Abstract
The Higashi‐Shikagoe limestone quarry is an open‐pit mine situated in Hokkaido Prefecture, Japan, that has experienced four slope failure incidents since 1996. The rock slope behaviour has been monitored since the first failure event by measuring the rock slope surface displacement using an automated polar system. Recent measurements have revealed a gradual decrease of the distance between the beam generator and mirrors over time; however, the displacements and decrease rate differs between the centre and left‐ and right‐hand sides of the quarry. This implies that the deformation characteristics of the rock slope and factors influencing the slope deformation differ at the centre and left‐ and right‐hand sides of the quarry. In this study, the two‐dimensional finite element method was used to identify the causes of slope deformation by investigating the effects of limestone excavation at the foot of the rock slope, the deterioration of a ∼70 m‐thick clay layer at the rock slope foot wall, and shear failure owing to rainfall infiltration. The numerical results show that slope deformation on the left‐hand side and centre of the quarry are induced by clay deterioration, whereas the right‐hand side of the quarry is deformed owing to floor excavation and/or shear sliding. The rock slope is presently stable because the magnitude of the rate of displacement decrease is small and no acceleration is observed.
Highlights
Rock slope stability poses a major challenge to rock engineering projects worldwide, including open-pit mines
The change in distances from 11 automated polar system (APS) monitoring points installed at the leftand right-hand sides and centre of the quarry was analysed to investigate the overall characteristics of the rock slope deformation
The decrease in distance reaches a maximum at the slope foot as shown in Figure 10(c). ese results indicate that the factors that influence the slope deformation on the lefthand side and central part of the quarry are likely similar, but differ from those that influence the slope deformation on the right-hand side of the slope
Summary
Rock slope stability poses a major challenge to rock engineering projects worldwide, including open-pit mines. E above studies indicate that the rock slope deformation at the Higashi-Shikagoe limestone quarry may be induced by rainfall and/or earthquake activity. E results of these studies indicate that the rock slope at the Higashi-Shikagoe limestone quarry likely deforms owing to deterioration of the clay seam at the foot wall of the rock slope. Ese studies indicate that excavation is expected to be a significant cause of the slope deformation at the Higashi-Shikagoe limestone quarry. Us, understanding the elastoplastic behaviour of clay rock is deemed necessary in assessing slope stability at Higashi-Shikagoe limestone quarry. E present study aims at clarifying the causes of longterm slope deformation at Higashi-Shikagoe limestone quarry using numerical simulation and to assess the rock slope stability considering the impact of the clay layer. Countermeasures such as planting and support systems installation (shotcrete and rock bolts shown in Figure 2) have been undertaken since 2018
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