An 80-m high low wall slope at Mae Moh mine, Lampang, Thailand, sits on a low friction interface between an under burden claystone and a thin clay layer called G1. By 2012, the slope must be partially undercut for mining, approximately 1 million tons of lignite. Stability of the sizable slope will be questionable when being undercut and mined. To study the behaviors of the undercut slope lying on an inclined bedding plane, a number of physical models and numerical models are studied. For the physical models, a 1.0 m × 0.45 m × 0.80 m (W×H×D) undercut slope model was constructed by using humid sand, acrylic and an aluminum work frame, low friction Teflon sheet as a smooth interface and sand paper adhered with acrylic plate as side supports. Moist sand physical properties, its strength and all interface frictions were experimentally determined beforehand. Five potentiometers and a camera were installed and employed to monitor and digitally record the crest and the slope face displacements. Stresses in various locations and directions are also measured by installing eight pressure gauges. Concurrently, the numerical model of the undercut slope is created based on the physical model dimensions and the moist sand properties, strength and its interface frictions. 3DEC®, a three dimensional discrete element program, is selected for simulating and studying the behavior of the undercut slope. The behaviors of the undercut slope examined from both physical and numerical models have shown similar tendencies toward measured displacements and stresses during undercutting. Moreover, the buckling failure mode of both slope models is discovered excitedly. The results provide further understandings of the undercut slope behaviors. The better understandings help engineers to design and monitor the undercut slope.

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