Heaping instabilities in a layered Bi-disperse granular bed Ning Zheng, Ping-Ping Wen, Qing-Fan Shi, Pik-Yin Lai and C. K. Chan EPL, 100 4 (2012) 44002 Published online: 30 November 2012 DOI: 10.1209/0295-5075/100/44002