geomechanical properties defined and the geotechnical zoning established, 2D numerical modeling was performed using the RS2 software. The study of drift geometry showed that an arched crown section optimizes stress redistribution and reduces rock mass displacements. Based on these results, the support systems were designed for the different geotechnical zones defined within the orebody. A heavier support was deemed necessary in zones intersected by faults. Two mining methods were tested — Bench-and-fill (currently used) and Cut-and-fill — to minimize the stress state within the rock mass. Finally, the extraction sequence of a sill pillar was simulated. The analysis confirmed that the global stability of the entire mining block critically depends on the initial extraction of the primary benches and the stiffness of the pastefill material, thereby ensuring the confinement and stability required for the subsequent extraction of the secondary benches.
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Palavras-chave
Stability Analysis Numerical Modelling Mining Geomechanics Mining Methods Aljustrel Mines Análise de estabilidade Modelação numérica Geomecânica mineira Métodos de lavra Minas de Aljustrel