Mohammad Hossein Khosravi - School of Mining, College of Engineering, University of Tehran
Hassan Sarfaraz - School of Mining, College of Engineering, University of Tehran
Mahmoud Esmailvandi - School of Mining, College of Engineering, University of Tehran
Thirapong Pipatpongsa - Department of Urban Management, Kyoto University, Japan

Determining the maximum stable undercut span is an important parameter in undercut slopes design. The maximum stable undercut span isa function of slope geometry, the strength parameters of the slope material, condition of discontinuities, underground water condition, etc.However, the desired production capacity and therefore the size of excavating equipment will sometimes ask for a wider undercut span. Theinfluence of arching phenomenon in geo-material on the stability of undercut slopes is investigated earlier. It is believed that due to thearching effect, some load transfer from the undercut area into stationary remaining side toes leads to a more stable slope. However, thetransferred load may result in ploughing failure of side toes. One technique for preventing the ploughing failure is application of counterweightbalance on side toes. In this study, the influence of counterweight size on the stability of the undercut slopes was investigated through a seriesof numerical model tests using FLAC3D software. It was concluded that there was a meaningful relationship between the counterweightbalance size and the maximum stable undercut span where increasing a counterweight size resulted in a wider stable span. Finally, thenumerical results were compared with pre-conducted physical modeling test and a nonlinear relationship was proposed between thecounterweight size and the maximum stable undercut span.

numerical modeling, Arching Effect, Undercut Slopes, Counterweight Balance