(Special session/Open call for public) YARO15: Research activities on rock engineering during the COVID-19 pandemic

[3K0101-08-08] EFFECTS OF EXCAVATION AT THE FOOT OF CLAY ZONE ON ROCK SLOPE DEFORMATION IN A LIMESTONE OPEN-PIT QUARRY

○Clement Amagu¹, Cheng Zhang¹, Kazuki Minami¹, Jun-ichi Kodama¹, Kazuyuki Shioya², Tomoyuki Yamaguchi², Atsushi Sainoki³, Daisuke Fukuda¹, Yoshiaki Fujii¹ (1. Hokkaido University, 2. Nittetsu Mining Co. Ltd., 3. Kumamoto University)

Chairman:Atsushi SAINOKI (Kumamoto University)

Keywords:Rock slope stability, Clay zone, Deformation measurement, Excavation, 2D finite element method

Excavation activities during mining of an open slope often cause changes in stress state of rock mass and deformation of the rock slope. Ensuring stability of rock slopes during an operation stages has been a major challenge in an open-pit mining, particularly when the rock mass included weak rock formation (clay seam). Therefore, understanding mechanism of rock slope deformation in an open-pit mine subject to continuous excavation will provide a good check on the degree of slopes stability, not only for economics purposes, but also to ensure safety operation. Previously, the effects of limestone excavation at the foot of the rock slope, the deterioration of about 70-m-thick clay layer at the rock slope foot wall and shear failure owing to rainfall infiltration have been investigated; but the influences of an expected change in stress state within the clay zone on rock slope deformation were not clarified. In this study, the effect of plastic behaviour of clay rock in a limestone quarry subject to excavation was investigated by two-dimensional finite element method (2-D FEM). At first, deformation characteristics of the rock slopes were clarified by the analyzing displacement data measured by automated polar system (APS) over the periods of five years. The measured results show that the distance between the beam generator and mirrors decreases gradually with time at the range of 20 to 100 mm approximately with maximum displacements of about 100 mm observed at middle of the rock slope. The simulated results revealed that the clay exhibited plastic behaviour arising from stress state redistribution due to mining of limestone at the pit floor. The comparison between measured and simulated results indicates plastic behaviour of the clay zone have insignificant effects on the rock slope deformation at the limestone open-pit quarry.